[clangd] Fix incorrect operator< impl for HighlightingToken

[nridge]

Not sure how to write a test for this, short of writing unit tests for the operator< itself. The consequence of this bug is that the sort/unique pass on the highlighting tokens is buggy, but as of https://github.com/clangd/clangd/issues/1057 resolveConflict() fixes up that kind of bugginess.

In any case, it's an obvious fix.

[kadircet]

Oopsy :/ Thanks for the fix!

Regarding the test, if you came looking for this piece due to a particular issue, it might be nice to have that included in the test suite (assuming it can be minimized).
If not, I think it would still be valuable to include a simple unittest that just tests operator< by creating HighlightingTokens to make sure we don't make similar mistakes in the future.

[nridge]

Add semantic highlighting testcase

clang-tools-extra/clangd/SemanticHighlighting.cpp

llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, HighlightingModifier K) {
   }
 }
 
 bool operator==(const HighlightingToken &L, const HighlightingToken &R) {
   return std::tie(L.R, L.Kind, L.Modifiers) ==
          std::tie(R.R, R.Kind, R.Modifiers);
 }
 bool operator<(const HighlightingToken &L, const HighlightingToken &R) {
-  return std::tie(L.R, L.Kind, R.Modifiers) <
+  return std::tie(L.R, L.Kind, L.Modifiers) <
          std::tie(R.R, R.Kind, R.Modifiers);
 }
 
 std::vector<SemanticToken>
 toSemanticTokens(llvm::ArrayRef<HighlightingToken> Tokens) {
   assert(std::is_sorted(Tokens.begin(), Tokens.end()));
   std::vector<SemanticToken> Result;
   const HighlightingToken *Last = nullptr;

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

)cpp",
         using $Primitive_decl[[MyTypedef]] = int;
         enum $Enum_decl[[MyEnum]] : $Primitive[[MyTypedef]] {};
       )cpp",
       // Enum base specifier
       R"cpp(
         typedef int $Primitive_decl[[MyTypedef]];
         enum $Enum_decl[[MyEnum]] : $Primitive[[MyTypedef]] {};
       )cpp",
-  };
+      // Issue 1096
+      R"cpp(
+        void $Function_decl[[Foo]]();
+        // Use <: :> digraphs for deprecated attribute to avoid conflict with annotation syntax
+        <:<:deprecated:>:> void $Function_decl_deprecated[[Foo]](int* $Parameter_decl[[x]]);
+        void $Function_decl[[Foo]](int $Parameter_decl[[x]]);
+        template <typename $TemplateParameter_decl[[T]]>
+        void $Function_decl[[Bar]]($TemplateParameter[[T]] $Parameter_decl[[x]]) {
+            $Function_deprecated[[Foo]]($Parameter[[x]]); 
+            $Function_deprecated[[Foo]]($Parameter[[x]]); 
+            $Function_deprecated[[Foo]]($Parameter[[x]]); 
+        }
+      )cpp"};
   for (const auto &TestCase : TestCases)
     // Mask off scope modifiers to keep the tests manageable.
     // They're tested separately.
     checkHighlightings(TestCase, {}, ~ScopeModifierMask);
 
   checkHighlightings(R"cpp(
     class $Class_decl[[A]] {
       #include "imp.h"