[clangd] Do not treat line as inactive if skipped range ends at character position 0

[nridge]

Summary

Fixes https://github.com/clangd/clangd/issues/602

[hokein]

thanks!

clang-tools-extra/clangd/SemanticHighlighting.cpp

std::vector<HighlightingToken> collect(ParsedAST &AST) && {
     auto SortedSkippedRanges = AST.getMacros().SkippedRanges;
     llvm::sort(SortedSkippedRanges);
     auto It = NonConflicting.begin();
     for (const Range &R : SortedSkippedRanges) {
       // Create one token for each line in the skipped range, so it works
       // with line-based diffing.
       assert(R.start.line <= R.end.line);
       for (int Line = R.start.line; Line <= R.end.line; ++Line) {
+        // If the end of the inactive range is at the beginning
+        // of a line, that line is not inactive.
+        if (Line == R.end.line && R.end.character == 0)
+          continue;
         // Copy tokens before the inactive line
         for (; It != NonConflicting.end() && It->R.start.line < Line; ++It)
           WithInactiveLines.push_back(std::move(*It));
         // Add a token for the inactive line itself.
         auto StartOfLine = positionToOffset(MainCode, Position{Line, 0});
         if (StartOfLine) {
           StringRef LineText =
               MainCode.drop_front(*StartOfLine).take_until([](char C) {

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

 $InactiveCode[[#endif]]
 
       // A declaration to cause the preamble to end.
       int $Variable[[EndPreamble]];
 
       // Code after the preamble.
       // Code inside inactive blocks does not get regular highlightings
       // because it's not part of the AST.
-$InactiveCode[[#ifdef test]]
+      #define $Macro[[test2]]
+$InactiveCode[[#if defined(test)]]
 $InactiveCode[[int Inactive2;]]
+$InactiveCode[[#elif defined(test2)]]
+      int $Variable[[Active1]];
+$InactiveCode[[#else]]
+$InactiveCode[[int Inactive3;]]
 $InactiveCode[[#endif]]
 
       #ifndef $Macro[[test]]
-      int $Variable[[Active1]];
+      int $Variable[[Active2]];
       #endif
 
 $InactiveCode[[#ifdef test]]
-$InactiveCode[[int Inactive3;]]
+$InactiveCode[[int Inactive4;]]
 $InactiveCode[[#else]]
-      int $Variable[[Active2]];
+      int $Variable[[Active3]];
       #endif
     )cpp",
       // Argument to 'sizeof...'
       R"cpp(
       template <typename... $TemplateParameter[[Elements]]>
       struct $Class[[TupleSize]] {
         static const int $StaticField[[size]] =
 sizeof...($TemplateParameter[[Elements]]);