[clang] Make signature help work with dependent args

Fixes https://github.com/clangd/clangd/issues/490

Differential Revision: https://reviews.llvm.org/D85826

1 files changed, 35 insertions, 18 deletions

diff --git a/clang/lib/Sema/SemaCodeComplete.cpp b/clang/lib/Sema/SemaCodeComplete.cpp
index 0a8a270..cf38b10 100644
--- a/clang/lib/Sema/SemaCodeComplete.cpp
+++ b/clang/lib/Sema/SemaCodeComplete.cpp
@@ -5500,7 +5500,7 @@ typedef CodeCompleteConsumer::OverloadCandidate ResultCandidate;
 
 static void mergeCandidatesWithResults(
     Sema &SemaRef, SmallVectorImpl<ResultCandidate> &Results,
-    OverloadCandidateSet &CandidateSet, SourceLocation Loc) {
+    OverloadCandidateSet &CandidateSet, SourceLocation Loc, size_t ArgSize) {
   // Sort the overload candidate set by placing the best overloads first.
   llvm::stable_sort(CandidateSet, [&](const OverloadCandidate &X,
                                       const OverloadCandidate &Y) {
@@ -5510,8 +5510,19 @@ static void mergeCandidatesWithResults(
 
   // Add the remaining viable overload candidates as code-completion results.
   for (OverloadCandidate &Candidate : CandidateSet) {
-    if (Candidate.Function && Candidate.Function->isDeleted())
-      continue;
+    if (Candidate.Function) {
+      if (Candidate.Function->isDeleted())
+        continue;
+      if (!Candidate.Function->isVariadic() &&
+          Candidate.Function->getNumParams() <= ArgSize &&
+          // Having zero args is annoying, normally we don't surface a function
+          // with 2 params, if you already have 2 params, because you are
+          // inserting the 3rd now. But with zero, it helps the user to figure
+          // out there are no overloads that take any arguments. Hence we are
+          // keeping the overload.
+          ArgSize > 0)
+        continue;
+    }
     if (Candidate.Viable)
       Results.push_back(ResultCandidate(Candidate.Function));
   }
@@ -5562,22 +5573,25 @@ QualType Sema::ProduceCallSignatureHelp(Scope *S, Expr *Fn,
 
   // FIXME: Provide support for variadic template functions.
   // Ignore type-dependent call expressions entirely.
-  if (!Fn || Fn->isTypeDependent() || anyNullArguments(Args) ||
-      Expr::hasAnyTypeDependentArguments(Args)) {
+  if (!Fn || Fn->isTypeDependent() || anyNullArguments(Args))
     return QualType();
-  }
+  // In presence of dependent args we surface all possible signatures using the
+  // non-dependent args in the prefix. Afterwards we do a post filtering to make
+  // sure provided candidates satisfy parameter count restrictions.
+  auto ArgsWithoutDependentTypes =
+      Args.take_while([](Expr *Arg) { return !Arg->isTypeDependent(); });
 
+  SmallVector<ResultCandidate, 8> Results;
+
+  Expr *NakedFn = Fn->IgnoreParenCasts();
   // Build an overload candidate set based on the functions we find.
   SourceLocation Loc = Fn->getExprLoc();
   OverloadCandidateSet CandidateSet(Loc, OverloadCandidateSet::CSK_Normal);
 
