llvmorg-github-actions[bot] wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
Author: Nico Weber (nico)
<details>
<summary>Changes</summary>
If substituting the parameter mappings of a normalized constraint failed,
Sema::getNormalizedAssociatedConstraints() returned nullptr, but it stored the
partially substituted normal form in NormalizationCache. So the first lookup
for such a declaration failed, but every later lookup returned the broken
normal form, and subsumption checking and the ambiguous-constraint diagnostics
then continued with it.
I believe this wasn't intentional:
- Before #<!-- -->161671 (e9972debc98c), normalization was a single step, and a
failure was cached as nullptr.
- #<!-- -->161671 added the parameter mapping substitution step. It inserted
the normal form into the cache before substituting, and returned nullptr if the
substitution then failed, leaving the non-null normal form in the cache.
- #<!-- -->165352 (2984a8db804e) moved the insertion after the substitution to
not use an invalidated iterator, but kept inserting the normal form if the
substitution failed.
Instead, cache failed substitution as nullptr, like a failed normalization.
This removes diagnostics that were only emitted because the second lookup
continued with the broken normal form. #<!-- -->161671 added these to
temp.constr.normal/p1.cpp:
- A second "'type name' declared as a pointer to a reference" error (with its
notes) for the same broken concept. For
template<typename T> concept Foo = True<T*>;
template<typename T> concept Bar = Foo<T&>;
template<typename T> requires Bar<T> struct S { };
template<typename T> requires Bar<T> && true struct
S<T> { };
the error got reported once for the partial specialization, and also for the
primary template after. Now, we only have the first report.
- A "similar constraint expressions not considered equivalent" note and its
"similar constraint expression here" note, which we computed from the broken
normal form. The actual problem in that test is the broken constraint, which is
still diagnosed.
This also makes it possible to key the normalization cache by constraint
expression without changing which diagnostics are emitted for failures, which I
want to do in a follow-up.
---
Full diff: https://github.com/llvm/llvm-project/pull/227086.diff
2 Files Affected:
- (modified) clang/lib/Sema/SemaConcept.cpp (+2-7)
- (modified) clang/test/CXX/temp/temp.constr/temp.constr.normal/p1.cpp (+3-8)
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</details>
https://github.com/llvm/llvm-project/pull/227086
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