[PATCH] D110216: [clang] retain type sugar in auto / template argument deduction

[Matheus Izvekov via Phabricator via cfe-commits]

mizvekov added inline comments.


================
Comment at: clang/lib/Sema/SemaTemplateDeduction.cpp:1643
 
-      return Param == Arg? Sema::TDK_Success : Sema::TDK_NonDeducedMismatch;
+      return ParDesug == ArgDesug ? Sema::TDK_Success
+                                  : Sema::TDK_NonDeducedMismatch;
----------------
mizvekov wrote:
> rsmith wrote:
> > This looks wrong to me: we should be comparing the types, not how they're written. `Context.hasSameType(Param, Arg)` (or `Context.hasSameUnqualifiedType(Param, Arg)` in the `TDF_IgnoreQualifiers` case) would be appropriate here.
> You are right, but the reason we don't get into any troubles here is because this is dead code anyway, the non-dependent case will always be handled above :)
> 
> Although perhaps, I wonder if we should dig down into non-dependent types anyway, in case the types are too complex and it's not immediately obvious what does not match, we could perhaps improve the diagnostic?
> 
> I will experiment a little bit with this idea.
Here are the results of this experiment:
```
error: 'note' diagnostics expected but not seen:
  File SemaCXX\cxx1z-noexcept-function-type.cpp Line 21: could not match 'void (I) noexcept(false)' (aka 'void (int) noexcept(false)') against 'void (int) noexcept'
error: 'note' diagnostics seen but not expected:
  File SemaCXX\cxx1z-noexcept-function-type.cpp Line 21: candidate template ignored: failed template argument deduction

error: 'note' diagnostics expected but not seen:
  File SemaCXX\deduced-return-type-cxx14.cpp Line 146: candidate template ignored: could not match 'auto ()' against 'int ()'
  File SemaCXX\deduced-return-type-cxx14.cpp Line 161: candidate template ignored: could not match 'auto ()' against 'void ()'
error: 'note' diagnostics seen but not expected:
  File SemaCXX\deduced-return-type-cxx14.cpp Line 146: candidate template ignored: could not match 'auto' against 'int'
  File SemaCXX\deduced-return-type-cxx14.cpp Line 161: candidate template ignored: could not match 'auto' against 'void'

error: 'note' diagnostics expected but not seen:
  File SemaCXX\pass-object-size.cpp Line 62 (directive at SemaCXX\pass-object-size.cpp:69): candidate address cannot be taken because parameter 1 has pass_object_size attribute
  File SemaCXX\pass-object-size.cpp Line 56 (directive at SemaCXX\pass-object-size.cpp:74): candidate address cannot be taken because parameter 1 has pass_object_size attribute
  File SemaCXX\pass-object-size.cpp Line 62 (directive at SemaCXX\pass-object-size.cpp:75): candidate address cannot be taken because parameter 1 has pass_object_size attribute
error: 'note' diagnostics seen but not expected:
  File SemaCXX\pass-object-size.cpp Line 56: candidate template ignored: failed template argument deduction
  File SemaCXX\pass-object-size.cpp Line 62: candidate template ignored: failed template argument deduction
  File SemaCXX\pass-object-size.cpp Line 62: candidate template ignored: failed template argument deduction

error: 'note' diagnostics expected but not seen:
  File SemaTemplate\deduction.cpp Line 316: deduced non-type template argument does not have the same type as the corresponding template parameter ('std::nullptr_t' vs 'int *')
  File SemaTemplate\deduction.cpp Line 323: values of conflicting types
error: 'note' diagnostics seen but not expected:
  File SemaTemplate\deduction.cpp Line 275: candidate template ignored: could not match 'const int' against 'int'
  File SemaTemplate\deduction.cpp Line 316: candidate template ignored: could not match 'int *' against 'std::nullptr_t'
  File SemaTemplate\deduction.cpp Line 323: candidate template ignored: could not match 'int *' against 'std::nullptr_t'

error: 'note' diagnostics expected but not seen:
  File SemaTemplate\explicit-instantiation.cpp Line 64: candidate template ignored: could not match 'void ()' against 'void (float *)'
  File SemaTemplate\explicit-instantiation.cpp Line 70: candidate template ignored: could not match 'void (int *)' against 'void (float *)'
error: 'note' diagnostics seen but not expected:
  File SemaTemplate\explicit-instantiation.cpp Line 70: candidate template ignored: could not match 'int' against 'float'
  File SemaTemplate\explicit-instantiation.cpp Line 64: candidate template ignored: failed template argument deduction
```

It's interesting to note that it reveals several cases we give too generic 'failed template argument deduction' errors, like the different noexcept specifications, function prototypes with different amount of parameters, and the 'pass_object_size attribute' case.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D110216/new/

https://reviews.llvm.org/D110216