[clangd] Turn on RecoveryAST for clangd by default.

[sammccall]

clang-tools-extra/clangd/tool/ClangdMain.cpp

285

Ah actually in other options, we set the default in the struct and reference it here. Can we do that here too?

[hokein]

address review comment.

clang-tools-extra/clangd/ClangdServer.h

struct Options {
     /// If set, enable clang-tidy in clangd and use to it get clang-tidy
     /// configurations for a particular file.
     /// Clangd supports only a small subset of ClangTidyOptions, these options
     /// (Checks, CheckOptions) are about which clang-tidy checks will be
     /// enabled.
     ClangTidyOptionsBuilder GetClangTidyOptions;
 
     /// If true, turn on the `-frecovery-ast` clang flag.
-    bool BuildRecoveryAST = false;
+    bool BuildRecoveryAST = true;
 
     /// If true, turn on the `-frecovery-ast-type` clang flag.
     bool PreserveRecoveryASTType = false;
 
     /// Clangd's workspace root. Relevant for "workspace" operations not bound
     /// to a particular file.
     /// FIXME: If not set, should use the current working directory.
     llvm::Optional<std::string> WorkspaceRoot;
private:
   // When set, provides clang-tidy options for a specific file.
   ClangTidyOptionsBuilder GetClangTidyOptions;
 
   // If this is true, suggest include insertion fixes for diagnostic errors that
   // can be caused by missing includes (e.g. member access in incomplete type).
   bool SuggestMissingIncludes = false;
 
   // If true, preserve expressions in AST for broken code.
-  bool BuildRecoveryAST = false;
+  bool BuildRecoveryAST = true;
   // If true, preserve the type for recovery AST.
   bool PreserveRecoveryASTType = false;
 
   std::function<bool(const Tweak &)> TweakFilter;
 
   // GUARDED_BY(CachedCompletionFuzzyFindRequestMutex)
   llvm::StringMap<llvm::Optional<FuzzyFindRequest>>
       CachedCompletionFuzzyFindRequestByFile;

clang-tools-extra/clangd/tool/ClangdMain.cpp

opt<bool> CrossFileRename{
     cat(Features),
     desc("Enable cross-file rename feature."),
     init(true),
 };
 
 opt<bool> RecoveryAST{
     "recovery-ast",
     cat(Features),
-    desc("Preserve expressions in AST for broken code (C++ only). Note that "
-         "this feature is experimental and may lead to crashes"),
-    init(false),
-    Hidden,
+    desc("Preserve expressions in AST for broken code (C++ only)."),
+    init(ClangdServer::Options().BuildRecoveryAST),
 };
+
 opt<bool> RecoveryASTType{
     "recovery-ast-type",
     cat(Features),
     desc("Preserve the type for recovery AST. Note that "
          "this feature is experimental and may lead to crashes"),
     init(false),
     Hidden,
 };