llvm-native-core 0.1.11

//! clang_cxx23 — C++23 and C++26 standard features for the Clang frontend.
//!
//! This module provides parsing, semantic analysis, and code generation support
//! for C++23 and C++26 language features. Implementation is clean-room,
//! reconstructed from ISO/IEC 14882:2024 (C++23) working drafts and published
//! WG21 papers.
//!
//! Features covered:
//! - Deducing this (explicit object parameter) — P0847R7
//! - if consteval — P1938R3
//! - static operator() — P1169R4
//! - Multidimensional subscript operator — P2128R6
//! - auto(x) and auto{x} decay-copy — P0849R8
//! - #warning preprocessor directive — P2437R1
//! - #elifdef / #elifndef — P2334R1
//! - Literal suffix for size_t (uz, z) — P0330R8
//! - constexpr extensions (virtual, try-catch, dynamic_cast)
//! - std::unreachable() — P0627R6
//! - Monadic operations for std::optional — P0798R8
//! - std::expected<T,E> — P0323R12
//! - Ranges extensions — P2321R2, P2374R4, etc.

use std::collections::{BTreeMap, HashMap};
use std::fmt;

// ═══════════════════════════════════════════════════════════════════════════════
// Deducing This (Explicit Object Parameter) — P0847R7
// ═══════════════════════════════════════════════════════════════════════════════

/// Represents the kind of explicit object parameter.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ExplicitObjectKind {
    /// `this auto&& self` — deduced reference
    DeducedRef,
    /// `this auto& self` — deduced lvalue reference
    DeducedLvalueRef,
    /// `this auto self` — deduced by value
    DeducedByValue,
    /// `this const auto& self` — deduced const lvalue reference
    DeducedConstLvalueRef,
    /// `this auto const& self` — alternative const spelling
    DeducedConstRefAlt,
}

impl ExplicitObjectKind {
    pub fn from_param_str(s: &str) -> Option<Self> {
        match s {
            "this auto&& self" | "this auto&&" => Some(Self::DeducedRef),
            "this auto& self" | "this auto&" => Some(Self::DeducedLvalueRef),
            "this auto self" | "this auto" => Some(Self::DeducedByValue),
            "this const auto& self" | "this const auto&" => Some(Self::DeducedConstLvalueRef),
            "this auto const& self" | "this auto const&" => Some(Self::DeducedConstRefAlt),
            _ => None,
        }
    }

    pub fn is_reference(&self) -> bool {
        matches!(
            self,
            Self::DeducedRef
                | Self::DeducedLvalueRef
                | Self::DeducedConstLvalueRef
                | Self::DeducedConstRefAlt
        )
    }

    pub fn is_const(&self) -> bool {
        matches!(self, Self::DeducedConstLvalueRef | Self::DeducedConstRefAlt)
    }
}

/// Represents a function with an explicit object parameter (deducing this).
#[derive(Debug, Clone)]
pub struct ExplicitObjectFunction {
    /// The name of the function/member function
    pub name: String,
    /// The explicit object parameter kind
    pub explicit_param: ExplicitObjectKind,
    /// Name of the explicit object parameter (e.g., "self")
    pub param_name: String,
    /// Remaining regular parameters after the explicit one
    pub regular_params: Vec<FunctionParam>,
    /// Return type (can be deduced via auto)
    pub return_type: DeducedReturnType,
    /// Whether this is a member function
    pub is_member: bool,
    /// Whether the function is constexpr
    pub is_constexpr: bool,
    /// The class name if this is a member
    pub class_name: Option<String>,
    /// Whether the function is static (static + explicit object is allowed in C++23)
    pub is_static: bool,
}

#[derive(Debug, Clone, PartialEq)]
pub enum DeducedReturnType {
    Auto,
    AutoRef,
    AutoConstRef,
    Explicit(String),
    Void,
}

/// A function parameter descriptor.
#[derive(Debug, Clone, PartialEq)]
pub struct FunctionParam {
    pub name: String,
    pub type_desc: String,
    pub default_value: Option<String>,
}

impl ExplicitObjectFunction {
    pub fn new(name: &str, kind: ExplicitObjectKind, param_name: &str) -> Self {
        Self {
            name: name.to_string(),
            explicit_param: kind,
            param_name: param_name.to_string(),
            regular_params: Vec::new(),
            return_type: DeducedReturnType::Auto,
            is_member: false,
            is_constexpr: false,
            class_name: None,
            is_static: false,
        }
    }

    /// Generates a pseudo-signature string for display.
    pub fn signature(&self) -> String {
        let class_prefix = if let Some(ref cls) = self.class_name {
            format!("{}::", cls)
        } else {
            String::new()
        };
        let static_prefix = if self.is_static { "static " } else { "" };
        let constexpr_prefix = if self.is_constexpr { "constexpr " } else { "" };
        let ret = match &self.return_type {
            DeducedReturnType::Auto => "auto".to_string(),
            DeducedReturnType::AutoRef => "auto&".to_string(),
            DeducedReturnType::AutoConstRef => "const auto&".to_string(),
            DeducedReturnType::Explicit(t) => t.clone(),
            DeducedReturnType::Void => "void".to_string(),
        };
        let explicit = format!("this auto&& {}", self.param_name);
        let params: Vec<String> = std::iter::once(explicit)
            .chain(self.regular_params.iter().map(|p| {
                if let Some(ref def) = p.default_value {
                    format!("{} {} = {}", p.type_desc, p.name, def)
                } else {
                    format!("{} {}", p.type_desc, p.name)
                }
            }))
            .collect();
        format!(
            "{}{}{}{}({})",
            constexpr_prefix,
            static_prefix,
            ret,
            format!("{}operator()", class_prefix),
            params.join(", ")
        )
    }

    /// Returns whether the function can be called with an lvalue argument.
    pub fn can_bind_lvalue(&self) -> bool {
        match self.explicit_param {
            ExplicitObjectKind::DeducedRef
            | ExplicitObjectKind::DeducedLvalueRef
            | ExplicitObjectKind::DeducedConstLvalueRef
            | ExplicitObjectKind::DeducedConstRefAlt => true,
            ExplicitObjectKind::DeducedByValue => true,
        }
    }

    /// Returns whether the function can be called with an rvalue argument.
    pub fn can_bind_rvalue(&self) -> bool {
        match self.explicit_param {
            ExplicitObjectKind::DeducedRef | ExplicitObjectKind::DeducedByValue => true,
            ExplicitObjectKind::DeducedLvalueRef
            | ExplicitObjectKind::DeducedConstLvalueRef
            | ExplicitObjectKind::DeducedConstRefAlt => false,
        }
    }
}

/// Parser for deducing-this syntax.
pub struct DeducingThisParser {
    pub enabled: bool,
    pub diagnostics: Vec<DeducingThisDiag>,
}

#[derive(Debug, Clone)]
pub struct DeducingThisDiag {
    pub message: String,
    pub is_error: bool,
}

impl DeducingThisParser {
    pub fn new() -> Self {
        Self {
            enabled: true,
            diagnostics: Vec::new(),
        }
    }

    /// Parse a parameter declaration to detect explicit object parameter syntax.
    pub fn parse_param(&mut self, param_str: &str) -> Option<ExplicitObjectKind> {
        let trimmed = param_str.trim();
        if !trimmed.starts_with("this ") {
            return None;
        }
        ExplicitObjectKind::from_param_str(trimmed)
    }

    /// Validate that an explicit object parameter is used correctly.
    pub fn validate(&mut self, func: &ExplicitObjectFunction) -> bool {
        let mut valid = true;

        // An explicit object parameter must be the first parameter
        // Static member functions cannot have explicit object parameters
        // (unless combined with static operator() in C++23)
        if func.is_static && !func.is_member {
            self.diagnostics.push(DeducingThisDiag {
                message: format!(
                    "free function '{}' cannot have an explicit object parameter",
                    func.name
                ),
                is_error: true,
            });
            valid = false;
        }

        // Constructors and destructors cannot have explicit object parameters
        if func.name == func.class_name.clone().unwrap_or_default() {
            self.diagnostics.push(DeducingThisDiag {
                message: "constructors cannot have explicit object parameters".to_string(),
                is_error: true,
            });
            valid = false;
        }

        if func.name.starts_with('~') {
            self.diagnostics.push(DeducingThisDiag {
                message: "destructors cannot have explicit object parameters".to_string(),
                is_error: true,
            });
            valid = false;
        }

        // Virtual functions with explicit object params need care
        // They can still be called virtually but can't be overridden trivially

        valid
    }

    /// Generate the deduced type for `this` in an explicit object function.
    pub fn deduce_this_type(&self, func: &ExplicitObjectFunction, call_is_lvalue: bool) -> String {
        match func.explicit_param {
            ExplicitObjectKind::DeducedRef => {
                if call_is_lvalue {
                    "auto&".to_string()
                } else {
                    "auto&&".to_string()
                }
            }
            ExplicitObjectKind::DeducedLvalueRef => "auto&".to_string(),
            ExplicitObjectKind::DeducedByValue => "auto".to_string(),
            ExplicitObjectKind::DeducedConstLvalueRef | ExplicitObjectKind::DeducedConstRefAlt => {
                "const auto&".to_string()
            }
        }
    }
}

impl Default for DeducingThisParser {
    fn default() -> Self {
        Self::new()
    }
}

/// Code generation support for deducing-this functions.
pub struct DeducingThisCodeGen {
    pub enabled: bool,
}

impl DeducingThisCodeGen {
    pub fn new() -> Self {
        Self { enabled: true }
    }

    /// Emit the LLVM IR function type for a deducing-this call operator.
    pub fn emit_call_operator_type(&self, _func: &ExplicitObjectFunction) -> String {
        // In a real implementation, this would emit the LLVM function type
        // with the deduced 'self' parameter as the first argument.
        "void (%class.Foo*, i32)*".to_string()
    }

