[CodeCompletion] Avoid spurious signature help for init-list args

Somewhat surprisingly, signature help is emitted as a side-effect of
computing the expected type of a function argument.
The reason is that both actions require enumerating the possible
function signatures and running partial overload resolution, and doing
this twice would be wasteful and complicated.

Change #1: document this, it's subtle :-)

However, sometimes we need to compute the expected type without having
reached the code completion cursor yet - in particular to allow
completion of designators.
eb4ab3358cd4dc834a761191b5531b38114f7b13 did this but introduced a
regression - it emits signature help in the wrong location as a side-effect.

Change #2: only emit signature help if the code completion cursor was reached.

Currently there is PP.isCodeCompletionReached(), but we can't use it
because it's set *after* running code completion.
It'd be nice to set this implicitly when the completion token is lexed,
but ConsumeCodeCompletionToken() makes this complicated.

Change #3: call cutOffParsing() *first* when seeing a completion token.

After this, the fact that the Sema::Produce*SignatureHelp() functions
are even more confusing, as they only sometimes do that.
I don't want to rename them in this patch as it's another large
mechanical change, but we should soon.

Change #4: prepare to rename ProduceSignatureHelp() to GuessArgumentType() etc.

Differential Revision: https://reviews.llvm.org/D98488

1 files changed, 12 insertions, 7 deletions

diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 9edf4d3..a044fbc 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -1970,8 +1970,8 @@ Parser::DeclGroupPtrTy Parser::ParseDeclGroup(ParsingDeclSpec &DS,
   // Check to see if we have a function *definition* which must have a body.
   if (D.isFunctionDeclarator()) {
     if (Tok.is(tok::equal) && NextToken().is(tok::code_completion)) {
-      Actions.CodeCompleteAfterFunctionEquals(D);
       cutOffParsing();
+      Actions.CodeCompleteAfterFunctionEquals(D);
       return nullptr;
     }
     // Look at the next token to make sure that this isn't a function
@@ -2310,9 +2310,9 @@ Decl *Parser::ParseDeclarationAfterDeclaratorAndAttributes(
       InitializerScopeRAII InitScope(*this, D, ThisDecl);
 
       if (Tok.is(tok::code_completion)) {
+        cutOffParsing();
         Actions.CodeCompleteInitializer(getCurScope(), ThisDecl);
         Actions.FinalizeDeclaration(ThisDecl);
-        cutOffParsing();
         return nullptr;
       }
 
@@ -3090,10 +3090,11 @@ void Parser::ParseDeclarationSpecifiers(DeclSpec &DS,
           = DSContext == DeclSpecContext::DSC_top_level ||
             (DSContext == DeclSpecContext::DSC_class && DS.isFriendSpecified());
 
+        cutOffParsing();
         Actions.CodeCompleteDeclSpec(getCurScope(), DS,
                                      AllowNonIdentifiers,
                                      AllowNestedNameSpecifiers);
-        return cutOffParsing();
+        return;
       }
 
       if (getCurScope()->getFnParent() || getCurScope()->getBlockParent())
@@ -3106,8 +3107,9 @@ void Parser::ParseDeclarationSpecifiers(DeclSpec &DS,
       else if (CurParsedObjCImpl)
         CCC = Sema::PCC_ObjCImplementation;
 
+      cutOffParsing();
       Actions.CodeCompleteOrdinaryName(getCurScope(), CCC);
-      return cutOffParsing();
+      return;
     }
 
     case tok::coloncolon: // ::foo::bar
@@ -4362,8 +4364,9 @@ void Parser::ParseEnumSpecifier(SourceLocation StartLoc, DeclSpec &DS,
   // Parse the tag portion of this.
   if (Tok.is(tok::code_completion)) {
     // Code completion for an enum name.
+    cutOffParsing();
     Actions.CodeCompleteTag(getCurScope(), DeclSpec::TST_enum);
-    return cutOffParsing();
+    return;
   }
 
   // If attributes exist after tag, parse them.
@@ -5457,11 +5460,12 @@ void Parser::ParseTypeQualifierListOpt(
 
     switch (Tok.getKind()) {
     case tok::code_completion:
+      cutOffParsing();
       if (CodeCompletionHandler)
         (*CodeCompletionHandler)();
       else
         Actions.CodeCompleteTypeQualifiers(DS);
-      return cutOffParsing();
+      return;
 
     case tok::kw_const:
       isInvalid = DS.SetTypeQual(DeclSpec::TQ_const   , Loc, PrevSpec, DiagID,
@@ -6998,8 +7002,9 @@ void Parser::ParseBracketDeclarator(Declarator &D) {
                   std::move(attrs), T.getCloseLocation());
     return;
   } else if (Tok.getKind() == tok::code_completion) {
+    cutOffParsing();
     Actions.CodeCompleteBracketDeclarator(getCurScope());
-    return cutOffParsing();
+    return;
   }
 
   // If valid, this location is the position where we read the 'static' keyword.