[CSSimplify] Detect and diagnose attempts to specialize types with invalid number of arguments

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -13631,6 +13631,7 @@ ConstraintSystem::simplifyExplicitGenericArgumentsConstraint(
   }
 
   // Map the generic parameters we have over to their opened types.
+  bool hasParameterPack = false;
   SmallVector<Type, 2> openedGenericParams;
   auto genericParamDepth = genericParams->getParams()[0]->getDepth();
   for (const auto &openedType : openedTypes) {
@@ -13652,6 +13653,7 @@ ConstraintSystem::simplifyExplicitGenericArgumentsConstraint(
 
         auto *expansion = PackExpansionType::get(patternType, shapeType);
         openedGenericParams.push_back(expansion);
+        hasParameterPack = true;
       } else {
         openedGenericParams.push_back(Type(openedType.second));
       }
@@ -13674,8 +13676,15 @@ ConstraintSystem::simplifyExplicitGenericArgumentsConstraint(
   auto specializedArgs = type2->castTo<PackType>()->getElementTypes();
   PackMatcher matcher(openedGenericParams, specializedArgs, getASTContext(),
                       isPackExpansionType);
-  if (matcher.match())
-    return SolutionKind::Error;
+  if (matcher.match()) {
+    if (!shouldAttemptFixes())
+      return SolutionKind::Error;
+
+    auto *fix = IgnoreGenericSpecializationArityMismatch::create(
+        *this, decl, openedGenericParams.size(), specializedArgs.size(),
+        hasParameterPack, getConstraintLocator(locator));
+    return recordFix(fix) ? SolutionKind::Error : SolutionKind::Solved;
+  }
 
   // Bind the opened generic parameters to the specialization arguments.
   for (const auto &pair : matcher.pairs) {

test/Macros/macro_and_typealias.swift

@@ -7,14 +7,21 @@
 @freestanding(expression) public macro Print<each Value>(_ value: repeat each Value) = #externalMacro(module: "MacroDefinition", type: "PrintMacro")
 @freestanding(expression) public macro OtherPrint<each Value>(_ value: repeat each Value) = #externalMacro(module: "MacroDefinition", type: "PrintMacro")
 @freestanding(expression) public macro ConcretePrint(_ value: Any) = #externalMacro(module: "MacroDefinition", type: "PrintMacro")
+@freestanding(expression) public macro MultiPrint(_ value: Any) = #externalMacro(module: "MacroDefinition", type: "PrintMacro")
 
 public struct Printer<Value> {
   init(_: (Value) -> Void) {}
 }
 
+public struct MultiPrinter<T, U> {
+  // expected-note@-1 {{'T' declared as parameter to type 'MultiPrinter'}}
+  // expected-note@-2 {{'U' declared as parameter to type 'MultiPrinter'}}
+}
+
 typealias Print = Printer
 typealias OtherPrint<T> = Printer<T>
 typealias ConcretePrint = Printer<Any>
+typealias MultiPrint = MultiPrinter
 
 struct Test {
   struct Object {
@@ -26,6 +33,10 @@ struct Test {
       compute(root: $0, \.prop)
     }
 
+    let _ = Print<Object, Int> {
+      // expected-error@-1 {{generic type 'Print' specialized with too many type parameters (got 2, but expected 1)}}
+    }
+
     let _ = OtherPrint<Object> { // Ok
       compute(root: $0, \.prop)
     }
@@ -34,6 +45,11 @@ struct Test {
       compute(root: $0, \.prop) // expected-error {{value of type 'Any' has no member 'prop'}}
       // expected-note@-1 {{cast 'Any' to 'AnyObject' or use 'as!' to force downcast to a more specific type to access members}}
     }
+
+    let _ = MultiPrint<Int>()
+    // expected-error@-1 {{generic type 'MultiPrint' specialized with too few type parameters (got 1, but expected 2)}}
+    // expected-error@-2 {{generic parameter 'T' could not be inferred}}
+    // expected-error@-3 {{generic parameter 'U' could not be inferred}}
   }
 
   func compute<R, V>(root: R, _: KeyPath<R, V>) {}

test/Macros/macros_diagnostics.swift

@@ -96,8 +96,7 @@ macro genericDeclMacro<T: Numeric, U: Numeric>(_ x: T, _ y: U)
 // expected-note @-2 {{where 'U' = 'String'}}
 
 func testDiags(a: Int, b: Int) {
-  // FIXME: Bad diagnostic.
-  let s = #stringify<Int, Int>(a + b) // expected-error{{type of expression is ambiguous without a type annotation}}
+  let s = #stringify<Int, Int>(a + b) // expected-error{{generic type 'stringify' specialized with too many type parameters (got 2, but expected 1)}}
 
   _ = #stringify()
   // expected-error@-1{{missing argument for parameter #1 in macro expansion}}