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

Differential Revision: https://reviews.llvm.org/D124154

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

@@ -178,6 +178,8 @@ private:
 
   // 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() ||

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

@@ -23,6 +23,8 @@ 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; };");