[Diagnostics] Don't print pack element archetypes in diagnostics

Author: xedin

lib/Sema/CSDiagnostics.h

@@ -22,6 +22,7 @@
 #include "swift/AST/Decl.h"
 #include "swift/AST/DiagnosticEngine.h"
 #include "swift/AST/Expr.h"
+#include "swift/AST/GenericEnvironment.h"
 #include "swift/AST/Identifier.h"
 #include "swift/AST/OperatorNameLookup.h"
 #include "swift/AST/Types.h"
@@ -123,6 +124,11 @@ class FailureDiagnostic {
         return resolvedType->is<UnresolvedType>() && GP ? GP : resolvedType;
       }
 
+      if (type->hasElementArchetype()) {
+        auto *env = getDC()->getGenericEnvironmentOfContext();
+        return env->mapElementTypeIntoPackContext(type);
+      }
+
       if (auto *packType = type->getAs<PackType>()) {
         if (packType->getNumElements() == 1) {
           auto eltType = resolveType(packType->getElementType(0));

test/Constraints/pack-expansion-expressions.swift

@@ -66,18 +66,16 @@ func outerArchetype<each T, U>(t: repeat each T, u: U) where repeat each T: P {
 func sameElement<each T, U>(t: repeat each T, u: U) where repeat each T: P, repeat each T == U {
 // expected-error@-1{{same-element requirements are not yet supported}}
 
-  // FIXME: Opened element archetypes in diagnostics
   let _: (repeat each T) = (repeat (each t).f(u))
-  // expected-error@-1 {{cannot convert value of type 'U' to expected argument type 'τ_1_0'}}
+  // expected-error@-1 {{cannot convert value of type 'U' to expected argument type 'each T'}}
 }
 
 func forEachEach<each C, U>(c: repeat each C, function: (U) -> Void)
     where repeat each C: Collection, repeat (each C).Element == U {
     // expected-error@-1{{same-element requirements are not yet supported}}
 
-  // FIXME: Opened element archetypes in diagnostics
   _ = (repeat (each c).forEach(function))
-  // expected-error@-1 {{cannot convert value of type '(U) -> Void' to expected argument type '(τ_1_0.Element) throws -> Void'}}
+  // expected-error@-1 {{cannot convert value of type '(U) -> Void' to expected argument type '(each C.Element) throws -> Void'}}
 }
 
 func typeReprPacks<each T: ExpressibleByIntegerLiteral>(_ t: repeat each T) {