[ConstraintSystem] Use an explicit generic argument constraint for

UnresolvedSpecializeExpr.

The eager generic argument matching code in CSGen for unresolved
specializations was incorrect because it didn't account for parameter
packs. Fortunately, a constraint to delay explicit generic argument
matching already exists for macros. Use it here.

Author: hborla

lib/Sema/CSGen.cpp

@@ -1810,49 +1810,11 @@ namespace {
       if (AnyMetatypeType *meta = baseTy->getAs<AnyMetatypeType>()) {
         if (BoundGenericType *bgt
               = meta->getInstanceType()->getAs<BoundGenericType>()) {
-          ArrayRef<Type> typeVars = bgt->getGenericArgs();
-          auto specializations = expr->getUnresolvedParams();
-
-          // If we have too many generic arguments, complain.
-          if (specializations.size() > typeVars.size()) {
-            de.diagnose(expr->getSubExpr()->getLoc(),
-                        diag::type_parameter_count_mismatch,
-                        bgt->getDecl()->getName(), typeVars.size(),
-                        specializations.size(),
-                        /*too many arguments*/ false,
-                        /*isParameterPack?*/ false)
-                .highlight(
-                    SourceRange(expr->getLAngleLoc(), expr->getRAngleLoc()));
-            de.diagnose(bgt->getDecl(), diag::kind_declname_declared_here,
-                        DescriptiveDeclKind::GenericType,
-                        bgt->getDecl()->getName());
+          auto *overloadLocator = CS.getConstraintLocator(expr->getSubExpr());
+          if (addSpecializationConstraint(overloadLocator, bgt,
+                                          expr->getUnresolvedParams())) {
             return Type();
           }
-
-          // Bind the specified generic arguments to the type variables in the
-          // open type.
-          auto *const locator = CS.getConstraintLocator(expr);
-          auto options =
-              TypeResolutionOptions(TypeResolverContext::InExpression);
-          for (size_t i = 0, e = specializations.size(); i < e; ++i) {
-            PackExpansionExpr *elementEnv = nullptr;
-            if (!PackElementEnvironments.empty()) {
-              options |= TypeResolutionFlags::AllowPackReferences;
-              elementEnv = PackElementEnvironments.back();
-            }
-
-            const auto result = TypeResolution::resolveContextualType(
-                specializations[i], CS.DC, options,
-                // Introduce type variables for unbound generics.
-                OpenUnboundGenericType(CS, locator),
-                HandlePlaceholderType(CS, locator),
-                OpenPackElementType(CS, locator, elementEnv));
-            if (result->hasError())
-              return Type();
-
-            CS.addConstraint(ConstraintKind::Bind, typeVars[i], result,
-                             locator);
-          }
 
           return baseTy;
         } else {

lib/Sema/CSSimplify.cpp

@@ -13520,7 +13520,26 @@ ConstraintSystem::simplifyExplicitGenericArgumentsConstraint(
   auto genericParamDepth = genericParams->getParams()[0]->getDepth();
   for (const auto &openedType : getOpenedTypes(overloadLocator)) {
     if (openedType.first->getDepth() == genericParamDepth) {
-      openedGenericParams.push_back(Type(openedType.second));
+      // A generic argument list containing pack references expects
+      // those packs to be wrapped in pack expansion types. If this
+      // opened type represents the generic argument for a parameter
+      // pack, wrap generate the appropriate shape constraints and
+      // add a pack expansion to the argument list.
+      if (openedType.first->isParameterPack()) {
+        auto patternType = openedType.second;
+        auto *shapeLoc = getConstraintLocator(
+            locator.withPathElement(ConstraintLocator::PackShape));
+        auto *shapeType = createTypeVariable(shapeLoc,
+                                            TVO_CanBindToPack |
+                                            TVO_CanBindToHole);
+        addConstraint(ConstraintKind::ShapeOf,
+                      shapeType, patternType, shapeLoc);
+
+        auto *expansion = PackExpansionType::get(patternType, shapeType);
+        openedGenericParams.push_back(expansion);
+      } else {
+        openedGenericParams.push_back(Type(openedType.second));
+      }
     }
   }
   assert(openedGenericParams.size() == genericParams->size());

test/Macros/macro_expand_variadic.swift

@@ -2,18 +2,32 @@
 
 // RUN: %empty-directory(%t)
 // RUN: %host-build-swift -swift-version 5 -emit-library -o %t/%target-library-name(MacroDefinition) -module-name=MacroDefinition %S/Inputs/variadic_macros.swift -g -no-toolchain-stdlib-rpath
-// RUN: %target-typecheck-verify-swift -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) -module-name MacroUser -DTEST_DIAGNOSTICS -swift-version 5
-// RUN: %target-build-swift -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) %s -o %t/main -module-name MacroUser -swift-version 5
+// RUN: %target-typecheck-verify-swift -disable-availability-checking -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) -module-name MacroUser -DTEST_DIAGNOSTICS -swift-version 5
+// RUN: %target-build-swift -Xfrontend -disable-availability-checking -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) %s -o %t/main -module-name MacroUser -swift-version 5
 // RUN: %target-codesign %t/main
 // RUN: %target-run %t/main | %FileCheck %s
 
 @freestanding(expression) macro print<each Value>(_ value: repeat each Value) = #externalMacro(module: "MacroDefinition", type: "PrintMacro")
 
+@freestanding(expression) macro Print<each Value>(_ value: repeat each Value) = #externalMacro(module: "MacroDefinition", type: "PrintMacro")
+
+struct Print<each Value> {
+  init() {}
+}
+
+func testAmbiguity() {
+  let _ = Print<Int>()
+}
+
 func testIt() {
   // CHECK: hello
   // CHECK: [1, 2, 3, 4, 5]
   #print("hello", [1, 2, 3, 4, 5])
 
+  // CHECK: hello
+  // CHECK: [1, 2, 3, 4, 5]
+  #print<String, [Int]>("hello", [1, 2, 3, 4, 5])
+
   // CHECK: world
   #print("world")
 }