    /// Lower a call to a deducing-this operator to LLVM IR.
    pub fn lower_call(&self, object_ptr: &str, args: &[String]) -> String {
        format!(
            "call void @operator()(ptr noundef {}, i32 {})",
            object_ptr,
            args.join(", i32 ")
        )
    }
}

impl Default for DeducingThisCodeGen {
    fn default() -> Self {
        Self::new()
    }
}

// ═══════════════════════════════════════════════════════════════════════════════
// if consteval — P1938R3
// ═══════════════════════════════════════════════════════════════════════════════

/// Represents the result of evaluating an `if consteval` condition.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum IfConstevalResult {
    /// We are in an immediate function context — take the consteval branch.
    ImmediateContext,
    /// We are not in an immediate function context — take the else branch.
    NonImmediateContext,
}

/// Context tracker for `if consteval` statements.
#[derive(Debug, Clone)]
pub struct ConstevalContext {
    /// Stack of consteval/non-consteval contexts
    stack: Vec<bool>,
    /// Current depth
    depth: usize,
}

impl ConstevalContext {
    pub fn new() -> Self {
        Self {
            stack: Vec::new(),
            depth: 0,
        }
    }

    /// Enter a new context. `true` means we are in a consteval context.
    pub fn enter(&mut self, is_consteval: bool) {
        self.stack.push(is_consteval);
        self.depth += 1;
    }

    /// Leave the current context.
    pub fn leave(&mut self) {
        if self.depth > 0 {
            self.stack.pop();
            self.depth -= 1;
        }
    }

    /// Check if we are currently in a consteval context.
    pub fn is_consteval(&self) -> bool {
        self.stack.last().copied().unwrap_or(false)
    }

    /// Evaluate an `if consteval` condition.
    pub fn evaluate_if_consteval(&self) -> IfConstevalResult {
        if self.is_consteval() {
            IfConstevalResult::ImmediateContext
        } else {
            IfConstevalResult::NonImmediateContext
        }
    }
}

impl Default for ConstevalContext {
    fn default() -> Self {
        Self::new()
    }
}

/// Parser for `if consteval` statements.
pub struct IfConstevalParser {
    pub contexts: ConstevalContext,
}

impl IfConstevalParser {
    pub fn new() -> Self {
        Self {
            contexts: ConstevalContext::new(),
        }
    }

    /// Parse a token sequence to detect `if consteval`.
    pub fn detect_consteval(&self, tokens: &[&str]) -> bool {
        if tokens.len() >= 2 {
            return tokens[0] == "if" && tokens[1] == "consteval";
        }
        false
    }

    /// Parse the body of `if consteval { ... } else { ... }`.
    pub fn parse_body(&mut self, is_immediate_context: bool, body: &str) -> String {
        self.contexts.enter(is_immediate_context);
        let result = body.to_string();
        self.contexts.leave();
        result
    }
}

// ═══════════════════════════════════════════════════════════════════════════════
// static operator() — P1169R4
// ═══════════════════════════════════════════════════════════════════════════════

/// Represents a static call operator.
#[derive(Debug, Clone)]
pub struct StaticOperatorCall {
    /// The enclosing class or lambda type name
    pub class_name: String,
    /// Parameter types
    pub params: Vec<String>,
    /// Return type
    pub return_type: String,
    /// Whether it's a lambda
    pub is_lambda: bool,
    /// Whether it captures anything (static lambdas have no captures)
    pub has_captures: bool,
}

impl StaticOperatorCall {
    pub fn new(class_name: &str) -> Self {
        Self {
            class_name: class_name.to_string(),
            params: Vec::new(),
            return_type: "void".to_string(),
            is_lambda: false,
            has_captures: false,
        }
    }

    /// Validate that a static operator() is well-formed.
    pub fn validate(&self) -> Result<(), String> {
        if self.is_lambda {
            // In C++23, static lambdas must have no captures
            if self.has_captures {
                return Err(
                    "static lambda cannot have captures (lambda with static operator())".to_string(),
                );
            }
        }
        // The static operator() cannot be virtual
        // It cannot be const, volatile, or ref-qualified
        Ok(())
    }

    /// The mangled name for the static operator().
    pub fn mangled_name(&self) -> String {
        format!("_ZN{}clE", self.class_name.len())
    }
}

/// Enum for the kind of call operator.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum CallOperatorKind {
    /// Non-static, non-const
    Mutable,
    /// Non-static, const-qualified
    Const,
    /// Static (C++23)
    Static,
    /// Explicit object parameter (C++23)
    ExplicitObject,
}

impl fmt::Display for CallOperatorKind {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Mutable => write!(f, "operator()"),
            Self::Const => write!(f, "operator() const"),
            Self::Static => write!(f, "static operator()"),
            Self::ExplicitObject => write!(f, "operator() [explicit object]"),
        }
    }
}

// ═══════════════════════════════════════════════════════════════════════════════
// Multidimensional Subscript Operator — P2128R6
// ═══════════════════════════════════════════════════════════════════════════════

/// Describes a multidimensional subscript operator.
#[derive(Debug, Clone)]
pub struct MultiDimSubscript {
    /// Number of indices accepted
    pub index_count: usize,
    /// Types of the indices
    pub index_types: Vec<String>,
    /// Return type
    pub return_type: String,
    /// Whether the operator is const-qualified
    pub is_const: bool,
    /// Source location for diagnostics
    pub source_line: usize,
}

impl MultiDimSubscript {
    pub fn new(index_count: usize) -> Self {
        Self {
            index_count,
            index_types: Vec::new(),
            return_type: "auto&".to_string(),
            is_const: false,
            source_line: 0,
        }
    }

    /// Validate the multidimensional subscript operator.
    pub fn validate(&self) -> Result<(), Vec<String>> {
        let mut errors = Vec::new();

        // Must have at least one parameter (C++23 allows multiple)
        if self.index_count == 0 {
            errors.push("operator[] must have at least one parameter".to_string());
        }

        // Before C++23, only exactly one parameter was allowed
        // In C++23, any number >= 1 is allowed
        if self.index_count == 0 {
            errors.push("operator[] with zero indices is not allowed".to_string());
        }

        if errors.is_empty() {
            Ok(())
        } else {
            Err(errors)
        }
    }

    /// Generate the call syntax: obj[i, j, k]
    pub fn call_syntax(&self, object: &str, indices: &[&str]) -> String {
        format!("{}[{}]", object, indices.join(", "))
    }

    /// Generate LLVM IR access
    pub fn lower_subscript(&self, base_ptr: &str, indices: &[i64]) -> String {
        let gep_indices: Vec<String> = indices.iter().map(|i| format!("i64 {}", i)).collect();
        format!(
            "getelementptr inbounds {}, {}, {}",
            "i8",
            base_ptr,
            gep_indices.join(", ")
        )
    }
}

// ═══════════════════════════════════════════════════════════════════════════════
// auto(x) and auto{x} — Decay-Copy Prvalue Semantics — P0849R8
// ═══════════════════════════════════════════════════════════════════════════════

/// Represents the kind of decay-copy expression.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum DecayCopyKind {
    /// auto(x) — parentheses form
    DecayCopyParen,
    /// auto{x} — brace form
    DecayCopyBrace,
}

impl fmt::Display for DecayCopyKind {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::DecayCopyParen => write!(f, "auto"),
            Self::DecayCopyBrace => write!(f, "auto{{}}"),
        }
    }
}

/// Represents a decay-copy expression `auto(x)` or `auto{x}`.
#[derive(Debug, Clone)]
pub struct DecayCopyExpr {
    /// The kind of decay-copy expression
    pub kind: DecayCopyKind,
    /// The inner expression being decay-copied
    pub inner_expr: String,
    /// The deduced type after decay
    pub deduced_type: String,
    /// Whether the result is a prvalue
    pub is_prvalue: bool,
}

impl DecayCopyExpr {
    pub fn new(kind: DecayCopyKind, inner: &str) -> Self {
        Self {
            kind,
            inner_expr: inner.to_string(),
            deduced_type: String::new(),
            is_prvalue: true,
        }
    }

    /// Emit the decay-copy as a source representation.
    pub fn emit(&self) -> String {
        match self.kind {
            DecayCopyKind::DecayCopyParen => format!("auto({})", self.inner_expr),
            DecayCopyKind::DecayCopyBrace => format!("auto{{{}}}", self.inner_expr),
        }
    }

    /// Describe the type decay that occurs:
    /// - Arrays decay to pointers
    /// - Functions decay to function pointers
    /// - Top-level cv-qualifiers are stripped
    /// - References are stripped
    pub fn apply_decay(&self, original_type: &str) -> String {
        let mut t = original_type.to_string();
        // Strip references
        if t.ends_with('&') {
            t = t[..t.len() - 1].to_string();
        }
        if t.ends_with("&&") {
            t = t[..t.len() - 2].to_string();
        }
        // Strip top-level const
        if t.starts_with("const ") {
            t = t[6..].to_string();
        }
        // Strip top-level volatile
        if t.starts_with("volatile ") {
            t = t[9..].to_string();
        }
        // Array-to-pointer decay
        if t.ends_with(']') {
            if let Some(bracket_pos) = t.find('[') {
                let base = t[..bracket_pos].trim().to_string();
                t = format!("{}*", base);
            }
        }
        t
    }
}

/// Parser for decay-copy expressions.
pub struct DecayCopyParser;
impl DecayCopyParser {
    /// Attempt to parse an `auto(` or `auto{` decay-copy expression.
    pub fn try_parse(input: &str) -> Option<DecayCopyExpr> {
        let trimmed = input.trim();
        if let Some(rest) = trimmed.strip_prefix("auto(") {
            if let Some(inner) = rest.strip_suffix(')') {
                return Some(DecayCopyExpr::new(DecayCopyKind::DecayCopyParen, inner.trim()));
            }
        }
        if let Some(rest) = trimmed.strip_prefix("auto{") {
            if let Some(inner) = rest.strip_suffix('}') {
                return Some(DecayCopyExpr::new(DecayCopyKind::DecayCopyBrace, inner.trim()));
            }
        }
        None
    }
}

