[clangd] Fix a declare-constructor tweak crash on incomplete fields.

[sammccall]

clang-tools-extra/clangd/refactor/tweaks/MemberwiseConstructor.cpp

182

Fail instead?

[hokein]

clang-tools-extra/clangd/refactor/tweaks/MemberwiseConstructor.cpp

182

Fail seems too strict, the tweak is entirely unavailable if there is any incomplete-type field decls in a class, I think it is still useful to make the tweak available.

clang-tools-extra/clangd/refactor/tweaks/MemberwiseConstructor.cpp

FieldAction Visit##T##Type(const T##Type *) { return Action; }
     };
 #undef ALWAYS
     return Visitor(Class->getASTContext())
         .Visit(Field->getType().getCanonicalType().getTypePtr());
   }
 
   // Decide what to do with a field of type C.
   static FieldAction considerClassValue(const CXXRecordDecl &C) {
+    if (!C.hasDefinition())
+      return Skip;
     // We can't always tell if C is copyable/movable without doing Sema work.
     // We assume operations are possible unless we can prove not.
     bool CanCopy = C.hasUserDeclaredCopyConstructor() ||
                    C.needsOverloadResolutionForCopyConstructor() ||
                    !C.defaultedCopyConstructorIsDeleted();
     bool CanMove = C.hasUserDeclaredMoveConstructor() ||
                    (C.needsOverloadResolutionForMoveConstructor() ||
                     !C.defaultedMoveConstructorIsDeleted());

clang-tools-extra/clangd/unittests/tweaks/MemberwiseConstructorTests.cpp

 using testing::Eq;
 using testing::HasSubstr;
 using testing::Not;
 
 TWEAK_TEST(MemberwiseConstructor);
 
 TEST_F(MemberwiseConstructorTest, Availability) {
   EXPECT_AVAILABLE("^struct ^S ^{ int x, y; };");
+  // Verify no crashes on incomplete member fields.
+  EXPECT_UNAVAILABLE("/*error-ok*/class Forward; class ^A { Forward f;}");
   EXPECT_UNAVAILABLE("struct S { ^int ^x, y; }; struct ^S;");
   EXPECT_UNAVAILABLE("struct ^S {};");
   EXPECT_UNAVAILABLE("union ^S { int x; };");
   EXPECT_UNAVAILABLE("struct ^S { int x = 0; };");
   EXPECT_UNAVAILABLE("struct ^S { struct { int x; }; };");
   EXPECT_UNAVAILABLE("struct ^{ int x; } e;");
 }