[CodeCompletion] Signature help for template argument lists

Provide signature while typing template arguments: Foo< ^here >
Here the parameters are e.g. "typename x", and the result type is e.g.
"struct" (class template) or "int" (variable template) or "bool (std::string)"
(function template).

Multiple overloads are possible when a template name is used for several
overloaded function templates.

Fixes https://github.com/clangd/clangd/issues/299

Differential Revision: https://reviews.llvm.org/D116352

1 files changed, 28 insertions, 12 deletions

diff --git a/clang/lib/Parse/ParseTemplate.cpp b/clang/lib/Parse/ParseTemplate.cpp
index 45af61a..204b534 100644
--- a/clang/lib/Parse/ParseTemplate.cpp
+++ b/clang/lib/Parse/ParseTemplate.cpp
@@ -1222,7 +1222,6 @@ bool Parser::ParseGreaterThanInTemplateList(SourceLocation LAngleLoc,
   return false;
 }
 
-
 /// Parses a template-id that after the template name has
 /// already been parsed.
 ///
@@ -1234,11 +1233,13 @@ bool Parser::ParseGreaterThanInTemplateList(SourceLocation LAngleLoc,
 /// token that forms the template-id. Otherwise, we will leave the
 /// last token in the stream (e.g., so that it can be replaced with an
 /// annotation token).
-bool
-Parser::ParseTemplateIdAfterTemplateName(bool ConsumeLastToken,
-                                         SourceLocation &LAngleLoc,
-                                         TemplateArgList &TemplateArgs,
-                                         SourceLocation &RAngleLoc) {
+///
+/// \param NameHint is not required, and merely affects code completion.
+bool Parser::ParseTemplateIdAfterTemplateName(bool ConsumeLastToken,
+                                              SourceLocation &LAngleLoc,
+                                              TemplateArgList &TemplateArgs,
+                                              SourceLocation &RAngleLoc,
+                                              TemplateTy Template) {
   assert(Tok.is(tok::less) && "Must have already parsed the template-name");
 
   // Consume the '<'.
@@ -1251,7 +1252,7 @@ Parser::ParseTemplateIdAfterTemplateName(bool ConsumeLastToken,
     if (!Tok.isOneOf(tok::greater, tok::greatergreater,
                      tok::greatergreatergreater, tok::greaterequal,
                      tok::greatergreaterequal))
-      Invalid = ParseTemplateArgumentList(TemplateArgs);
+      Invalid = ParseTemplateArgumentList(TemplateArgs, Template, LAngleLoc);
 
     if (Invalid) {
       // Try to find the closing '>'.
@@ -1332,8 +1333,8 @@ bool Parser::AnnotateTemplateIdToken(TemplateTy Template, TemplateNameKind TNK,
   TemplateArgList TemplateArgs;
   bool ArgsInvalid = false;
   if (!TypeConstraint || Tok.is(tok::less)) {
-    ArgsInvalid = ParseTemplateIdAfterTemplateName(false, LAngleLoc,
-                                                   TemplateArgs, RAngleLoc);
+    ArgsInvalid = ParseTemplateIdAfterTemplateName(
+        false, LAngleLoc, TemplateArgs, RAngleLoc, Template);
     // If we couldn't recover from invalid arguments, don't form an annotation
     // token -- we don't know how much to annotate.
     // FIXME: This can lead to duplicate diagnostics if we retry parsing this
@@ -1585,19 +1586,34 @@ ParsedTemplateArgument Parser::ParseTemplateArgument() {
 ///       template-argument-list: [C++ 14.2]
 ///         template-argument
 ///         template-argument-list ',' template-argument
-bool
-Parser::ParseTemplateArgumentList(TemplateArgList &TemplateArgs) {
+///
+/// \param Template is only used for code completion, and may be null.
+bool Parser::ParseTemplateArgumentList(TemplateArgList &TemplateArgs,
+                                       TemplateTy Template,
+                                       SourceLocation OpenLoc) {
 
   ColonProtectionRAIIObject ColonProtection(*this, false);
 
+  auto RunSignatureHelp = [&] {
+    if (!Template)
+      return QualType();
+    CalledSignatureHelp = true;
+    return Actions.ProduceTemplateArgumentSignatureHelp(Template, TemplateArgs,
+                                                        OpenLoc);
+  };
+
   do {
+    PreferredType.enterFunctionArgument(Tok.getLocation(), RunSignatureHelp);
     ParsedTemplateArgument Arg = ParseTemplateArgument();
     SourceLocation EllipsisLoc;
     if (TryConsumeToken(tok::ellipsis, EllipsisLoc))
       Arg = Actions.ActOnPackExpansion(Arg, EllipsisLoc);
 
-    if (Arg.isInvalid())
+    if (Arg.isInvalid()) {
+      if (PP.isCodeCompletionReached() && !CalledSignatureHelp)
+        RunSignatureHelp();
       return true;
+    }
 
     // Save this template argument.
     TemplateArgs.push_back(Arg);