[clangd][remote] Add Windows paths support

[ArcsinX]

Summary

Without this patch 6 marshalling tests fail on Windows.
This patch contains the following changes:

• Allow paths with Windows slashes (convert to the POSIX style instead of assertion)
• Add support for URI with Windows path.
• Change the value of the second parameter of several llvm::sys::path::convert_to_slash() calls: we should use windows instead of posix to ensure UNIX slashes in the path.
• Port RemoteMarshallingTest::IncludeHeaderURI test to Windows.

[kbobyrev]

Hi, thanks for flagging the issue! Could you please give more information where exactly the tests fail (e.g. logs with assertions)? This way I could understand where exactly the failure happens.

I can understand what you're trying to do but the patch introduces the behaviour which is unintended as of right now. The convention is to use POSIX paths everywhere in the Marshalling code since the end result will be a URI anyway. The patch changes it to Windows slashes which is orthogonal to this direction.

You're right about llvm::Expected<clangd::FuzzyFindRequest> Marshaller::fromProtobuf needing to convert to the native path though since there aren't any URIs in the end. Also, I think we should convert roots to the POSIX instead of asserting it.

I'm really curious what failures beyond FuzzyFindRequest are on Windows and I'd be happy to fix those but unfortunately I don't have a Windows machine to run the tests myself :(

[ArcsinX]

In D89529#2334407, @kbobyrev wrote:

Hi, thanks for flagging the issue! Could you please give more information where exactly the tests fail (e.g. logs with assertions)? This way I could understand where exactly the failure happens.

With current implementation I could not pass Windows path (e.g. C:\a\b\c) to Marshaller constructor because of assert(RemoteIndexRoot == llvm::sys::path::convert_to_slash(RemoteIndexRoot));, because on Windows llvm::sys::path::convert_to_slash(RemoteIndexRoot) converts C:\a\b\c to C:/a/b/c

Another problem is that Windows URI paths are not supported without this patch (e.g. URI=file:///X:/path => Body=/X:/path, and /X:/path does not start with X:\path)

The third problem, that without conversion local Windows paths to native slashes, mixed-slash paths appears at path::append() calls and we again face the problem when some paths does not start with given prefix (but it should)

I can understand what you're trying to do but the patch introduces the behaviour which is unintended as of right now. The convention is to use POSIX paths everywhere in the Marshalling code since the end result will be a URI anyway. The patch changes it to Windows slashes which is orthogonal to this direction.

Idea is to use native slashes (Windows slashes on Windows) *for local paths only* and UNIX slashes inside the wire.

Just to clarify why I changed llvm::sys::path::convert_to_slash(Result, llvm::sys::path::Style::posix) to llvm::sys::path::convert_to_slash(Result, llvm::sys::path::Style::windows):

• llvm::sys::path::convert_to_slash(Result, llvm::sys::path::Style::posix) no-op on any platform and does nothing with '\' in Windows paths.
• llvm::sys::path::convert_to_slash(Result, llvm::sys::path::Style::windows) replaces '\' with '/' on any platform.

[ArcsinX]

Logs:

D:\work\llvm-project\build>ninja check-clangd
[6/7] Running the Clangd regression tests
llvm-lit.py: D:\work\llvm-project\build\bin\..\..\llvm\utils\lit\lit\llvm\config.py:347: note: using clang: d:\work\llvm-project\build\bin\clang.exe
-- Testing: 905 tests, 8 workers --
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70
FAIL: Clangd Unit Tests :: ./ClangdTests.exe/RemoteMarshallingTest.IncludeHeaderURIs (665 of 905)
******************** TEST 'Clangd Unit Tests :: ./ClangdTests.exe/RemoteMarshallingTest.IncludeHeaderURIs' FAILED ********************
Note: Google Test filter = RemoteMarshallingTest.IncludeHeaderURIs
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from RemoteMarshallingTest
[ RUN      ] RemoteMarshallingTest.IncludeHeaderURIs
D:\work\llvm-project\clang-tools-extra\clangd\unittests\remote\MarshallingTests.cpp(256): error: Value of: bool(Serialized)
  Actual: false
Expected: true
[  FAILED  ] RemoteMarshallingTest.IncludeHeaderURIs (1 ms)
[----------] 1 test from RemoteMarshallingTest (1 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (1 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] RemoteMarshallingTest.IncludeHeaderURIs

