fix(ngcc): handle aliases in UMD export declarations (#38959)

Sometimes UMD exports appear in the following form:

```
exports.MyClass = alias1 = alias2 = <<declaration>>
```

Previously the declaration of the export would have been captured
as `alias1 = alias2 = <<declaration>>`, which the `PartialInterpreter`
would have failed on, since it cannot handle assignments.

Now we skip over these aliases capturing only the `<<declaration>>`
expression.

Fixes #38947

PR Close #38959

packages/compiler-cli/ngcc/src/host/esm2015_host.ts

@@ -2311,7 +2311,7 @@ function isInitializedVariableClassDeclaration(node: ts.Node):
  * var MyClass = alias1 = alias2 = <<declaration>>
  * ```
  *
- * @node the LHS of a variable declaration.
+ * @param node the LHS of a variable declaration.
  * @returns the original AST node or the RHS of a series of assignments in a variable
  *     declaration.
  */

packages/compiler-cli/ngcc/src/host/umd_host.ts

@@ -15,6 +15,7 @@ import {BundleProgram} from '../packages/bundle_program';
 import {FactoryMap, getTsHelperFnFromIdentifier, stripExtension} from '../utils';
 
 import {DefinePropertyReexportStatement, ExportDeclaration, ExportsStatement, extractGetterFnExpression, findNamespaceOfIdentifier, findRequireCallReference, isDefinePropertyReexportStatement, isExportsStatement, isExternalImport, isRequireCall, isWildcardReexportStatement, WildcardReexportStatement} from './commonjs_umd_utils';
+import {isAssignment} from './esm2015_host';
 import {Esm5ReflectionHost} from './esm5_host';
 import {stripParentheses} from './utils';
 
@@ -134,7 +135,7 @@ export class UmdReflectionHost extends Esm5ReflectionHost {
 
   private extractBasicUmdExportDeclaration(statement: ExportsStatement): ExportDeclaration {
     const name = statement.expression.left.name.text;
-    const exportExpression = statement.expression.right;
+    const exportExpression = skipAliases(statement.expression.right);
     return this.extractUmdExportDeclaration(name, exportExpression);
   }
 
@@ -400,3 +401,20 @@ function getRequiredModulePath(wrapperFn: ts.FunctionExpression, paramIndex: num
 export function isExportIdentifier(node: ts.Node): node is ts.Identifier {
   return ts.isIdentifier(node) && node.text === 'exports';
 }
+
+/**
+ * Find the far right hand side of a sequence of aliased assignements of the form
+ *
+ * ```
+ * exports.MyClass = alias1 = alias2 = <<declaration>>
+ * ```
+ *
+ * @param node the expression to parse
+ * @returns the original `node` or the far right expression of a series of assignments.
+ */
+export function skipAliases(node: ts.Expression): ts.Expression {
+  while (isAssignment(node)) {
+    node = node.right;
+  }
+  return node;
+}

packages/compiler-cli/ngcc/test/host/umd_host_spec.ts

@@ -638,7 +638,8 @@ runInEachFileSystem(() => {
               `  exports.d = b;\n` +
               `  exports.e = e;\n` +
               `  exports.DirectiveX = core.Directive;\n` +
-              `  exports.SomeClass = SomeClass;\n` +
+              `  var SomeClass_1;\n` +
+              `  exports.SomeClass = SomeClass_1 = SomeClass;\n` +
               `})));\n`,
         },
         {