Fix a crash when transforming functions in modules.

When transforming a module declaration and block, parse tree nodes
contained in the module block have their parent pointers reset due to
`shouldEmitModuleDeclaration` calling into `isInstantiatedModule`, which
needs to set parent pointers to operate.

That causes a crash when later transforming any nodes within the module,
as retrieving their source file in `getSourceFileOfNode` (via
`getOrCreateEmitNode`) fails, due to their new synthesized parent nodes
not being in a source file.

This change avoids the issue by using the parse tree node in `ts.ts` to
decide whether a module declaration should be emitted (i.e. whether the
module contains values).

This means transformers cannot add values to modules that previously did
not contain any.

Fixes microsoft#34644.

src/compiler/transformers/ts.ts

@@ -2452,7 +2452,12 @@ namespace ts {
          *
          * @param node The module declaration node.
          */
-        function shouldEmitModuleDeclaration(node: ModuleDeclaration) {
+        function shouldEmitModuleDeclaration(nodeIn: ModuleDeclaration) {
+            const node = getParseTreeNode(nodeIn, isModuleDeclaration);
+            if (!node) {
+                // If we can't find a parse tree node, assume the node is instantiated.
+                return true;
+            }
             return isInstantiatedModule(node, !!compilerOptions.preserveConstEnums || !!compilerOptions.isolatedModules);
         }
 

src/testRunner/unittests/transform.ts

@@ -447,6 +447,35 @@ namespace Foo {
             }).outputText;
         });
 
+        testBaseline("transformUpdateModuleMember", () => {
+            return transpileModule(`
+module MyModule {
+    const myVariable = 1;
+    function foo(param: string) {}
+}
+`, {
+                transformers: {
+                    before: [renameVariable],
+                },
+                compilerOptions: {
+                    target: ScriptTarget.ES2015,
+                    newLine: NewLineKind.CarriageReturnLineFeed,
+                }
+            }).outputText;
+
+            function renameVariable(context: TransformationContext) {
+                    return (sourceFile: SourceFile): SourceFile => {
+                        return visitNode(sourceFile, rootTransform, isSourceFile);
+                    };
+                    function rootTransform<T extends Node>(node: T): Node {
+                        if (isVariableDeclaration(node)) {
+                            return updateVariableDeclaration(node, createIdentifier("newName"), /* type */ undefined, node.initializer);
+                        }
+                        return visitEachChild(node, rootTransform, context);
+                    }
+            }
+        });
+
         // https://github.com/Microsoft/TypeScript/issues/24709
         testBaseline("issue24709", () => {
             const fs = vfs.createFromFileSystem(Harness.IO, /*caseSensitive*/ true);

tests/baselines/reference/transformApi/transformsCorrectly.transformUpdateModuleMember.js

@@ -0,0 +1,5 @@
+var MyModule;
+(function (MyModule) {
+    const newName = 1;
+    function foo(param) { }
+})(MyModule || (MyModule = {}));