llvm/llvm-project

auto allowed with a type in C++

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#164,273 opened on Oct 20, 2025

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Description

We currently allow something like this in C++: https://godbolt.org/z/7fabbGfe6

void f() {
  auto int x = 1;
}

It looks like this was allowed as an extension in C++ because it was valid C but I don't think it makes sense to support this anymore.

Contributor guide

Research direction
Investigate the parsing of `auto` in C++ and remove the C compatibility extension that allows a type after auto.
Tech stack
cpp
Domain
tooling
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
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
C++Git
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30