[clangd] Add ArgumentLists config option under Completion

The new config option is a more flexible version of
--function-arg-placeholders, allowing users more detailed control
of what is inserted in argument list position when clangd completes
the name of a function in a function call context.

Fixes llvm#63565

Author: MK-Alias

clang-tools-extra/clangd/ClangdServer.cpp

@@ -451,6 +451,7 @@ void ClangdServer::codeComplete(PathRef File, Position Pos,
 
     CodeCompleteOpts.MainFileSignals = IP->Signals;
     CodeCompleteOpts.AllScopes = Config::current().Completion.AllScopes;
+    CodeCompleteOpts.ArgumentLists = Config::current().Completion.ArgumentLists;
     // FIXME(ibiryukov): even if Preamble is non-null, we may want to check
     // both the old and the new version in case only one of them matches.
     CodeCompleteResult Result = clangd::codeComplete(

clang-tools-extra/clangd/CodeComplete.cpp

@@ -21,6 +21,7 @@
 #include "AST.h"
 #include "CodeCompletionStrings.h"
 #include "Compiler.h"
+#include "Config.h"
 #include "ExpectedTypes.h"
 #include "Feature.h"
 #include "FileDistance.h"
@@ -350,8 +351,7 @@ struct CodeCompletionBuilder {
                         CodeCompletionContext::Kind ContextKind,
                         const CodeCompleteOptions &Opts,
                         bool IsUsingDeclaration, tok::TokenKind NextTokenKind)
-      : ASTCtx(ASTCtx),
-        EnableFunctionArgSnippets(Opts.EnableFunctionArgSnippets),
+      : ASTCtx(ASTCtx), ArgumentLists(Opts.ArgumentLists),
         IsUsingDeclaration(IsUsingDeclaration), NextTokenKind(NextTokenKind) {
     Completion.Deprecated = true; // cleared by any non-deprecated overload.
     add(C, SemaCCS, ContextKind);
@@ -561,14 +561,23 @@ struct CodeCompletionBuilder {
   }
 
   std::string summarizeSnippet() const {
+    /// localize ArgumentLists tests for better readability
+    const bool None = ArgumentLists == Config::ArgumentListsPolicy::None;
+    const bool Open =
+        ArgumentLists == Config::ArgumentListsPolicy::OpenDelimiter;
+    const bool Delim = ArgumentLists == Config::ArgumentListsPolicy::Delimiters;
+    const bool Full =
+        ArgumentLists == Config::ArgumentListsPolicy::FullPlaceholders ||
+        (!None && !Open && !Delim); // <-- failsafe: Full is default
+
     if (IsUsingDeclaration)
       return "";
     auto *Snippet = onlyValue<&BundledEntry::SnippetSuffix>();
     if (!Snippet)
       // All bundles are function calls.
       // FIXME(ibiryukov): sometimes add template arguments to a snippet, e.g.
       // we need to complete 'forward<$1>($0)'.
-      return "($0)";
+      return None ? "" : (Open ? "(" : "($0)");
 
     if (Snippet->empty())
       return "";
@@ -607,7 +616,7 @@ struct CodeCompletionBuilder {
         return "";
       }
     }
-    if (EnableFunctionArgSnippets)
+    if (Full)
       return *Snippet;
 
     // Replace argument snippets with a simplified pattern.
@@ -622,9 +631,9 @@ struct CodeCompletionBuilder {
 
       bool EmptyArgs = llvm::StringRef(*Snippet).ends_with("()");
       if (Snippet->front() == '<')
-        return EmptyArgs ? "<$1>()$0" : "<$1>($0)";
+        return None ? "" : (Open ? "<" : (EmptyArgs ? "<$1>()$0" : "<$1>($0)"));
       if (Snippet->front() == '(')
-        return EmptyArgs ? "()" : "($0)";
+        return None ? "" : (Open ? "(" : (EmptyArgs ? "()" : "($0)"));
       return *Snippet; // Not an arg snippet?
     }
     // 'CompletionItemKind::Interface' matches template type aliases.
@@ -638,7 +647,7 @@ struct CodeCompletionBuilder {
       // e.g. Foo<${1:class}>.
       if (llvm::StringRef(*Snippet).ends_with("<>"))
         return "<>"; // can happen with defaulted template arguments.
-      return "<$0>";
+      return None ? "" : (Open ? "<" : "<$0>");
     }
     return *Snippet;
   }
@@ -654,7 +663,8 @@ struct CodeCompletionBuilder {
   ASTContext *ASTCtx;
   CodeCompletion Completion;
   llvm::SmallVector<BundledEntry, 1> Bundled;
-  bool EnableFunctionArgSnippets;
+  /// the way argument lists are handled.
+  Config::ArgumentListsPolicy ArgumentLists;
   // No snippets will be generated for using declarations and when the function
   // arguments are already present.
   bool IsUsingDeclaration;

clang-tools-extra/clangd/CodeComplete.h

@@ -17,6 +17,7 @@
 
 #include "ASTSignals.h"
 #include "Compiler.h"
+#include "Config.h"
 #include "Protocol.h"
 #include "Quality.h"
 #include "index/Index.h"
@@ -96,17 +97,17 @@ struct CodeCompleteOptions {
   /// '->' on member access etc.
   bool IncludeFixIts = false;
 
