cpd-semantic 0.1.1

//! Functions for `--semantic`.
//!
//! JavaScript and TypeScript (and the scripts of Vue, Svelte and Astro
//! components) come from cpd-tokenizer's oxc extractor, the one
//! `--similarity` compares. This module adds the languages only `--semantic`
//! reads: Rust (a source scanner), Python (the ruff parser) and, through
//! tree-sitter grammars, C, C++, C#, Go, Java, Kotlin, PHP, Ruby, Scala and
//! Swift. They find where functions are and what they are called; their
//! `kinds` stay empty.

mod grammars;

use cpd_tokenizer::functions::{FunctionExtractor, RawFunction};
use cpd_tokenizer::line_index::LineIndex;

/// The extractors of this module, consulted after cpd-tokenizer's.
static EXTRACTORS: &[&dyn FunctionExtractor] = &[
    &RustExtractor,
    &PythonExtractor,
    &grammars::C,
    &grammars::CPP,
    &grammars::CSHARP,
    &grammars::GO,
    &grammars::JAVA,
    &grammars::KOTLIN,
    &grammars::PHP,
    &grammars::RUBY,
    &grammars::SCALA,
    &grammars::SWIFT,
];

/// The extractor serving `format` for `--semantic`: cpd-tokenizer's own
/// first, then this module's.
pub fn extractor_for(format: &str) -> Option<&'static dyn FunctionExtractor> {
    cpd_tokenizer::functions::extractor_for(format).or_else(|| {
        EXTRACTORS
            .iter()
            .copied()
            .find(|e| e.formats().contains(&format))
    })
}

/// Every function of a source. Empty for formats without an extractor and
/// for sources that fail to parse.
pub fn extract_functions(source: &str, format: &str) -> Vec<RawFunction> {
    cpd_tokenizer::functions::extract_with(extractor_for(format), source, format)
}

/// Python through the ruff parser: every `def` and `async def`, methods and
/// nested functions included. The span starts at `def` (or `async`), so
/// decorators stay out as Rust attributes do.
pub struct PythonExtractor;

impl FunctionExtractor for PythonExtractor {
    fn grammar(&self) -> &'static str {
        "python"
    }

    fn formats(&self) -> &'static [&'static str] {
        &["python"]
    }

    fn extract(&self, source: &str, _format: &str) -> Vec<RawFunction> {
        use ruff_python_ast::visitor::source_order::SourceOrderVisitor;
        let Ok(parsed) = ruff_python_parser::parse_module(source) else {
            return Vec::new();
        };
        let line_index = LineIndex::new(source.as_bytes());
        let mut visitor = PythonFunctions {
            source,
            line_index: &line_index,
            out: Vec::new(),
        };
        visitor.visit_body(&parsed.syntax().body);
        visitor.out.sort_by_key(|f| f.start.offset);
        visitor.out
    }
}

struct PythonFunctions<'s> {
    source: &'s str,
    line_index: &'s LineIndex,
    out: Vec<RawFunction>,
}

impl<'a> ruff_python_ast::visitor::source_order::SourceOrderVisitor<'a> for PythonFunctions<'_> {
    fn visit_stmt(&mut self, stmt: &'a ruff_python_ast::Stmt) {
        if let ruff_python_ast::Stmt::FunctionDef(f) = stmt {
            let name_start = f.name.range.start().to_usize();
            let end = f.range.end().to_usize();
            // `def` is the last keyword before the name; `async` precedes it.
            let head = &self.source[..name_start];
            if let Some(def) = head.rfind("def") {
                let before = head[..def].trim_end();
                let start = match f.is_async && before.ends_with("async") {
                    true => before.len() - "async".len(),
                    false => def,
                };
                self.out.push(RawFunction {
                    grammar: "python",
                    name: f.name.to_string(),
                    start: self.line_index.location(start),
                    end: self.line_index.location(end),
                    head: self.line_index.location(start),
                    kinds: Vec::new(),
                });
            }
        }
        ruff_python_ast::visitor::source_order::walk_stmt(self, stmt);
    }
}

