[clangd] Fix code completion in MACROs with stringification.

[ioeric]

Summary

Currently, we only handle the first callback from sema code completion
and ignore results from potential following callbacks. This causes
causes loss of completion results when multiple contexts are tried by Sema.

For example, we wouldn't get any completion result in the following completion
as the first attemped context is natural language which has no
candidate. The parser would backtrack and tried a completion with AST
semantic, which would find candidate "::x".

void f(const char*, int);
#define F(x) f(#x, x)
int x;
void main() {
	F(::^);
}

To fix this, we only process a sema callback when it gives completion results or
the context supports index-based completion.

[ioeric]

• Fix broken test

[ilya-biryukov]

LGTM.

clang-tools-extra/trunk/clangd/CodeComplete.cpp

Info.UnresolvedQualifier =
                            SM, clang::LangOptions()).ltrim("::");
   // Sema excludes the trailing "::".
   if (!Info.UnresolvedQualifier->empty())
     *Info.UnresolvedQualifier += "::";
 
   return Info.scopesForIndexQuery();
 }
 
+// Should we perform index-based completion in a context of the specified kind?
+// FIXME: consider allowing completion, but restricting the result types.
+bool contextAllowsIndex(enum CodeCompletionContext::Kind K) {
+  switch (K) {
+  case CodeCompletionContext::CCC_TopLevel:
+  case CodeCompletionContext::CCC_ObjCInterface:
+  case CodeCompletionContext::CCC_ObjCImplementation:
+  case CodeCompletionContext::CCC_ObjCIvarList:
+  case CodeCompletionContext::CCC_ClassStructUnion:
+  case CodeCompletionContext::CCC_Statement:
+  case CodeCompletionContext::CCC_Expression:
+  case CodeCompletionContext::CCC_ObjCMessageReceiver:
+  case CodeCompletionContext::CCC_EnumTag:
+  case CodeCompletionContext::CCC_UnionTag:
+  case CodeCompletionContext::CCC_ClassOrStructTag:
+  case CodeCompletionContext::CCC_ObjCProtocolName:
+  case CodeCompletionContext::CCC_Namespace:
+  case CodeCompletionContext::CCC_Type:
+  case CodeCompletionContext::CCC_Name: // FIXME: why does ns::^ give this?
+  case CodeCompletionContext::CCC_PotentiallyQualifiedName:
+  case CodeCompletionContext::CCC_ParenthesizedExpression:
+  case CodeCompletionContext::CCC_ObjCInterfaceName:
+  case CodeCompletionContext::CCC_ObjCCategoryName:
+    return true;
+  case CodeCompletionContext::CCC_Other: // Be conservative.
+  case CodeCompletionContext::CCC_OtherWithMacros:
+  case CodeCompletionContext::CCC_DotMemberAccess:
+  case CodeCompletionContext::CCC_ArrowMemberAccess:
+  case CodeCompletionContext::CCC_ObjCPropertyAccess:
+  case CodeCompletionContext::CCC_MacroName:
+  case CodeCompletionContext::CCC_MacroNameUse:
+  case CodeCompletionContext::CCC_PreprocessorExpression:
+  case CodeCompletionContext::CCC_PreprocessorDirective:
+  case CodeCompletionContext::CCC_NaturalLanguage:
+  case CodeCompletionContext::CCC_SelectorName:
+  case CodeCompletionContext::CCC_TypeQualifiers:
+  case CodeCompletionContext::CCC_ObjCInstanceMessage:
+  case CodeCompletionContext::CCC_ObjCClassMessage:
+  case CodeCompletionContext::CCC_Recovery:
+    return false;
+  }
+  llvm_unreachable("unknown code completion context");
+}
+
 // The CompletionRecorder captures Sema code-complete output, including context.
 // It filters out ignored results (but doesn't apply fuzzy-filtering yet).
 // It doesn't do scoring or conversion to CompletionItem yet, as we want to
 // merge with index results first.
 // Generally the fields and methods of this object should only be used from
 // within the callback.
 struct CompletionRecorder : public CodeCompleteConsumer {
   CompletionRecorder(const CodeCompleteOptions &Opts,
struct CompletionRecorder : public CodeCompleteConsumer {
   std::vector<CodeCompletionResult> Results;
   CodeCompletionContext CCContext;
   Sema *CCSema = nullptr; // Sema that created the results.
   // FIXME: Sema is scary. Can we store ASTContext and Preprocessor, instead?
 
   void ProcessCodeCompleteResults(class Sema &S, CodeCompletionContext Context,
                                   CodeCompletionResult *InResults,
                                   unsigned NumResults) override final {
+    // If a callback is called without any sema result and the context does not
+    // support index-based completion, we simply skip it to give way to
+    // potential future callbacks with results.
+    if (NumResults == 0 && !contextAllowsIndex(Context.getKind()))
+      return;
     if (CCSema) {
       log(llvm::formatv(
           "Multiple code complete callbacks (parser backtracked?). "
           "Dropping results from context {0}, keeping results from {1}.",
-          getCompletionKindString(this->CCContext.getKind()),
-          getCompletionKindString(Context.getKind())));
+          getCompletionKindString(Context.getKind()),
+          getCompletionKindString(this->CCContext.getKind())));
       return;
     }
     // Record the completion context.
     CCSema = &S;
     CCContext = Context;
 
