fix(parser): Error::expected for const init, clearer for-of error, op…

[tkshsbcue]

Summary

Three parser improvements aligning with maintainer feedback: (1) Use Error::expected instead of Error::general for const declaration missing initializer. (2) Replace vague "unexpected token" with a descriptive message for invalid let in for-of. (3) Replace operator lexer unimplemented! with proper syntax error.

Motivation

Error::expected for const — "Expected initializer for const declaration" is an "expected X, got Y" pattern. Using Error::expected(["="], found, span, context) matches the rest of the parser and gives a clearer message.

For-of let message — The previous "unexpected token" was vague. Replacing with "'let' cannot be used as the iterable in a for-of loop" explains the issue (mirrors the nearby async error).

Operator lexer — unimplemented!("operator {}", op) panics on unknown operator bytes. Replacing with Error::syntax returns a recoverable parse error instead.

Changes

File	Change
lexical.rs	Error::general("Expected initializer...") → Error::expected(["="], next.to_string(interner), next.span(), "const declaration")
for_statement.rs	Error::general("unexpected token") → Error::general("'let' cannot be used as the iterable in a for-of loop", position)
operator.rs	unimplemented!("operator {}", op) → Err(Error::syntax(format!("unexpected operator '{}'", char::from(op)), start_pos.position()))

Testing

• cargo test -p boa_parser — 296 tests pass
• cargo clippy -p boa_parser — no warnings

[tkshsbcue]

Hi @jedel1043 , I came across a few interesting cases while compiling. I think improving the error handling in this part could make the user experience better.

Thanks!

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	49,713	49,713	0
Ignored	2,262	2,262	0
Failed	988	988	0
Panics	0	0	0
Conformance	93.86%	93.86%	0.00%

Tested main commit: c3fb70b89ace585cfafa7ca00920869633c27c2a
Tested PR commit: 0579b8f4347dc53f3dc9e201bfa97b3815cc528e
Compare commits: c3fb70b...0579b8f

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.42%. Comparing base (6ddc2b4) to head (0579b8f).
⚠️ Report is 824 commits behind head on main.

Files with missing lines	Patch %	Lines
core/parser/src/lexer/operator.rs	0.00%	5 Missing ⚠️
.../statement/declaration/hoistable/class_decl/mod.rs	0.00%	5 Missing ⚠️
core/parser/src/lexer/error.rs	0.00%	3 Missing ⚠️
...er/src/parser/statement/iteration/for_statement.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #4973       +/-   ##
===========================================
+ Coverage   47.24%   58.42%   +11.18%     
===========================================
  Files         476      556       +80     
  Lines       46892    61165    +14273     
===========================================
+ Hits        22154    35737    +13583     
- Misses      24738    25428      +690     

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[jedel1043]

We have an Error::unexpected variant for cases like this.

[tkshsbcue]

@jedel1043 Switched to Error::unexpected per your suggestion.

[tkshsbcue]

@jedel1043 i hope you can review my PR

[tkshsbcue]

hey @jedel1043 if there are any fixes i need to do lemme know

[jedel1043]

Thanks! This should also give much better error messages so that's good