[clangd] Implement LSP 3.17 positionEncoding (#142903)

This PR adds support for the `positionEncoding` client capability
introduced in LSP 3.17. Clangd can now negotiate the position encoding
with the client during initialization.

Fix clangd/clangd#1746

Co-authored-by: kadir çetinkaya <[email protected]>

Author: someoneinjd

clang-tools-extra/clangd/ClangdLSPServer.cpp

@@ -494,9 +494,9 @@ static std::vector<llvm::StringRef> semanticTokenModifiers() {
 void ClangdLSPServer::onInitialize(const InitializeParams &Params,
                                    Callback<llvm::json::Value> Reply) {
   // Determine character encoding first as it affects constructed ClangdServer.
-  if (Params.capabilities.offsetEncoding && !Opts.Encoding) {
+  if (Params.capabilities.PositionEncodings && !Opts.Encoding) {
     Opts.Encoding = OffsetEncoding::UTF16; // fallback
-    for (OffsetEncoding Supported : *Params.capabilities.offsetEncoding)
+    for (OffsetEncoding Supported : *Params.capabilities.PositionEncodings)
       if (Supported != OffsetEncoding::UnsupportedEncoding) {
         Opts.Encoding = Supported;
         break;
@@ -686,13 +686,19 @@ void ClangdLSPServer::onInitialize(const InitializeParams &Params,
   ServerCaps["executeCommandProvider"] =
       llvm::json::Object{{"commands", Commands}};
 
+  if (Opts.Encoding)
+    ServerCaps["positionEncoding"] = *Opts.Encoding;
+
   llvm::json::Object Result{
       {{"serverInfo",
         llvm::json::Object{
             {"name", "clangd"},
             {"version", llvm::formatv("{0} {1} {2}", versionString(),
                                       featureString(), platformString())}}},
        {"capabilities", std::move(ServerCaps)}}};
+
+  // TODO: offsetEncoding capability is a deprecated clangd extension and should
+  // be deleted.
   if (Opts.Encoding)
     Result["offsetEncoding"] = *Opts.Encoding;
   Reply(std::move(Result));

clang-tools-extra/clangd/Protocol.cpp

@@ -497,10 +497,19 @@ bool fromJSON(const llvm::json::Value &Params, ClientCapabilities &R,
       if (auto Cancel = StaleRequestSupport->getBoolean("cancel"))
         R.CancelsStaleRequests = *Cancel;
     }
+    if (auto *PositionEncodings = General->get("positionEncodings")) {
+      R.PositionEncodings.emplace();
+      if (!fromJSON(*PositionEncodings, *R.PositionEncodings,
+                    P.field("general").field("positionEncodings")))
+        return false;
+    }
   }
   if (auto *OffsetEncoding = O->get("offsetEncoding")) {
-    R.offsetEncoding.emplace();
-    if (!fromJSON(*OffsetEncoding, *R.offsetEncoding,
+    R.PositionEncodings.emplace();
+    elog("offsetEncoding capability is a deprecated clangd extension that'll "
+         "go away with clangd 23. Migrate to standard positionEncodings "
+         "capability introduced by LSP 3.17");
+    if (!fromJSON(*OffsetEncoding, *R.PositionEncodings,
                   P.field("offsetEncoding")))
       return false;
   }
@@ -536,8 +545,11 @@ bool fromJSON(const llvm::json::Value &Params, ClientCapabilities &R,
       }
     }
     if (auto *OffsetEncoding = Experimental->get("offsetEncoding")) {
-      R.offsetEncoding.emplace();
-      if (!fromJSON(*OffsetEncoding, *R.offsetEncoding,
+      R.PositionEncodings.emplace();
+      elog("offsetEncoding capability is a deprecated clangd extension that'll "
+           "go away with clangd 23. Migrate to standard positionEncodings "
+           "capability introduced by LSP 3.17");
+      if (!fromJSON(*OffsetEncoding, *R.PositionEncodings,
                     P.field("offsetEncoding")))
         return false;
     }

clang-tools-extra/clangd/Protocol.h

@@ -528,8 +528,9 @@ struct ClientCapabilities {
   /// textDocument.semanticHighlightingCapabilities.semanticHighlighting
   bool TheiaSemanticHighlighting = false;
 
-  /// Supported encodings for LSP character offsets. (clangd extension).
-  std::optional<std::vector<OffsetEncoding>> offsetEncoding;
+  /// Supported encodings for LSP character offsets.
+  /// general.positionEncodings
+  std::optional<std::vector<OffsetEncoding>> PositionEncodings;
 
   /// The content format that should be used for Hover requests.
   /// textDocument.hover.contentEncoding

clang-tools-extra/clangd/test/positionencoding.test

@@ -0,0 +1,32 @@
+# RUN: clangd -lit-test < %s | FileCheck -strict-whitespace %s
+# This test verifies that we can negotiate UTF-8 offsets via the positionEncodings capability introduced in LSP 3.17.
+{"jsonrpc":"2.0","id":0,"method":"initialize","params":{"processId":123,"rootPath":"clangd","capabilities":{"general":{"positionEncodings":["utf-8","utf-16"]}},"trace":"off"}}
+# CHECK: "positionEncoding": "utf-8"
+---
+{"jsonrpc":"2.0","method":"textDocument/didOpen","params":{"textDocument":{"uri":"test:///main.cpp","languageId":"cpp","version":1,"text":"/*ö*/int x;\nint y=x;"}}}
+---
+{"jsonrpc":"2.0","id":1,"method":"textDocument/definition","params":{"textDocument":{"uri":"test:///main.cpp"},"position":{"line":1,"character":6}}}
+# /*ö*/int x;
+# 01234567890
+# x is character (and utf-16) range [9,10) but byte range [10,11).
+#      CHECK:  "id": 1,
+# CHECK-NEXT:  "jsonrpc": "2.0",
+# CHECK-NEXT:  "result": [
+# CHECK-NEXT:    {
+# CHECK-NEXT:      "range": {
+# CHECK-NEXT:        "end": {
+# CHECK-NEXT:          "character": 11,
+# CHECK-NEXT:          "line": 0
+# CHECK-NEXT:        },
+# CHECK-NEXT:        "start": {
+# CHECK-NEXT:          "character": 10,
+# CHECK-NEXT:          "line": 0
+# CHECK-NEXT:        }
+# CHECK-NEXT:      },
+# CHECK-NEXT:      "uri": "file://{{.*}}/main.cpp"
+# CHECK-NEXT:    }
+# CHECK-NEXT:  ]
+---
+{"jsonrpc":"2.0","id":10000,"method":"shutdown"}
+---
+{"jsonrpc":"2.0","method":"exit"}