/// Rust by scanning the source: every `fn` with a body — free functions,
/// methods, trait methods with a default body, and functions nested in
/// them.
///
/// A scan, not a parse: it knows Rust's comments (nested block comments
/// included), strings, raw strings and character literals — so a brace or a
/// `fn` inside one of them is not code, and a lifetime `'a` is not the start
/// of a character — and that is all it needs to find where a function's
/// item starts (its first keyword, after doc comments and attributes) and
/// where its body's braces close. `fn` followed by anything but a name (a
/// function pointer type, a macro fragment) opens nothing.
pub struct RustExtractor;

impl FunctionExtractor for RustExtractor {
    fn grammar(&self) -> &'static str {
        "rust"
    }

    fn formats(&self) -> &'static [&'static str] {
        &["rust"]
    }

    fn extract(&self, source: &str, _format: &str) -> Vec<RawFunction> {
        let line_index = LineIndex::new(source.as_bytes());
        let mut out: Vec<RawFunction> = scan_rust_functions(source)
            .into_iter()
            .map(|(name, start, end)| RawFunction {
                grammar: "rust",
                name,
                start: line_index.location(start),
                end: line_index.location(end),
                head: line_index.location(start),
                kinds: Vec::new(),
            })
            .collect();
        out.sort_by_key(|f| f.start.offset);
        out
    }
}

/// `(name, item start, end after the closing brace)` of every Rust function
/// with a body.
fn scan_rust_functions(source: &str) -> Vec<(String, usize, usize)> {
    let b = source.as_bytes();
    let mut out = Vec::new();
    // Functions whose body is open: (name, item start, depth inside body).
    let mut open: Vec<(String, usize, usize)> = Vec::new();
    let mut depth = 0usize;
    // Start of the item being read: the first code byte after the last
    // `;`, `{`, `}` or attribute `]`.
    let mut item_start: Option<usize> = None;
    // A `fn NAME` whose body has not started: (name, item start).
    let mut pending: Option<(String, usize)> = None;
    // Parentheses and brackets inside a pending signature.
    let mut nesting = 0usize;
    let mut i = 0;
    while i < b.len() {
        let c = b[i];
        if c.is_ascii_whitespace() {
            i += 1;
            continue;
        }
        if let Some(next) = skip_rust_trivia(b, i) {
            i = next;
            continue;
        }
        if item_start.is_none() {
            item_start = Some(i);
        }
        if let Some(next) = skip_rust_literal(b, i) {
            i = next;
            continue;
        }
        if c.is_ascii_alphabetic() || c == b'_' || c >= 0x80 {
            let word_end = word_end(b, i);
            if &b[i..word_end] == b"fn" && pending.is_none() {
                let name_start = skip_space_and_trivia(b, word_end);
                let name_end = word_end_if_ident(b, name_start);
                if name_end > name_start {
                    let name = source[name_start..name_end].to_string();
                    pending = Some((name, item_start.unwrap_or(i)));
                    nesting = 0;
                    i = name_end;
                    continue;
                }
            }
            i = word_end;
            continue;
        }
        match c {
            b'(' | b'[' if pending.is_some() => nesting += 1,
            b')' | b']' if pending.is_some() => nesting = nesting.saturating_sub(1),
            b';' if pending.is_some() && nesting == 0 => {
                // A declaration without a body.
                pending = None;
                item_start = None;
            }
            b'{' => {
                depth += 1;
                if nesting == 0
                    && let Some((name, start)) = pending.take()
                {
                    open.push((name, start, depth));
                }
                if pending.is_none() {
                    item_start = None;
                }
            }
            b'}' => {
                if let Some((_, _, d)) = open.last()
                    && *d == depth
                {
                    let (name, start, _) = open.pop().unwrap_or_default();
                    out.push((name, start, i + 1));
                }
                depth = depth.saturating_sub(1);
                if pending.is_none() {
                    item_start = None;
                }
            }
            b';' | b']' if pending.is_none() => item_start = None,
            _ => {}
        }
        i += 1;
    }
    out
}