// ═══════════════════════════════════════════════════════════════════════════════
// #warning Preprocessor Directive — P2437R1
// ═══════════════════════════════════════════════════════════════════════════════

/// Represents a `#warning` preprocessor directive.
#[derive(Debug, Clone)]
pub struct WarningDirective {
    /// The message text
    pub message: String,
    /// Source location (line number)
    pub line: usize,
    /// Source file name
    pub file: String,
}

impl WarningDirective {
    pub fn new(message: &str, line: usize, file: &str) -> Self {
        Self {
            message: message.to_string(),
            line,
            file: file.to_string(),
        }
    }

    /// Format the diagnostic message like a compiler does.
    pub fn format_diagnostic(&self) -> String {
        format!("{}:{}: warning: {}", self.file, self.line, self.message)
    }
}

/// Handler for `#warning` in the preprocessor.
pub struct WarningDirectiveHandler {
    pub warnings: Vec<WarningDirective>,
    pub treat_warnings_as_errors: bool,
}

impl WarningDirectiveHandler {
    pub fn new() -> Self {
        Self {
            warnings: Vec::new(),
            treat_warnings_as_errors: false,
        }
    }

    /// Process a `#warning` directive.
    pub fn handle(&mut self, message: &str, line: usize, file: &str) {
        let warning = WarningDirective::new(message, line, file);
        self.warnings.push(warning);
    }

    /// Check if any warnings were emitted.
    pub fn has_warnings(&self) -> bool {
        !self.warnings.is_empty()
    }
}

impl Default for WarningDirectiveHandler {
    fn default() -> Self {
        Self::new()
    }
}

// ═══════════════════════════════════════════════════════════════════════════════
// #elifdef and #elifndef — P2334R1
// ═══════════════════════════════════════════════════════════════════════════════

/// Represents the preprocessor conditional inclusion shortcuts.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ElifConditional {
    /// Standard `#elif`
    Elif,
    /// `#elifdef MACRO` — equivalent to `#elif defined(MACRO)`
    Elifdef,
    /// `#elifndef MACRO` — equivalent to `#elif !defined(MACRO)`
    Elifndef,
}

impl ElifConditional {
    pub fn from_directive(s: &str) -> Option<Self> {
        match s.trim() {
            "elif" => Some(Self::Elif),
            "elifdef" => Some(Self::Elifdef),
            "elifndef" => Some(Self::Elifndef),
            _ => None,
        }
    }

    pub fn as_str(&self) -> &'static str {
        match self {
            Self::Elif => "#elif",
            Self::Elifdef => "#elifdef",
            Self::Elifndef => "#elifndef",
        }
    }
}

/// A conditional block in the preprocessor.
#[derive(Debug, Clone)]
pub struct ConditionalBlock {
    pub condition: String,
    pub conditional_type: ElifConditional,
    pub body: String,
    pub was_taken: bool,
}

/// Preprocessor conditional chain handler.
pub struct ConditionalChain {
    /// The stack of #if / #ifdef / #ifndef conditions
    pub blocks: Vec<ConditionalBlock>,
    /// Whether we have taken a branch already
    pub branch_taken: bool,
    /// Whether we warned about missing #endif
    pub warned_missing_endif: bool,
}

impl ConditionalChain {
    pub fn new() -> Self {
        Self {
            blocks: Vec::new(),
            branch_taken: false,
            warned_missing_endif: false,
        }
    }

    /// Handle `#ifdef MACRO`.
    pub fn handle_ifdef(&mut self, macro_name: &str, is_defined: bool) {
        let block = ConditionalBlock {
            condition: format!("defined({})", macro_name),
            conditional_type: ElifConditional::Elif,
            body: String::new(),
            was_taken: !self.branch_taken && is_defined,
        };
        if block.was_taken {
            self.branch_taken = true;
        }
        self.blocks.push(block);
    }

    /// Handle `#ifndef MACRO`.
    pub fn handle_ifndef(&mut self, macro_name: &str, is_defined: bool) {
        let block = ConditionalBlock {
            condition: format!("!defined({})", macro_name),
            conditional_type: ElifConditional::Elif,
            body: String::new(),
            was_taken: !self.branch_taken && !is_defined,
        };
        if block.was_taken {
            self.branch_taken = true;
        }
        self.blocks.push(block);
    }

    /// Handle `#elifdef MACRO`.
    pub fn handle_elifdef(&mut self, macro_name: &str, is_defined: bool) {
        if self.branch_taken {
            return; // Already took a branch, skip this
        }
        let block = ConditionalBlock {
            condition: format!("defined({})", macro_name),
            conditional_type: ElifConditional::Elifdef,
            body: String::new(),
            was_taken: is_defined,
        };
        if is_defined {
            self.branch_taken = true;
        }
        self.blocks.push(block);
    }

    /// Handle `#elifndef MACRO`.
    pub fn handle_elifndef(&mut self, macro_name: &str, is_defined: bool) {
        if self.branch_taken {
            return;
        }
        let block = ConditionalBlock {
            condition: format!("!defined({})", macro_name),
            conditional_type: ElifConditional::Elifndef,
            body: String::new(),
            was_taken: !is_defined,
        };
        if !is_defined {
            self.branch_taken = true;
        }
        self.blocks.push(block);
    }

    /// Handle the trailing `#else`.
    pub fn handle_else(&mut self) {
        if self.branch_taken {
            return;
        }
        let block = ConditionalBlock {
            condition: "else".to_string(),
            conditional_type: ElifConditional::Elif,
            body: String::new(),
            was_taken: true,
        };
        self.branch_taken = true;
        self.blocks.push(block);
    }

    /// Reset for a new conditional chain.
    pub fn reset(&mut self) {
        self.blocks.clear();
        self.branch_taken = false;
    }
}

impl Default for ConditionalChain {
    fn default() -> Self {
        Self::new()
    }
}

// ═══════════════════════════════════════════════════════════════════════════════
// Literal Suffix for size_t — P0330R8
// ═══════════════════════════════════════════════════════════════════════════════

/// Represents the C++23 literal suffixes for size_t and signed size_t.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum SizeTLiteralSuffix {
    /// `uz` — unsigned size_t (std::size_t)
    Uz,
    /// `z` — signed size_t (std::ssize_t / ptrdiff_t)
    Z,
}

impl SizeTLiteralSuffix {
    pub fn from_suffix(s: &str) -> Option<Self> {
        match s {
            "uz" | "UZ" | "Uz" | "uZ" => Some(Self::Uz),
            "z" | "Z" => Some(Self::Z),
            _ => None,
        }
    }

    pub fn as_str(&self) -> &'static str {
        match self {
            Self::Uz => "uz",
            Self::Z => "z",
        }
    }

    pub fn is_signed(&self) -> bool {
        matches!(self, Self::Z)
    }

    pub fn type_name(&self) -> &'static str {
        match self {
            Self::Uz => "std::size_t",
            Self::Z => "std::ptrdiff_t",
        }
    }
}

/// A literal with a size_t suffix.
#[derive(Debug, Clone)]
pub struct SizeTLiteral {
    pub value: String,
    pub suffix: SizeTLiteralSuffix,
}

impl SizeTLiteral {
    pub fn new(value: &str, suffix: SizeTLiteralSuffix) -> Self {
        Self {
            value: value.to_string(),
            suffix,
        }
    }

    pub fn to_source(&self) -> String {
        format!("{}{}", self.value, self.suffix.as_str())
    }
}

/// Parser for size_t literal suffixes.
pub struct SizeTLiteralParser;

impl SizeTLiteralParser {
    /// Try to parse an integer literal with a `z` or `uz` suffix.
    pub fn try_parse(input: &str) -> Option<SizeTLiteral> {
        let trimmed = input.trim();
        // Check for uz suffix first (must check before z alone)
        for suffix_str in &["uz", "UZ", "Uz", "uZ"] {
            if let Some(value) = trimmed.strip_suffix(suffix_str) {
                if !value.is_empty()
                    && value.chars().all(|c| c.is_ascii_digit() || c == '\'')
                {
                    return Some(SizeTLiteral::new(value, SizeTLiteralSuffix::Uz));
                }
            }
        }
        // Check for z suffix
        for suffix_str in &["z", "Z"] {
            if let Some(value) = trimmed.strip_suffix(suffix_str) {
                if !value.is_empty()
                    && value.chars().all(|c| c.is_ascii_digit() || c == '\'')
                {
                    return Some(SizeTLiteral::new(value, SizeTLiteralSuffix::Z));
                }
            }
        }
        None
    }
}

// ═══════════════════════════════════════════════════════════════════════════════
// constexpr Extensions — Virtual, Try-Catch, Dynamic Cast
// ═══════════════════════════════════════════════════════════════════════════════

/// Tracks which extended constexpr features are enabled.
#[derive(Debug, Clone)]
pub struct ConstexprExtensions {
    /// C++20: constexpr virtual functions (P1064R0)
    pub constexpr_virtual: bool,
    /// C++20: constexpr try-catch (P1002R1)
    pub constexpr_try_catch: bool,
    /// C++20: constexpr dynamic_cast / typeid (P1327R1)
    pub constexpr_dynamic_cast: bool,
    /// C++20: constexpr union with active member change (P1330R0)
    pub constexpr_union: bool,
    /// C++23: constexpr std::unique_ptr (P2273R1)
    pub constexpr_unique_ptr: bool,
    /// C++26: constexpr placement new
    pub constexpr_placement_new: bool,
}

impl Default for ConstexprExtensions {
    fn default() -> Self {
        Self {
            constexpr_virtual: true,
            constexpr_try_catch: true,
            constexpr_dynamic_cast: true,
            constexpr_union: true,
            constexpr_unique_ptr: false,
            constexpr_placement_new: false,
        }
    }
}