-  /// Whether to generate snippets for function arguments on code-completion.
-  /// Needs snippets to be enabled as well.
-  bool EnableFunctionArgSnippets = true;
-
   /// Whether to include index symbols that are not defined in the scopes
   /// visible from the code completion point. This applies in contexts without
   /// explicit scope qualifiers.
   ///
   /// Such completions can insert scope qualifiers.
   bool AllScopes = false;
 
+  /// The way argument list on calls '()' and generics '<>' are handled.
+  Config::ArgumentListsPolicy ArgumentLists =
+      Config::ArgumentListsPolicy::FullPlaceholders;
+
   /// Whether to use the clang parser, or fallback to text-based completion
   /// (using identifiers in the current file and symbol indexes).
   enum CodeCompletionParse {

clang-tools-extra/clangd/Config.h

@@ -126,11 +126,25 @@ struct Config {
     std::vector<std::string> FullyQualifiedNamespaces;
   } Style;
 
+  /// controls the completion options for argument lists.
+  enum class ArgumentListsPolicy {
+    /// nothing, no argument list and also NO Delimiters "()" or "<>".
+    None,
+    /// open, only opening delimiter "(" or "<".
+    OpenDelimiter,
+    /// empty pair of delimiters "()" or "<>".
+    Delimiters,
+    /// full name of both type and variable.
+    FullPlaceholders,
+  };
+
   /// Configures code completion feature.
   struct {
     /// Whether code completion includes results that are not visible in current
     /// scopes.
     bool AllScopes = true;
+    /// controls the completion options for argument lists.
+    ArgumentListsPolicy ArgumentLists = ArgumentListsPolicy::FullPlaceholders;
   } Completion;
 
   /// Configures hover feature.

clang-tools-extra/clangd/ConfigCompile.cpp

@@ -622,6 +622,21 @@ struct FragmentCompiler {
             C.Completion.AllScopes = AllScopes;
           });
     }
+    if (F.ArgumentLists) {
+      if (auto Val =
+              compileEnum<Config::ArgumentListsPolicy>("ArgumentLists",
+                                                       *F.ArgumentLists)
+                  .map("None", Config::ArgumentListsPolicy::None)
+                  .map("OpenDelimiter",
+                       Config::ArgumentListsPolicy::OpenDelimiter)
+                  .map("Delimiters", Config::ArgumentListsPolicy::Delimiters)
+                  .map("FullPlaceholders",
+                       Config::ArgumentListsPolicy::FullPlaceholders)
+                  .value())
+        Out.Apply.push_back([Val](const Params &, Config &C) {
+          C.Completion.ArgumentLists = *Val;
+        });
+    }
   }
 
   void compile(Fragment::HoverBlock &&F) {

clang-tools-extra/clangd/ConfigFragment.h

@@ -32,6 +32,7 @@
 #ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_CONFIGFRAGMENT_H
 #define LLVM_CLANG_TOOLS_EXTRA_CLANGD_CONFIGFRAGMENT_H
 
+#include "Config.h"
 #include "ConfigProvider.h"
 #include "llvm/Support/SMLoc.h"
 #include "llvm/Support/SourceMgr.h"
@@ -308,6 +309,13 @@ struct Fragment {
     /// Whether code completion should include suggestions from scopes that are
     /// not visible. The required scope prefix will be inserted.
     std::optional<Located<bool>> AllScopes;
+    /// How to present the argument list between '()' and '<>':
+    /// valid values are enum Config::ArgumentListsPolicy values:
+    ///   None: Nothing at all
+    ///   OpenDelimiter: only opening delimiter "(" or "<"
+    ///   Delimiters: empty pair of delimiters "()" or "<>"
+    ///   FullPlaceholders: full name of both type and parameter
+    std::optional<Located<std::string>> ArgumentLists;
   };
   CompletionBlock Completion;
 

clang-tools-extra/clangd/ConfigYAML.cpp

@@ -230,6 +230,10 @@ class Parser {
       if (auto AllScopes = boolValue(N, "AllScopes"))
         F.AllScopes = *AllScopes;
     });
+    Dict.handle("ArgumentLists", [&](Node &N) {
+      if (auto ArgumentLists = scalarValue(N, "ArgumentLists"))
+        F.ArgumentLists = *ArgumentLists;
+    });
     Dict.parse(N);
   }
 

