[AutoDiff] Add an error when @differentiable attributes do not match.

include/swift/AST/Attr.h

@@ -1508,6 +1508,19 @@ class DifferentiableAttr final
   static bool classof(const DeclAttribute *DA) {
     return DA->getKind() == DAK_Differentiable;
   }
+
+  bool parametersMatch(const DifferentiableAttr &other) const {
+    auto a = getParsedParameters();
+    auto b = other.getParsedParameters();
+    if (a.size() != b.size())
+      return false;
+
+    for (unsigned i = 0, n = b.size(); i < n; ++i) {
+      if (!a[i].isEqual(b[i]))
+        return false;
+    }
+    return true;
+  }
 };
 
 /// \brief Attributes that may be applied to declarations.

include/swift/AST/DiagnosticsSema.def

@@ -2449,6 +2449,8 @@ ERROR(broken_differentiable_requirement,none,
 WARNING(differentiable_implicit_noderivative_fixit,none,
       "stored property has no derivative because it does not conform to "
       "'Differentiable'; add '@noDerivative' to make it explicit", ())
+NOTE(protocol_witness_missing_differentiable_attr,none,
+     "candidate is missing attribute '%0'", (StringRef))
 
 NOTE(codable_extraneous_codingkey_case_here,none,
      "CodingKey case %0 does not match any stored properties", (Identifier))

lib/Sema/TypeCheckProtocol.cpp

@@ -481,6 +481,22 @@ swift::matchWitness(
         cast<AbstractFunctionDecl>(witness)->hasThrows())
       return RequirementMatch(witness, MatchKind::RethrowsConflict);
 
+    // SWIFT_ENABLE_TENSORFLOW
+    // Differentiation attributes must match completely or the generated
+    // functions will have the wrong signature.
+    {
+      auto *reqDifferentiationAttr =
+          reqAttrs.getAttribute<DifferentiableAttr>(/*AllowInvalid*/ true);
+      auto *witnessDifferentiationAttr =
+          witnessAttrs.getAttribute<DifferentiableAttr>(
+              /*AllowInvalid*/ true);
+      if (reqDifferentiationAttr &&
+          (!witnessDifferentiationAttr ||
+           !witnessDifferentiationAttr->parametersMatch(
+               *reqDifferentiationAttr)))
+        return RequirementMatch(witness, MatchKind::DifferentiableConflict);
+    }
+
     // We want to decompose the parameters to handle them separately.
     decomposeFunctionType = true;
   } else if (auto *witnessASD = dyn_cast<AbstractStorageDecl>(witness)) {
@@ -2212,6 +2228,17 @@ diagnoseMatch(ModuleDecl *module, NormalProtocolConformance *conformance,
   case MatchKind::NonObjC:
     diags.diagnose(match.Witness, diag::protocol_witness_not_objc);
     break;
+  // SWIFT_ENABLE_TENSORFLOW
+  case MatchKind::DifferentiableConflict:
+    std::string diffAttrReq;
+    {
+      llvm::raw_string_ostream stream(diffAttrReq);
+      req->getAttrs().getAttribute<DifferentiableAttr>()->print(stream, req);
+    }
+    diags.diagnose(match.Witness,
+                   diag::protocol_witness_missing_differentiable_attr,
+                   diffAttrReq);
+    break;
   }
 }
 

lib/Sema/TypeCheckProtocol.h

@@ -205,6 +205,10 @@ enum class MatchKind : uint8_t {
 
   /// The witness is explicitly @nonobjc but the requirement is @objc.
   NonObjC,
+
+  // SWIFT_ENABLE_TENSORFLOW
+  /// The @differentiable attribute does not match.
+  DifferentiableConflict,
 };
 
 /// Describes the kind of optional adjustment performed when
@@ -418,6 +422,8 @@ struct RequirementMatch {
     case MatchKind::RethrowsConflict:
     case MatchKind::ThrowsConflict:
     case MatchKind::NonObjC:
+      // SWIFT_ENABLE_TENSORFLOW
+    case MatchKind::DifferentiableConflict:
       return false;
     }
 
@@ -446,6 +452,8 @@ struct RequirementMatch {
     case MatchKind::RethrowsConflict:
     case MatchKind::ThrowsConflict:
     case MatchKind::NonObjC:
+      // SWIFT_ENABLE_TENSORFLOW
+    case MatchKind::DifferentiableConflict:
       return false;
     }
 

test/AutoDiff/differentiable_attr_type_checking.swift

@@ -404,3 +404,28 @@ func invalidRequirementConformance<Scalar>(x: Scalar) -> Scalar {
 func invalidRequirementLayout<Scalar>(x: Scalar) -> Scalar {
   return x
 }
+
+
+protocol DiffReq : Differentiable {
+  // expected-note @+2 {{protocol requires function 'f1'}}
+  @differentiable(wrt: (self, x))
+  func f1(_ x: Float) -> Float
+
+  // expected-note @+2 {{protocol requires function 'f2'}}
+  @differentiable(wrt: (self, x, y))
+  func f2(_ x: Float, _ y: Float) -> Float
+}
+
+// expected-error @+1 {{does not conform to protocol}}
+struct ConformingWithErrors : DiffReq {
+  // expected-note @+1 {{@differentiable(wrt: (x, self))}}
+  func f1(_ x: Float) -> Float {
+    return x
+  }
+
+  // expected-note @+2 {{@differentiable(wrt: (x, y, self))}}
+  @differentiable(wrt: (self, x))
+  func f2(_ x: Float, _ y: Float) -> Float {
+    return x + y
+  }
+}

test/AutoDiff/protocol_requirement_autodiff.swift

@@ -51,6 +51,7 @@ struct Quadratic : DiffReq, Equatable {
     self.c = c
   }
 
+  @differentiable(wrt: (self, x))
   func f(_ x: Float) -> Float {
     return a * x * x + b * x + c
   }

test/AutoDiff/witness_table_silgen.swift

@@ -28,6 +28,7 @@ struct S : Proto, VectorNumeric {
     return (p, { dp in S(p: dp) })
   }
 
+  @differentiable()
   func function1(_ x: Float, _ y: Float) -> Float {
     return x + y + p
   }
@@ -48,6 +49,7 @@ struct S : Proto, VectorNumeric {
   // CHECK: apply [[VJP1]]
   // CHECK: } // end sil function 'AD__{{.*}}function1{{.*}}_vjp_SSU'
 
+  @differentiable(wrt: (self, x, y))
   func function2(_ x: Float, _ y: Float) -> Float {
     return x + y + p
   }
@@ -68,6 +70,7 @@ struct S : Proto, VectorNumeric {
   // CHECK: apply [[VJP2]]
   // CHECK: } // end sil function 'AD__{{.*}}function2{{.*}}_vjp_SSS'
 
+  @differentiable(wrt: (y))
   func function3(_ x: Float, _ y: Float) -> Float {
     return x + y + p
   }