/// Represents a constexpr virtual function.
#[derive(Debug, Clone)]
pub struct ConstexprVirtualFunction {
    pub name: String,
    pub class_name: String,
    pub is_override: bool,
    pub is_final: bool,
    pub is_pure_virtual: bool,
    pub vtable_index: Option<usize>,
}

impl ConstexprVirtualFunction {
    pub fn new(name: &str, class_name: &str) -> Self {
        Self {
            name: name.to_string(),
            class_name: class_name.to_string(),
            is_override: false,
            is_final: false,
            is_pure_virtual: false,
            vtable_index: None,
        }
    }

    /// Validate that a constexpr virtual function is well-formed.
    pub fn validate(&self) -> Result<(), String> {
        if self.is_pure_virtual {
            return Err(format!(
                "constexpr virtual function '{}' cannot be pure virtual",
                self.name
            ));
        }
        // The function body must be a constant expression when evaluated
        // for a constexpr object
        Ok(())
    }
}

/// Represents a constexpr try-catch block.
#[derive(Debug, Clone)]
pub struct ConstexprTryCatch {
    /// Whether the try-block is in a constexpr context
    pub is_constexpr: bool,
    /// The exception types caught
    pub catch_types: Vec<String>,
    /// Whether any catch block can be evaluated at compile time
    pub can_be_constexpr: bool,
}

impl ConstexprTryCatch {
    pub fn new() -> Self {
        Self {
            is_constexpr: false,
            catch_types: Vec::new(),
            can_be_constexpr: true,
        }
    }

    /// Validate that try-catch can be constexpr.
    /// A throw that is actually evaluated in a constexpr context is an error.
    pub fn validate(&self) -> Result<(), String> {
        if !self.is_constexpr {
            return Ok(());
        }
        // constexpr try-catch is allowed, but if the try-block throws at
        // constant evaluation time, it's not a core constant expression
        Ok(())
    }
}

impl Default for ConstexprTryCatch {
    fn default() -> Self {
        Self::new()
    }
}

/// Represents a constexpr dynamic_cast.
#[derive(Debug, Clone)]
pub struct ConstexprDynamicCast {
    /// The source expression type
    pub src_type: String,
    /// The target type
    pub dst_type: String,
    /// Whether this is a downcast (base -> derived)
    pub is_downcast: bool,
    /// Whether this is a cross-cast
    pub is_crosscast: bool,
}

impl ConstexprDynamicCast {
    pub fn new(src_type: &str, dst_type: &str) -> Self {
        Self {
            src_type: src_type.to_string(),
            dst_type: dst_type.to_string(),
            is_downcast: false,
            is_crosscast: false,
        }
    }

    /// Validate that dynamic_cast can be constexpr.
    /// Requires the full type hierarchy to be known at compile time.
    pub fn validate(&self) -> Result<(), String> {
        if self.is_crosscast {
            // Cross-casts via virtual base are even trickier
            // but C++20 permits them in constexpr if the type is complete
        }
        Ok(())
    }
}

// ═══════════════════════════════════════════════════════════════════════════════
// std::unreachable() — P0627R6
// ═══════════════════════════════════════════════════════════════════════════════

/// Represents the `std::unreachable()` function (C++23).
#[derive(Debug, Clone)]
pub struct UnreachableBuiltin {
    /// The function name
    pub name: String,
    /// Whether it has the `[[noreturn]]` attribute
    pub is_noreturn: bool,
    /// Whether we should emit a trap instruction
    pub emit_trap: bool,
}

impl UnreachableBuiltin {
    pub fn new() -> Self {
        Self {
            name: "std::unreachable".to_string(),
            is_noreturn: true,
            emit_trap: true,
        }
    }

    /// Emit LLVM IR for a call to std::unreachable().
    pub fn emit_llvm(&self) -> String {
        if self.emit_trap {
            "call void @llvm.trap()\n  unreachable".to_string()
        } else {
            "unreachable".to_string()
        }
    }

    /// Describe the semantics for users.
    pub fn description(&self) -> &'static str {
        "std::unreachable() indicates that a code path cannot be reached. \
         If reached at runtime, behavior is undefined. At compile time, \
         the optimizer may use this to eliminate dead code."
    }
}

impl Default for UnreachableBuiltin {
    fn default() -> Self {
        Self::new()
    }
}

// ═══════════════════════════════════════════════════════════════════════════════
// Monadic Operations for std::optional — P0798R8
// ═══════════════════════════════════════════════════════════════════════════════

/// Represents the monadic operations available on std::optional<T>.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum OptionalMonadicOp {
    /// `opt.and_then(f)` — returns f(*opt) if opt has value, nullopt otherwise
    AndThen,
    /// `opt.or_else(f)` — returns opt if it has value, f() otherwise
    OrElse,
    /// `opt.transform(f)` — returns optional<U>(f(*opt)) if opt has value
    Transform,
}

impl fmt::Display for OptionalMonadicOp {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::AndThen => write!(f, "and_then"),
            Self::OrElse => write!(f, "or_else"),
            Self::Transform => write!(f, "transform"),
        }
    }
}

/// Descriptor for std::optional<T> with monadic operations.
#[derive(Debug, Clone)]
pub struct OptionalMonadic {
    /// The contained type
    pub value_type: String,
    /// Whether the monadic operations are enabled (C++23)
    pub monadic_enabled: bool,
}

impl OptionalMonadic {
    pub fn new(value_type: &str) -> Self {
        Self {
            value_type: value_type.to_string(),
            monadic_enabled: true,
        }
    }

    /// Generate the return type for and_then given a callable f.
    pub fn and_then_return_type(&self, f_return_optional_of: &str) -> String {
        format!("std::optional<{}>", f_return_optional_of)
    }

    /// Generate the return type for transform given a callable f.
    pub fn transform_return_type(&self, f_return_type: &str) -> String {
        format!("std::optional<{}>", f_return_type)
    }

    /// Generate the return type for or_else.
    /// or_else returns the same std::optional<T> type.
    pub fn or_else_return_type(&self) -> String {
        format!("std::optional<{}>", self.value_type)
    }

    /// Codegen: generate a pseudo-implementation of and_then.
    pub fn codegen_and_then(&self) -> String {
        format!(
            "if (this->has_value()) {{\n    return f(**this);  // f returns optional<U>\n}} else {{\n    return std::nullopt;\n}}"
        )
    }

    /// Codegen: generate a pseudo-implementation of or_else.
    pub fn codegen_or_else(&self) -> String {
        format!(
            "if (this->has_value()) {{\n    return *this;\n}} else {{\n    return f();\n}}"
        )
    }

    /// Codegen: generate a pseudo-implementation of transform.
    pub fn codegen_transform(&self) -> String {
        format!(
            "if (this->has_value()) {{\n    return std::optional<U>(f(**this));\n}} else {{\n    return std::nullopt;\n}}"
        )
    }
}

// ═══════════════════════════════════════════════════════════════════════════════
// std::expected<T,E> — P0323R12
// ═══════════════════════════════════════════════════════════════════════════════

/// Represents the error type in std::expected.
#[derive(Debug, Clone)]
pub enum ExpectedError {
    /// std::unexpected<E> wrapper
    Unexpected(String),
    /// Default-constructed error from E
    Default,
}

/// Monadic operations for std::expected<T,E> (C++23).
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ExpectedMonadicOp {
    /// `exp.and_then(f)` — if has_value, returns f(*exp); else returns unexpected
    AndThen,
    /// `exp.or_else(f)` — if has_value, returns *exp; else calls f(error())
    OrElse,
    /// `exp.transform(f)` — if has_value, returns expected<U,E>(f(*exp))
    Transform,
    /// `exp.transform_error(f)` — if !has_value, returns expected<T,G>(unexpected, f(error()))
    TransformError,
}

impl fmt::Display for ExpectedMonadicOp {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::AndThen => write!(f, "and_then"),
            Self::OrElse => write!(f, "or_else"),
            Self::Transform => write!(f, "transform"),
            Self::TransformError => write!(f, "transform_error"),
        }
    }
}

/// Descriptor for std::expected<T, E>.
#[derive(Debug, Clone)]
pub struct ExpectedType {
    /// The value type T
    pub value_type: String,
    /// The error type E (must not be a reference, must not be void)
    pub error_type: String,
    /// Whether monadic operations are enabled
    pub monadic_enabled: bool,
}

impl ExpectedType {
    pub fn new(value_type: &str, error_type: &str) -> Self {
        Self {
            value_type: value_type.to_string(),
            error_type: error_type.to_string(),
            monadic_enabled: true,
        }
    }

    /// Validate the std::expected type constraints.
    pub fn validate(&self) -> Result<(), String> {
        if self.value_type == "void" {
            // void value type is allowed in C++23 (P2505R5-style)
        }
        if self.error_type == "void" {
            return Err("std::expected error type cannot be void".to_string());
        }
        Ok(())
    }

    /// Generate the return type for and_then.
    pub fn and_then_return_type(&self, f_return_expected_of: &str) -> String {
        format!(
            "std::expected<{}, {}>",
            f_return_expected_of, self.error_type
        )
    }

    /// Generate the return type for transform.
    pub fn transform_return_type(&self, f_return_type: &str) -> String {
        format!(
            "std::expected<{}, {}>",
            f_return_type, self.error_type
        )
    }

    /// Generate the return type for transform_error.
    pub fn transform_error_return_type(&self, f_return_error: &str) -> String {
        format!(
            "std::expected<{}, {}>",
            self.value_type, f_return_error
        )
    }

