Merge pull request #38941 from xedin/improve-inout-variadic-inference-for-closures

[ConstraintSystem] Always propagate inout/variadic flags to type-less…

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -8831,11 +8831,16 @@ bool ConstraintSystem::resolveClosure(TypeVariableType *typeVar,
     auto param = inferredClosureType->getParams()[i];
     auto *paramDecl = paramList->get(i);
 
-    // In case of anonymous parameters let's infer flags from context
-    // that helps to infer variadic and inout earlier.
-    if (closure->hasAnonymousClosureVars()) {
-      if (auto contextualParam = getContextualParamAt(i))
-        param = param.withFlags(contextualParam->getParameterFlags());
+    // In case of anonymous or name-only parameters, let's infer inout/variadic
+    // flags from context, that helps to propagate type information into the
+    // internal type of the parameter and reduces inference solver has to make.
+    if (!paramDecl->getTypeRepr()) {
+      if (auto contextualParam = getContextualParamAt(i)) {
+        auto flags = param.getParameterFlags();
+        param =
+            param.withFlags(flags.withInOut(contextualParam->isInOut())
+                                 .withVariadic(contextualParam->isVariadic()));
+      }
     }
 
     if (paramDecl->hasAttachedPropertyWrapper()) {