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

@@ -242,13 +242,13 @@ opt<std::string> FallbackStyle{
     init(clang::format::DefaultFallbackStyle),
 };
 
-opt<bool> EnableFunctionArgSnippets{
+opt<int> EnableFunctionArgSnippets{
     "function-arg-placeholders",
     cat(Features),
-    desc("When disabled, completions contain only parentheses for "
-         "function calls. When enabled, completions also contain "
+    desc("When disabled (0), completions contain only parentheses for "
+         "function calls. When enabled (1), completions also contain "
          "placeholders for method parameters"),
-    init(CodeCompleteOptions().EnableFunctionArgSnippets),
+    init(-1),
 };
 
 opt<CodeCompleteOptions::IncludeInsertion> HeaderInsertion{
@@ -650,6 +650,7 @@ class FlagsConfigProvider : public config::Provider {
     std::optional<Config::CDBSearchSpec> CDBSearch;
     std::optional<Config::ExternalIndexSpec> IndexSpec;
     std::optional<Config::BackgroundPolicy> BGPolicy;
+    std::optional<Config::ArgumentListsPolicy> ArgumentLists;
 
     // If --compile-commands-dir arg was invoked, check value and override
     // default path.
@@ -694,13 +695,21 @@ class FlagsConfigProvider : public config::Provider {
       BGPolicy = Config::BackgroundPolicy::Skip;
     }
 
+    if (EnableFunctionArgSnippets >= 0) {
+      ArgumentLists = EnableFunctionArgSnippets
+                          ? Config::ArgumentListsPolicy::FullPlaceholders
+                          : Config::ArgumentListsPolicy::Delimiters;
+    }
+
     Frag = [=](const config::Params &, Config &C) {
       if (CDBSearch)
         C.CompileFlags.CDBSearch = *CDBSearch;
       if (IndexSpec)
         C.Index.External = *IndexSpec;
       if (BGPolicy)
         C.Index.Background = *BGPolicy;
+      if (ArgumentLists)
+        C.Completion.ArgumentLists = *ArgumentLists;
       if (AllScopesCompletion.getNumOccurrences())
         C.Completion.AllScopes = AllScopesCompletion;
 
@@ -916,7 +925,6 @@ clangd accepts flags on the commandline, and in the CLANGD_FLAGS environment var
     Opts.CodeComplete.IncludeIndicator.Insert.clear();
     Opts.CodeComplete.IncludeIndicator.NoInsert.clear();
   }
-  Opts.CodeComplete.EnableFunctionArgSnippets = EnableFunctionArgSnippets;
   Opts.CodeComplete.RunParser = CodeCompletionParse;
   Opts.CodeComplete.RankingModel = RankingModel;
 

clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp

@@ -11,6 +11,7 @@
 #include "ClangdServer.h"
 #include "CodeComplete.h"
 #include "Compiler.h"
+#include "Config.h"
 #include "Feature.h"
 #include "Matchers.h"
 #include "Protocol.h"
@@ -2595,10 +2596,10 @@ TEST(SignatureHelpTest, DynamicIndexDocumentation) {
               ElementsAre(AllOf(sig("foo() -> int"), sigDoc("Member doc"))));
 }
 
-TEST(CompletionTest, CompletionFunctionArgsDisabled) {
+TEST(CompletionTest, ArgumentListsPolicy) {
   CodeCompleteOptions Opts;
   Opts.EnableSnippets = true;
-  Opts.EnableFunctionArgSnippets = false;
+  Opts.ArgumentLists = Config::ArgumentListsPolicy::Delimiters;
 
   {
     auto Results = completions(
@@ -2670,6 +2671,26 @@ TEST(CompletionTest, CompletionFunctionArgsDisabled) {
     EXPECT_THAT(Results.Completions, UnorderedElementsAre(AllOf(
                                          named("FOO"), snippetSuffix("($0)"))));
   }
+  {
+    Opts.ArgumentLists = Config::ArgumentListsPolicy::None;
+    auto Results = completions(
+        R"cpp(
+      void xfoo(int x, int y);
+      void f() { xfo^ })cpp",
+        {}, Opts);
+    EXPECT_THAT(Results.Completions,
+                UnorderedElementsAre(AllOf(named("xfoo"), snippetSuffix(""))));
+  }
+  {
+    Opts.ArgumentLists = Config::ArgumentListsPolicy::OpenDelimiter;
+    auto Results = completions(
+        R"cpp(
+      void xfoo(int x, int y);
+      void f() { xfo^ })cpp",
+        {}, Opts);
+    EXPECT_THAT(Results.Completions,
+                UnorderedElementsAre(AllOf(named("xfoo"), snippetSuffix("("))));
+  }
 }
 
 TEST(CompletionTest, SuggestOverrides) {