 1 FAILED TEST

********************
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70
FAIL: Clangd Unit Tests :: ./ClangdTests.exe/RemoteMarshallingTest.RefSerialization (666 of 905)
******************** TEST 'Clangd Unit Tests :: ./ClangdTests.exe/RemoteMarshallingTest.RefSerialization' FAILED ********************
Note: Google Test filter = RemoteMarshallingTest.RefSerialization
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from RemoteMarshallingTest
[ RUN      ] RemoteMarshallingTest.RefSerialization
D:\work\llvm-project\clang-tools-extra\clangd\unittests\remote\MarshallingTests.cpp(228): error: Value of: bool(Serialized)
  Actual: false
Expected: true
[  FAILED  ] RemoteMarshallingTest.RefSerialization (0 ms)
[----------] 1 test from RemoteMarshallingTest (0 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (0 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] RemoteMarshallingTest.RefSerialization

 1 FAILED TEST

********************
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70
FAIL: Clangd Unit Tests :: ./ClangdTests.exe/RemoteMarshallingTest.URIToRelativePathTranslation (673 of 905)
******************** TEST 'Clangd Unit Tests :: ./ClangdTests.exe/RemoteMarshallingTest.URIToRelativePathTranslation' FAILED ********************
Note: Google Test filter = RemoteMarshallingTest.URIToRelativePathTranslation
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from RemoteMarshallingTest
[ RUN      ] RemoteMarshallingTest.URIToRelativePathTranslation
D:\work\llvm-project\clang-tools-extra\clangd\unittests\remote\MarshallingTests.cpp(436): error: Value of: bool(RelativePath)
  Actual: false
Expected: true
[  FAILED  ] RemoteMarshallingTest.URIToRelativePathTranslation (1 ms)
[----------] 1 test from RemoteMarshallingTest (1 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (1 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] RemoteMarshallingTest.URIToRelativePathTranslation

 1 FAILED TEST

********************
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70
FAIL: Clangd Unit Tests :: ./ClangdTests.exe/RemoteMarshallingTest.RelationsSerializion (675 of 905)
******************** TEST 'Clangd Unit Tests :: ./ClangdTests.exe/RemoteMarshallingTest.RelationsSerializion' FAILED ********************
Note: Google Test filter = RemoteMarshallingTest.RelationsSerializion
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from RemoteMarshallingTest
[ RUN      ] RemoteMarshallingTest.RelationsSerializion
D:\work\llvm-project\clang-tools-extra\clangd\unittests\remote\MarshallingTests.cpp(407): error: Value of: bool(Serialized)
  Actual: false
Expected: true
[  FAILED  ] RemoteMarshallingTest.RelationsSerializion (0 ms)
[----------] 1 test from RemoteMarshallingTest (0 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (1 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] RemoteMarshallingTest.RelationsSerializion

 1 FAILED TEST

********************
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70
FAIL: Clangd Unit Tests :: ./ClangdTests.exe/RemoteMarshallingTest.URITranslation (676 of 905)
******************** TEST 'Clangd Unit Tests :: ./ClangdTests.exe/RemoteMarshallingTest.URITranslation' FAILED ********************
Note: Google Test filter = RemoteMarshallingTest.URITranslation
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from RemoteMarshallingTest
[ RUN      ] RemoteMarshallingTest.URITranslation
D:\work\llvm-project\clang-tools-extra\clangd\unittests\remote\MarshallingTests.cpp(101): error: Value of: bool(Serialized)
  Actual: false
Expected: true
[  FAILED  ] RemoteMarshallingTest.URITranslation (1 ms)
[----------] 1 test from RemoteMarshallingTest (1 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (1 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] RemoteMarshallingTest.URITranslation

