[SIL] Fix computation of substituted error type against an abstraction pattern

We were attempting to perform substitution against the original pattern
even when it didn't have a substitution map, and then trying to cover
for the resulting errors by adjusting to `any Error`... which isn't
always correct. Do the substitution only when it makes sense.

Fixes rdar://119217570 & rdar://119219214.

Author: DougGregor

lib/SIL/IR/AbstractionPattern.cpp

@@ -1264,33 +1264,32 @@ AbstractionPattern::getFunctionThrownErrorType(
     return llvm::None;
 
   auto &ctx = substFnInterfaceType->getASTContext();
-  auto optErrorType = substFnInterfaceType->getEffectiveThrownErrorType();
+  auto substErrorType = substFnInterfaceType->getEffectiveThrownErrorType();
 
   if (isTypeParameterOrOpaqueArchetype()) {
-    if (!optErrorType)
+    if (!substErrorType)
       return llvm::None;
 
-    if (!(*optErrorType)->isEqual(ctx.getErrorExistentialType())) {
+    if (!(*substErrorType)->isEqual(ctx.getErrorExistentialType())) {
       llvm::errs() << "unsupported reabstraction\n";
       abort();
     }
 
-    return std::make_pair(AbstractionPattern(*optErrorType),
-                          (*optErrorType)->getCanonicalType());
+    return std::make_pair(AbstractionPattern(*substErrorType),
+                          (*substErrorType)->getCanonicalType());
   }
 
-  if (!optErrorType) {
-    Type origErrorSubstType =
-        optOrigErrorType->getType()
-          .subst(optOrigErrorType->getGenericSubstitutions());
-    if (origErrorSubstType->isNever())
-      optErrorType = ctx.getNeverType();
-    else
-      optErrorType = ctx.getErrorExistentialType();
+  if (!substErrorType) {
+    Type origErrorSubstType;
+    if (auto errorSubs = optOrigErrorType->getGenericSubstitutions()) {
+      substErrorType = optOrigErrorType->getType().subst(errorSubs);
+    } else {
+      substErrorType = optOrigErrorType->getType();
+    }
   }
 
   return std::make_pair(*optOrigErrorType,
-                        (*optErrorType)->getCanonicalType());
+                        (*substErrorType)->getCanonicalType());
 }
 
 AbstractionPattern

test/SILGen/typed_throws.swift

@@ -177,6 +177,27 @@ func forceTryErased() {
   try! mightThrowAny(arg: throwsMyBigErrorOrReturnsInt())
 }
 
+func takesClosureThrowingConcrete(_ body: () throws(MyError) -> ()) throws(MyError) {
+}
+
+// CHECK-LABEL: sil private [ossa] @$s12typed_throws30passesClosureWithReabstraction5countySi_tFyyXEfU_ : $@convention(thin) () -> @error MyError
+// CHECK: bb0:
+// CHECK-NEXT: debug_value undef : $MyError, var, name "$error", argno 1
+func passesClosureWithReabstraction(count: Int) {
+    try! takesClosureThrowingConcrete { }
+}
+
+func takesClosureThrowingConcreteAndRethrows(_ body: () throws(MyError) -> ()) rethrows {
+}
+
+// CHECK-LABEL: sil private [ossa] @$s12typed_throws42passesClosureWithReabstractionToRethrowing5countySi_tFyyXEfU_ : $@convention(thin) () -> @error MyError {
+// CHECK: bb0:
+// CHECK-NEXT:  debug_value undef : $MyError, var, name "$error", argno 1
+func passesClosureWithReabstractionToRethrowing(count: Int) {
+    try! takesClosureThrowingConcrete { }
+}
+
+
 // CHECK-LABEL:      sil_vtable MySubclass {
 // CHECK-NEXT:   #MyClass.init!allocator: <E where E : Error> (MyClass.Type) -> (() throws(E) -> ()) throws(E) -> MyClass : @$s12typed_throws10MySubclassC4bodyACyyxYKXE_txYKcs5ErrorRzlufC [override]
 // CHECK-NEXT:  #MyClass.f: (MyClass) -> () throws -> () : @$s12typed_throws10MySubclassC1fyyAA0C5ErrorOYKFAA0C5ClassCADyyKFTV [override]

test/SILGen/typed_throws_generic.swift

@@ -310,8 +310,8 @@ struct UntypedRes<Success>: P {
 }
 
 struct InfallibleRes<Success>: P {
-  // CHECK-LABEL: sil private [transparent] [thunk] [ossa] @$s20typed_throws_generic13InfallibleResVyxGAA1PA2aEP1fyy1EQzYKFTW : $@convention(witness_method: P) <τ_0_0> (@in_guaranteed InfallibleRes<τ_0_0>) -> @error_indirect any Error
-  // CHECK: bb0(%0 : $*any Error, %1 : $*InfallibleRes<τ_0_0>):
+  // CHECK-LABEL: sil private [transparent] [thunk] [ossa] @$s20typed_throws_generic13InfallibleResVyxGAA1PA2aEP1fyy1EQzYKFTW : $@convention(witness_method: P) <τ_0_0> (@in_guaranteed InfallibleRes<τ_0_0>) -> @error_indirect τ_0_0.E
+  // CHECK: bb0(%0 : $*@error_type τ_0_0.E, %1 : $*InfallibleRes<τ_0_0>):
   // CHECK: [[SELF:%.*]] = load [trivial] %1 : $*InfallibleRes<τ_0_0>
   // CHECK: [[WITNESS:%.*]] = function_ref @$s20typed_throws_generic13InfallibleResV1fyyF : $@convention(method) <τ_0_0> (InfallibleRes<τ_0_0>) -> ()
   // CHECK: = apply [[WITNESS]]<τ_0_0>([[SELF]]) : $@convention(method) <τ_0_0> (InfallibleRes<τ_0_0>)