     // Retain the results we might want.
     for (unsigned I = 0; I < NumResults; ++I) {
if (!Action.Execute()) {
     log("Execute() failed when running codeComplete for " + Input.FileName);
     return false;
   }
   Action.EndSourceFile();
 
   return true;
 }
 
-// Should we perform index-based completion in a context of the specified kind?
-// FIXME: consider allowing completion, but restricting the result types.
-bool contextAllowsIndex(enum CodeCompletionContext::Kind K) {
-  switch (K) {
-  case CodeCompletionContext::CCC_TopLevel:
-  case CodeCompletionContext::CCC_ObjCInterface:
-  case CodeCompletionContext::CCC_ObjCImplementation:
-  case CodeCompletionContext::CCC_ObjCIvarList:
-  case CodeCompletionContext::CCC_ClassStructUnion:
-  case CodeCompletionContext::CCC_Statement:
-  case CodeCompletionContext::CCC_Expression:
-  case CodeCompletionContext::CCC_ObjCMessageReceiver:
-  case CodeCompletionContext::CCC_EnumTag:
-  case CodeCompletionContext::CCC_UnionTag:
-  case CodeCompletionContext::CCC_ClassOrStructTag:
-  case CodeCompletionContext::CCC_ObjCProtocolName:
-  case CodeCompletionContext::CCC_Namespace:
-  case CodeCompletionContext::CCC_Type:
-  case CodeCompletionContext::CCC_Name: // FIXME: why does ns::^ give this?
-  case CodeCompletionContext::CCC_PotentiallyQualifiedName:
-  case CodeCompletionContext::CCC_ParenthesizedExpression:
-  case CodeCompletionContext::CCC_ObjCInterfaceName:
-  case CodeCompletionContext::CCC_ObjCCategoryName:
-    return true;
-  case CodeCompletionContext::CCC_Other: // Be conservative.
-  case CodeCompletionContext::CCC_OtherWithMacros:
-  case CodeCompletionContext::CCC_DotMemberAccess:
-  case CodeCompletionContext::CCC_ArrowMemberAccess:
-  case CodeCompletionContext::CCC_ObjCPropertyAccess:
-  case CodeCompletionContext::CCC_MacroName:
-  case CodeCompletionContext::CCC_MacroNameUse:
-  case CodeCompletionContext::CCC_PreprocessorExpression:
-  case CodeCompletionContext::CCC_PreprocessorDirective:
-  case CodeCompletionContext::CCC_NaturalLanguage:
-  case CodeCompletionContext::CCC_SelectorName:
-  case CodeCompletionContext::CCC_TypeQualifiers:
-  case CodeCompletionContext::CCC_ObjCInstanceMessage:
-  case CodeCompletionContext::CCC_ObjCClassMessage:
-  case CodeCompletionContext::CCC_Recovery:
-    return false;
-  }
-  llvm_unreachable("unknown code completion context");
-}
-
 // Should we allow index completions in the specified context?
 bool allowIndex(CodeCompletionContext &CC) {
   if (!contextAllowsIndex(CC.getKind()))
     return false;
   // We also avoid ClassName::bar (but allow namespace::bar).
   auto Scope = CC.getCXXScopeSpecifier();
   if (!Scope)
     return true;

clang-tools-extra/trunk/unittests/clangd/CodeCompleteTests.cpp

TEST(CompletionTest, BacktrackCrashes) {
   completions(R"cpp(
     struct FooBarBaz {};
     void test() {
       if (FooBarBaz * x^) {}
     }
 )cpp");
 }
 
+TEST(CompletionTest, CompleteInMacroWithStringification) {
+  auto Results = completions(R"cpp(
+void f(const char *, int x);
+#define F(x) f(#x, x)
+
+namespace ns {
+int X;
+int Y;
+}  // namespace ns
+
+int f(int input_num) {
+  F(ns::^)
+}
+)cpp");
+
+  EXPECT_THAT(Results.items,
+              UnorderedElementsAre(Named("X"), Named("Y")));
+}
+
+TEST(CompletionTest, CompleteInMacroAndNamespaceWithStringification) {
+  auto Results = completions(R"cpp(
+void f(const char *, int x);
+#define F(x) f(#x, x)
+
+namespace ns {
+int X;
+
+int f(int input_num) {
+  F(^)
+}
+}  // namespace ns
+)cpp");
+
+  EXPECT_THAT(Results.items, Contains(Named("X")));
+}
+
 TEST(CompletionTest, CompleteInExcludedPPBranch) {
   auto Results = completions(R"cpp(
     int bar(int param_in_bar) {
     }
 
     int foo(int param_in_foo) {
 #if 0
   par^