[Clang] Fix ClassifyImplicitMemberAccess to handle cases where the access in an unevaluated context is not within a CXXRecordDecl or CXXMethodDecl

[shafik]

Summary

ClassifyImplicitMemberAccess assumes that if we are not in a static context then the DeclContext must be a CXXRecordDecl or a CXXMethodDecl. In the case of the unevaluated context this may not be true.

This will lead to a crash because contextClass will remain a nullptr.

Fixes: https://github.com/llvm/llvm-project/issues/37792 and https://github.com/llvm/llvm-project/issues/48405

[aaron.ballman]

LGTM, though you should add a release note as well.

clang/lib/Sema/SemaExprMember.cpp

164–170

clang/test/SemaCXX/statements.cpp

60–61

This diagnostic isn't entirely unreasonable, but I think GCC gives a better diagnostic: https://godbolt.org/z/T4dbhnoo7

[shafik]

• Switched to using auto in two if statements
• Added Release notes

clang/test/SemaCXX/statements.cpp

60–61

Yeah, probably worth filing a bug for this after I land this.

clang/docs/ReleaseNotes.rst

 - Fix aggregate initialization inside lambda constexpr.
   (`#60936 <https://github.com/llvm/llvm-project/issues/60936>`_)
 - No longer issue a false positive diagnostic about a catch handler that cannot
   be reached despite being reachable. This fixes
   `#61177 <https://github.com/llvm/llvm-project/issues/61177>`_ in anticipation
   of `CWG2699 <https://wg21.link/CWG2699>_` being accepted by WG21.
 - Fix crash when parsing fold expression containing a delayed typo correction.
   (`#61326 <https://github.com/llvm/llvm-project/issues/61326>`_)
+- Fix crash when dealing with some member accesses outside of class or member
+  function context.
+  (`#37792 <https://github.com/llvm/llvm-project/issues/37792>`_) and
+  (`#48405 <https://github.com/llvm/llvm-project/issues/48405>`_)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Bug Fixes to Attribute Support
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Bug Fixes to C++ Support

clang/lib/Sema/SemaExprMember.cpp

if (isStaticContext) {
     if (hasNonInstance)
       return IMA_Mixed_StaticContext;
 
     return AbstractInstanceResult ? AbstractInstanceResult
                                   : IMA_Error_StaticContext;
   }
 
   CXXRecordDecl *contextClass;
-  if (CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(DC))
+  if (auto *MD = dyn_cast<CXXMethodDecl>(DC))
     contextClass = MD->getParent()->getCanonicalDecl();
-  else
+  else if (auto *RD = dyn_cast<CXXRecordDecl>(DC))
     contextClass = cast<CXXRecordDecl>(DC);
+  else
+    return AbstractInstanceResult ? AbstractInstanceResult
+                                  : IMA_Error_StaticContext;
 
   // [class.mfct.non-static]p3:
   // ...is used in the body of a non-static member function of class X,
   // if name lookup (3.4.1) resolves the name in the id-expression to a
   // non-static non-type member of some class C [...]
   // ...if C is not X or a base class of X, the class member access expression
   // is ill-formed.
   if (R.getNamingClass() &&

clang/test/SemaCXX/cxx1y-generic-lambdas.cpp

 
 namespace PR46637 {
   auto x = [](auto (*p)()) { return p(); };
   auto y = [](auto (*p)() -> auto) { return p(); };
   int f();
   void *v = x(f); // expected-error {{cannot initialize a variable of type 'void *' with an rvalue of type 'int'}}
   void *w = y(f); // expected-error {{cannot initialize a variable of type 'void *' with an rvalue of type 'int'}}
 }
+
+namespace GH37792 {
+struct A { int x; };
+
+void f() {
+  [](auto t) -> decltype(decltype(t)::x) { return 0; }(A());
+}
+}

clang/test/SemaCXX/statements.cpp

return ({ // expected-warning{{use of GNU statement expression extension}}
     ;
   });
 }
 
 void test8() {
   int a = test7(1);
   double b = test7(2.0);
 }
+
+namespace GH48405 {
+void foo() {
+  struct S {
+    int i;
+    int j = ({i;}); // expected-error {{invalid use of non-static data member 'i'}}
+                    // expected-error@-1 {{cannot initialize a member subobject of type 'int' with an rvalue of type 'void'}}
+        // expected-warning@-2 {{use of GNU statement expression extension}}
+  };
+}
+}