llvm/llvm-project

Clang elides the wrong part of the template type in error message.

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#180,046 opened on Feb 5, 2026

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clang:frontendgood first issue

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Description

Repro: https://godbolt.org/z/9bYzd3WPG

Error message:error: no viable conversion from returned value of type 'S3<S2<...>>' to function return type 'S3<S2<...>>'

Expected: error: no viable conversion from returned value of type 'S3<const S2<int>>' to function return type 'S3<S2<int>>'

Contributor guide

Research direction
Investigate the code path in Clang that formats template type strings, specifically the code that elides template arguments. Find where the elision logic incorrectly chooses to elide the 'const' qualifier inside a template argument.
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.
1-2 days
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
GitC++
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40