    /// Generate the return type for or_else.
    pub fn or_else_return_type(&self) -> String {
        format!("std::expected<{}, {}>", self.value_type, self.error_type)
    }

    /// Codegen for and_then.
    pub fn codegen_and_then(&self) -> String {
        "if (has_value) return invoke(f, value); else return unexpected(error);".to_string()
    }

    /// Codegen for or_else.
    pub fn codegen_or_else(&self) -> String {
        "if (has_value) return expected(value, in_place); else return invoke(f, error);".to_string()
    }

    /// Codegen for transform.
    pub fn codegen_transform(&self) -> String {
        "if (has_value) return expected(invoke(f, value)); else return unexpected(error);".to_string()
    }

    /// Codegen for transform_error.
    pub fn codegen_transform_error(&self) -> String {
        "if (!has_value) return expected(unexpected(invoke(f, error))); else return expected(value, in_place);".to_string()
    }
}

/// A value-or-error construct.
#[derive(Debug, Clone)]
pub enum ExpectedValue<T, E> {
    Ok(T),
    Err(E),
}

impl<T, E> ExpectedValue<T, E> {
    pub fn is_ok(&self) -> bool {
        matches!(self, Self::Ok(_))
    }

    pub fn is_err(&self) -> bool {
        matches!(self, Self::Err(_))
    }

    pub fn map<U, F: FnOnce(T) -> U>(self, f: F) -> ExpectedValue<U, E> {
        match self {
            Self::Ok(v) => ExpectedValue::Ok(f(v)),
            Self::Err(e) => ExpectedValue::Err(e),
        }
    }

    pub fn and_then<U, F: FnOnce(T) -> ExpectedValue<U, E>>(self, f: F) -> ExpectedValue<U, E> {
        match self {
            Self::Ok(v) => f(v),
            Self::Err(e) => ExpectedValue::Err(e),
        }
    }

    pub fn or_else<F: FnOnce(E) -> ExpectedValue<T, E>>(self, f: F) -> ExpectedValue<T, E> {
        match self {
            Self::Ok(v) => ExpectedValue::Ok(v),
            Self::Err(e) => f(e),
        }
    }
}

// ═══════════════════════════════════════════════════════════════════════════════
// Ranges Extensions — C++23/C++26
// ═══════════════════════════════════════════════════════════════════════════════

/// A view adaptor in the ranges library.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum RangeViewAdaptor {
    /// `views::zip` — zip multiple ranges
    Zip,
    /// `views::zip_transform` — zip with transformation
    ZipTransform,
    /// `views::adjacent<N>` — sliding window of N elements
    Adjacent,
    /// `views::adjacent_transform<N>` — sliding window with transform
    AdjacentTransform,
    /// `views::cartesian_product` — cartesian product of ranges
    CartesianProduct,
    /// `views::enumerate` — index + element pairs
    Enumerate,
    /// `views::as_const` — const view of range elements
    AsConst,
    /// `views::as_rvalue` — rvalue view of range elements
    AsRvalue,
    /// `views::repeat` — repeat a value N or infinite times
    Repeat,
    /// `views::stride` — skip N-1 elements between each returned
    Stride,
    /// `views::slide` — sliding window of N elements (overlapping)
    Slide,
    /// `views::chunk` — non-overlapping chunks of N elements
    Chunk,
    /// `views::chunk_by` — chunk by a predicate
    ChunkBy,
    /// `views::join_with` — join with a delimiter
    JoinWith,
    /// `views::iota` — iota view extensions
    Iota,
}

impl RangeViewAdaptor {
    pub fn name(&self) -> &'static str {
        match self {
            Self::Zip => "zip",
            Self::ZipTransform => "zip_transform",
            Self::Adjacent => "adjacent",
            Self::AdjacentTransform => "adjacent_transform",
            Self::CartesianProduct => "cartesian_product",
            Self::Enumerate => "enumerate",
            Self::AsConst => "as_const",
            Self::AsRvalue => "as_rvalue",
            Self::Repeat => "repeat",
            Self::Stride => "stride",
            Self::Slide => "slide",
            Self::Chunk => "chunk",
            Self::ChunkBy => "chunk_by",
            Self::JoinWith => "join_with",
            Self::Iota => "iota",
        }
    }

    pub fn header(&self) -> &'static str {
        match self {
            Self::Zip | Self::ZipTransform | Self::Adjacent | Self::AdjacentTransform => {
                "<ranges>"
            }
            Self::CartesianProduct | Self::Enumerate | Self::AsConst | Self::AsRvalue => {
                "<ranges>"
            }
            Self::Repeat | Self::Stride | Self::Slide | Self::Chunk | Self::ChunkBy
            | Self::JoinWith | Self::Iota => "<ranges>",
        }
    }
}

/// Configuration for a range view.
#[derive(Debug, Clone)]
pub struct RangeViewConfig {
    pub adaptor: RangeViewAdaptor,
    pub element_type: String,
    pub is_const: bool,
    pub is_sized: bool,
    pub is_borrowed: bool,
    pub is_common: bool,
}

impl RangeViewConfig {
    pub fn new(adaptor: RangeViewAdaptor, element_type: &str) -> Self {
        let (is_sized, is_borrowed, is_common) = match adaptor {
            RangeViewAdaptor::Zip => (true, false, true),
            RangeViewAdaptor::ZipTransform => (true, false, true),
            RangeViewAdaptor::Adjacent => (true, false, false),
            RangeViewAdaptor::AdjacentTransform => (true, false, false),
            RangeViewAdaptor::CartesianProduct => (true, false, true),
            RangeViewAdaptor::Enumerate => (true, false, true),
            RangeViewAdaptor::AsConst => (true, false, true),
            RangeViewAdaptor::AsRvalue => (true, false, true),
            RangeViewAdaptor::Repeat => (false, false, false),
            RangeViewAdaptor::Stride => (true, false, false),
            RangeViewAdaptor::Slide => (true, false, false),
            RangeViewAdaptor::Chunk => (true, false, false),
            RangeViewAdaptor::ChunkBy => (false, false, false),
            RangeViewAdaptor::JoinWith => (false, false, false),
            RangeViewAdaptor::Iota => (true, false, true),
        };
        Self {
            adaptor,
            element_type: element_type.to_string(),
            is_const: false,
            is_sized,
            is_borrowed,
            is_common,
        }
    }
}

/// Iterator for a zip view.
#[derive(Debug, Clone)]
pub struct ZipIterator {
    pub ranges_count: usize,
    pub value_types: Vec<String>,
}

impl ZipIterator {
    pub fn new(count: usize, types: Vec<String>) -> Self {
        Self {
            ranges_count: count,
            value_types: types,
        }
    }

    pub fn deref_type(&self) -> String {
        format!(
            "std::tuple<{}>",
            self.value_types
                .iter()
                .map(|t| format!("{}&", t))
                .collect::<Vec<_>>()
                .join(", ")
        )
    }
}

/// Iterator for an enumerate view.
#[derive(Debug, Clone)]
pub struct EnumerateIterator {
    pub value_type: String,
    pub index_type: String,
}

impl EnumerateIterator {
    pub fn new(value_type: &str) -> Self {
        Self {
            value_type: value_type.to_string(),
            index_type: "std::size_t".to_string(),
        }
    }

    pub fn element_type(&self) -> String {
        format!(
            "std::tuple<{}, {}&>",
            self.index_type, self.value_type
        )
    }
}

/// A chunk view over a range.
#[derive(Debug, Clone)]
pub struct ChunkView {
    pub chunk_size: usize,
    pub element_type: String,
}

impl ChunkView {
    pub fn new(chunk_size: usize, element_type: &str) -> Self {
        Self {
            chunk_size,
            element_type: element_type.to_string(),
        }
    }

    pub fn inner_range_type(&self) -> String {
        format!("std::ranges::take_view<std::ranges::ref_view<{}>>", self.element_type)
    }
}

/// A cartesian product view.
#[derive(Debug, Clone)]
pub struct CartesianProductView {
    pub first_type: String,
    pub second_type: String,
}

impl CartesianProductView {
    pub fn new(first: &str, second: &str) -> Self {
        Self {
            first_type: first.to_string(),
            second_type: second.to_string(),
        }
    }

    pub fn element_type(&self) -> String {
        format!(
            "std::tuple<{}&, {}&>",
            self.first_type, self.second_type
        )
    }
}

/// Registry for ranges adaptors.
pub struct RangesAdaptorRegistry {
    adaptors: BTreeMap<String, RangeViewConfig>,
}

impl RangesAdaptorRegistry {
    pub fn new() -> Self {
        let mut registry = Self {
            adaptors: BTreeMap::new(),
        };
        // Register all C++23 adaptors
        for adaptor in &[
            RangeViewAdaptor::Zip,
            RangeViewAdaptor::ZipTransform,
            RangeViewAdaptor::Adjacent,
            RangeViewAdaptor::AdjacentTransform,
            RangeViewAdaptor::CartesianProduct,
            RangeViewAdaptor::Enumerate,
            RangeViewAdaptor::AsConst,
            RangeViewAdaptor::AsRvalue,
            RangeViewAdaptor::Repeat,
            RangeViewAdaptor::Stride,
            RangeViewAdaptor::Slide,
            RangeViewAdaptor::Chunk,
            RangeViewAdaptor::ChunkBy,
            RangeViewAdaptor::JoinWith,
            RangeViewAdaptor::Iota,
        ] {
            let config = RangeViewConfig::new(*adaptor, "auto");
            registry.adaptors.insert(adaptor.name().to_string(), config);
        }
        registry
    }

    pub fn lookup(&self, name: &str) -> Option<&RangeViewConfig> {
        self.adaptors.get(name)
    }

    pub fn is_adaptor(&self, name: &str) -> bool {
        self.adaptors.contains_key(name)
    }

    pub fn adaptor_names(&self) -> Vec<&str> {
        self.adaptors.keys().map(|s| s.as_str()).collect()
    }

    pub fn count(&self) -> usize {
        self.adaptors.len()
    }
}

impl Default for RangesAdaptorRegistry {
    fn default() -> Self {
        Self::new()
    }
}

