Issues from a bug hunt over master (eb087382 to cd641cbc) #9109

Found by a bug hunt over the 16 commits from eb087382 to cd641cbc (26–27 October 2026).

The hunt started from the changes in those commits, looked for regressions, and reported older bugs it ran into along the way. Every finding was reproduced on a build of cd641cbc, checked again by an independent pass, and compiled at b123b7c3 to tell regressions apart from older bugs. Existing issues were searched first, and related ones are linked from each issue.

In numbers: 11 issues covering 22 findings. Three more suspected problems turned out not to be bugs and are not filed. 5 are regressions in this range: the untagged Date case in the first issue, both line-ending problems, the failwith placeholder, and the per-module copyWithin type.

Wrong code or wrong values

• x !== true && x !== false is simplified to false when x is not a boolean #9098 x !== true && x !== false is simplified to false when x is not a boolean (regression for one shape)
• Float constants never compare equal in the JS simplifier: x == 2.5 && x == 2.5 compiles to false #9099 Float constants never compare equal in the JS simplifier: x == 2.5 && x == 2.5 compiles to false
• bsc -format changes string literals that contain line breaks, and is not idempotent on \r\r\n #9100 bsc -format changes string literals that contain line breaks, and is not idempotent on \r\r\n (regression)
• Formatter moves an attribute in front of ~a as x: int onto x #9101 Formatter moves an attribute in front of ~a as x: int onto x
• TypedArray: copyWithin/copyAllWithin are typed as returning array, and TypedArray.map can change the element type #9103 TypedArray: copyWithin/copyAllWithin are typed as returning array, and TypedArray.map can change the element type
• JSX: plain and preserve mode evaluate children and props in different orders #9104 JSX: plain and preserve mode evaluate children and props in different orders

Tooling and diagnostics

• Editor code actions generate failwith("TODO"), which no longer exists #9102 Editor code actions generate failwith("TODO"), which no longer exists (regression)
• Coercion hint: suggestion that doesn't compile after a parenthesized operand, and the hint names the expanded type #9105 Coercion hint: suggestion that doesn't compile after a parenthesized operand, and the hint names the expanded type

Parser and printer

• Parser rejects private @attr {…} and a doc comment before a non-record type #9106 Parser rejects private @attr {…} and a doc comment before a non-record type
• Formatter: five cases where comments and doc comments are placed wrongly #9107 Formatter: five cases where comments and doc comments are placed wrongly
• Lexer rejects a UTF-8 BOM, and a lone \r does not end a line #9108 Lexer rejects a UTF-8 BOM, and a lone \r does not end a line

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