refactor(@schematics/angular): add jsonc-parser to parse and modify JSON files

Currently, interaction with JSON AST is complex and requires a lot of boiler-platting. With this change we add `jsonc-parser` and add a basic helper class to greatly simplify such interaction.

This would come in handle when writing new migrations in 10.1+

**Note**: this is a private implementation and shouldn't be used by 3rd parties.

Author: alan-agius4

package.json

@@ -157,6 +157,7 @@
     "jasmine-spec-reporter": "~5.0.0",
     "jest-worker": "26.0.0",
     "jquery": "^3.3.1",
+    "jsonc-parser": "2.2.1",
     "karma": "~5.0.0",
     "karma-chrome-launcher": "~3.1.0",
     "karma-coverage-istanbul-reporter": "~3.0.0",

packages/schematics/angular/BUILD.bazel

@@ -82,6 +82,7 @@ ts_library(
         "@npm//@types/browserslist",
         "@npm//@types/caniuse-lite",
         "@npm//@types/node",
+        "@npm//jsonc-parser",
         "@npm//rxjs",
         "@npm//tslint",
     ],
@@ -119,6 +120,7 @@ ts_library(
         "//packages/schematics/angular/third_party/github.com/Microsoft/TypeScript",
         "@npm//@types/browserslist",
         "@npm//@types/caniuse-lite",
+        "@npm//jsonc-parser",
         "@npm//rxjs",
         "@npm//tslint",
     ],

packages/schematics/angular/package.json

@@ -10,6 +10,7 @@
   "schematics": "./collection.json",
   "dependencies": {
     "@angular-devkit/core": "0.0.0",
-    "@angular-devkit/schematics": "0.0.0"
+    "@angular-devkit/schematics": "0.0.0",
+    "jsonc-parser": "2.2.1"
   }
 }

packages/schematics/angular/utility/json-file.ts

@@ -0,0 +1,82 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import { JsonValue } from '@angular-devkit/core';
+import { Tree } from '@angular-devkit/schematics';
+import { Node, applyEdits, findNodeAtLocation, getNodeValue, modify, parseTree } from 'jsonc-parser';
+
+export type JSONPath = (string | number)[];
+
+/** @internal */
+export class JSONFile {
+  private content: string;
+  error: undefined | Error;
+
+  constructor(
+    private readonly host: Tree,
+    private readonly path: string,
+  ) {
+    const buffer = this.host.read(this.path);
+    if (buffer) {
+      this.content = buffer.toString();
+    } else {
+      this.error = new Error(`Could not read ${path}.`);
+    }
+  }
+
+  private _jsonAst: Node | undefined;
+  private get JsonAst(): Node {
+    if (this._jsonAst) {
+      return this._jsonAst;
+    }
+
+    this._jsonAst = parseTree(this.content);
+
+    return this._jsonAst;
+  }
+
+  get(jsonPath: JSONPath): unknown {
+    if (jsonPath.length === 0) {
+      return getNodeValue(this.JsonAst);
+    }
+
+    const node = findNodeAtLocation(this.JsonAst, jsonPath);
+
+    return node === undefined ? undefined : getNodeValue(node);
+  }
+
+  modify(jsonPath: JSONPath, value: JsonValue | undefined, getInsertionIndex?: (properties: string[]) => number): void {
+    if (!getInsertionIndex) {
+      const property = jsonPath.slice(-1)[0];
+      getInsertionIndex = properties => [...properties, property].sort().findIndex(p => p === property);
+    }
+
+    const edits = modify(
+      this.content,
+      jsonPath,
+      value,
+      {
+        getInsertionIndex,
+        formattingOptions: {
+          insertSpaces: true,
+          tabSize: 2,
+        },
+      },
+    );
+
+    this.content = applyEdits(this.content, edits);
+    this.host.overwrite(this.path, this.content);
+    this._jsonAst = undefined;
+  }
+
+  remove(jsonPath: JSONPath): void {
+    if (this.get(jsonPath) !== undefined) {
+      this.modify(jsonPath, undefined);
+    }
+  }
+}

yarn.lock

@@ -7832,6 +7832,11 @@ json5@^2.1.0, json5@^2.1.2:
   dependencies:
     minimist "^1.2.5"
 
+[email protected]:
+  version "2.2.1"
+  resolved "https://registry.yarnpkg.com/jsonc-parser/-/jsonc-parser-2.2.1.tgz#db73cd59d78cce28723199466b2a03d1be1df2bc"
+  integrity sha512-o6/yDBYccGvTz1+QFevz6l6OBZ2+fMVu2JZ9CIhzsYRX4mjaK5IyX9eldUdCmga16zlgQxyrj5pt9kzuj2C02w==
+
 jsonfile@^4.0.0:
   version "4.0.0"
   resolved "https://registry.yarnpkg.com/jsonfile/-/jsonfile-4.0.0.tgz#8771aae0799b64076b76640fca058f9c10e33ecb"