fixup! feat(material/schematics): set up a system for migrating scss …

…* also implements the migrator for the button

src/material/schematics/ng-generate/mdc-migration/index.ts

@@ -62,9 +62,8 @@ export default function (options: Schema): Rule {
   console.log('Directory:', migrationDir);
 
   const migrators: StyleMigrator[] = [];
-  const components = [...componentsToMigrate];
   for (let i = 0; i < MIGRATORS.length; i++) {
-    if (components.includes(MIGRATORS[i].component)) {
+    if (componentsToMigrate.has(MIGRATORS[i].component)) {
       migrators.push(MIGRATORS[i]);
     }
   }

src/material/schematics/ng-generate/mdc-migration/rules/style-migrator.ts

@@ -12,6 +12,7 @@ import * as postcss from 'postcss';
 export interface ClassNameChange {
   /** The legacy class name. */
   old: string;
+
   /** The new class name. */
   new: string;
 }
@@ -24,6 +25,8 @@ export interface MixinChange {
   /** The name(s) of the new scss mixin(s). */
   new: string[];
 }
+
+/** StyleMigrator implements the basic case for migrating old component styles to new ones. */
 export abstract class StyleMigrator {
   /** The name of the component that this migration handles. */
   abstract component: string;
@@ -54,7 +57,11 @@ export abstract class StyleMigrator {
   replaceMixin(namespace: string, atRule: postcss.AtRule): void {
     const change = this.mixinChanges.find(c => {
       return atRule.params.includes(`${namespace}.${c.old}`);
-    })!;
+    });
+
+    if (!change) {
+      return;
+    }
 
     // Cloning & inserting the first node before changing the
     // indentation preserves the indentation of the first node (e.g. 3 newlines).