llvm/llvm-project

missing parenthesis for function-like macro invocation could have better diagnostic

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#123,038 opened on Jan 15, 2025

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clang:diagnosticsgood first issue

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Description

Consider:

$ cat /tmp/a.c
#define FOO() 42
int x = FOO;

The compiler will error because we forgot to use parens for FOO:

$ clang -c /tmp/a.c
/tmp/a.c:2:9: error: use of undeclared identifier 'FOO'
    2 | int x = FOO;
      |         ^
1 error generated.

It would be nice if the compiler diagnostic included a note pointing out that FOO does exist, but as a function-like macro it requires parenthesis.

Contributor guide

Research direction
Inspect the diagnostic emission for undeclared identifiers in Clang's Sema or Lexer; trace how function like macros are resolved and add a note when they are used without parentheses.
Tech stack
ccpp
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
CC++
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40