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

[hokein]

Summary

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

[kadircet]

clang-tools-extra/clangd/IncludeFixer.cpp

71

nit: maybe revert this change, or put err_incomplete_type to the last position to make the list alphabetically ordered.

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

709

should this be $type[[a]] ?

711

i don't follow what we gain by this change?

715

why do we need c++17 ?

738

can you move this back to original position ?

[hokein]

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

709

yeah, but this is the actual diagnostic range, though it is wired.

715

The newly-added test case is using C++17 feature (structure binding), needs this flag to suppress a diagnostic warning.

738

yeah, I reordered the list.

there are two orders: the one listed here, and the one listed in IncludeFixer.cpp.

The motivation is to make them aligned, so that it would be easier to compare and spot the difference. The current state is not friendly to readers.

[hokein]

update: don't change the order in test.

[kadircet]

still LGTM

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

715

ah okay i see it now, structured binding wasn't obvious from the test case above (i thought there was a typo :D

738

i don't think the orderings in the source vs test is that relevant, but SGTM if it helps you. mainly because:

• as it might be harder in future to trigger diagnostics in the order we want
• it is an invariant hard to maintain without at least the reviewer or author of changes knowing about(and remembering) it

[hokein]

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

738

yeah, it does help me, especially when I start adding more diagnostics.

clang-tools-extra/clangd/IncludeFixer.cpp

private:
   std::vector<DeclContext *> Visited;
 };
 
 } // namespace
 
 std::vector<Fix> IncludeFixer::fix(DiagnosticsEngine::Level DiagLevel,
                                    const clang::Diagnostic &Info) const {
   switch (Info.getID()) {
+  case diag::err_incomplete_base_class:
   case diag::err_incomplete_type:
   case diag::err_incomplete_member_access:
-  case diag::err_incomplete_base_class:
   case diag::err_incomplete_nested_name_spec:
     // Incomplete type diagnostics should have a QualType argument for the
     // incomplete type.
     for (unsigned Idx = 0; Idx < Info.getNumArgs(); ++Idx) {
       if (Info.getArgKind(Idx) == DiagnosticsEngine::ak_qualtype) {
         auto QT = QualType::getFromOpaquePtr((void *)Info.getRawArg(Idx));
         if (const Type *T = QT.getTypePtrOrNull())
           if (T->isIncompleteType())

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

buildIndexWithSymbol(llvm::ArrayRef<SymbolWithHeader> Syms) {
   }
   return MemIndex::build(std::move(Slab).build(), RefSlab(), RelationSlab());
 }
 
 TEST(IncludeFixerTest, IncompleteType) {
   Annotations Test(R"cpp(// error-ok
 $insert[[]]namespace ns {
   class X;
-  $nested[[X::]]Nested n;
 }
 class Y : $base[[public ns::X]] {};
 int main() {
   ns::X *x;
+  auto& $type[[[]]a] = *x;
   x$access[[->]]f();
+  $nested[[ns::X::]]Nested n;
 }
   )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();
 
   EXPECT_THAT(
       TU.build().getDiagnostics(),
       UnorderedElementsAre(
-          AllOf(Diag(Test.range("nested"),
-                     "incomplete type 'ns::X' named in nested name specifier"),
-                DiagName("incomplete_nested_name_spec"),
-                WithFix(Fix(Test.range("insert"), "#include \"x.h\"\n",
-                            "Add include \"x.h\" for symbol ns::X"))),
           AllOf(Diag(Test.range("base"), "base class has incomplete type"),
                 DiagName("incomplete_base_class"),
                 WithFix(Fix(Test.range("insert"), "#include \"x.h\"\n",
                             "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"))),
           AllOf(Diag(Test.range("access"),
                      "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"))),
+          AllOf(Diag(Test.range("nested"),
+                     "incomplete type 'ns::X' named in nested name specifier"),
+                DiagName("incomplete_nested_name_spec"),
+                WithFix(Fix(Test.range("insert"), "#include \"x.h\"\n",
                             "Add include \"x.h\" for symbol ns::X")))));
 }
 
 TEST(IncludeFixerTest, NoSuggestIncludeWhenNoDefinitionInHeader) {
   Annotations Test(R"cpp(// error-ok
 $insert[[]]namespace ns {
   class X;
 }