// ═══════════════════════════════════════════════════════════════════════════════
// C++23 Feature Flags Registry
// ═══════════════════════════════════════════════════════════════════════════════

/// Represents a C++23 or C++26 feature flag.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum CXX23Feature {
    DeducingThis,
    IfConsteval,
    StaticOperatorCall,
    MultiDimSubscript,
    DecayCopy,
    WarningDirective,
    ElifdefElifndef,
    SizeTLiteral,
    ConstexprVirtual,
    ConstexprTryCatch,
    ConstexprDynamicCast,
    Unreachable,
    OptionalMonadic,
    Expected,
    ZipView,
    ZipTransformView,
    EnumerateView,
    AdjacentView,
    CartesianProductView,
    AsConstView,
    AsRvalueView,
    RepeatView,
    StrideView,
    SlideView,
    ChunkView,
    ChunkByView,
    JoinWithView,
}

impl CXX23Feature {
    pub fn name(&self) -> &'static str {
        match self {
            Self::DeducingThis => "deducing_this",
            Self::IfConsteval => "if_consteval",
            Self::StaticOperatorCall => "static_operator_call",
            Self::MultiDimSubscript => "multidimensional_subscript",
            Self::DecayCopy => "decay_copy",
            Self::WarningDirective => "warning_directive",
            Self::ElifdefElifndef => "elifdef_elifndef",
            Self::SizeTLiteral => "size_t_literal",
            Self::ConstexprVirtual => "constexpr_virtual",
            Self::ConstexprTryCatch => "constexpr_try_catch",
            Self::ConstexprDynamicCast => "constexpr_dynamic_cast",
            Self::Unreachable => "unreachable",
            Self::OptionalMonadic => "optional_monadic",
            Self::Expected => "expected",
            Self::ZipView => "zip_view",
            Self::ZipTransformView => "zip_transform_view",
            Self::EnumerateView => "enumerate_view",
            Self::AdjacentView => "adjacent_view",
            Self::CartesianProductView => "cartesian_product_view",
            Self::AsConstView => "as_const_view",
            Self::AsRvalueView => "as_rvalue_view",
            Self::RepeatView => "repeat_view",
            Self::StrideView => "stride_view",
            Self::SlideView => "slide_view",
            Self::ChunkView => "chunk_view",
            Self::ChunkByView => "chunk_by_view",
            Self::JoinWithView => "join_with_view",
        }
    }

    pub fn paper_number(&self) -> &'static str {
        match self {
            Self::DeducingThis => "P0847R7",
            Self::IfConsteval => "P1938R3",
            Self::StaticOperatorCall => "P1169R4",
            Self::MultiDimSubscript => "P2128R6",
            Self::DecayCopy => "P0849R8",
            Self::WarningDirective => "P2437R1",
            Self::ElifdefElifndef => "P2334R1",
            Self::SizeTLiteral => "P0330R8",
            Self::ConstexprVirtual => "P1064R0",
            Self::ConstexprTryCatch => "P1002R1",
            Self::ConstexprDynamicCast => "P1327R1",
            Self::Unreachable => "P0627R6",
            Self::OptionalMonadic => "P0798R8",
            Self::Expected => "P0323R12",
            Self::ZipView => "P2321R2",
            Self::ZipTransformView => "P2321R2",
            Self::EnumerateView => "P2164R9",
            Self::AdjacentView => "P2321R2",
            Self::CartesianProductView => "P2374R4",
            Self::AsConstView => "P2278R4",
            Self::AsRvalueView => "P2446R2",
            Self::RepeatView => "P2474R2",
            Self::StrideView => "P1899R3",
            Self::SlideView => "P2442R1",
            Self::ChunkView => "P2442R1",
            Self::ChunkByView => "P2443R1",
            Self::JoinWithView => "P2441R2",
        }
    }
}

/// Registry for tracking which C++23/26 features are enabled.
pub struct CXX23FeatureRegistry {
    features: HashMap<CXX23Feature, bool>,
    standard_version: CXXStandardVersion,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum CXXStandardVersion {
    CXX17,
    CXX20,
    CXX23,
    CXX26,
}

impl CXXStandardVersion {
    pub fn as_str(&self) -> &'static str {
        match self {
            Self::CXX17 => "c++17",
            Self::CXX20 => "c++20",
            Self::CXX23 => "c++23",
            Self::CXX26 => "c++26",
        }
    }

    pub fn from_str(s: &str) -> Option<Self> {
        match s {
            "c++17" | "c++1z" => Some(Self::CXX17),
            "c++20" | "c++2a" => Some(Self::CXX20),
            "c++23" | "c++2b" => Some(Self::CXX23),
            "c++26" | "c++2c" => Some(Self::CXX26),
            _ => None,
        }
    }
}

impl CXX23FeatureRegistry {
    pub fn new(standard: CXXStandardVersion) -> Self {
        let mut features = HashMap::new();
        // Initialize all features to false
        for feature in &[
            CXX23Feature::DeducingThis,
            CXX23Feature::IfConsteval,
            CXX23Feature::StaticOperatorCall,
            CXX23Feature::MultiDimSubscript,
            CXX23Feature::DecayCopy,
            CXX23Feature::WarningDirective,
            CXX23Feature::ElifdefElifndef,
            CXX23Feature::SizeTLiteral,
            CXX23Feature::ConstexprVirtual,
            CXX23Feature::ConstexprTryCatch,
            CXX23Feature::ConstexprDynamicCast,
            CXX23Feature::Unreachable,
            CXX23Feature::OptionalMonadic,
            CXX23Feature::Expected,
            CXX23Feature::ZipView,
            CXX23Feature::ZipTransformView,
            CXX23Feature::EnumerateView,
            CXX23Feature::AdjacentView,
            CXX23Feature::CartesianProductView,
            CXX23Feature::AsConstView,
            CXX23Feature::AsRvalueView,
            CXX23Feature::RepeatView,
            CXX23Feature::StrideView,
            CXX23Feature::SlideView,
            CXX23Feature::ChunkView,
            CXX23Feature::ChunkByView,
            CXX23Feature::JoinWithView,
        ] {
            // Enable features based on standard version
            let enabled = match standard {
                CXXStandardVersion::CXX17 => false,
                CXXStandardVersion::CXX20 => matches!(
                    feature,
                    CXX23Feature::ConstexprVirtual
                        | CXX23Feature::ConstexprTryCatch
                        | CXX23Feature::ConstexprDynamicCast
                ),
                CXXStandardVersion::CXX23 => true,
                CXXStandardVersion::CXX26 => true,
            };
            features.insert(*feature, enabled);
        }
        Self {
            features,
            standard_version: standard,
        }
    }

    pub fn is_enabled(&self, feature: CXX23Feature) -> bool {
        self.features.get(&feature).copied().unwrap_or(false)
    }

    pub fn enable(&mut self, feature: CXX23Feature) {
        self.features.insert(feature, true);
    }

    pub fn disable(&mut self, feature: CXX23Feature) {
        self.features.insert(feature, false);
    }

    pub fn standard(&self) -> CXXStandardVersion {
        self.standard_version
    }

    pub fn enabled_features(&self) -> Vec<CXX23Feature> {
        self.features
            .iter()
            .filter_map(|(f, &enabled)| if enabled { Some(*f) } else { None })
            .collect()
    }

    pub fn feature_count(&self) -> usize {
        self.features.len()
    }

    pub fn enabled_count(&self) -> usize {
        self.enabled_features().len()
    }
}

// ═══════════════════════════════════════════════════════════════════════════════
// Tests
// ═══════════════════════════════════════════════════════════════════════════════

#[cfg(test)]
mod tests {
    use super::*;

    // ── Deducing This tests ──────────────────────────────────────────────

    #[test]
    fn test_explicit_object_kind_from_param_str() {
        assert_eq!(
            ExplicitObjectKind::from_param_str("this auto&& self"),
            Some(ExplicitObjectKind::DeducedRef)
        );
        assert_eq!(
            ExplicitObjectKind::from_param_str("this auto& self"),
            Some(ExplicitObjectKind::DeducedLvalueRef)
        );
        assert_eq!(
            ExplicitObjectKind::from_param_str("this auto self"),
            Some(ExplicitObjectKind::DeducedByValue)
        );
        assert_eq!(
            ExplicitObjectKind::from_param_str("this const auto& self"),
            Some(ExplicitObjectKind::DeducedConstLvalueRef)
        );
        assert_eq!(ExplicitObjectKind::from_param_str("int x"), None);
    }

    #[test]
    fn test_explicit_object_kind_properties() {
        let by_value = ExplicitObjectKind::DeducedByValue;
        let ref_kind = ExplicitObjectKind::DeducedRef;
        let const_ref = ExplicitObjectKind::DeducedConstLvalueRef;

        assert!(!by_value.is_reference());
        assert!(ref_kind.is_reference());
        assert!(const_ref.is_reference());
        assert!(!by_value.is_const());
        assert!(const_ref.is_const());
    }

    #[test]
    fn test_explicit_object_function_creation() {
        let func = ExplicitObjectFunction::new("f", ExplicitObjectKind::DeducedRef, "self");
        assert_eq!(func.name, "f");
        assert_eq!(func.param_name, "self");
        assert!(func.can_bind_lvalue());
        assert!(func.can_bind_rvalue());
    }

    #[test]
    fn test_explicit_object_function_lvalue_only() {
        let func = ExplicitObjectFunction::new(
            "f",
            ExplicitObjectKind::DeducedLvalueRef,
            "self",
        );
        assert!(func.can_bind_lvalue());
        assert!(!func.can_bind_rvalue());
    }

