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feat: add extern let declarations for JS FFI

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Add support for `extern let name: Type` and `extern let name: Type = "jsName"`
syntax for declaring external JavaScript values. This follows the same pattern
as extern fn across all compiler passes: parser, typechecker, interpreter
(runtime error placeholder), JS backend (emits JS name directly without
mangling), formatter, linter, modules, and symbol table.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Brandon Lucas
2026-02-20 19:29:44 -05:00
parent 1b629aaae4
commit 667a94b4dc
10 changed files with 161 additions and 2 deletions
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54
src/parser.rs
View File

@@ -238,7 +238,7 @@ impl Parser {
match self.peek_kind() {
TokenKind::Fn => Ok(Declaration::Function(self.parse_function_decl(visibility, doc)?)),
TokenKind::Extern => Ok(Declaration::ExternFn(self.parse_extern_fn_decl(visibility, doc)?)),
TokenKind::Extern => self.parse_extern_decl(visibility, doc),
TokenKind::Effect => Ok(Declaration::Effect(self.parse_effect_decl(doc)?)),
TokenKind::Handler => Ok(Declaration::Handler(self.parse_handler_decl()?)),
TokenKind::Type => Ok(Declaration::Type(self.parse_type_decl(visibility, doc)?)),
@@ -324,6 +324,58 @@ impl Parser {
})
}
/// Parse extern declaration: dispatch to extern fn or extern let
fn parse_extern_decl(&mut self, visibility: Visibility, doc: Option<String>) -> Result<Declaration, ParseError> {
// Peek past 'extern' to see if it's 'fn' or 'let'
if self.pos + 1 < self.tokens.len() {
match &self.tokens[self.pos + 1].kind {
TokenKind::Fn => Ok(Declaration::ExternFn(self.parse_extern_fn_decl(visibility, doc)?)),
TokenKind::Let => Ok(Declaration::ExternLet(self.parse_extern_let_decl(visibility, doc)?)),
_ => Err(self.error("Expected 'fn' or 'let' after 'extern'")),
}
} else {
Err(self.error("Expected 'fn' or 'let' after 'extern'"))
}
}
/// Parse extern let declaration: extern let name: Type = "jsName"
fn parse_extern_let_decl(&mut self, visibility: Visibility, doc: Option<String>) -> Result<ExternLetDecl, ParseError> {
let start = self.current_span();
self.expect(TokenKind::Extern)?;
self.expect(TokenKind::Let)?;
let name = self.parse_ident()?;
// Type annotation
self.expect(TokenKind::Colon)?;
let typ = self.parse_type()?;
// Optional JS name override: = "jsName"
let js_name = if self.check(TokenKind::Eq) {
self.advance();
match self.peek_kind() {
TokenKind::String(s) => {
let name = s.clone();
self.advance();
Some(name)
}
_ => return Err(self.error("Expected string literal for JS name in extern let")),
}
} else {
None
};
let span = start.merge(self.previous_span());
Ok(ExternLetDecl {
visibility,
doc,
name,
typ,
js_name,
span,
})
}
/// Parse extern function declaration: extern fn name<T>(params): ReturnType = "jsName"
fn parse_extern_fn_decl(&mut self, visibility: Visibility, doc: Option<String>) -> Result<ExternFnDecl, ParseError> {
let start = self.current_span();