-  SmallVector<ResultCandidate, 8> Results;
-
-  Expr *NakedFn = Fn->IgnoreParenCasts();
-  if (auto ULE = dyn_cast<UnresolvedLookupExpr>(NakedFn))
-    AddOverloadedCallCandidates(ULE, Args, CandidateSet,
+  if (auto ULE = dyn_cast<UnresolvedLookupExpr>(NakedFn)) {
+    AddOverloadedCallCandidates(ULE, ArgsWithoutDependentTypes, CandidateSet,
                                 /*PartialOverloading=*/true);
-  else if (auto UME = dyn_cast<UnresolvedMemberExpr>(NakedFn)) {
+  } else if (auto UME = dyn_cast<UnresolvedMemberExpr>(NakedFn)) {
     TemplateArgumentListInfo TemplateArgsBuffer, *TemplateArgs = nullptr;
     if (UME->hasExplicitTemplateArgs()) {
       UME->copyTemplateArgumentsInto(TemplateArgsBuffer);
@@ -5587,7 +5601,8 @@ QualType Sema::ProduceCallSignatureHelp(Scope *S, Expr *Fn,
     // Add the base as first argument (use a nullptr if the base is implicit).
     SmallVector<Expr *, 12> ArgExprs(
         1, UME->isImplicitAccess() ? nullptr : UME->getBase());
-    ArgExprs.append(Args.begin(), Args.end());
+    ArgExprs.append(ArgsWithoutDependentTypes.begin(),
+                    ArgsWithoutDependentTypes.end());
     UnresolvedSet<8> Decls;
     Decls.append(UME->decls_begin(), UME->decls_end());
     const bool FirstArgumentIsBase = !UME->isImplicitAccess() && UME->getBase();
@@ -5606,7 +5621,7 @@ QualType Sema::ProduceCallSignatureHelp(Scope *S, Expr *Fn,
         Results.push_back(ResultCandidate(FD));
       else
         AddOverloadCandidate(FD, DeclAccessPair::make(FD, FD->getAccess()),
-                             Args, CandidateSet,
+                             ArgsWithoutDependentTypes, CandidateSet,
                              /*SuppressUserConversions=*/false,
                              /*PartialOverloading=*/true);
 
@@ -5621,7 +5636,8 @@ QualType Sema::ProduceCallSignatureHelp(Scope *S, Expr *Fn,
         LookupQualifiedName(R, DC);
         R.suppressDiagnostics();
         SmallVector<Expr *, 12> ArgExprs(1, NakedFn);
-        ArgExprs.append(Args.begin(), Args.end());
+        ArgExprs.append(ArgsWithoutDependentTypes.begin(),
+                        ArgsWithoutDependentTypes.end());
         AddFunctionCandidates(R.asUnresolvedSet(), ArgExprs, CandidateSet,
                               /*ExplicitArgs=*/nullptr,
                               /*SuppressUserConversions=*/false,
@@ -5635,7 +5651,8 @@ QualType Sema::ProduceCallSignatureHelp(Scope *S, Expr *Fn,
         T = T->getPointeeType();
 
       if (auto FP = T->getAs<FunctionProtoType>()) {
-        if (!TooManyArguments(FP->getNumParams(), Args.size(),
+        if (!TooManyArguments(FP->getNumParams(),
+                              ArgsWithoutDependentTypes.size(),
                               /*PartialOverloading=*/true) ||
             FP->isVariadic())
           Results.push_back(ResultCandidate(FP));
@@ -5644,7 +5661,7 @@ QualType Sema::ProduceCallSignatureHelp(Scope *S, Expr *Fn,
         Results.push_back(ResultCandidate(FT));
     }
   }
-  mergeCandidatesWithResults(*this, Results, CandidateSet, Loc);
+  mergeCandidatesWithResults(*this, Results, CandidateSet, Loc, Args.size());
   QualType ParamType =
       ProduceSignatureHelp(*this, S, Results, Args.size(), OpenParLoc);
   return !CandidateSet.empty() ? ParamType : QualType();
@@ -5685,7 +5702,7 @@ QualType Sema::ProduceConstructorSignatureHelp(Scope *S, QualType Type,
   }
 
   SmallVector<ResultCandidate, 8> Results;
-  mergeCandidatesWithResults(*this, Results, CandidateSet, Loc);
+  mergeCandidatesWithResults(*this, Results, CandidateSet, Loc, Args.size());
   return ProduceSignatureHelp(*this, S, Results, Args.size(), OpenParLoc);
 }