[clangd] Add a missing include-fixer test for incomplete_type, NFC.

Also sort the list to make it easier to verify with the implementation
code.

Differential Revision: https://reviews.llvm.org/D88964

Author: hokein

clang-tools-extra/clangd/IncludeFixer.cpp

@@ -68,10 +68,10 @@ class VisitedContextCollector : public VisibleDeclConsumer {
 std::vector<Fix> IncludeFixer::fix(DiagnosticsEngine::Level DiagLevel,
                                    const clang::Diagnostic &Info) const {
   switch (Info.getID()) {
-  case diag::err_incomplete_type:
-  case diag::err_incomplete_member_access:
-  case diag::err_incomplete_base_class:
   case diag::err_incomplete_nested_name_spec:
+  case diag::err_incomplete_base_class:
+  case diag::err_incomplete_member_access:
+  case diag::err_incomplete_type:
     // Incomplete type diagnostics should have a QualType argument for the
     // incomplete type.
     for (unsigned Idx = 0; Idx < Info.getNumArgs(); ++Idx) {

clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp

@@ -708,9 +708,11 @@ class Y : $base[[public ns::X]] {};
 int main() {
   ns::X *x;
   x$access[[->]]f();
+  auto& $type[[[]]a] = *x;
 }
   )cpp");
   auto TU = TestTU::withCode(Test.code());
+  TU.ExtraArgs.push_back("-std=c++17");
   auto Index = buildIndexWithSymbol(
       {SymbolWithHeader{"ns::X", "unittest:///x.h", "\"x.h\""}});
   TU.ExternalIndex = Index.get();
@@ -731,7 +733,13 @@ int main() {
                      "member access into incomplete type 'ns::X'"),
                 DiagName("incomplete_member_access"),
                 WithFix(Fix(Test.range("insert"), "#include \"x.h\"\n",
-                            "Add include \"x.h\" for symbol ns::X")))));
+                            "Add include \"x.h\" for symbol ns::X"))),
+          AllOf(
+              Diag(Test.range("type"),
+                   "incomplete type 'ns::X' where a complete type is required"),
+              DiagName("incomplete_type"),
+              WithFix(Fix(Test.range("insert"), "#include \"x.h\"\n",
+                          "Add include \"x.h\" for symbol ns::X")))));
 }
 
 TEST(IncludeFixerTest, NoSuggestIncludeWhenNoDefinitionInHeader) {