[clang-tools-extra] Preserve original RemoteIndexPath to correctly trim index symbols paths depending on platform (PR #217745)

[Oganesyan Levon via cfe-commits]

https://github.com/ilev4ik created https://github.com/llvm/llvm-project/pull/217745

After using version after the fix here: #2646. I faced the next problem: symbols location slashes were converted to posix ones before trimming prefix

>From 46d82eee715080c2ce080cc5652a4c8cef95d03f Mon Sep 17 00:00:00 2001
From: Levon <ilev4ik at gmail.com>
Date: Thu, 20 Aug 2026 19:52:04 +0300
Subject: [PATCH 1/2] marshaller build on linux respects windows paths in
 index.dex

---
 .../clangd/index/remote/marshalling/Marshalling.cpp    | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/clang-tools-extra/clangd/index/remote/marshalling/Marshalling.cpp b/clang-tools-extra/clangd/index/remote/marshalling/Marshalling.cpp
index db77b8caf5679..abb3fe0a9a98d 100644
--- a/clang-tools-extra/clangd/index/remote/marshalling/Marshalling.cpp
+++ b/clang-tools-extra/clangd/index/remote/marshalling/Marshalling.cpp
@@ -264,7 +264,9 @@ FuzzyFindRequest Marshaller::toProtobuf(const clangd::FuzzyFindRequest &From) {
   RPCRequest.set_restricted_for_code_completion(From.RestrictForCodeCompletion);
   for (const auto &Path : From.ProximityPaths) {
     llvm::SmallString<256> RelativePath = llvm::StringRef(Path);
-    if (replace_path_prefix(RelativePath, LocalIndexRoot, ""))
+    bool IsWindowsIndex = is_absolute(Path.substr(1), Style::windows);
+    if (replace_path_prefix(RelativePath, LocalIndexRoot, "",
+                            IsWindowsIndex ? Style::windows : Style::native))
       RPCRequest.add_proximity_paths(
           convert_to_slash(RelativePath, Style::windows));
   }
@@ -396,9 +398,11 @@ llvm::Expected<std::string> Marshaller::uriToRelativePath(llvm::StringRef URI) {
   llvm::SmallString<256> Result = ParsedURI->body();
   llvm::StringRef Path(Result);
   // Check for Windows paths (URI=file:///X:/path => Body=/X:/path)
-  if (is_absolute(Path.substr(1), Style::windows))
+  bool IsWindowsIndex = is_absolute(Path.substr(1), Style::windows);
+  if (IsWindowsIndex)
     Result = Path.drop_front().str();
-  if (!replace_path_prefix(Result, RemoteIndexRoot, ""))
+  if (!replace_path_prefix(Result, RemoteIndexRoot, "",
+                           IsWindowsIndex ? Style::windows : Style::native))
     return error("File path '{0}' doesn't start with '{1}'.", Result.str(),
                  RemoteIndexRoot);
   assert(Result == convert_to_slash(Result, Style::windows));

>From e1123bf9cd68f705f3daf4fe592675208017dbd3 Mon Sep 17 00:00:00 2001
From: Levon <ilev4ik at gmail.com>
Date: Thu, 20 Aug 2026 22:44:18 +0300
Subject: [PATCH 2/2] preserve original RemoteIndexPath to correctly trim
 prefix