 1 FAILED TEST

********************
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70
FAIL: Clangd Unit Tests :: ./ClangdTests.exe/RemoteMarshallingTest.SymbolSerialization (677 of 905)
******************** TEST 'Clangd Unit Tests :: ./ClangdTests.exe/RemoteMarshallingTest.SymbolSerialization' FAILED ********************
Note: Google Test filter = RemoteMarshallingTest.SymbolSerialization
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from RemoteMarshallingTest
[ RUN      ] RemoteMarshallingTest.SymbolSerialization
D:\work\llvm-project\clang-tools-extra\clangd\unittests\remote\MarshallingTests.cpp(154): error: Value of: bool(Serialized)
  Actual: false
Expected: true
[  FAILED  ] RemoteMarshallingTest.SymbolSerialization (1 ms)
[----------] 1 test from RemoteMarshallingTest (1 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (1 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] RemoteMarshallingTest.SymbolSerialization

 1 FAILED TEST

********************
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90..
********************
Failed Tests (6):
  Clangd Unit Tests :: ./ClangdTests.exe/RemoteMarshallingTest.IncludeHeaderURIs
  Clangd Unit Tests :: ./ClangdTests.exe/RemoteMarshallingTest.RefSerialization
  Clangd Unit Tests :: ./ClangdTests.exe/RemoteMarshallingTest.RelationsSerializion
  Clangd Unit Tests :: ./ClangdTests.exe/RemoteMarshallingTest.SymbolSerialization
  Clangd Unit Tests :: ./ClangdTests.exe/RemoteMarshallingTest.URIToRelativePathTranslation
  Clangd Unit Tests :: ./ClangdTests.exe/RemoteMarshallingTest.URITranslation


Testing Time: 38.88s
  Unsupported:   7
  Passed     : 892
  Failed     :   6
FAILED: tools/clang/tools/extra/clangd/test/CMakeFiles/check-clangd
cmd.exe /C "cd /D D:\work\llvm-project\build\tools\clang\tools\extra\clangd\test && C:\Users\p00538580\AppData\Local\Programs\Python\Python38-32\python.exe D:/work/llvm-project/build/./bin/llvm-lit.py -sv D:/work/llvm-project/build/tools/clang/tools/extra/clangd/test/../unittests D:/work/llvm-project/build/tools/clang/tools/extra/clangd/test"
ninja: build stopped: subcommand failed.

[kbobyrev]

In D89529#2334475, @ArcsinX wrote:

In D89529#2334407, @kbobyrev wrote:

Hi, thanks for flagging the issue! Could you please give more information where exactly the tests fail (e.g. logs with assertions)? This way I could understand where exactly the failure happens.

With current implementation I could not pass Windows path (e.g. C:\a\b\c) to Marshaller constructor because of assert(RemoteIndexRoot == llvm::sys::path::convert_to_slash(RemoteIndexRoot));, because on Windows llvm::sys::path::convert_to_slash(RemoteIndexRoot) converts C:\a\b\c to C:/a/b/c

Yes, I mentioned it above. The solution would be to just convert to the POSIX path instead of asserting it.

Another problem is that Windows URI paths are not supported without this patch (e.g. URI=file:///X:/path => Body=/X:/path, and /X:/path does not start with X:\path)

This is an interesting problem and I think this should be covered by the URI code that we have but I should check. This might have been triggered by a different issue.

The third problem, that without conversion local Windows paths to native slashes, mixed-slash paths appears at path::append() calls and we again face the problem when some paths does not start with given prefix (but it should)

Yes, I mentioned it above. This is not an actual problem if all the paths within marshalling are POSIX style. There is a problem with

I can understand what you're trying to do but the patch introduces the behaviour which is unintended as of right now. The convention is to use POSIX paths everywhere in the Marshalling code since the end result will be a URI anyway. The patch changes it to Windows slashes which is orthogonal to this direction.

