<type_traits>: underlying_type fails to diagnose incomplete enums
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compiler
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- C++
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Description
Describe the bug
underlying_type violates the Mandates: in [meta.trans.other] that requires it to diagnose incomplete enumeration types.
Command-line test case
#include <type_traits>
enum E {
x = sizeof(std::underlying_type_t<E>)
};
Expected behavior
Should explode, but doesn't.
Contributor 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.
Research direction
Start by compiling the provided test case with MSVC and tracing how std::underlying_type_t is handled through <type_traits>. Compare the result with the mandate for incomplete enumeration types, then add regression coverage showing that the example diagnoses the incomplete enum and run the relevant type_traits tests.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- cpp
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100