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A brace inside an f-string interpolation comment silently changes the resulting value

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Valutazione

Difficoltà
3/5
Tempo stimato
1-2 giorni
Idoneità per principianti
76/100
Tipo di issue
Bug
Chiarezza
Specificata chiaramente
Stato di attività
Attiva
Stack tecnologico
c
Ambito
compilers

Direzione di ricerca

Start in src/lexer.c at the interpolation boundary scanner around lines 399 and 422, then read the comment and f-string rules in docs/SPEC.md. Reproduce the issue and compare it with the existing #334/#344 quoted-character cases. Add regression coverage for braces in comments, preserving nested braces and quoted # or braces, and verify the evaluated output is exactly 3\n.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

area:runtime-vm bug found-by:code-review kind:silent-wrong

A closing brace inside an f-string interpolation's comment terminates interpolation before the comment ends. The program succeeds but treats the remaining expression as literal text, changing its value.

Reproduce

Save and run this exact two-line program:

print of f"{1 # }
 + 2}"

Actual: exit 0, empty stderr, stdout shown as an escaped string:

"1\n + 2}\n"

Expected: 3\n. The } after # belongs to the comment; the actual expression is 1 + 2.

Paired control: change only the comment text from } to comment:

print of f"{1 # comment
 + 2}"

This exits 0 and prints 3\n. The ordinary parenthesized-expression control also handles the same brace-containing comment correctly:

print of (1 # }
 + 2)

It exits 0 and prints 3\n. This is not a request to introduce multiline expressions: the paired f-string control already accepts and evaluates one.

Cause and contract

The interpolation boundary scanner extracts the expression before recursively tokenizing it. It skips quoted string literals but has no comment state, and counts every exposed {/}. A } in the comment ends extraction; the following newline and + 2} become f-string literal text. The inner tokenizer recognizes the comment only after the boundary was chosen incorrectly.

The lexical contract says comments extend from # to end of line, and f-strings interpolate expressions. Boundary recognition must honor those lexical states.

Regression acceptance

  • The reproducer prints exactly 3\n, matching both controls.
  • Test opening and closing braces within comments, including multiple brace characters.
  • Retain genuine nested-expression brace handling and quoted #/brace characters; # inside a string must not start a comment.
  • Assert exact output after evaluation, not parse success alone: the current defective program exits successfully.

The existing #334/#344 cases cover braces inside quoted strings, not braces inside comments. No matching open or closed report was found.

Verification

Confirmed on a fresh default release build of b91768e23c5a874a64e76e4af9ab291e6aa49983, with inherited EIGS_* variables cleared. Each reproducer and paired control was executed; no runtime or test source was changed. This is a current correctness defect, not a proposed v1 language restriction.

Lingua principale
C
Stelle
3
Fork
7
Merge medio
3h 56m
PR unite (30g)
102

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