kconfig-parser 0.1.1

/*
 Cargo KConfig - KConfig parser
 Copyright (C) 2022  Sjoerd van Leent

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THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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*/

//! This file contains the macro lexer, which behaves like a regular lexer,
//! but captures all macro statements and evaluates them.

use std::collections::{HashMap, HashSet, VecDeque};
use std::hash::{Hash, Hasher};

use super::{
    structs::{Lexicon, Token},
    LexerBase,
};

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Symbol {
    name: String,
    line: usize,
    column: usize,
    value: String,
}

impl Hash for Symbol {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.name.hash(state);
    }
}

impl Symbol {
    pub fn name(&self) -> String {
        self.name.to_string()
    }

    pub fn value(&self) -> String {
        self.value.to_string()
    }
}

/// The macro lexer interprets and evaluates assignment statements and
/// expressions.
pub struct MacroLexer<LB, U>
where
    LB: LexerBase,
    U: Clone,
{
    /// This table composes the found symbols and their assignments.
    symbol_table: HashSet<Symbol>,

    /// This is the foundation lexer on which the macro lexer applies
    /// macro interpretation
    base_lexer: LB,

    /// A queue is used to contain specified tokens for look-ahead
    /// purposes, this queue contains already expanded tokens.
    expanded_q: VecDeque<Token>,

    /// A queue is used to contain specified tokens for look-ahead
    /// purposes, this queue contains not expanded tokens.
    raw_q: VecDeque<Token>,

    /// A map of functions which can be executed. The first parameter
    /// contains the arguments to the macro, the second parameter the
    /// file/stream name, where applicable, the third and fourth
    /// parameters the row and column of the cursor and finally the
    /// user object as created while constructing the Macro lexer
    functions:
        HashMap<String, fn(Vec<String>, &str, usize, usize, &U) -> Result<Vec<Lexicon>, String>>,

    /// A user struct, object or value which can be used by the
    /// functions to utilize behavior defined on it.
    user_object: U,
}

impl<LB, U> MacroLexer<LB, U>
where
    LB: LexerBase,
    U: Clone,
{
    /// Creates a new macro lexer, given an original base lexer. This
    /// will interpret all tokens necessary for macro interpretation
    /// and expansion, and result into tokens specific for the user
    /// of this lexer.
    pub fn new(base_lexer: LB, user_object: &U) -> Self {
        Self {
            symbol_table: HashSet::new(),
            base_lexer,
            expanded_q: VecDeque::new(),
            raw_q: VecDeque::new(),
            functions: HashMap::new(),
            user_object: user_object.clone(),
        }
    }

    /// Retrieves the symbol table to be used apart from the Macro Lexer
    pub fn symbol_table(&self) -> HashSet<Symbol> {
        self.symbol_table.clone()
    }

    /// Adds a macro function to be able to be called by the interpreter
    pub fn add_fn(
        &mut self,
        name: &str,
        func: fn(Vec<String>, &str, usize, usize, &U) -> Result<Vec<Lexicon>, String>,
    ) {
        self.functions.insert(name.to_string(), func);
    }

    /// Interprets a macro call, typically only existing out of either
    /// identifiers or commas.
    fn interpret(&mut self, mut tokens: VecDeque<Token>) -> Vec<Token> {
        // If the first identifier starts with "call", contains a space
        // and further characters, it is a call macro, and needs to
        // be separated from the rest of the macro call.
        let mut is_call = false;

        let token = match tokens.front() {
            Some(t) => {
                let (c, t) = is_call_token(t);
                is_call = c;
                if is_call {
                    tokens.pop_front();
                    tokens.push_front(t.clone());
                };
                t
            }
            _ => Token::create_eot(0, 0),
        };

        let mut identifiers = match macro_simplify(&tokens) {
            Ok(i) => i,
            Err(s) => return vec![create_error(&tokens, s)],
        };

        if identifiers.len() == 1 && !is_call {
            let identifier = identifiers.front().unwrap();
            for symbol in &self.symbol_table {
                if symbol.name.eq(identifier) {
                    let value = &symbol.value;
                    let (column, line) = get_tokens_column_line(&tokens);
                    return vec![Token::create(
                        Lexicon::Identifier(value.to_string()),
                        column,
                        line,
                        value,
                    )];
                };
            }
        };

        if identifiers.len() > 0 {
            let name = identifiers.pop_front().unwrap();
            let result = match self.functions.get(&name) {
                Some(f) => {
                    let arguments = Vec::from_iter(identifiers);
                    let line = token.line();
                    let column = token.column();
                    let stream = self.base_lexer.current_stream();
                    match f(
                        arguments,
                        &stream.unwrap_or_default(),
                        line,
                        column,
                        &self.user_object,
                    ) {
                        Ok(s) => s,
                        Err(s) => {
                            return vec![create_error(
                                &tokens,
                                &format!("Expansion {} failed: {}", name, s),
                            )]
                        }
                    }
                }
                None => {
                    return vec![create_error(
                        &tokens,
                        &format!("Expansion with name {} not found", name),
                    )]
                }
            };

