discourse: use parser combinators for config (#1824)

Summary:
This patch changes the Discourse plugin’s config parsing to use the
parser combinator approach, which simplifies it and removes the need for
all the tests.

Test Plan:
Prior to deleting the tests, they passed, except for the test that
mirror options could not be partially populated; the partial parsing now
works correctly.

wchargin-branch: discourse-config-combinator

src/plugins/discourse/config.js

@@ -1,67 +1,33 @@
 // @flow
 
-import {type MirrorOptions} from "./mirror";
+import * as Combo from "../../util/combo";
+import {optionsShapeParser, type MirrorOptions} from "./mirror";
 
 export type DiscourseConfig = {|
   +serverUrl: string,
   +mirrorOptions?: $Shape<MirrorOptions>,
 |};
 
-type JsonObject =
+const parser: Combo.Parser<DiscourseConfig> = (() => {
-  | string
+  const C = Combo;
-  | number
+  return C.object(
-  | boolean
+    {
-  | null
+      serverUrl: C.fmap(C.string, (serverUrl) => {
-  | JsonObject[]
-  | {[string]: JsonObject};
-
-export function parseConfig(raw: JsonObject): DiscourseConfig {
-  if (raw == null || typeof raw !== "object" || Array.isArray(raw)) {
-    throw new Error("bad config: " + JSON.stringify(raw));
-  }
-  let mirrorOptions = undefined;
-  const {serverUrl} = raw;
-  if (typeof serverUrl !== "string") {
-    throw new Error("serverUrl not string: " + JSON.stringify(serverUrl));
-  }
         const httpRE = new RegExp(/^https?:\/\//);
         if (!httpRE.test(serverUrl)) {
           throw new Error(
             "expected server url to start with 'https://' or 'http://'"
           );
         }
-  if (raw.mirrorOptions !== undefined) {
+        return serverUrl;
-    const {mirrorOptions: rawMO} = raw;
+      }),
-    if (rawMO == null || typeof rawMO !== "object" || Array.isArray(rawMO)) {
+    },
-      throw new Error("bad config: " + JSON.stringify(rawMO));
+    {
+      mirrorOptions: optionsShapeParser,
     }
-    const {recheckCategoryDefinitionsAfterMs} = rawMO;
+  );
-    let {recheckTopicsInCategories} = rawMO;
+})();
 
-    if (!Array.isArray(recheckTopicsInCategories)) {
+export function parseConfig(raw: Combo.JsonObject): DiscourseConfig {
-      throw new Error(
+  return parser.parseOrThrow(raw);
-        "mirrorOptions.recheckTopicsInCategories must be array, got " +
-          JSON.stringify(recheckTopicsInCategories)
-      );
-    }
-    if (!recheckTopicsInCategories.every((x) => typeof x === "number")) {
-      throw new Error(
-        "mirrorOptions.recheckTopicsInCategories must all be numbers, got " +
-          JSON.stringify(recheckTopicsInCategories)
-      );
-    }
-    recheckTopicsInCategories = recheckTopicsInCategories.map((x) => Number(x));
-    if (typeof recheckCategoryDefinitionsAfterMs !== "number") {
-      throw new Error(
-        "recheckCategoryDefinitionsAfterMs must be number, got " +
-          JSON.stringify(recheckCategoryDefinitionsAfterMs)
-      );
-    }
-    mirrorOptions = {
-      recheckCategoryDefinitionsAfterMs,
-      recheckTopicsInCategories,
-    };
-  }
-
-  return {serverUrl, mirrorOptions};
 }

src/plugins/discourse/config.test.js

@@ -1,72 +0,0 @@
-// @flow
-
-import {parseConfig} from "./config";
-
-describe("plugins/discourse/config", () => {
-  describe("parseConfig", () => {
-    it("works on a config with just a serverUrl", () => {
-      const config = {serverUrl: "https://server.io"};
-      expect(parseConfig(config)).toEqual(config);
-    });
-    it("errors if the serverUrl is not a url", () => {
-      const config = {serverUrl: "1234"};
-      expect(() => parseConfig(config)).toThrowError();
-    });
-    it("errors if the serverUrl is not a string", () => {
-      const config = {serverUrl: 234};
-      expect(() => parseConfig(config)).toThrowError();
-    });
-    it("errors if the serverUrl is missing", () => {
-      const config = {};
-      expect(() => parseConfig(config)).toThrowError();
-    });
-    it("errors if the config is not an object", () => {
-      const config = [];
-      expect(() => parseConfig(config)).toThrowError();
-    });
-    it("works on a config with mirror options", () => {
-      const config = {
-        serverUrl: "https://server.io",
-        mirrorOptions: {
-          recheckCategoryDefinitionsAfterMs: 12,
-          recheckTopicsInCategories: [1, 2, 3, 4],
-        },
-      };
-      expect(parseConfig(config)).toEqual(config);
-    });
-    it("errors on a config with missing mirror options", () => {
-      const c1 = {
-        serverUrl: "https://server.io",
-        mirrorOptions: {
-          recheckTopicsInCategories: [1, 2, 3, 4],
-        },
-      };
-      expect(() => parseConfig(c1)).toThrowError();
-      const c2 = {
-        serverUrl: "https://server.io",
-        mirrorOptions: {
-          recheckCategoryDefinitionsAfterMs: 12,
-        },
-      };
-      expect(() => parseConfig(c2)).toThrowError();
-    });
-    it("errors with bad config options", () => {
-      const c1 = {
-        serverUrl: "https://server.io",
-        mirrorOptions: {
-          recheckTopicsInCategories: 12,
-          recheckCategoryDefinitionsAfterMs: 12,
-        },
-      };
-      expect(() => parseConfig(c1)).toThrowError();
-      const c2 = {
-        serverUrl: "https://server.io",
-        mirrorOptions: {
-          recheckTopicsInCategories: [1, 2, 3, 4],
-          recheckCategoryDefinitionsAfterMs: "foo",
-        },
-      };
-      expect(() => parseConfig(c2)).toThrowError();
-    });
-  });
-});

src/plugins/discourse/mirror.js

@@ -1,5 +1,6 @@
 // @flow
 
+import * as Combo from "../../util/combo";
 import type {TaskReporter} from "../../util/taskReporter";
 import type {Discourse, CategoryId, Topic, TopicLatest} from "./fetch";
 import {MirrorRepository} from "./mirrorRepository";
@@ -17,6 +18,17 @@ export type MirrorOptions = {|
   +recheckTopicsInCategories: $ReadOnlyArray<CategoryId>,
 |};
 
+const optionsParserFields = {
+  recheckCategoryDefinitionsAfterMs: Combo.number,
+  recheckTopicsInCategories: Combo.array<number>(Combo.number),
+};
+export const optionsParser: Combo.Parser<MirrorOptions> = Combo.object(
+  optionsParserFields
+);
+export const optionsShapeParser: Combo.Parser<
+  $Shape<MirrorOptions>
+> = Combo.shape(optionsParserFields);
+
 const defaultOptions: MirrorOptions = {
   recheckCategoryDefinitionsAfterMs: 24 * 3600 * 1000, // 24h
   recheckTopicsInCategories: [],