/// The end of a comment starting at `i`, if one does.
fn skip_rust_trivia(b: &[u8], i: usize) -> Option<usize> {
    if b[i] != b'/' {
        return None;
    }
    match b.get(i + 1) {
        Some(b'/') => Some(
            b[i..]
                .iter()
                .position(|&c| c == b'\n')
                .map_or(b.len(), |p| i + p + 1),
        ),
        Some(b'*') => {
            // Block comments nest in Rust.
            let mut level = 0usize;
            let mut j = i;
            while j < b.len() {
                if b[j] == b'/' && b.get(j + 1) == Some(&b'*') {
                    level += 1;
                    j += 2;
                } else if b[j] == b'*' && b.get(j + 1) == Some(&b'/') {
                    level -= 1;
                    j += 2;
                    if level == 0 {
                        return Some(j);
                    }
                } else {
                    j += 1;
                }
            }
            Some(b.len())
        }
        _ => None,
    }
}

/// The end of a string, raw string, byte string or character literal
/// starting at `i`, if one does. A lifetime or label (`'a`) is not one.
fn skip_rust_literal(b: &[u8], i: usize) -> Option<usize> {
    let mut j = i;
    // Prefixes: b"..", r"..", br"..", c"..", r#".."#.
    while j < b.len() && matches!(b[j], b'b' | b'r' | b'c') && j - i < 2 {
        j += 1;
    }
    let raw = b[i..j].contains(&b'r');
    let mut hashes = 0;
    if raw {
        while b.get(j) == Some(&b'#') {
            hashes += 1;
            j += 1;
        }
    }
    match b.get(j) {
        Some(b'"') if j == i || raw || b[i..j].iter().all(|&p| p == b'b' || p == b'c') => {
            j += 1;
            while j < b.len() {
                if !raw && b[j] == b'\\' {
                    j += 2;
                    continue;
                }
                if b[j] == b'"'
                    && b.len() >= j + 1 + hashes
                    && b[j + 1..j + 1 + hashes].iter().all(|&h| h == b'#')
                {
                    return Some(j + 1 + hashes);
                }
                j += 1;
            }
            Some(b.len())
        }
        Some(b'\'') if !raw && (j == i || b[i..j] == *b"b") => {
            // `'x'`, `'\n'`, `'\u{..}'`, `'é'`; anything else is a lifetime.
            let k = j + 1;
            if b.get(k) == Some(&b'\\') {
                let close = b[k..].iter().position(|&c| c == b'\'').map(|p| k + p);
                // Skip the escaped quote of `'\''`.
                let close = match close {
                    Some(p) if p == k + 1 => b[k + 2..]
                        .iter()
                        .position(|&c| c == b'\'')
                        .map(|q| k + 2 + q),
                    other => other,
                };
                return close.map(|p| p + 1);
            }
            let ch_len = utf8_len(b.get(k).copied()?);
            (b.get(k + ch_len) == Some(&b'\'')).then_some(k + ch_len + 1)
        }
        _ => None,
    }
}

fn utf8_len(first: u8) -> usize {
    match first {
        0xF0..=0xFF => 4,
        0xE0..=0xEF => 3,
        0xC0..=0xDF => 2,
        _ => 1,
    }
}

fn word_end(b: &[u8], i: usize) -> usize {
    let mut j = i;
    while j < b.len() && (b[j].is_ascii_alphanumeric() || b[j] == b'_' || b[j] >= 0x80) {
        j += 1;
    }
    j
}

/// End of the identifier at `i` (a raw identifier `r#name` included), or
/// `i` when none starts there.
fn word_end_if_ident(b: &[u8], i: usize) -> usize {
    match b.get(i) {
        Some(c) if c.is_ascii_alphabetic() || *c == b'_' || *c >= 0x80 => {
            if b[i] == b'r' && b.get(i + 1) == Some(&b'#') {
                word_end(b, i + 2)
            } else {
                word_end(b, i)
            }
        }
        _ => i,
    }
}

fn skip_space_and_trivia(b: &[u8], mut i: usize) -> usize {
    loop {
        while i < b.len() && b[i].is_ascii_whitespace() {
            i += 1;
        }
        match (i < b.len()).then(|| skip_rust_trivia(b, i)).flatten() {
            Some(next) => i = next,
            None => return i,
        }
    }
}

