[clangd] Implement fold range for #pragma region (#168177)

The implementation is based on the directive tree.

Fixes clangd/clangd#1623

Author: hokein

clang-tools-extra/clangd/SemanticSelection.cpp

@@ -11,9 +11,13 @@
 #include "Protocol.h"
 #include "Selection.h"
 #include "SourceCode.h"
+#include "support/Bracket.h"
+#include "support/DirectiveTree.h"
+#include "support/Token.h"
 #include "clang/AST/DeclBase.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/SourceManager.h"
+#include "clang/Basic/TokenKinds.h"
 #include "clang/Tooling/Syntax/BuildTree.h"
 #include "clang/Tooling/Syntax/Nodes.h"
 #include "clang/Tooling/Syntax/TokenBufferTokenManager.h"
@@ -22,9 +26,6 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Error.h"
-#include "support/Bracket.h"
-#include "support/DirectiveTree.h"
-#include "support/Token.h"
 #include <optional>
 #include <queue>
 #include <vector>
@@ -163,6 +164,69 @@ llvm::Expected<SelectionRange> getSemanticRanges(ParsedAST &AST, Position Pos) {
   return std::move(Head);
 }
 
+class PragmaRegionFinder {
+  // Record the token range of a region:
+  //
+  //   #pragma region name[[
+  //   ...
+  //   ]]#pragma endregion
+  std::vector<Token::Range> &Ranges;
+  const TokenStream &Code;
+  // Stack of starting token (the name of the region) indices for nested #pragma
+  // region.
+  std::vector<unsigned> Stack;
+
+public:
+  PragmaRegionFinder(std::vector<Token::Range> &Ranges, const TokenStream &Code)
+      : Ranges(Ranges), Code(Code) {}
+
+  void walk(const DirectiveTree &T) {
+    for (const auto &C : T.Chunks)
+      std::visit(*this, C);
+  }
+
+  void operator()(const DirectiveTree::Code &C) {}
+
+  void operator()(const DirectiveTree::Directive &D) {
+    // Get the tokens that make up this directive.
+    auto Tokens = Code.tokens(D.Tokens);
+    if (Tokens.empty())
+      return;
+    const Token &HashToken = Tokens.front();
+    assert(HashToken.Kind == tok::hash);
+    const Token &Pragma = HashToken.nextNC();
+    if (Pragma.text() != "pragma")
+      return;
+    const Token &Value = Pragma.nextNC();
+
+    // Handle "#pragma region name"
+    if (Value.text() == "region") {
+      // Find the last token at the same line.
+      const Token *T = &Value.next();
+      while (T < Tokens.end() && T->Line == Pragma.Line)
+        T = &T->next();
+      --T;
+      Stack.push_back(T->OriginalIndex);
+      return;
+    }
+
+    // Handle "#pragma endregion"
+    if (Value.text() == "endregion") {
+      if (Stack.empty())
+        return; // unmatched end region; ignore.
+
+      unsigned StartIdx = Stack.back();
+      Stack.pop_back();
+      Ranges.push_back(Token::Range{StartIdx, HashToken.OriginalIndex});
+    }
+  }
+
+  void operator()(const DirectiveTree::Conditional &C) {
+    for (const auto &[_, SubTree] : C.Branches)
+      walk(SubTree);
+  }
+};
+
 // FIXME(kirillbobyrev): Collect comments, PP conditional regions, includes and
 // other code regions (e.g. public/private/protected sections of classes,
 // control flow statement bodies).
@@ -286,6 +350,17 @@ getFoldingRanges(const std::string &Code, bool LineFoldingOnly) {
     }
     AddFoldingRange(Start, End, FoldingRange::COMMENT_KIND);
   }
+
+  // #pragma region
+  std::vector<Token::Range> Ranges;
+  PragmaRegionFinder(Ranges, OrigStream).walk(DirectiveStructure);
+  auto Ts = OrigStream.tokens();
+  for (const auto &R : Ranges) {
+    auto End = StartPosition(Ts[R.End]);
+    if (LineFoldingOnly)
+      End.line--;
+    AddFoldingRange(EndPosition(Ts[R.Begin]), End, FoldingRange::REGION_KIND);
+  }
   return Result;
 }
 

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

@@ -410,6 +410,22 @@ TEST(FoldingRanges, PseudoParserWithoutLineFoldings) {
             Variable = 3;
         #
       )cpp",
+      R"cpp(
+        #pragma region R1[[
+        
+        #pragma region R2[[
+         constexpr int a = 2;
+        ]]#pragma endregion
+        
+        ]]#pragma endregion
+      )cpp",
+      R"cpp(
+        #pragma region[[
+        ]]#pragma endregion
+
+        #pragma /*comment1*/ region /*comment2*/name[[
+        ]]#pragma endregion
+      )cpp",
   };
   for (const char *Test : Tests) {
     auto T = Annotations(Test);
@@ -470,6 +486,12 @@ TEST(FoldingRanges, PseudoParserLineFoldingsOnly) {
         //[[ foo
         /* bar */]]
       )cpp",
+      R"cpp(
+        #pragma region abc[[
+        constexpr int a = 2;
+        ]]
+        #pragma endregion
+      )cpp",
       // FIXME: Support folding template arguments.
       // R"cpp(
       // template <[[typename foo, class bar]]> struct baz {};