[Variadic Generics] fixit for pack expansion on a non-pack generic type

Author: sophiapoirier

lib/Sema/TypeCheckType.cpp

@@ -4579,8 +4579,15 @@ NeverNullType TypeResolver::resolvePackElement(PackElementTypeRepr *repr,
     return ErrorType::get(ctx);
 
   if (!packReference->isParameterPack()) {
-    ctx.Diags.diagnose(repr->getLoc(), diag::each_non_pack,
-                       packReference);
+    auto diag =
+        ctx.Diags.diagnose(repr->getLoc(), diag::each_non_pack, packReference);
+    if (auto *packIdent = dyn_cast<IdentTypeRepr>(repr->getPackType())) {
+      if (auto *packIdentBinding = packIdent->getBoundDecl()) {
+        if (packIdentBinding->getLoc().isValid()) {
+          diag.fixItInsert(packIdentBinding->getLoc(), "each ");
+        }
+      }
+    }
     return packReference;
   }
 

test/Constraints/pack-expansion-expressions.swift

@@ -91,10 +91,14 @@ func returnRepeatTuple<each T>(_ t: repeat each T) -> (repeat T) { // expected-e
   fatalError()
 }
 
-func paremeterAsPackTypeWithoutExpansion<each T>(_ t: T) -> repeat each T { // expected-error {{variadic expansion 'T' cannot appear outside of a function parameter list, function result, tuple element or generic argument list}}
+func parameterAsPackTypeWithoutExpansion<each T>(_ t: T) -> repeat each T { // expected-error {{variadic expansion 'T' cannot appear outside of a function parameter list, function result, tuple element or generic argument list}}
   fatalError()
 }
 
+func expansionOfNonPackType<T>(_ t: repeat each T) {}
+// expected-error@-1 {{'each' cannot be applied to non-pack type 'T'}}{{29-29=each }}
+// expected-error@-2 {{variadic expansion 'T' must contain at least one variadic generic parameter}}
+
 func tupleExpansion<each T, each U>(
   _ tuple1: (repeat each T),
   _ tuple2: (repeat each U)