fix SourceLoc-related crasher and add tests

Author: Marc Rasi

lib/Sema/DerivedConformanceDifferentiable.cpp

@@ -725,10 +725,12 @@ getOrSynthesizeTangentVectorStruct(DerivedConformance &derived, Identifier id) {
   SmallVector<VarDecl *, 8> diffProperties;
   getStoredPropertiesForDifferentiation(nominal, parentDC, diffProperties);
 
+  auto synthesizedLoc = derived.ConformanceDecl->getEndLoc();
   auto *structDecl =
-      new (C) StructDecl(SourceLoc(), C.Id_TangentVector, SourceLoc(),
+      new (C) StructDecl(synthesizedLoc, C.Id_TangentVector, synthesizedLoc,
                          /*Inherited*/ C.AllocateCopy(tvDesiredProtoTypeLocs),
                          /*GenericParams*/ {}, parentDC);
+  structDecl->setBraces({synthesizedLoc, synthesizedLoc});
   structDecl->setImplicit();
   structDecl->copyFormalAccessFrom(nominal, /*sourceIsParentContext*/ true);
 

test/AutoDiff/Sema/DerivedConformances/derived_differentiable.swift

@@ -135,3 +135,24 @@ extension AutoDeriveEncodableTV2: TangentVectorMustBeEncodable {}
 
 // CHECK-AST-LABEL: extension AutoDeriveEncodableTV2 : TangentVectorMustBeEncodable {
 // CHECK-AST:   internal struct TangentVector : {{(Encodable, Differentiable, AdditiveArithmetic)|(Encodable, AdditiveArithmetic, Differentiable)|(Differentiable, Encodable, AdditiveArithmetic)|(AdditiveArithmetic, Encodable, Differentiable)|(Differentiable, AdditiveArithmetic, Encodable)|(AdditiveArithmetic, Differentiable, Encodable)}} {
+
+protocol TangentVectorP: Differentiable {
+  var requirement: Int { get }
+}
+
+protocol TangentVectorConstrained: Differentiable where TangentVector: TangentVectorP {}
+
+struct StructWithTangentVectorConstrained: TangentVectorConstrained {
+  var x: Float
+}
+
+// `extension StructWithTangentVectorConstrained.TangentVector: TangentVectorP` gives
+// "error: type 'StructWithTangentVectorConstrained.TangentVector' does not conform to protocol 'TangentVectorP'",
+// maybe because it typechecks the conformance before seeing the extension. But this roundabout way
+// of stating the same thing works.
+extension TangentVectorP where Self == StructWithTangentVectorConstrained.TangentVector {
+  var requirement: Int { 42 }
+}
+
+// CHECK-AST-LABEL: internal struct StructWithTangentVectorConstrained : TangentVectorConstrained {
+// CHECK-AST:   internal struct TangentVector : {{(TangentVectorP, Differentiable, AdditiveArithmetic)|(TangentVectorP, AdditiveArithmetic, Differentiable)|(Differentiable, TangentVectorP, AdditiveArithmetic)|(AdditiveArithmetic, TangentVectorP, Differentiable)|(Differentiable, AdditiveArithmetic, TangentVectorP)|(AdditiveArithmetic, Differentiable, TangentVectorP)}} {

test/AutoDiff/Sema/DerivedConformances/derived_differentiable_diagnostics.swift

@@ -0,0 +1,15 @@
+// RUN: %target-swift-frontend -typecheck -verify %s
+
+import _Differentiation
+
+protocol TangentVectorP: Differentiable {
+  // expected-note @+1 {{protocol requires property 'requirement' with type 'Int'; do you want to add a stub?}}
+  var requirement: Int { get }
+}
+
+protocol TangentVectorConstrained: Differentiable where TangentVector: TangentVectorP {}
+
+struct StructWithTangentVectorConstrained: TangentVectorConstrained {
+  var x: Float
+}
+// expected-error @-1 {{type 'StructWithTangentVectorConstrained.TangentVector' does not conform to protocol 'TangentVectorP'}}