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

    /// Name, first line and last line of each function.
    fn spans(fns: &[RawFunction]) -> Vec<(&str, u32, u32)> {
        fns.iter()
            .map(|f| (f.name.as_str(), f.start.line, f.end.line))
            .collect()
    }

    #[test]
    fn rust_functions_methods_and_default_trait_methods_are_found() {
        let src = "use std::fmt;\n\n/// Adds.\npub fn add(a: i32, b: i32) -> i32 {\n    a + b\n}\n\nimpl Cart {\n    pub(crate) async fn total(&self) -> i64 {\n        fn cents(x: i64) -> i64 { x * 100 }\n        cents(self.sum)\n    }\n}\n\ntrait Named {\n    fn name(&self) -> String { String::new() }\n    fn id(&self) -> u32;\n}\n";
        let fns = extract_functions(src, "rust");
        assert_eq!(
            spans(&fns),
            vec![
                ("add", 4, 6),
                ("total", 9, 12),
                ("cents", 10, 10),
                ("name", 16, 16)
            ]
        );
        // The span starts at the visibility, after the doc comment, and ends
        // on the closing brace.
        let add = &fns[0];
        assert_eq!(
            &src[add.start.offset as usize..add.end.offset as usize],
            "pub fn add(a: i32, b: i32) -> i32 {\n    a + b\n}"
        );
        assert!(
            fns.iter()
                .all(|f| f.grammar == "rust" && f.kinds.is_empty())
        );
    }

    #[test]
    fn rust_braces_and_fn_inside_literals_and_comments_are_not_code() {
        let src = r####"fn lifetimes<'a>(x: &'a str) -> &'a str { if x == "{" { x } else { "}" } }
fn chars() -> [char; 3] { ['{', '\'', '}'] }
fn raw() -> &'static str { r##"fn fake() { "# }"## }
/* outer /* fn nested() { */ still comment */
fn pointer(f: fn(u32) -> u32) -> u32 { f(1) }
macro_rules! make { ($n:ident) => { fn $n() {} }; }
fn last() {}
"####;
        let names: Vec<(String, u32)> = extract_functions(src, "rust")
            .into_iter()
            .map(|f| (f.name, f.end.line))
            .collect();
        let expected = [
            ("lifetimes", 1),
            ("chars", 2),
            ("raw", 3),
            ("pointer", 5),
            ("last", 7),
        ];
        assert_eq!(
            names,
            expected
                .iter()
                .map(|(n, l)| (n.to_string(), *l))
                .collect::<Vec<_>>()
        );
    }

    #[test]
    fn python_functions_methods_and_nested_ones_start_at_def() {
        let src = "import os\n\n@cache\ndef load(path):\n    return open(path).read()\n\nclass Cart:\n    async def total(self):\n        def cents(x):\n            return x * 100\n        return cents(self.sum)\n";
        let fns = extract_functions(src, "python");
        assert_eq!(
            spans(&fns),
            vec![("load", 4, 5), ("total", 8, 11), ("cents", 9, 10)]
        );
        assert_eq!(&src[fns[0].start.offset as usize..][..8], "def load");
        assert_eq!(&src[fns[1].start.offset as usize..][..9], "async def");
        assert!(
            fns.iter()
                .all(|f| f.grammar == "python" && f.kinds.is_empty())
        );
        assert!(!supports_functions("python"));
        assert!(extract_functions("def broken(:\n", "python").is_empty());
    }

    #[test]
    fn rust_that_does_not_parse_still_yields_what_closes() {
        assert!(extract_functions("fn broken( {", "rust").is_empty());
        let fns = extract_functions("fn ok() { 1 }\nfn open() {", "rust");
        assert_eq!(fns.len(), 1);
        assert_eq!(fns[0].name, "ok");
    }

    #[test]
    fn similarity_does_not_compare_what_only_semantic_reads() {
        for format in ["rust", "python", "go"] {
            assert!(extractor_for(format).is_some(), "{format}");
            assert!(!supports_functions(format), "{format}");
        }
        assert_eq!(extractor_for("typescript").unwrap().grammar(), "oxc");
        assert!(extractor_for("haskell").is_none());
    }
}