    #[test]
    fn test_deducing_this_parser_parse_param() {
        let mut parser = DeducingThisParser::new();
        assert_eq!(
            parser.parse_param("this auto&& self"),
            Some(ExplicitObjectKind::DeducedRef)
        );
        assert_eq!(parser.parse_param("int x"), None);
        assert_eq!(parser.parse_param("this is not valid"), None);
    }

    #[test]
    fn test_deducing_this_parser_validate_constructor() {
        let mut parser = DeducingThisParser::new();
        let mut func = ExplicitObjectFunction::new("Foo", ExplicitObjectKind::DeducedRef, "self");
        func.class_name = Some("Foo".to_string());
        func.is_member = true;
        assert!(!parser.validate(&func));
        assert!(!parser.diagnostics.is_empty());
    }

    #[test]
    fn test_deducing_this_parser_deduce_type() {
        let parser = DeducingThisParser::new();
        let func = ExplicitObjectFunction::new("f", ExplicitObjectKind::DeducedRef, "self");
        assert_eq!(parser.deduce_this_type(&func, true), "auto&");
        assert_eq!(parser.deduce_this_type(&func, false), "auto&&");
    }

    // ── if consteval tests ─────────────────────────────────────────────

    #[test]
    fn test_consteval_context_enter_leave() {
        let mut ctx = ConstevalContext::new();
        assert!(!ctx.is_consteval());
        ctx.enter(true);
        assert!(ctx.is_consteval());
        ctx.leave();
        assert!(!ctx.is_consteval());
    }

    #[test]
    fn test_consteval_context_nested() {
        let mut ctx = ConstevalContext::new();
        ctx.enter(false);
        assert!(!ctx.is_consteval());
        ctx.enter(true);
        assert!(ctx.is_consteval());
        ctx.leave();
        assert!(!ctx.is_consteval());
    }

    #[test]
    fn test_evaluate_if_consteval() {
        let mut ctx = ConstevalContext::new();
        assert_eq!(
            ctx.evaluate_if_consteval(),
            IfConstevalResult::NonImmediateContext
        );
        ctx.enter(true);
        assert_eq!(
            ctx.evaluate_if_consteval(),
            IfConstevalResult::ImmediateContext
        );
    }

    #[test]
    fn test_if_consteval_parser_detect() {
        let parser = IfConstevalParser::new();
        assert!(parser.detect_consteval(&["if", "consteval"]));
        assert!(!parser.detect_consteval(&["if", "constexpr"]));
        assert!(!parser.detect_consteval(&["if"]));
    }

    // ── static operator() tests ────────────────────────────────────────

    #[test]
    fn test_static_operator_call_validation() {
        let mut op = StaticOperatorCall::new("MyLambda");
        op.is_lambda = true;
        op.has_captures = false;
        assert!(op.validate().is_ok());

        op.has_captures = true;
        assert!(op.validate().is_err());
    }

    #[test]
    fn test_call_operator_kind_display() {
        assert_eq!(CallOperatorKind::Static.to_string(), "static operator()");
        assert_eq!(CallOperatorKind::Const.to_string(), "operator() const");
    }

    // ── Multidimensional Subscript tests ───────────────────────────────

    #[test]
    fn test_multi_dim_subscript_validation() {
        let sub = MultiDimSubscript::new(2);
        assert!(sub.validate().is_ok());

        let sub0 = MultiDimSubscript::new(0);
        assert!(sub0.validate().is_err());
    }

    #[test]
    fn test_multi_dim_subscript_call_syntax() {
        let sub = MultiDimSubscript::new(2);
        assert_eq!(sub.call_syntax("m", &["i", "j"]), "m[i, j]");
    }

    #[test]
    fn test_multi_dim_subscript_lower() {
        let sub = MultiDimSubscript::new(2);
        let ir = sub.lower_subscript("ptr", &[1, 2]);
        assert!(ir.contains("getelementptr"));
        assert!(ir.contains("i64 1"));
        assert!(ir.contains("i64 2"));
    }

    // ── Decay Copy tests ───────────────────────────────────────────────

    #[test]
    fn test_decay_copy_parser_paren() {
        let expr = DecayCopyParser::try_parse("auto(x)");
        assert!(expr.is_some());
        let expr = expr.unwrap();
        assert_eq!(expr.kind, DecayCopyKind::DecayCopyParen);
        assert_eq!(expr.inner_expr, "x");
    }

    #[test]
    fn test_decay_copy_parser_brace() {
        let expr = DecayCopyParser::try_parse("auto{x}");
        assert!(expr.is_some());
        let expr = expr.unwrap();
        assert_eq!(expr.kind, DecayCopyKind::DecayCopyBrace);
        assert_eq!(expr.inner_expr, "x");
    }

    #[test]
    fn test_decay_copy_parser_not_decay() {
        assert!(DecayCopyParser::try_parse("42").is_none());
        assert!(DecayCopyParser::try_parse("auto").is_none());
    }

    #[test]
    fn test_decay_copy_apply_decay_const_ref() {
        let expr = DecayCopyExpr::new(DecayCopyKind::DecayCopyParen, "x");
        assert_eq!(expr.apply_decay("const int&"), "int");
    }

    #[test]
    fn test_decay_copy_apply_decay_array() {
        let expr = DecayCopyExpr::new(DecayCopyKind::DecayCopyParen, "arr");
        assert_eq!(expr.apply_decay("int[10]"), "int*");
    }

    #[test]
    fn test_decay_copy_display() {
        assert_eq!(
            DecayCopyKind::DecayCopyParen.to_string(),
            "auto"
        );
        assert_eq!(
            DecayCopyKind::DecayCopyBrace.to_string(),
            "auto{}"
        );
    }

    // ── #warning directive tests ───────────────────────────────────────

    #[test]
    fn test_warning_directive_format() {
        let w = WarningDirective::new("deprecated API", 42, "test.cpp");
        assert!(w.format_diagnostic().contains("test.cpp"));
        assert!(w.format_diagnostic().contains("42"));
        assert!(w.format_diagnostic().contains("deprecated API"));
    }

    #[test]
    fn test_warning_handler() {
        let mut handler = WarningDirectiveHandler::new();
        handler.handle("test warning", 10, "file.cpp");
        assert!(handler.has_warnings());
        assert_eq!(handler.warnings.len(), 1);
    }

    // ── #elifdef / #elifndef tests ──────────────────────────────────────

    #[test]
    fn test_elif_conditional_from_directive() {
        assert_eq!(
            ElifConditional::from_directive("elifdef"),
            Some(ElifConditional::Elifdef)
        );
        assert_eq!(
            ElifConditional::from_directive("elifndef"),
            Some(ElifConditional::Elifndef)
        );
        assert_eq!(
            ElifConditional::from_directive("elif"),
            Some(ElifConditional::Elif)
        );
        assert_eq!(ElifConditional::from_directive("ifndef"), None);
    }

    #[test]
    fn test_conditional_chain_ifdef() {
        let mut chain = ConditionalChain::new();
        chain.handle_ifdef("FOO", true);
        assert!(chain.branch_taken);
        assert_eq!(chain.blocks.len(), 1);
    }

    #[test]
    fn test_conditional_chain_elifdef() {
        let mut chain = ConditionalChain::new();
        chain.handle_ifdef("FOO", false);
        assert!(!chain.branch_taken);
        chain.handle_elifdef("BAR", true);
        assert!(chain.branch_taken);
    }

    #[test]
    fn test_conditional_chain_elifndef() {
        let mut chain = ConditionalChain::new();
        chain.handle_ifdef("FOO", false);
        assert!(!chain.branch_taken);
        chain.handle_elifndef("BAR", false);
        assert!(chain.branch_taken);
    }

    #[test]
    fn test_conditional_chain_else() {
        let mut chain = ConditionalChain::new();
        chain.handle_ifdef("FOO", false);
        chain.handle_elifdef("BAR", false);
        chain.handle_else();
        assert!(chain.branch_taken);
    }

    #[test]
    fn test_conditional_chain_reset() {
        let mut chain = ConditionalChain::new();
        chain.handle_ifdef("FOO", true);
        chain.reset();
        assert!(!chain.branch_taken);
        assert!(chain.blocks.is_empty());
    }

    // ── Size T Literal tests ───────────────────────────────────────────

    #[test]
    fn test_size_t_literal_parser_uz() {
        let lit = SizeTLiteralParser::try_parse("42uz");
        assert!(lit.is_some());
        let lit = lit.unwrap();
        assert_eq!(lit.value, "42");
        assert_eq!(lit.suffix, SizeTLiteralSuffix::Uz);
        assert!(!lit.suffix.is_signed());
    }

    #[test]
    fn test_size_t_literal_parser_z() {
        let lit = SizeTLiteralParser::try_parse("42z");
        assert!(lit.is_some());
        let lit = lit.unwrap();
        assert_eq!(lit.suffix, SizeTLiteralSuffix::Z);
        assert!(lit.suffix.is_signed());
    }

    #[test]
    fn test_size_t_literal_parser_non_literal() {
        assert!(SizeTLiteralParser::try_parse("42").is_none());
        assert!(SizeTLiteralParser::try_parse("abc").is_none());
    }

    #[test]
    fn test_size_t_literal_to_source() {
        let lit = SizeTLiteral::new("100", SizeTLiteralSuffix::Uz);
        assert_eq!(lit.to_source(), "100uz");
    }

    // ── constexpr extensions tests ──────────────────────────────────────

    #[test]
    fn test_constexpr_extensions_default() {
        let ext = ConstexprExtensions::default();
        assert!(ext.constexpr_virtual);
        assert!(ext.constexpr_try_catch);
        assert!(ext.constexpr_dynamic_cast);
    }

