[clangd] Ensure lambda init-capture gets semantic token

Prior to this patch, CollectExtraHighlightings would incorrectly produce
a token for the init-capture's type which overlapped the name and
resulted in both being dropped.

Fixes clangd/clangd#868

Differential Revision: https://reviews.llvm.org/D110130

clang-tools-extra/clangd/SemanticHighlighting.cpp

@@ -601,16 +601,24 @@ class CollectExtraHighlightings
     auto *AT = D->getType()->getContainedAutoType();
     if (!AT)
       return true;
-    if (auto K = kindForType(AT->getDeducedType().getTypePtrOrNull(),
-                             H.getResolver())) {
-      auto &Tok = H.addToken(D->getTypeSpecStartLoc(), *K)
-                      .addModifier(HighlightingModifier::Deduced);
-      const Type *Deduced = AT->getDeducedType().getTypePtrOrNull();
-      if (auto Mod = scopeModifier(Deduced))
-        Tok.addModifier(*Mod);
-      if (isDefaultLibrary(Deduced))
-        Tok.addModifier(HighlightingModifier::DefaultLibrary);
-    }
+    auto K =
+        kindForType(AT->getDeducedType().getTypePtrOrNull(), H.getResolver());
+    if (!K)
+      return true;
+    SourceLocation StartLoc = D->getTypeSpecStartLoc();
+    // The AutoType may not have a corresponding token, e.g. in the case of
+    // init-captures. In this case, StartLoc overlaps with the location
+    // of the decl itself, and producing a token for the type here would result
+    // in both it and the token for the decl being dropped due to conflict.
+    if (StartLoc == D->getLocation())
+      return true;
+    auto &Tok =
+        H.addToken(StartLoc, *K).addModifier(HighlightingModifier::Deduced);
+    const Type *Deduced = AT->getDeducedType().getTypePtrOrNull();
+    if (auto Mod = scopeModifier(Deduced))
+      Tok.addModifier(*Mod);
+    if (isDefaultLibrary(Deduced))
+      Tok.addModifier(HighlightingModifier::DefaultLibrary);
     return true;
   }
 

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

@@ -772,6 +772,14 @@ sizeof...($TemplateParameter[[Elements]]);
           $Function[[foo]]($Parameter[[x]]); 
         }
       )cpp",
+      // init-captures
+      R"cpp(
+        void $Function_decl[[foo]]() {
+          int $LocalVariable_decl[[a]], $LocalVariable_decl[[b]];
+          [ $LocalVariable_decl[[c]] = $LocalVariable[[a]],
+            $LocalVariable_decl[[d]]($LocalVariable[[b]]) ]() {}();
+        }
+      )cpp",
   };
   for (const auto &TestCase : TestCases)
     // Mask off scope modifiers to keep the tests manageable.
@@ -840,7 +848,7 @@ TEST(SemanticHighlighting, ScopeModifiers) {
       )cpp",
       R"cpp(
         // Lambdas are considered functions, not classes.
-        auto $Variable_fileScope[[x]] = [m(42)] { // FIXME: annotate capture
+        auto $Variable_fileScope[[x]] = [$LocalVariable_functionScope[[m]](42)] {
           return $LocalVariable_functionScope[[m]];
         };
       )cpp",