Implement logos-based tokenizer

Cargo.toml

@@ -7,6 +7,10 @@ edition = "2024"
 rowan = { version = "0.15", default-features = false }
 num-derive = { version = "0.4", default-features = false }
 num-traits = { version = "0.2", default-features = false, features = ["std"] }
+logos = { version = ">=0.13.0, <0.14.0", default-features = false, features = ["export_derive"] }
+
+[dev-dependencies]
+rstest = ">=0.18.0, <0.19.0"
 
 [lints.clippy]
 pedantic = { level = "warn", priority = -1 }

docs/parser-plan.md

@@ -33,7 +33,26 @@ transparently.
 Use `chumsky`'s text utilities (or integrate a `logos` lexer if preferred) to
 convert the source text into a stream of `(SyntaxKind, Span)` pairs. Each span
 records byte offsets so that the resulting CST can precisely mirror the input.
-Whitespace and comments should produce tokens so they can be preserved.
+Whitespace and comments should produce tokens so they can be preserved. The
+current implementation opts for a small `logos` lexer because it keeps the token
+definitions declarative while still interoperating smoothly with `chumsky`
+parsers.
+
+```mermaid
+sequenceDiagram
+    participant Client
+    participant Tokenizer
+    participant LogosLexer
+    participant SyntaxKind
+    Client->>Tokenizer: tokenize(src: &str)
+    Tokenizer->>LogosLexer: Token::lexer(src)
+    loop for each token
+        LogosLexer-->>Tokenizer: next() -> Token + span
+        Tokenizer->>SyntaxKind: map Token to SyntaxKind
+        Tokenizer-->>Tokenizer: collect (SyntaxKind, Span)
+    end
+    Tokenizer-->>Client: Vec<(SyntaxKind, Span)>
+```
 
 ## 4. Construct the Parser with `chumsky`
 

src/lib.rs

@@ -1,9 +1,11 @@
 //! Library crate for ddlint.
 //!
-//! Currently exposes only the parser language definitions.
+//! Exposes parser language definitions and lexical analysis functionality.
 
 #![forbid(unsafe_code)]
 
 pub mod language;
+pub mod tokenizer;
 
 pub use language::{DdlogLanguage, SyntaxKind};
+pub use tokenizer::{Span, tokenize};

