[clangd] Add add commit characters to the server capabilities

[kbobyrev]

Summary

Make it more convinient for the clients to select completion items by
providing a set of default characters (punctuation).

Related issue: https://github.com/clangd/clangd/issues/284

[sammccall]

clang-tools-extra/clangd/ClangdLSPServer.cpp

562

I think you're missing pipe and single-quote

[kbobyrev]

Add pipe and single quote to commit characters.

clang-tools-extra/clangd/ClangdLSPServer.cpp

llvm::json::Object Result{
             {"documentOnTypeFormattingProvider",
              llvm::json::Object{
                  {"firstTriggerCharacter", "\n"},
                  {"moreTriggerCharacter", {}},
              }},
             {"codeActionProvider", std::move(CodeActionProvider)},
             {"completionProvider",
              llvm::json::Object{
+                 {"allCommitCharacters", " \t()[]{}<>:;,+-/*%^&#?.=\"'|"},
                  {"resolveProvider", false},
                  // We do extra checks for '>' and ':' in completion to only
                  // trigger on '->' and '::'.
                  {"triggerCharacters", {".", ">", ":"}},
              }},
             {"signatureHelpProvider",
              llvm::json::Object{
                  {"triggerCharacters", {"(", ","}},

clang-tools-extra/clangd/Protocol.h

struct CompletionItem {
 
   /// This is Clangd extension.
   /// The score that Clangd calculates to rank completion items. This score can
   /// be used to adjust the ranking on the client side.
   /// NOTE: This excludes fuzzy matching score which is typically calculated on
   /// the client side.
   float score = 0.f;
 
+  // TODO: Add custom commitCharacters for some of the completion items. For
+  // example, it makes sense to use () only for the functions.
   // TODO(krasimir): The following optional fields defined by the language
   // server protocol are unsupported:
   //
   // data?: any - A data entry field that is preserved on a completion item
   //              between a completion and a completion resolve request.
 };
 llvm::json::Value toJSON(const CompletionItem &);
 llvm::raw_ostream &operator<<(llvm::raw_ostream &, const CompletionItem &);

clang-tools-extra/clangd/test/initialize-params.test

 # RUN: clangd -lit-test < %s | FileCheck -strict-whitespace %s
 # Test initialize request parameters with rootUri
 {"jsonrpc":"2.0","id":0,"method":"initialize","params":{"processId":123,"rootUri":"test:///workspace","capabilities":{},"trace":"off"}}
 #      CHECK:  "id": 0,
 # CHECK-NEXT:  "jsonrpc": "2.0",
 # CHECK-NEXT:  "result": {
 # CHECK-NEXT:    "capabilities": {
 # CHECK-NEXT:      "codeActionProvider": true,
 # CHECK-NEXT:      "completionProvider": {
+# CHECK-NEXT:        "allCommitCharacters": " \t()[]{}<>:;,+-/*%^&#?.=\"",
 # CHECK-NEXT:        "resolveProvider": false,
 # CHECK-NEXT:        "triggerCharacters": [
 # CHECK-NEXT:          ".",
 # CHECK-NEXT:          ">",
 # CHECK-NEXT:          ":"
 # CHECK-NEXT:        ]
 # CHECK-NEXT:      },
 # CHECK-NEXT:      "declarationProvider": true,