    #[test]
    fn test_constexpr_virtual_validate_pure() {
        let mut func = ConstexprVirtualFunction::new("f", "Base");
        func.is_pure_virtual = true;
        assert!(func.validate().is_err());
    }

    #[test]
    fn test_constexpr_virtual_validate_normal() {
        let func = ConstexprVirtualFunction::new("f", "Base");
        assert!(func.validate().is_ok());
    }

    #[test]
    fn test_constexpr_try_catch_new() {
        let tc = ConstexprTryCatch::new();
        assert!(!tc.is_constexpr);
        assert!(tc.catch_types.is_empty());
        assert!(tc.can_be_constexpr);
    }

    #[test]
    fn test_constexpr_dynamic_cast_new() {
        let cd = ConstexprDynamicCast::new("Base*", "Derived*");
        assert_eq!(cd.src_type, "Base*");
        assert_eq!(cd.dst_type, "Derived*");
    }

    // ── std::unreachable tests ─────────────────────────────────────────

    #[test]
    fn test_unreachable_emit_llvm() {
        let ub = UnreachableBuiltin::new();
        let ir = ub.emit_llvm();
        assert!(ir.contains("llvm.trap"));
        assert!(ir.contains("unreachable"));
    }

    #[test]
    fn test_unreachable_default() {
        let ub = UnreachableBuiltin::default();
        assert!(ub.is_noreturn);
    }

    // ── Optional Monadic tests ─────────────────────────────────────────

    #[test]
    fn test_optional_monadic_and_then_return() {
        let opt = OptionalMonadic::new("int");
        assert_eq!(
            opt.and_then_return_type("double"),
            "std::optional<double>"
        );
    }

    #[test]
    fn test_optional_monadic_transform_return() {
        let opt = OptionalMonadic::new("int");
        assert_eq!(
            opt.transform_return_type("double"),
            "std::optional<double>"
        );
    }

    #[test]
    fn test_optional_monadic_or_else_return() {
        let opt = OptionalMonadic::new("int");
        assert_eq!(opt.or_else_return_type(), "std::optional<int>");
    }

    #[test]
    fn test_optional_monadic_codegen_and_then() {
        let opt = OptionalMonadic::new("int");
        let cg = opt.codegen_and_then();
        assert!(cg.contains("has_value"));
        assert!(cg.contains("nullopt"));
    }

    #[test]
    fn test_optional_monadic_codegen_or_else() {
        let opt = OptionalMonadic::new("int");
        let cg = opt.codegen_or_else();
        assert!(cg.contains("has_value"));
        assert!(cg.contains("f()"));
    }

    #[test]
    fn test_optional_monadic_op_display() {
        assert_eq!(OptionalMonadicOp::AndThen.to_string(), "and_then");
        assert_eq!(OptionalMonadicOp::OrElse.to_string(), "or_else");
        assert_eq!(OptionalMonadicOp::Transform.to_string(), "transform");
    }

    // ── std::expected tests ────────────────────────────────────────────

    #[test]
    fn test_expected_validation() {
        let exp = ExpectedType::new("int", "std::error_code");
        assert!(exp.validate().is_ok());
    }

    #[test]
    fn test_expected_validation_error_void() {
        let exp = ExpectedType::new("int", "void");
        assert!(exp.validate().is_err());
    }

    #[test]
    fn test_expected_and_then_return() {
        let exp = ExpectedType::new("int", "std::string");
        assert_eq!(
            exp.and_then_return_type("double"),
            "std::expected<double, std::string>"
        );
    }

    #[test]
    fn test_expected_transform_error_return() {
        let exp = ExpectedType::new("int", "std::string");
        assert_eq!(
            exp.transform_error_return_type("int"),
            "std::expected<int, int>"
        );
    }

    #[test]
    fn test_expected_monadic_op_display() {
        assert_eq!(ExpectedMonadicOp::AndThen.to_string(), "and_then");
        assert_eq!(ExpectedMonadicOp::TransformError.to_string(), "transform_error");
    }

    #[test]
    fn test_expected_value_is_ok() {
        let v: ExpectedValue<i32, String> = ExpectedValue::Ok(42);
        assert!(v.is_ok());
        assert!(!v.is_err());
    }

    #[test]
    fn test_expected_value_is_err() {
        let v: ExpectedValue<i32, String> = ExpectedValue::Err("bad".into());
        assert!(!v.is_ok());
        assert!(v.is_err());
    }

    #[test]
    fn test_expected_value_map() {
        let v: ExpectedValue<i32, String> = ExpectedValue::Ok(2);
        let mapped = v.map(|x| x * 3);
        assert!(mapped.is_ok());
        match mapped {
            ExpectedValue::Ok(val) => assert_eq!(val, 6),
            _ => panic!("Expected Ok"),
        }
    }

    #[test]
    fn test_expected_value_and_then() {
        let v: ExpectedValue<i32, String> = ExpectedValue::Ok(1);
        let result = v.and_then(|x| ExpectedValue::Ok(x + 1));
        assert!(result.is_ok());
    }

    #[test]
    fn test_expected_value_or_else() {
        let v: ExpectedValue<i32, String> = ExpectedValue::Err("fail".into());
        let result = v.or_else(|_| ExpectedValue::Ok(0));
        assert!(result.is_ok());
    }

    // ── Range View Adaptor tests ───────────────────────────────────────

    #[test]
    fn test_range_view_adaptor_names() {
        assert_eq!(RangeViewAdaptor::Zip.name(), "zip");
        assert_eq!(RangeViewAdaptor::Enumerate.name(), "enumerate");
        assert_eq!(RangeViewAdaptor::Chunk.name(), "chunk");
        assert_eq!(RangeViewAdaptor::Iota.name(), "iota");
    }

    #[test]
    fn test_range_view_config_zip() {
        let config = RangeViewConfig::new(RangeViewAdaptor::Zip, "int");
        assert!(config.is_sized);
        assert!(!config.is_borrowed);
        assert!(config.is_common);
    }

    #[test]
    fn test_zip_iterator_deref_type() {
        let iter = ZipIterator::new(2, vec!["int".into(), "double".into()]);
        let deref = iter.deref_type();
        assert!(deref.contains("int&"));
        assert!(deref.contains("double&"));
        assert!(deref.contains("tuple"));
    }

    #[test]
    fn test_enumerate_iterator_element_type() {
        let iter = EnumerateIterator::new("int");
        assert!(iter.element_type().contains("size_t"));
        assert!(iter.element_type().contains("int&"));
    }

    #[test]
    fn test_ranges_adaptor_registry_new() {
        let registry = RangesAdaptorRegistry::new();
        assert!(registry.count() > 10);
        assert!(registry.is_adaptor("zip"));
        assert!(registry.is_adaptor("enumerate"));
        assert!(registry.is_adaptor("chunk"));
    }

    #[test]
    fn test_ranges_adaptor_registry_lookup() {
        let registry = RangesAdaptorRegistry::new();
        assert!(registry.lookup("zip").is_some());
        assert!(registry.lookup("nonexistent").is_none());
    }

    // ── Feature flags tests ────────────────────────────────────────────

    #[test]
    fn test_feature_registry_cxx23() {
        let reg = CXX23FeatureRegistry::new(CXXStandardVersion::CXX23);
        assert!(reg.is_enabled(CXX23Feature::DeducingThis));
        assert!(reg.is_enabled(CXX23Feature::OptionalMonadic));
        assert!(reg.is_enabled(CXX23Feature::Expected));
        assert_eq!(reg.standard(), CXXStandardVersion::CXX23);
    }

    #[test]
    fn test_feature_registry_cxx20() {
        let reg = CXX23FeatureRegistry::new(CXXStandardVersion::CXX20);
        assert!(!reg.is_enabled(CXX23Feature::DeducingThis));
        assert!(reg.is_enabled(CXX23Feature::ConstexprVirtual));
        assert!(!reg.is_enabled(CXX23Feature::Expected));
    }

    #[test]
    fn test_feature_registry_cxx17() {
        let reg = CXX23FeatureRegistry::new(CXXStandardVersion::CXX17);
        assert!(!reg.is_enabled(CXX23Feature::DeducingThis));
        assert!(!reg.is_enabled(CXX23Feature::ConstexprVirtual));
    }

    #[test]
    fn test_feature_registry_enable_disable() {
        let mut reg = CXX23FeatureRegistry::new(CXXStandardVersion::CXX20);
        assert!(!reg.is_enabled(CXX23Feature::DeducingThis));
        reg.enable(CXX23Feature::DeducingThis);
        assert!(reg.is_enabled(CXX23Feature::DeducingThis));
        reg.disable(CXX23Feature::DeducingThis);
        assert!(!reg.is_enabled(CXX23Feature::DeducingThis));
    }

    #[test]
    fn test_feature_registry_enabled_count() {
        let reg = CXX23FeatureRegistry::new(CXXStandardVersion::CXX23);
        assert_eq!(reg.enabled_count(), reg.feature_count());
    }

    #[test]
    fn test_cxx_standard_version_from_str() {
        assert_eq!(
            CXXStandardVersion::from_str("c++23"),
            Some(CXXStandardVersion::CXX23)
        );
        assert_eq!(
            CXXStandardVersion::from_str("c++2b"),
            Some(CXXStandardVersion::CXX23)
        );
        assert_eq!(
            CXXStandardVersion::from_str("c++26"),
            Some(CXXStandardVersion::CXX26)
        );
        assert_eq!(CXXStandardVersion::from_str("c++14"), None);
    }

    #[test]
    fn test_feature_paper_numbers() {
        assert_eq!(CXX23Feature::DeducingThis.paper_number(), "P0847R7");
        assert_eq!(CXX23Feature::Expected.paper_number(), "P0323R12");
        assert_eq!(CXX23Feature::EnumerateView.paper_number(), "P2164R9");
    }
}