[AutoDiff] NFC: move isDifferentiableProgrammingEnabled.

Move `isDifferentiableProgrammingEnabled` to AutoDiff.h so it's more accessible.

Author: dan-zheng

include/swift/AST/AutoDiff.h

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2019 Apple Inc. and the Swift project authors
+// Copyright (c) 2019 - 2020 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See https://swift.org/LICENSE.txt for license information
@@ -31,6 +31,7 @@
 namespace swift {
 
 class AnyFunctionType;
+class SourceFile;
 class SILFunctionType;
 class TupleType;
 
@@ -392,6 +393,9 @@ class TangentSpace {
 /// derivative generic signature.
 using SILDifferentiabilityWitnessKey = std::pair<StringRef, AutoDiffConfig>;
 
+/// Returns `true` iff differentiable programming is enabled.
+bool isDifferentiableProgrammingEnabled(SourceFile &SF);
+
 /// Automatic differentiation utility namespace.
 namespace autodiff {
 

lib/AST/AutoDiff.cpp

@@ -13,6 +13,7 @@
 #include "swift/AST/AutoDiff.h"
 #include "swift/AST/ASTContext.h"
 #include "swift/AST/GenericEnvironment.h"
+#include "swift/AST/ImportCache.h"
 #include "swift/AST/Module.h"
 #include "swift/AST/TypeCheckRequests.h"
 #include "swift/AST/Types.h"
@@ -124,6 +125,23 @@ void AutoDiffConfig::print(llvm::raw_ostream &s) const {
   s << ')';
 }
 
+bool swift::isDifferentiableProgrammingEnabled(SourceFile &SF) {
+  auto &ctx = SF.getASTContext();
+  // Return true if differentiable programming is explicitly enabled.
+  if (ctx.LangOpts.EnableExperimentalDifferentiableProgramming)
+    return true;
+  // Otherwise, return true iff the `_Differentiation` module is imported in
+  // the given source file.
+  bool importsDifferentiationModule = false;
+  for (auto import : namelookup::getAllImports(&SF)) {
+    if (import.second->getName() == ctx.Id_Differentiation) {
+      importsDifferentiationModule = true;
+      break;
+    }
+  }
+  return importsDifferentiationModule;
+}
+
 // TODO(TF-874): This helper is inefficient and should be removed. Unwrapping at
 // most once (for curried method types) is sufficient.
 static void unwrapCurryLevels(AnyFunctionType *fnTy,

lib/Sema/TypeChecker.cpp

@@ -410,23 +410,6 @@ void swift::performWholeModuleTypeChecking(SourceFile &SF) {
 #endif
 }
 
-bool swift::isDifferentiableProgrammingEnabled(SourceFile &SF) {
-  auto &ctx = SF.getASTContext();
-  // Return true if differentiable programming is explicitly enabled.
-  if (ctx.LangOpts.EnableExperimentalDifferentiableProgramming)
-    return true;
-  // Otherwise, return true iff the `_Differentiation` module is imported in
-  // the given source file.
-  bool importsDifferentiationModule = false;
-  for (auto import : namelookup::getAllImports(&SF)) {
-    if (import.second->getName() == ctx.Id_Differentiation) {
-      importsDifferentiationModule = true;
-      break;
-    }
-  }
-  return importsDifferentiationModule;
-}
-
 bool swift::isAdditiveArithmeticConformanceDerivationEnabled(SourceFile &SF) {
   auto &ctx = SF.getASTContext();
   // Return true if `AdditiveArithmetic` derived conformances are explicitly

lib/Sema/TypeChecker.h

@@ -1520,9 +1520,6 @@ bool isMemberOperator(FuncDecl *decl, Type type);
 /// Complain if @objc or dynamic is used without importing Foundation.
 void diagnoseAttrsRequiringFoundation(SourceFile &SF);
 
-/// Returns `true` iff differentiable programming is enabled.
-bool isDifferentiableProgrammingEnabled(SourceFile &SF);
-
 /// Returns `true` iff `AdditiveArithmetic` derived conformances are enabled.
 bool isAdditiveArithmeticConformanceDerivationEnabled(SourceFile &SF);