prettierx: make flow-parser an optional dependency

- move flow-parser to devDependencies
- specify as optional in peerDependenciesMeta
- update dependency notes in package.json
- disable import/no-extraneous-dependencies when importing flow-parser
  in src/language-js/parser-flow.js
- add a few more comments

package.json

@@ -23,8 +23,8 @@
     "* installing dependencies from GitHub is not desired in prettierx",
     "  due to a possible issue with firewalls in certain organizations",
     "* latest updates of ci-info from GitHub are not needed for prettierx",
-    "* typescript is moved to devDependencies, and",
-    "  it is specified as optional in peerDependenciesMeta",
+    "* flow-parser & typescript are moved to devDependencies, and",
+    "  they are specified as optional in peerDependenciesMeta",
     "* codecov is removed from devDependencies",
     "<!-- -->"
   ],
@@ -52,7 +52,6 @@
     "fast-glob": "3.2.4",
     "find-parent-dir": "0.3.0",
     "find-project-root": "1.1.1",
-    "flow-parser": "0.122.0",
     "get-stream": "6.0.0",
     "globby": "11.0.1",
     "graphql": "15.3.0",
@@ -109,6 +108,7 @@
     "eslint-plugin-react": "7.20.5",
     "eslint-plugin-unicorn": "21.0.0",
     "execa": "4.0.3",
+    "flow-parser": "0.122.0",
     "jest": "26.3.0",
     "jest-snapshot-serializer-ansi": "1.0.0",
     "jest-snapshot-serializer-raw": "1.1.0",
@@ -129,6 +129,9 @@
     "webpack": "4.44.1"
   },
   "peerDependenciesMeta": {
+    "flow-parser": {
+      "optional": true
+    },
     "typescript": {
       "optional": true
     }

src/language-js/index.js

@@ -15,7 +15,8 @@ const languages = [
   createLanguage(require("linguist-languages/data/JavaScript"), () => ({
     name: "Flow",
     since: "0.0.0",
-    parsers: ["babel", "flow"],
+    parsers: ["babel", "flow"], // [prettierx] must use Babel by default
+    // (since the flow-parser is now an optional dependency in prettierx)
     vscodeLanguageIds: ["javascript"],
     aliases: [],
     filenames: [],

src/language-js/parser-flow.js

@@ -7,7 +7,9 @@ const locFns = require("./loc");
 const postprocess = require("./postprocess");
 
 function parse(text, parsers, opts) {
+  // [prettierx] optional dependency here:
   // Inline the require to avoid loading all the JS if we don't use it
+  // eslint-disable-next-line import/no-extraneous-dependencies
   const flowParser = require("flow-parser");
 
   const ast = flowParser.parse(text, {