Idea is to use native slashes (Windows slashes on Windows) *for local paths only* and UNIX slashes inside the wire.

Just to clarify why I changed llvm::sys::path::convert_to_slash(Result, llvm::sys::path::Style::posix) to llvm::sys::path::convert_to_slash(Result, llvm::sys::path::Style::windows):

• llvm::sys::path::convert_to_slash(Result, llvm::sys::path::Style::posix) no-op on any platform and does nothing with '\' in Windows paths.

Yeah you're right, I missed these convert_to_slash semantics and that should be changed.

• llvm::sys::path::convert_to_slash(Result, llvm::sys::path::Style::windows) replaces '\' with '/' on any platform.

We don't have actual filesystem paths anywhere outside FuzzyFindRequest, every other clangd struct stores URIs rather than paths. And when the URI is created it doesn't matter whether this path would be a Windows or POSIX, a URI is portable. Hence, the only place with native paths should be the FuzzyFindRequest translation.

[ArcsinX]

In D89529#2334517, @kbobyrev wrote:

In D89529#2334475, @ArcsinX wrote:

In D89529#2334407, @kbobyrev wrote:

Hi, thanks for flagging the issue! Could you please give more information where exactly the tests fail (e.g. logs with assertions)? This way I could understand where exactly the failure happens.

With current implementation I could not pass Windows path (e.g. C:\a\b\c) to Marshaller constructor because of assert(RemoteIndexRoot == llvm::sys::path::convert_to_slash(RemoteIndexRoot));, because on Windows llvm::sys::path::convert_to_slash(RemoteIndexRoot) converts C:\a\b\c to C:/a/b/c

Yes, I mentioned it above. The solution would be to just convert to the POSIX path instead of asserting it.

Ok, got your point. I will think about this.
But for me it's hard to see the reason why we need to store local paths in POSIX style instead of native. From my point of view, we need to ensure that paths inside the wire are in POSIX style and nothing more. E.g. clangd converts paths extracted from LSP to native style.

Another problem is that Windows URI paths are not supported without this patch (e.g. URI=file:///X:/path => Body=/X:/path, and /X:/path does not start with X:\path)

This is an interesting problem and I think this should be covered by the URI code that we have but I should check. This might have been triggered by a different issue.

https://github.com/llvm/llvm-project/blob/master/clang-tools-extra/clangd/URI.cpp#L51

The reason why I put this all together is that single change leads to the same amount of tests failures (test just fails by other reason).

[ArcsinX]

Convert RemoteIndexRoot and LocalIndexRoot to the POSIX style.

[ArcsinX]

In D89529#2334517, @kbobyrev wrote:

The solution would be to just convert to the POSIX path instead of asserting it.

I have updated the patch according to this advice.
It seems to me it looks more consistent now, thank you.

[kbobyrev]

In D89529#2337197, @ArcsinX wrote:

In D89529#2334517, @kbobyrev wrote:

The solution would be to just convert to the POSIX path instead of asserting it.

I have updated the patch according to this advice.
It seems to me it looks more consistent now, thank you.

Thank you for noticing it and taking action! The patch looks good, there are few comments that I left but it should be good to go afterwards.

clang-tools-extra/clangd/index/remote/marshalling/Marshalling.cpp

53

Please explicitly spell out StringRef here, otherwise visually it is appealing to put const auto there but it would be a StringRef which is no obvious.

59

nit: maybe it's time to change type of RemoteIndexRoot field to llvm::SmallString<256> and use !this->RemoteIndexRoot.endswith(PosixSeparator) instead of additional variable. Not really important for this patch but I should probably do it anyway if it's not changed in this patch.

98

Please add a comment explaining why it is needed here: these paths are not converted to URIs and have to be specific to the server platform in order for the query to work correctly.

334

nit: .str().str() is a bit unfortunate, I have had some discussions about this in the past and I guess explicit conversion via std::string(...) looks a bit cleaner.

clang-tools-extra/clangd/unittests/remote/MarshallingTests.cpp

242

Why remove this test?