            let (column, line) = get_tokens_column_line(&tokens);

            return result
                .iter()
                .map(|l| Token::create(l.clone(), column, line, &l.to_string()))
                .collect();
        }

        vec![create_error(&tokens, "Macro expansion failed")]
    }

    fn expand(&mut self) -> Vec<Token> {
        let mut input_tokens: VecDeque<Token> = VecDeque::new();

        let mut open_state = 0;
        let mut next = self.queued_next_token();
        while next.term() != Lexicon::Close || open_state != 0 {
            match next.term() {
                Lexicon::Open => {
                    open_state += 1;
                    input_tokens.push_back(next.clone());
                }
                Lexicon::Close => {
                    open_state -= 1;
                    input_tokens.push_back(next.clone());
                }
                Lexicon::MacroOpen => input_tokens.extend(self.expand()),
                _ => input_tokens.push_back(next.clone()),
            };
            next = self.queued_next_token();
        }

        self.interpret(input_tokens)
    }

    /// Extracts the next token from the lexer, but does not evaluate it yet.
    /// Pushes the token onto the queue, to be handled by macro_next_token().
    fn queue_raw_token(&mut self) -> Token {
        let result = self.queued_next_token();
        self.raw_q.push_back(result.clone());
        result
    }

    /// Extracts the next token from the queue, if the queue is depleted,
    /// fills the queue from the base lexer, then extracts it.
    fn queued_next_token(&mut self) -> Token {
        match self.raw_q.pop_front() {
            Some(t) => t,
            None => self.base_lexer.next_token(),
        }
    }

    fn macro_next_token(&mut self) -> Token {
        let token = self.queued_next_token();
        match token.term() {
            Lexicon::MacroOpen => {
                for token in self.expand() {
                    self.raw_q.push_back(token);
                }
                self.macro_next_token()
            }
            _ => token,
        }
    }
}

impl<LB, U> LexerBase for MacroLexer<LB, U>
where
    LB: LexerBase,
    U: Clone,
{
    fn next_token(&mut self) -> Token {
        // The macro lexer requires a lot of read ahead to perform
        // expression interpretation and expansion. Therefore, a look
        // ahead buffer is used.

        // If there still is a token in the queue, and it is not an
        // identifier or if the token is not the only one in the queuu,
        // then it can be popped and returned.

        if self.expanded_q.len() > 1 {
            return self.expanded_q.pop_front().unwrap();
        }

        match self.expanded_q.front() {
            Some(token) => match token.term() {
                Lexicon::Identifier(_) => (),
                _ => return self.expanded_q.pop_front().unwrap(),
            },
            None => (),
        }

        // If the queue is empty, the next element should be pushed on it,
        // if it is an identifier, otherwise is should be passed on.

        if self.expanded_q.len() < 1 {
            let next_token = self.macro_next_token();
            self.expanded_q.push_back(next_token);
        };

        // If the next token is an assignment, assignment evaluation should
        // take place, otherwise the token should be pushed onto the queue
        // the the queued token should be released.
        let token = self.macro_next_token();
        match token.term() {
            Lexicon::AppendAssignment | Lexicon::ImmediateAssignment => {
                let lhs = self.expanded_q.pop_front().unwrap();
                match lhs.term() {
                    Lexicon::Identifier(symbol_name) => {
                        let mut value = String::new();
                        let mut continue_scan = true;

                        while continue_scan {
                            let rhs = self.macro_next_token();
                            match rhs.term() {
                                Lexicon::EOT => continue_scan = false,
                                Lexicon::Error(_) => return rhs,
                                _ => {
                                    value += &rhs.raw();
                                }
                            }

                            if continue_scan {
                                let test = self.queue_raw_token();
                                if rhs.line() != test.line() {
                                    continue_scan = false;
                                }
                            }
                        }

                        value = value.replace("\n", "").replace("\r", "");

                        // Create the new symbol
                        let mut sym = Symbol {
                            name: symbol_name.to_string(),
                            line: lhs.line(),
                            column: lhs.column(),
                            value: value.to_string(),
                        };

                        // If the current assignment is an append assignment, find whether the
                        // symbol has already been used, acquire the value and prefix that value
                        // in front of the new symbol's value
                        if let Lexicon::AppendAssignment = token.term() {
                            for origin in self.symbol_table.iter() {
                                if origin.name.eq(&symbol_name) {
                                    sym.value = format!("{}{}", origin.value, sym.value)
                                }
                            }
                        }
                        self.symbol_table.insert(sym);
                        self.next_token()
                    }
                    _ => Token::create_error(
                        lhs.column(),
                        lhs.line(),
                        "Left-hand side value should be an identifier",
                    ),
                }
            }
            _ => {
                self.expanded_q.push_back(token);
                return self.expanded_q.pop_front().unwrap();
            }
        }
    }
}

