migrator: avoid inserting helper functions if a function with the same name exists in the source file. rdar://40108285

lib/Migrator/APIDiffMigratorPass.cpp

@@ -309,7 +309,15 @@ struct APIDiffMigratorPass : public ASTMigratorPass, public SourceEntityWalker {
   APIDiffMigratorPass(EditorAdapter &Editor, SourceFile *SF,
                       const MigratorOptions &Opts):
     ASTMigratorPass(Editor, SF, Opts),
-    FileEndLoc(SM.getRangeForBuffer(BufferID).getEnd()) {}
+    FileEndLoc(SM.getRangeForBuffer(BufferID).getEnd()) {
+      SmallVector<Decl*, 16> TopDecls;
+      SF->getTopLevelDecls(TopDecls);
+      for (auto *D: TopDecls) {
+        if (auto *FD = dyn_cast<FuncDecl>(D)) {
+          InsertedFunctions.insert(FD->getBaseName().getIdentifier().str());
+        }
+      }
+    }
 
   void run() {
     if (Opts.APIDigesterDataStorePaths.empty())

test/Migrator/avoid_insert_existing_functions.swift

@@ -0,0 +1,22 @@
+// REQUIRES: objc_interop
+// RUN: %empty-directory(%t.mod)
+// RUN: %target-swift-frontend -emit-module -o %t.mod/Cities.swiftmodule %S/Inputs/Cities.swift -module-name Cities -parse-as-library
+// RUN: %empty-directory(%t) && %target-swift-frontend -c -update-code -primary-file %s  -I %t.mod -api-diff-data-file %S/Inputs/string-representable.json -emit-migrated-file-path %t/avoid_insert_existing_functions.swift.result -disable-migrator-fixits -o /dev/null
+// RUN: diff -u %S/avoid_insert_existing_functions.swift.expected %t/avoid_insert_existing_functions.swift.result
+
+import Cities
+
+typealias NewAttribute = String
+
+func foo(_ c: Container) -> String {
+  c.Value = ""
+  return c.Value
+}
+
+fileprivate func convertToNewAttribute(_ input: String) -> NewAttribute {
+ return ""
+}
+
+fileprivate func convertFromNewAttribute(_ input: NewAttribute) -> String {
+ return ""
+}

test/Migrator/avoid_insert_existing_functions.swift.expected

@@ -0,0 +1,22 @@
+// REQUIRES: objc_interop
+// RUN: %empty-directory(%t.mod)
+// RUN: %target-swift-frontend -emit-module -o %t.mod/Cities.swiftmodule %S/Inputs/Cities.swift -module-name Cities -parse-as-library
+// RUN: %empty-directory(%t) && %target-swift-frontend -c -update-code -primary-file %s  -I %t.mod -api-diff-data-file %S/Inputs/string-representable.json -emit-migrated-file-path %t/avoid_insert_existing_functions.swift.result -disable-migrator-fixits -o /dev/null
+// RUN: diff -u %S/avoid_insert_existing_functions.swift.expected %t/avoid_insert_existing_functions.swift.result
+
+import Cities
+
+typealias NewAttribute = String
+
+func foo(_ c: Container) -> String {
+  c.Value = convertToNewAttribute("")
+  return convertFromNewAttribute(c.Value)
+}
+
+fileprivate func convertToNewAttribute(_ input: String) -> NewAttribute {
+ return ""
+}
+
+fileprivate func convertFromNewAttribute(_ input: NewAttribute) -> String {
+ return ""
+}