[clangd] Added highlighting for constructor initializers.

[jvikstrom]

Summary

Constructor initializers were not being highlighted. This adds highlighting for them by using TraverseConstructorInitializer. Uses the Traverse* because there is no visit for CXXCtorInitializer.

[jvikstrom]

Fixed case where initializer was base class initializer which would cause crash.

clang-tools-extra/clangd/SemanticHighlighting.cpp

 //===--- SemanticHighlighting.cpp - ------------------------- ---*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "SemanticHighlighting.h"
 #include "Logger.h"
 #include "Protocol.h"
 #include "SourceCode.h"
 #include "clang/AST/ASTContext.h"
+#include "clang/AST/DeclCXX.h"
 #include "clang/AST/RecursiveASTVisitor.h"
 #include <algorithm>
 
 namespace clang {
 namespace clangd {
 namespace {
 
 // Collects all semantic tokens in an ASTContext.
if (NestedNameSpecifier *NNS = NNSLoc.getNestedNameSpecifier())
       if (NNS->getKind() == NestedNameSpecifier::Namespace ||
           NNS->getKind() == NestedNameSpecifier::NamespaceAlias)
         addToken(NNSLoc.getLocalBeginLoc(), HighlightingKind::Namespace);
 
     return RecursiveASTVisitor<
         HighlightingTokenCollector>::TraverseNestedNameSpecifierLoc(NNSLoc);
   }
 
+  bool TraverseConstructorInitializer(CXXCtorInitializer *CI) {
+    addToken(CI->getSourceLocation(), CI->getMember());
+    return RecursiveASTVisitor<
+        HighlightingTokenCollector>::TraverseConstructorInitializer(CI);
+  }
+
 private:
   void addTypeLoc(SourceLocation Loc, const TypeLoc &TL) {
     if (const Type *TP = TL.getTypePtr()) {
       if (const TagDecl *TD = TP->getAsTagDecl())
         addToken(Loc, TD);
       if (TP->isBuiltinType())
         // Builtins must be special cased as they do not have a TagDecl.
         addToken(Loc, HighlightingKind::Primitive);

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

const char *TestCases[] = {
     R"cpp(
       struct $Class[[B]] {};
       struct $Class[[A]] {
         $Class[[B]] $Field[[BB]];
         $Class[[A]] &operator=($Class[[A]] &&$Variable[[O]]);
       };
 
       $Class[[A]] &$Class[[A]]::operator=($Class[[A]] &&$Variable[[O]]) = default;
+    )cpp",
+    R"cpp(
+      enum $Enum[[En]] {};
+      class $Class[[Foo]] {};
+      class $Class[[Bar]] {
+        $Class[[Foo]] $Field[[Fo]];
+        $Enum[[En]] $Field[[E]];
+        $Primitive[[int]] $Field[[I]];
+        $Class[[Bar]] ($Class[[Foo]] $Variable[[F]],
+                $Enum[[En]] $Variable[[E]])
+        : $Field[[Fo]] ($Variable[[F]]), $Field[[E]] ($Variable[[E]]),
+          $Field[[I]] (123) {}
+      };
     )cpp"};
   for (const auto &TestCase : TestCases) {
     checkHighlightings(TestCase);
   }
 }
 
 TEST(SemanticHighlighting, GeneratesHighlightsWhenFileChange) {
   class HighlightingsCounterDiagConsumer : public DiagnosticsConsumer {