[ArcsinX]

clang-tools-extra/clangd/unittests/remote/MarshallingTests.cpp

242

As far as I understand, idea of this code is to use absolute path (i.e. /usr/local/user/home/project/Header.h) to be relative to "/". I do not know how to make this on Windows.

Also, Marshaller ProtobufMarshaller(convert_to_slash("/"), convert_to_slash("/")); leads to assertions on Windows:

    assert(llvm::sys::path::is_absolute(RemoteIndexRoot));
...
    assert(llvm::sys::path::is_absolute(LocalIndexRoot));

[ArcsinX]

clang-tools-extra/clangd/index/remote/marshalling/Marshalling.cpp

59

But llvm::sys::path::convert_to_slash() returns std::string.
Could you give me an advice how to copy std::string into llvm::SmallString<256> here?

E.g. the following code looks strange for me

  llvm::Optional<llvm::SmallString<256>> RemoteIndexRoot;

....

    this->RemoteIndexRoot = llvm::SmallString<256>(llvm::sys::path::convert_to_slash(
        RemoteIndexRoot, llvm::sys::path::Style::windows));

[kbobyrev]

clang-tools-extra/clangd/index/remote/marshalling/Marshalling.cpp

59

Hmm, yeah right nevermind, this should be OK for this patch, I'll deal with this later.

clang-tools-extra/clangd/unittests/remote/MarshallingTests.cpp

242

Ah, I see now, makes sense! Yeah, okay then in this case this should be something like testPath("project/Header.h") which will be absolut path (what we want) and also relative to testPath("") (test path root).

[ArcsinX]

auto => StringRef
add comment for llvm::sys::path::native() call
Result.str().str() => std::string(Result)
add back removed test

[ArcsinX]

clang-tools-extra/clangd/index/remote/marshalling/Marshalling.cpp

59

So, I have made no changes here

98

Add more comments in try to explain, that Path is a relative path here and it could be with any slashes, so convert it to native to make sure it's compatible with the current system.

clang-tools-extra/clangd/unittests/remote/MarshallingTests.cpp

242

Thanks for advice, fixed

[kbobyrev]

Also, please hit "Done" on the comments you resolved so that it's easier to track which ones are fixed, otherwise it's hard to follow :(

The patch looks good now, almost ready to go: comments are not really clear right now, I suggested possible alternatives.

clang-tools-extra/clangd/index/remote/marshalling/Marshalling.cpp

96

We normally don't escape variable names a-la Markdown.

Right now it's no very clear what it means, maybe just Construct full path using local prefix. or optionally just remove this one.

99

Maybe just FuzzyFindRequest requires proximity paths to have platform-native format in order for SymbolIndex to process the query correctly..

[ArcsinX]

Comments fixes

[kbobyrev]

Thank you for the patch! Ready to land it now.

Please update the patch message before commiting though:

Without this patch 7 marshalling tests fails on Windows.
This patch contains the following changes:
Allow paths with Windows slashes.

This is not correct anymore, right?

Add support for URI with Windows path.
Change the value of the second parameter of several llvm::sys::path::convert_to_slash() calls: We should use windows instead of posix to ensure UNIX slashes in the path.
Remove part of RemoteMarshallingTest::IncludeHeaderURI test which could not be ported on Windows.

This should not be the case anymor.

[ArcsinX]

In D89529#2338794, @kbobyrev wrote:

Thank you for the patch! Ready to land it now.

Thank you for review!

Please update the patch message before commiting though:

Without this patch 7 marshalling tests fails on Windows.

7 => 6

This patch contains the following changes:
Allow paths with Windows slashes.

This is not correct anymore, right?

We allow paths with Windows slashes now (convert to the POSIX style instead of assertion). I have updated description about this.

Add support for URI with Windows path.
Change the value of the second parameter of several llvm::sys::path::convert_to_slash() calls: We should use windows instead of posix to ensure UNIX slashes in the path.
Remove part of RemoteMarshallingTest::IncludeHeaderURI test which could not be ported on Windows.

