[clangd] Check for other clangd extension capabilities under 'experimental' (#116531)

This is a follow-up to PR114699, with the same motivation: to support
clients which only support adding custom (language-specific or
server-specific) capabilities under 'experimental'.

Author: HighCommander4

clang-tools-extra/clangd/Protocol.cpp

@@ -511,6 +511,35 @@ bool fromJSON(const llvm::json::Value &Params, ClientCapabilities &R,
         if (auto EditsNearCursor = Completion->getBoolean("editsNearCursor"))
           R.CompletionFixes |= *EditsNearCursor;
       }
+      if (auto *References = TextDocument->getObject("references")) {
+        if (auto ContainerSupport = References->getBoolean("container")) {
+          R.ReferenceContainer |= *ContainerSupport;
+        }
+      }
+      if (auto *Diagnostics = TextDocument->getObject("publishDiagnostics")) {
+        if (auto CodeActions = Diagnostics->getBoolean("codeActionsInline")) {
+          R.DiagnosticFixes |= *CodeActions;
+        }
+      }
+      if (auto *InactiveRegions =
+              TextDocument->getObject("inactiveRegionsCapabilities")) {
+        if (auto InactiveRegionsSupport =
+                InactiveRegions->getBoolean("inactiveRegions")) {
+          R.InactiveRegions |= *InactiveRegionsSupport;
+        }
+      }
+    }
+    if (auto *Window = Experimental->getObject("window")) {
+      if (auto Implicit =
+              Window->getBoolean("implicitWorkDoneProgressCreate")) {
+        R.ImplicitProgressCreation |= *Implicit;
+      }
+    }
+    if (auto *OffsetEncoding = Experimental->get("offsetEncoding")) {
+      R.offsetEncoding.emplace();
+      if (!fromJSON(*OffsetEncoding, *R.offsetEncoding,
+                    P.field("offsetEncoding")))
+        return false;
     }
   }
 

clang-tools-extra/clangd/Protocol.h

@@ -452,6 +452,7 @@ struct ClientCapabilities {
   std::optional<SymbolKindBitset> WorkspaceSymbolKinds;
 
   /// Whether the client accepts diagnostics with codeActions attached inline.
+  /// This is a clangd extension.
   /// textDocument.publishDiagnostics.codeActionsInline.
   bool DiagnosticFixes = false;
 
@@ -475,6 +476,7 @@ struct ClientCapabilities {
 
   /// Client supports displaying a container string for results of
   /// textDocument/reference (clangd extension)
+  /// textDocument.references.container
   bool ReferenceContainer = false;
 
   /// Client supports hierarchical document symbols.
@@ -563,6 +565,7 @@ struct ClientCapabilities {
 
   /// Whether the client supports the textDocument/inactiveRegions
   /// notification. This is a clangd extension.
+  /// textDocument.inactiveRegionsCapabilities.inactiveRegions
   bool InactiveRegions = false;
 };
 bool fromJSON(const llvm::json::Value &, ClientCapabilities &,