A brace inside an f-string interpolation comment silently changes the resulting value
Maintainers usually reply within 1 day
Nobody has claimed this yet.
Assessment
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Newbie friendliness
- 76/100
Research direction
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.
Written by the indexing model from the issue text.
Description
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.
- Dominant language
- C
- Stars
- 3
- Forks
- 7
- Avg merge
- 3h 56m
- Merged PRs (30d)
- 102
Getting set up
Starts the project's dev container in your browser, under your own GitHub account.
- Ships a Dockerfile or Docker Compose file
- Has a pull request template
- Read the contributing guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
More from InauguralSystems/EigenScript
-
area:lint-tooling bug
Difficulty 2/5 1-3 hours Newbie friendliness 88/100
InauguralSystems/EigenScript#1340 ·
Maintainers usually reply within 1 day
-
area:stdlib found-by:code-review kind:silent-wrong
Difficulty 2/5 1-3 hours Newbie friendliness 88/100
InauguralSystems/EigenScript#1338 ·
Maintainers usually reply within 1 day
-
area:lint-tooling found-by:critic kind:docs-drift
Difficulty 2/5 1-3 hours Newbie friendliness 76/100
InauguralSystems/EigenScript#1335 ·
Maintainers usually reply within 1 day
-
area:ci found-by:critic kind:gate-defect
Difficulty 2/5 1-3 hours Newbie friendliness 86/100
InauguralSystems/EigenScript#1311 ·
Maintainers usually reply within 1 day
-
enrolment: decide test_gc_runner_controls.py (exempt vs enrol) and whether floors need a ratchetOpenarea:gates found-by:critic kind:decision
Difficulty 2/5 1-3 hours Newbie friendliness 65/100
InauguralSystems/EigenScript#1280 · 1 comment ·
Maintainers usually reply within 1 day
All issues in InauguralSystems/EigenScript
Similar issues
-
Difficulty 2/5 1-3 hours Newbie friendliness 78/100
libretro/libretro-common#233 ·
-
[Bug]: chunk_span_bounds and _validated_chunk_spans reject Pydantic models ChunkSpan and AudioFileOpen
Difficulty 2/5 1-3 hours Newbie friendliness 78/100
BasedHardware/omi#19047 ·
Maintainers usually reply within 1 day
-
Difficulty 2/5 1-3 hours Newbie friendliness 88/100
Maintainers usually reply within 1 day
-
Difficulty 2/5 1-3 hours Newbie friendliness 82/100
-
Difficulty 2/5 1-3 hours Newbie friendliness 76/100
obsproject/obs-studio#13936 · 2 comments ·
Maintainers usually reply within 1 day