/// If the token is an identifier, and starts with the call semantics,
/// it is "special" as it identifies a call.
fn is_call_token(token: &Token) -> (bool, Token) {
    match token.term() {
        Lexicon::Identifier(s) => {
            if s.starts_with("call ")
                || s.starts_with("call\t")
                || s.starts_with("call\r")
                || s.starts_with("call\n")
            {
                let result = Token::create(
                    Lexicon::Identifier(s[4..].trim().to_string()),
                    token.column(),
                    token.line(),
                    &"$(call ",
                );
                (true, result.clone())
            } else {
                (false, token.clone())
            }
        }
        _ => (false, token.clone()),
    }
}

/// Because macros can contain adjecent identifiers because of earlier
/// macro expansions, the identifiers are to be interpreted as a single
/// identifier, for example:
///
/// FOO := foo
/// BAR := bar
/// $($(FOO)$(BAR))
///
/// $(FOO) would be replaced with "foo" and $(BAR) would be replaced
/// with "bar". But "foobar" should be the identifier resulting from
/// that statement.
fn macro_simplify(tokens: &VecDeque<Token>) -> Result<VecDeque<String>, &str> {
    let mut simplified: VecDeque<String> = VecDeque::new();
    let mut compiled_string: String = "".to_string();
    for token in tokens {
        match token.term() {
            Lexicon::Identifier(s) => {
                compiled_string = format!("{}{}", compiled_string, s);
            }
            Lexicon::Comma => {
                simplified.push_back(compiled_string.to_string());
                compiled_string = "".to_string();
            }
            _ => return Err(&"Expected macro identifier or comma"),
        }
    }
    simplified.push_back(compiled_string.to_string());
    Ok(simplified)
}

fn get_tokens_column_line(tokens: &VecDeque<Token>) -> (usize, usize) {
    match tokens.front() {
        Some(t) => (t.column(), t.line()),
        _ => (0, 0),
    }
}

fn create_error(tokens: &VecDeque<Token>, err_msg: &str) -> Token {
    let (column, line) = get_tokens_column_line(tokens);
    Token::create_error(column, line, err_msg)
}

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

    fn create_lexer(s: &str) -> MacroLexer<Lexer<&[u8]>, ()> {
        MacroLexer::new(Lexer::create(s.as_bytes()), &())
    }

    #[test]
    fn test_basic_expansion() {
        let mut l = create_lexer(&"FOO := foo\n$(FOO)");
        assert_eq!(
            Lexicon::Identifier("foo".to_string()),
            l.next_token().term()
        );
        assert_eq!(Lexicon::EOT, l.next_token().term());
    }

    #[test]
    fn test_dual_expansion() {
        let mut l = create_lexer(&"FOO := foo\nBAR := bar\n$(FOO) $(BAR)");
        assert_eq!(
            Lexicon::Identifier("foo".to_string()),
            l.next_token().term()
        );
        assert_eq!(
            Lexicon::Identifier("bar".to_string()),
            l.next_token().term()
        );
        assert_eq!(Lexicon::EOT, l.next_token().term());
    }

    fn foo_func(
        params: Vec<String>,
        _: &str,
        _: usize,
        _: usize,
        _: &(),
    ) -> Result<Vec<Lexicon>, String> {
        match params.len() {
            1 => Ok(vec![Lexicon::Identifier(
                params.first().unwrap().to_string(),
            )]),
            _ => Err("Expected exactly one parameter".to_string()),
        }
    }

    #[test]
    fn test_simple_macro_expansion() {
        let mut l = create_lexer(&"$(call func,foo)");
        l.add_fn("func", foo_func);
        assert_eq!(
            Lexicon::Identifier("foo".to_string()),
            l.next_token().term()
        );
        assert_eq!(Lexicon::EOT, l.next_token().term());
    }

    #[test]
    fn test_abbrev_macro_expansion() {
        let mut l = create_lexer(&"$(func,foo)");
        l.add_fn("func", foo_func);
        assert_eq!(
            Lexicon::Identifier("foo".to_string()),
            l.next_token().term()
        );
        assert_eq!(Lexicon::EOT, l.next_token().term());
    }

    #[test]
    fn test_recursive_macro_expansion() {
        let mut l = create_lexer(&"FOO := foo\nBAR := $(call func,$(FOO))\n$(BAR)");
        l.add_fn("func", foo_func);
        assert_eq!(
            Lexicon::Identifier("foo".to_string()),
            l.next_token().term()
        );
        assert_eq!(Lexicon::EOT, l.next_token().term());
    }
}