add test

src/testRunner/unittests/reuseProgramStructure.ts

@@ -399,6 +399,29 @@ namespace ts {
             assert.isDefined(program2.getSourceFile("/a.ts")!.resolvedModules!.get("a"), "'a' is not an unresolved module after re-use");
         });
 
+        it("works with updated SourceFiles", () => {
+            const files = [
+                { name: "/a.ts", text: SourceText.New("", "", 'import * as a from "a";a;') },
+                { name: "/types/zzz/index.d.ts", text: SourceText.New("", "", 'declare module "a" { }') },
+            ];
+            const host = createTestCompilerHost(files, target);
+            const options: CompilerOptions = { target, typeRoots: ["/types"] };
+            const program1 = createProgram(["/a.ts"], options, host);
+            let sourceFile = program1.getSourceFile("/a.ts")!;
+            assert.isDefined(sourceFile, "'/a.ts' is included in the program");
+            sourceFile = updateSourceFile(sourceFile, "'use strict';" + sourceFile.text, { newLength: "'use strict';".length, span: { start: 0, length: 0 } });
+            assert.strictEqual(sourceFile.statements[2].getSourceFile(), sourceFile, "parent pointers are updated");
+            const updateHost: TestCompilerHost = {
+                ...host,
+                getSourceFile(fileName) {
+                    return fileName === sourceFile.fileName ? sourceFile : program1.getSourceFile(fileName);
+                }
+            };
+            const program2 = createProgram(["/a.ts"], options, updateHost, program1);
+            assert.isDefined(program2.getSourceFile("/a.ts")!.resolvedModules!.get("a"), "'a' is not an unresolved module after re-use");
+            assert.strictEqual(sourceFile.statements[2].getSourceFile(), sourceFile, "parent pointers are not altered");
+        });
+
         it("resolved type directives cache follows type directives", () => {
             const files = [
                 { name: "/a.ts", text: SourceText.New("/// <reference types='typedefs'/>", "", "var x = $") },