This should not be the case anymor.

I have changed: "Remove" => "Port to Windows"

clang-tools-extra/clangd/index/remote/marshalling/Marshalling.cpp

llvm::Expected<llvm::DenseSet<SymbolID>> getIDs(IDRange IDs) {
   return Result;
 }
 
 } // namespace
 
 Marshaller::Marshaller(llvm::StringRef RemoteIndexRoot,
                        llvm::StringRef LocalIndexRoot)
     : Strings(Arena) {
+  llvm::StringRef PosixSeparator =
+      llvm::sys::path::get_separator(llvm::sys::path::Style::posix);
   if (!RemoteIndexRoot.empty()) {
     assert(llvm::sys::path::is_absolute(RemoteIndexRoot));
-    assert(RemoteIndexRoot ==
-           llvm::sys::path::convert_to_slash(RemoteIndexRoot));
-    this->RemoteIndexRoot = RemoteIndexRoot.str();
-    if (!RemoteIndexRoot.endswith(llvm::sys::path::get_separator()))
-      *this->RemoteIndexRoot += llvm::sys::path::get_separator();
+    this->RemoteIndexRoot = llvm::sys::path::convert_to_slash(
+        RemoteIndexRoot, llvm::sys::path::Style::windows);
+    llvm::StringRef Path(*this->RemoteIndexRoot);
+    if (!Path.endswith(PosixSeparator))
+      *this->RemoteIndexRoot += PosixSeparator;
   }
   if (!LocalIndexRoot.empty()) {
     assert(llvm::sys::path::is_absolute(LocalIndexRoot));
-    assert(LocalIndexRoot == llvm::sys::path::convert_to_slash(LocalIndexRoot));
-    this->LocalIndexRoot = LocalIndexRoot.str();
-    if (!LocalIndexRoot.endswith(llvm::sys::path::get_separator()))
-      *this->LocalIndexRoot += llvm::sys::path::get_separator();
+    this->LocalIndexRoot = llvm::sys::path::convert_to_slash(
+        LocalIndexRoot, llvm::sys::path::Style::windows);
+    llvm::StringRef Path(*this->LocalIndexRoot);
+    if (!Path.endswith(PosixSeparator))
+      *this->LocalIndexRoot += PosixSeparator;
   }
   assert(!RemoteIndexRoot.empty() || !LocalIndexRoot.empty());
 }
 
 llvm::Expected<clangd::LookupRequest>
 Marshaller::fromProtobuf(const LookupRequest *Message) {
   clangd::LookupRequest Req;
   auto IDs = getIDs(Message->ids());
Marshaller::fromProtobuf(const FuzzyFindRequest *Message) {
   Result.Query = Message->query();
   for (const auto &Scope : Message->scopes())
     Result.Scopes.push_back(Scope);
   Result.AnyScope = Message->any_scope();
   if (Message->limit())
     Result.Limit = Message->limit();
   Result.RestrictForCodeCompletion = Message->restricted_for_code_completion();
   for (const auto &Path : Message->proximity_paths()) {
     llvm::SmallString<256> LocalPath = llvm::StringRef(*RemoteIndexRoot);
     llvm::sys::path::append(LocalPath, Path);
+    // FuzzyFindRequest requires proximity paths to have platform-native format
+    // in order for SymbolIndex to process the query correctly.
+    llvm::sys::path::native(LocalPath);
     Result.ProximityPaths.push_back(std::string(LocalPath));
   }
   for (const auto &Type : Message->preferred_types())
     Result.ProximityPaths.push_back(Type);
   return Result;
 }
 
 llvm::Expected<clangd::RefsRequest>
FuzzyFindRequest Marshaller::toProtobuf(const clangd::FuzzyFindRequest &From) {
   RPCRequest.set_any_scope(From.AnyScope);
   if (From.Limit)
     RPCRequest.set_limit(*From.Limit);
   RPCRequest.set_restricted_for_code_completion(From.RestrictForCodeCompletion);
   for (const auto &Path : From.ProximityPaths) {
     llvm::SmallString<256> RelativePath = llvm::StringRef(Path);
     if (llvm::sys::path::replace_path_prefix(RelativePath, *LocalIndexRoot, ""))
       RPCRequest.add_proximity_paths(llvm::sys::path::convert_to_slash(
-          RelativePath, llvm::sys::path::Style::posix));
+          RelativePath, llvm::sys::path::Style::windows));
   }
   for (const auto &Type : From.PreferredTypes)
     RPCRequest.add_preferred_types(Type);
   return RPCRequest;
 }
 
