[all-commits] [llvm/llvm-project] 0dd568: [clang][Sema] Fix assertion in `tryDiagnoseOverloa...

[Alejandro Álvarez Ayllón via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 0dd56858fe188419182a57d0e03c8cd0aa693867
      https://github.com/llvm/llvm-project/commit/0dd56858fe188419182a57d0e03c8cd0aa693867
  Author: Alejandro Álvarez Ayllón <alejandro.alvarez at sonarsource.com>
  Date:   2024-09-18 (Wed, 18 Sep 2024)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/lib/Sema/SemaCast.cpp
    A clang/test/Parser/cxx-bad-cast-diagnose-broken-template.cpp

  Log Message:
  -----------
  [clang][Sema] Fix assertion in `tryDiagnoseOverloadedCast` (#108021)

Fixed an assertion failure in debug mode, and potential crashes in
release mode, when
diagnosing a failed cast caused indirectly by a failed implicit
conversion to the type of the constructor parameter.

For instance

```
template<typename>
struct StringTrait {};

template< int N >
struct StringTrait< const char[ N ] > {
  typedef char CharType;
  static const MissingIntT length = N - 1;
};

class String {
public:
  template <typename T>
  String(T& str, typename StringTrait<T>::CharType = 0);
};


class Exception {
public:
  Exception(String const&);
};

void foo() {
  throw Exception("some error");
}
```

`Exception(String const&)` is a matching constructor for `Exception`
from a `const char*`, via an implicit conversion to `String`. However,
the instantiation of the `String` constructor will fail because of the
missing type `MissingIntT` inside the specialization of `StringTrait`.

When trying to emit a diagnosis, `tryDiagnoseOverloadedCast` expects not
to have a matching constructor, but there is; it just could not be
instantiated.



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