src/tokenizer.rs

@@ -0,0 +1,237 @@
+//! Lexical analysis for `DDlog` source.
+//!
+//! This module exposes a `tokenize` function which converts raw source text into
+//! a sequence of `(SyntaxKind, Span)` pairs. It uses the `logos` crate to
+//! recognise tokens so that the CST can mirror the input exactly.
+
+use logos::Logos;
+
+use crate::SyntaxKind;
+
+/// Byte range for a token within the source.
+pub type Span = std::ops::Range<usize>;
+
+#[derive(Logos, Debug, Clone, Copy, PartialEq, Eq)]
+enum Token {
+    #[regex(r"[ \t\r\n]+")]
+    Whitespace,
+    #[regex(r"/\*([^*]|\*[^/])*\*/", priority = 2)]
+    #[regex(r"//[^\n]*")]
+    Comment,
+    #[regex(r"[A-Za-z_][A-Za-z0-9_]*")]
+    Ident,
+    #[regex(r"[0-9]+")]
+    Number,
+    #[regex(r#""([^"\\]|\\.)*""#)]
+    String,
+    #[token("(")]
+    LParen,
+    #[token(")")]
+    RParen,
+    #[token("{")]
+    LBrace,
+    #[token("}")]
+    RBrace,
+    #[token("[")]
+    LBracket,
+    #[token("]")]
+    RBracket,
+    #[token(";")]
+    Semi,
+    #[token(",")]
+    Comma,
+    #[token(".")]
+    Dot,
+    #[token("::")]
+    ColonColon,
+    #[token(":")]
+    Colon,
+    #[token("|")]
+    Pipe,
+    #[token("&")]
+    Amp,
+    #[token("==")]
+    EqEq,
+    #[token("=")]
+    Eq,
+    #[token(":-")]
+    Implies,
+    #[token("%")]
+    Percent,
+    #[token("*")]
+    Star,
+    #[token("/")]
+    Slash,
+    #[token("+")]
+    Plus,
+    #[token("-")]
+    Minus,
+    #[token("->")]
+    Arrow,
+    #[token("=>")]
+    FatArrow,
+    #[token("<=")]
+    Lte,
+    #[token("<=>")]
+    Spaceship,
+    #[token(">=")]
+    Gte,
+    #[token("<")]
+    Lt,
+    #[token(">")]
+    Gt,
+    #[token("!=")]
+    Neq,
+    #[token(">>")]
+    Shr,
+    #[token("<<")]
+    Shl,
+    #[token("~")]
+    Tilde,
+    #[token("@")]
+    At,
+    #[token("#")]
+    Hash,
+    #[token("'")]
+    Apostrophe,
+}
+
+fn keyword_kind(ident: &str) -> Option<SyntaxKind> {
+    Some(match ident {
+        "abstract" => SyntaxKind::K_ABSTRACT,
+        "Aggregate" => SyntaxKind::K_AGGREGATE,
+        "and" => SyntaxKind::K_AND,
+        "apply" => SyntaxKind::K_APPLY,
+        "as" => SyntaxKind::K_AS,
+        "async" => SyntaxKind::K_ASYNC,
+        "await" => SyntaxKind::K_AWAIT,
+        "become" => SyntaxKind::K_BECOME,
+        "bigint" => SyntaxKind::K_BIGINT,
+        "bit" => SyntaxKind::K_BIT,
+        "bool" => SyntaxKind::K_BOOL,
+        "box" => SyntaxKind::K_BOX,
+        "break" => SyntaxKind::K_BREAK,
+        "const" => SyntaxKind::K_CONST,
+        "continue" => SyntaxKind::K_CONTINUE,
+        "crate" => SyntaxKind::K_CRATE,
+        "do" => SyntaxKind::K_DO,
+        "double" => SyntaxKind::K_DOUBLE,
+        "dyn" => SyntaxKind::K_DYN,
+        "else" => SyntaxKind::K_ELSE,
+        "extern" => SyntaxKind::K_EXTERN,
+        "false" => SyntaxKind::K_FALSE,
+        "final" => SyntaxKind::K_FINAL,
+        "fn" => SyntaxKind::K_FN,
+        "FlatMap" => SyntaxKind::K_FLATMAP,
+        "float" => SyntaxKind::K_FLOAT,
+        "for" => SyntaxKind::K_FOR,
+        "function" => SyntaxKind::K_FUNCTION,
+        "if" => SyntaxKind::K_IF,
+        "impl" => SyntaxKind::K_IMPL,
+        "import" => SyntaxKind::K_IMPORT,
+        "in" => SyntaxKind::K_IN,
+        "input" => SyntaxKind::K_INPUT,
+        "Inspect" => SyntaxKind::K_INSPECT,
+        "let" => SyntaxKind::K_LET,
+        "loop" => SyntaxKind::K_LOOP,
+        "macro" => SyntaxKind::K_MACRO,
+        "match" => SyntaxKind::K_MATCH,
+        "mod" => SyntaxKind::K_MOD,
+        "move" => SyntaxKind::K_MOVE,
+        "multiset" => SyntaxKind::K_MULTISET,
+        "mut" => SyntaxKind::K_MUT,
+        "not" => SyntaxKind::K_NOT,
+        "or" => SyntaxKind::K_OR,
+        "override" => SyntaxKind::K_OVERRIDE,
+        "output" => SyntaxKind::K_OUTPUT,