---
 .../index/remote/marshalling/Marshalling.cpp  | 25 +++++++++++--------
 .../unittests/remote/MarshallingTests.cpp     |  9 ++-----
 2 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/clang-tools-extra/clangd/index/remote/marshalling/Marshalling.cpp b/clang-tools-extra/clangd/index/remote/marshalling/Marshalling.cpp
index abb3fe0a9a98d..a8302fd28776e 100644
--- a/clang-tools-extra/clangd/index/remote/marshalling/Marshalling.cpp
+++ b/clang-tools-extra/clangd/index/remote/marshalling/Marshalling.cpp
@@ -58,17 +58,22 @@ Marshaller::Marshaller(llvm::StringRef RemoteIndexRoot,
                        llvm::StringRef LocalIndexRoot)
     : Strings(Arena) {
   llvm::StringRef PosixSeparator = get_separator(Style::posix);
+  llvm::StringRef WindowsSeparator = get_separator(Style::windows);
+  const bool IsWindows = is_absolute(RemoteIndexRoot, Style::windows);
+  const bool IsPosix = is_absolute(RemoteIndexRoot, Style::posix);
   if (!RemoteIndexRoot.empty()) {
-    assert(is_absolute(RemoteIndexRoot, Style::posix) ||
-           is_absolute(RemoteIndexRoot, Style::windows));
-    this->RemoteIndexRoot = convert_to_slash(RemoteIndexRoot, Style::windows);
+    assert(IsPosix || IsWindows);
+    this->RemoteIndexRoot = RemoteIndexRoot;
     llvm::StringRef Path(this->RemoteIndexRoot);
-    if (!is_separator(this->RemoteIndexRoot.back(), Style::posix))
+    if (IsPosix && !is_separator(this->RemoteIndexRoot.back(), Style::posix))
       this->RemoteIndexRoot += PosixSeparator;
+    else if (IsWindows &&
+             !is_separator(this->RemoteIndexRoot.back(), Style::windows))
+      this->RemoteIndexRoot += WindowsSeparator;
   }
+
   if (!LocalIndexRoot.empty()) {
-    assert(is_absolute(LocalIndexRoot, Style::posix) ||
-           is_absolute(LocalIndexRoot, Style::windows));
+    assert(IsPosix || IsWindows);
     this->LocalIndexRoot = convert_to_slash(LocalIndexRoot, Style::windows);
     llvm::StringRef Path(this->LocalIndexRoot);
     if (!is_separator(this->LocalIndexRoot.back(), Style::posix))
@@ -266,7 +271,7 @@ FuzzyFindRequest Marshaller::toProtobuf(const clangd::FuzzyFindRequest &From) {
     llvm::SmallString<256> RelativePath = llvm::StringRef(Path);
     bool IsWindowsIndex = is_absolute(Path.substr(1), Style::windows);
     if (replace_path_prefix(RelativePath, LocalIndexRoot, "",
-                            IsWindowsIndex ? Style::windows : Style::native))
+                            IsWindowsIndex ? Style::windows : Style::posix))
       RPCRequest.add_proximity_paths(
           convert_to_slash(RelativePath, Style::windows));
   }
@@ -402,11 +407,11 @@ llvm::Expected<std::string> Marshaller::uriToRelativePath(llvm::StringRef URI) {
   if (IsWindowsIndex)
     Result = Path.drop_front().str();
   if (!replace_path_prefix(Result, RemoteIndexRoot, "",
-                           IsWindowsIndex ? Style::windows : Style::native))
+                           IsWindowsIndex ? Style::windows : Style::posix))
     return error("File path '{0}' doesn't start with '{1}'.", Result.str(),
                  RemoteIndexRoot);
-  assert(Result == convert_to_slash(Result, Style::windows));
-  return std::string(Result);
+
+  return std::string(convert_to_slash(Result, Style::windows));
 }
 
 clangd::SymbolLocation::Position
diff --git a/clang-tools-extra/clangd/unittests/remote/MarshallingTests.cpp b/clang-tools-extra/clangd/unittests/remote/MarshallingTests.cpp
index fe0dc4a67622c..4ce79cd310c0a 100644
--- a/clang-tools-extra/clangd/unittests/remote/MarshallingTests.cpp
+++ b/clang-tools-extra/clangd/unittests/remote/MarshallingTests.cpp
@@ -465,14 +465,9 @@ TEST(RemoteMarshallingTest, CrossPlatformPathsRoundTrip) {
   Location.End.setLine(3);
   Location.End.setColumn(4);
   // Construct the URI as a Windows machine would have serialized it into the
-  // index: file:///C:/remote/project/lib/File.cpp.
+  // index: file:///C:\remote\project\lib\File.cpp.
   Location.FileURI =
-      Strings
-          .save("file:///" +
-                convert_to_slash(RemoteIndexRoot,
-                                 llvm::sys::path::Style::windows) +
-                "lib/File.cpp")
-          .begin();
+      Strings.save("file:///" + RemoteIndexRoot + "lib\\File.cpp").begin();
   Ref.Location = Location;
 
   auto Serialized = ProtobufMarshaller.toProtobuf(Ref);