[Clang][Sema] Fix crash when diagnosing near-match for 'constexpr' redeclaration in C++11

Author: sdkrystian

clang/docs/ReleaseNotes.rst

@@ -758,6 +758,8 @@ Bug Fixes to C++ Support
 - Fix a bug with checking constrained non-type template parameters for equivalence. Fixes (#GH77377).
 - Fix a bug where the last argument was not considered when considering the most viable function for
   explicit object argument member functions. Fixes (#GH92188).
+- Fix a C++11 crash when a non-const non-static member function is defined out-of-line with
+  the ``constexpr`` specifier.
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/include/clang/Sema/DeclSpec.h

@@ -1527,20 +1527,20 @@ struct DeclaratorChunk {
 
     /// Retrieve the location of the 'const' qualifier.
     SourceLocation getConstQualifierLoc() const {
-      assert(MethodQualifiers);
-      return MethodQualifiers->getConstSpecLoc();
+      return MethodQualifiers ? MethodQualifiers->getConstSpecLoc()
+                              : SourceLocation();
     }
 
     /// Retrieve the location of the 'volatile' qualifier.
     SourceLocation getVolatileQualifierLoc() const {
-      assert(MethodQualifiers);
-      return MethodQualifiers->getVolatileSpecLoc();
+      return MethodQualifiers ? MethodQualifiers->getVolatileSpecLoc()
+                              : SourceLocation();
     }
 
     /// Retrieve the location of the 'restrict' qualifier.
     SourceLocation getRestrictQualifierLoc() const {
-      assert(MethodQualifiers);
-      return MethodQualifiers->getRestrictSpecLoc();
+      return MethodQualifiers ? MethodQualifiers->getRestrictSpecLoc()
+                              : SourceLocation();
     }
 
     /// Retrieve the location of the 'mutable' qualifier, if any.

clang/lib/Sema/SemaDecl.cpp

@@ -9217,15 +9217,15 @@ static NamedDecl *DiagnoseInvalidRedeclaration(
         << Idx << FDParam->getType()
         << NewFD->getParamDecl(Idx - 1)->getType();
     } else if (FDisConst != NewFDisConst) {
-      SemaRef.Diag(FD->getLocation(), diag::note_member_def_close_const_match)
-          << NewFDisConst << FD->getSourceRange().getEnd()
-          << (NewFDisConst
-                  ? FixItHint::CreateRemoval(ExtraArgs.D.getFunctionTypeInfo()
-                                                 .getConstQualifierLoc())
-                  : FixItHint::CreateInsertion(ExtraArgs.D.getFunctionTypeInfo()
-                                                   .getRParenLoc()
-                                                   .getLocWithOffset(1),
-                                               " const"));
+      auto DB = SemaRef.Diag(FD->getLocation(),
+                             diag::note_member_def_close_const_match)
+                << NewFDisConst << FD->getSourceRange().getEnd();
+      if (const auto &FTI = ExtraArgs.D.getFunctionTypeInfo(); !NewFDisConst)
+        DB << FixItHint::CreateInsertion(FTI.getRParenLoc().getLocWithOffset(1),
+                                         " const");
+      else if (SourceLocation ConstLoc = FTI.getConstQualifierLoc();
+               ConstLoc.isValid())
+        DB << FixItHint::CreateRemoval(ConstLoc);
     } else
       SemaRef.Diag(FD->getLocation(),
                    IsMember ? diag::note_member_def_close_match

clang/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p1.cpp

@@ -154,3 +154,14 @@ namespace {
   // FIXME: We should diagnose this prior to C++17.
   const int &r = A::n;
 }
+
+#if __cplusplus < 201402L
+namespace ImplicitConstexprDef {
+  struct A {
+    void f(); // expected-note {{member declaration does not match because it is not const qualified}}
+  };
+
+  constexpr void A::f() { } // expected-warning {{'constexpr' non-static member function will not be implicitly 'const' in C++14; add 'const' to avoid a change in behavior}}
+                            // expected-error@-1 {{out-of-line definition of 'f' does not match any declaration in 'ImplicitConstexprDef::A'}}
+}
+#endif