+        "priv" => SyntaxKind::K_PRIV,
+        "pub" => SyntaxKind::K_PUB,
+        "ref" => SyntaxKind::K_REF,
+        "relation" => SyntaxKind::K_RELATION,
+        "return" => SyntaxKind::K_RETURN,
+        "self" => SyntaxKind::K_SELF,
+        "Self" => SyntaxKind::K_SELF_TYPE,
+        "signed" => SyntaxKind::K_SIGNED,
+        "skip" => SyntaxKind::K_SKIP,
+        "static" => SyntaxKind::K_STATIC,
+        "stream" => SyntaxKind::K_STREAM,
+        "struct" => SyntaxKind::K_STRUCT,
+        "super" => SyntaxKind::K_SUPER,
+        "trait" => SyntaxKind::K_TRAIT,
+        "transformer" => SyntaxKind::K_TRANSFORMER,
+        "try" => SyntaxKind::K_TRY,
+        "true" => SyntaxKind::K_TRUE,
+        "type" => SyntaxKind::K_TYPE,
+        "typedef" => SyntaxKind::K_TYPEDEF,
+        "typeof" => SyntaxKind::K_TYPEOF,
+        "_" => SyntaxKind::K_UNDERSCORE,
+        "unsafe" => SyntaxKind::K_UNSAFE,
+        "unsized" => SyntaxKind::K_UNSIZED,
+        "use" => SyntaxKind::K_USE,
+        "var" => SyntaxKind::K_VAR,
+        "virtual" => SyntaxKind::K_VIRTUAL,
+        "where" => SyntaxKind::K_WHERE,
+        "while" => SyntaxKind::K_WHILE,
+        "yield" => SyntaxKind::K_YIELD,
+        _ => return None,
+    })
+}
+
+/// Tokenise the provided `DDlog` source.
+#[must_use]
+pub fn tokenize(src: &str) -> Vec<(SyntaxKind, Span)> {
+    let mut lexer = Token::lexer(src);
+    let mut out = Vec::new();
+    while let Some(result) = lexer.next() {
+        let span = lexer.span();
+        let text = src.get(span.clone()).unwrap_or("");
+        let Ok(token) = result else {
+            out.push((SyntaxKind::N_ERROR, span));
+            continue;
+        };
+        let kind = match token {
+            Token::Whitespace => SyntaxKind::T_WHITESPACE,
+            Token::Comment => SyntaxKind::T_COMMENT,
+            Token::Ident => keyword_kind(text).unwrap_or(SyntaxKind::T_IDENT),
+            Token::Number => SyntaxKind::T_NUMBER,
+            Token::String => SyntaxKind::T_STRING,
+            Token::LParen => SyntaxKind::T_LPAREN,
+            Token::RParen => SyntaxKind::T_RPAREN,
+            Token::LBrace => SyntaxKind::T_LBRACE,
+            Token::RBrace => SyntaxKind::T_RBRACE,
+            Token::LBracket => SyntaxKind::T_LBRACKET,
+            Token::RBracket => SyntaxKind::T_RBRACKET,
+            Token::Semi => SyntaxKind::T_SEMI,
+            Token::Comma => SyntaxKind::T_COMMA,
+            Token::Dot => SyntaxKind::T_DOT,
+            Token::ColonColon => SyntaxKind::T_COLON_COLON,
+            Token::Colon => SyntaxKind::T_COLON,
+            Token::Pipe => SyntaxKind::T_PIPE,
+            Token::Amp => SyntaxKind::T_AMP,
+            Token::EqEq => SyntaxKind::T_EQEQ,
+            Token::Eq => SyntaxKind::T_EQ,
+            Token::Implies => SyntaxKind::T_IMPLIES,
+            Token::Percent => SyntaxKind::T_PERCENT,
+            Token::Star => SyntaxKind::T_STAR,
+            Token::Slash => SyntaxKind::T_SLASH,
+            Token::Plus => SyntaxKind::T_PLUS,
+            Token::Minus => SyntaxKind::T_MINUS,
+            Token::Arrow => SyntaxKind::T_ARROW,
+            Token::FatArrow => SyntaxKind::T_FAT_ARROW,
+            Token::Lte => SyntaxKind::T_LTE,
+            Token::Spaceship => SyntaxKind::T_SPACESHIP,
+            Token::Gte => SyntaxKind::T_GTE,
+            Token::Lt => SyntaxKind::T_LT,
+            Token::Gt => SyntaxKind::T_GT,
+            Token::Neq => SyntaxKind::T_NEQ,
+            Token::Shr => SyntaxKind::T_SHR,
+            Token::Shl => SyntaxKind::T_SHL,
+            Token::Tilde => SyntaxKind::T_TILDE,
+            Token::At => SyntaxKind::T_AT,
+            Token::Hash => SyntaxKind::T_HASH,
+            Token::Apostrophe => SyntaxKind::T_APOSTROPHE,
+        };
+        out.push((kind, span));
+    }
+    out
+}