Merge pull request #72570 from ahoppen/ahoppen/parameter-pack-pattern-crash

[CodeCompletion] Fix a crash when completing the call pattern of a function that takes a parameter pack

Author: ahoppen

lib/Sema/CSApply.cpp

@@ -98,8 +98,15 @@ Solution::computeSubstitutions(NullablePtr<ValueDecl> decl,
   TypeSubstitutionMap subs;
   for (const auto &opened : openedTypes->second) {
     auto type = getFixedType(opened.second);
-    if (opened.first->isParameterPack() && !type->is<PackType>())
-      type = PackType::getSingletonPackExpansion(type);
+    if (opened.first->isParameterPack()) {
+      if (type->is<PlaceholderType>()) {
+        auto &ctx = type->getASTContext();
+        type =
+        PackType::get(ctx, {PackExpansionType::get(ctx.TheUnresolvedType,
+                                                   ctx.TheUnresolvedType)});
+      } else if (!type->is<PackType>())
+        type = PackType::getSingletonPackExpansion(type);
+    }
     subs[opened.first] = type;
   }
 

test/IDE/complete_parameter_pack_as_call_argument.swift

@@ -0,0 +1,7 @@
+// RUN: %batch-code-completion
+
+struct Mixer<each Source: Signal>: Signal {}
+
+print(Mixer(#^COMPLETE^#))
+
+// COMPLETE: Decl[Constructor]/CurrNominal/Flair[ArgLabels]: ['('][')'][#Mixer<repeat each Source>#];