 RefsRequest Marshaller::toProtobuf(const clangd::RefsRequest &From) {
   RefsRequest RPCRequest;

 llvm::Expected<std::string> Marshaller::uriToRelativePath(llvm::StringRef URI) {
   assert(RemoteIndexRoot);
   auto ParsedURI = URI::parse(URI);
   if (!ParsedURI)
     return ParsedURI.takeError();
   if (ParsedURI->scheme() != "file")
     return error("Can not use URI schemes other than file, given: '{0}'.", URI);
   llvm::SmallString<256> Result = ParsedURI->body();
+  llvm::StringRef Path(Result);
+  // Check for Windows paths (URI=file:///X:/path => Body=/X:/path)
+  if (llvm::sys::path::is_absolute(Path.substr(1),
+                                   llvm::sys::path::Style::windows))
+    Result = Path.drop_front();
   if (!llvm::sys::path::replace_path_prefix(Result, *RemoteIndexRoot, ""))
     return error("File path '{0}' doesn't start with '{1}'.", Result.str(),
                  *RemoteIndexRoot);
-  // Make sure the result has UNIX slashes.
-  return llvm::sys::path::convert_to_slash(Result,
-                                           llvm::sys::path::Style::posix);
+  assert(Result == llvm::sys::path::convert_to_slash(
+                       Result, llvm::sys::path::Style::windows));
+  return std::string(Result);
 }
 
 clangd::SymbolLocation::Position
 Marshaller::fromProtobuf(const Position &Message) {
   clangd::SymbolLocation::Position Result;
   Result.setColumn(static_cast<uint32_t>(Message.column()));
   Result.setLine(static_cast<uint32_t>(Message.line()));
   return Result;

clang-tools-extra/clangd/unittests/remote/MarshallingTests.cpp

 TEST(RemoteMarshallingTest, IncludeHeaderURIs) {
   llvm::BumpPtrAllocator Arena;
   llvm::UniqueStringSaver Strings(Arena);
 
   clangd::Symbol Sym = createSymbol("remote/", Strings);
 
   clangd::Symbol::IncludeHeaderWithReferences Header;
   // Add only valid headers.
-  Header.IncludeHeader = Strings.save(
-      URI::createFile("/usr/local/user/home/project/Header.h").toString());
+  Header.IncludeHeader =
+      Strings.save(URI::createFile(testPath("project/Header.h")).toString());
   Header.References = 21;
   Sym.IncludeHeaders.push_back(Header);
   Header.IncludeHeader = Strings.save("<iostream>");
   Header.References = 100;
   Sym.IncludeHeaders.push_back(Header);
   Header.IncludeHeader = Strings.save("\"cstdio\"");
   Header.References = 200;
   Sym.IncludeHeaders.push_back(Header);
 
-  Marshaller ProtobufMarshaller(convert_to_slash("/"), convert_to_slash("/"));
+  Marshaller ProtobufMarshaller(testPath(""), testPath(""));
 
   auto Serialized = ProtobufMarshaller.toProtobuf(Sym);
   ASSERT_TRUE(bool(Serialized));
   EXPECT_EQ(static_cast<size_t>(Serialized->headers_size()),
             Sym.IncludeHeaders.size());
   auto Deserialized = ProtobufMarshaller.fromProtobuf(*Serialized);
   ASSERT_TRUE(bool(Deserialized));
   EXPECT_EQ(toYAML(Sym), toYAML(*Deserialized));