[Sema] cast to CXXRecordDecl correctly when diag a default comparison…

… method

Fixed: llvm/llvm-project#62791
Fixed: llvm/llvm-project#62102
in c++20, default comparison is supported. `getLexicalDeclContext` maybe cannot
get the `CXXRecord` if default comparison defined out of `CXXRecord`.
This patch want to get these information from the first function argument.

Reviewed By: #clang-language-wg, erichkeane

Differential Revision: https://reviews.llvm.org/D151365

clang/docs/ReleaseNotes.rst

@@ -445,6 +445,9 @@ Bug Fixes in This Version
   (`#62789 <https://github.com/llvm/llvm-project/issues/62789>`_).
 - Fix a crash when instantiating a non-type template argument in a dependent scope.
   (`#62533 <https://github.com/llvm/llvm-project/issues/62533>`_).
+- Fix crash when diagnosing default comparison method.
+  (`#62791 <https://github.com/llvm/llvm-project/issues/62791>`_) and
+  (`#62102 <https://github.com/llvm/llvm-project/issues/62102>`_).
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -961,11 +961,13 @@ void Sema::PrintInstantiationStack() {
             << MD->isExplicitlyDefaulted() << DFK.asSpecialMember()
             << Context.getTagDeclType(MD->getParent());
       } else if (DFK.isComparison()) {
+        QualType RecordType = FD->getParamDecl(0)
+                                  ->getType()
+                                  .getNonReferenceType()
+                                  .getUnqualifiedType();
         Diags.Report(Active->PointOfInstantiation,
                      diag::note_comparison_synthesized_at)
-            << (int)DFK.asComparison()
-            << Context.getTagDeclType(
-                   cast<CXXRecordDecl>(FD->getLexicalDeclContext()));
+            << (int)DFK.asComparison() << RecordType;
       }
       break;
     }

clang/test/CXX/class/class.compare/class.spaceship/p1.cpp

@@ -227,5 +227,5 @@ namespace Preference {
     A a;
     std::strong_ordering operator<=>(const B&) const = default; // expected-error {{call to deleted constructor of 'A'}}
   };
-  bool x = B() < B(); // expected-note {{in defaulted three-way comparison operator for 'Preference::B' first required here}}
+  bool x = B() < B(); // expected-note {{in defaulted three-way comparison operator for 'B' first required here}}
 }

clang/test/SemaCXX/cxx20-default-compare.cpp

@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 %s -std=c++23 -verify -Wfloat-equal
+
+struct Foo {
+  float val;
+  bool operator==(const Foo &) const;
+  friend bool operator==(const Foo &, const Foo &);
+  friend bool operator==(Foo, Foo );
+};
+
+// Declare the defaulted comparison function as a member function.
+bool Foo::operator==(const Foo &) const = default; // expected-warning {{comparing floating point with == or != is unsafe}} expected-note {{in defaulted equality comparison operator for 'Foo' first required here}}
+
+// Declare the defaulted comparison function as a non-member function.
+bool operator==(const Foo &, const Foo &) = default;  // expected-warning {{comparing floating point with == or != is unsafe}} expected-note {{in defaulted equality comparison operator for 'Foo' first required here}}
+
+// Declare the defaulted comparison function as a non-member function. Arguments are passed by value.
+bool operator==(Foo, Foo) = default;  // expected-warning {{comparing floating point with == or != is unsafe}} expected-note {{in defaulted equality comparison operator for 'Foo' first required here}}