cli2: add sketch of plugin loading (#1810)

Summary:
This adds a `CliPlugin` interface and a basic implementation for the
GitHub plugin.

Paired with @decentralion.

Test Plan:
Create a new directory `/tmp/test-instance`, with:

```
// sourcecred.json
{"bundledPlugins": ["sourcecred/github"]}

// config/sourcecred/github/config.json
{"repositories": ["sourcecred/example-github"]}
```

Then, run

```
yarn backend &&
(cd /tmp/test-instance && node "$OLDPWD/bin/sc2.js" load)
```

and observe that the new instance has a cache directory containing a
GitHub database.

wchargin-branch: cli2-load

src/cli2/bundledPlugins.js

@@ -0,0 +1,12 @@
+// @flow
+
+import type {CliPlugin} from "./cliPlugin";
+import {GithubCliPlugin} from "../plugins/github/cliPlugin";
+
+/**
+ * Returns an object mapping owner-name pairs to CLI plugin
+ * declarations; keys are like `sourcecred/github`.
+ */
+export function bundledPlugins(): {[pluginId: string]: CliPlugin} {
+  return {"sourcecred/github": new GithubCliPlugin()};
+}

src/cli2/cliPlugin.js

@@ -0,0 +1,17 @@
+// @flow
+
+import type {PluginDeclaration} from "../analysis/pluginDeclaration";
+import type {WeightedGraph} from "../core/weightedGraph";
+import type {ReferenceDetector} from "../core/references/referenceDetector";
+
+export interface CliPlugin {
+  declaration(): PluginDeclaration;
+  load(PluginDirectoryContext): Promise<void>;
+  graph(PluginDirectoryContext, ReferenceDetector): Promise<WeightedGraph>;
+  referenceDetector(PluginDirectoryContext): Promise<ReferenceDetector>;
+}
+
+export interface PluginDirectoryContext {
+  configDirectory(): string;
+  cacheDirectory(): string;
+}

src/cli2/common.js

@@ -0,0 +1,61 @@
+// @flow
+
+import {join as pathJoin} from "path";
+import fs from "fs-extra";
+
+import type {PluginDirectoryContext} from "./cliPlugin";
+import {parse as parseConfig, type InstanceConfig} from "./instanceConfig";
+
+export async function loadInstanceConfig(
+  baseDir: string
+): Promise<InstanceConfig> {
+  const projectFilePath = pathJoin(baseDir, "sourcecred.json");
+  const contents = await fs.readFile(projectFilePath);
+  return Promise.resolve(parseConfig(JSON.parse(contents)));
+}
+
+// Make a directory, if it doesn't exist.
+function mkdirx(path: string) {
+  try {
+    fs.mkdirSync(path);
+  } catch (e) {
+    if (e.code !== "EEXIST") {
+      throw e;
+    }
+  }
+}
+
+export function makePluginDir(
+  baseDir: string,
+  prefix: $ReadOnlyArray<string>,
+  pluginId: string
+): string {
+  const idParts = pluginId.split("/");
+  if (idParts.length !== 2) {
+    throw new Error(`Bad plugin name: ${pluginId}`);
+  }
+  const [pluginOwner, pluginName] = idParts;
+  const pathComponents = [...prefix, pluginOwner, pluginName];
+  let path = baseDir;
+  for (const pc of pathComponents) {
+    path = pathJoin(path, pc);
+    mkdirx(path);
+  }
+  return path;
+}
+
+export function pluginDirectoryContext(
+  baseDir: string,
+  pluginName: string
+): PluginDirectoryContext {
+  const cacheDir = makePluginDir(baseDir, ["cache"], pluginName);
+  const configDir = makePluginDir(baseDir, ["config"], pluginName);
+  return {
+    configDirectory() {
+      return configDir;
+    },
+    cacheDirectory() {
+      return cacheDir;
+    },
+  };
+}

src/cli2/instanceConfig.js

@@ -0,0 +1,55 @@
+// @flow
+
+import {CliPlugin} from "./cliPlugin";
+import {bundledPlugins as getAllBundledPlugins} from "./bundledPlugins";
+
+type PluginName = string;
+
+export type InstanceConfig = {|
+  +bundledPlugins: Map<PluginName, CliPlugin>,
+|};
+
+export type RawInstanceConfig = {|
+  +bundledPlugins: $ReadOnlyArray<BundledPluginSpec>,
+|};
+
+// Plugin identifier, like `sourcecred/identity`. Version number is
+// implicit from the SourceCred version. This is a stopgap until we have
+// a plugin system that admits external, dynamically loaded
+// dependencies.
+export type BundledPluginSpec = string;
+
+type JsonObject =
+  | string
+  | number
+  | boolean
+  | null
+  | JsonObject[]
+  | {[string]: JsonObject};
+
+export function parse(raw: JsonObject): InstanceConfig {
+  if (raw == null || typeof raw !== "object" || Array.isArray(raw)) {
+    throw new Error("bad config: " + JSON.stringify(raw));
+  }
+  const {bundledPlugins: rawBundledPlugins} = raw;
+  if (!Array.isArray(rawBundledPlugins)) {
+    console.warn(JSON.stringify(raw));
+    throw new Error(
+      "bad bundled plugins: " + JSON.stringify(rawBundledPlugins)
+    );
+  }
+  const allBundledPlugins = getAllBundledPlugins();
+  const bundledPlugins = new Map();
+  for (const name of rawBundledPlugins) {
+    if (typeof name !== "string") {
+      throw new Error("bad bundled plugin: " + JSON.stringify(name));
+    }
+    const plugin = allBundledPlugins[name];
+    if (plugin == null) {
+      throw new Error("bad bundled plugin: " + JSON.stringify(name));
+    }
+    bundledPlugins.set(name, plugin);
+  }
+  const result = {bundledPlugins};
+  return result;
+}

src/cli2/load.js

@@ -0,0 +1,24 @@
+// @flow
+
+import type {Command} from "./command";
+import {loadInstanceConfig, pluginDirectoryContext} from "./common";
+
+function die(std, message) {
+  std.err("fatal: " + message);
+  return 1;
+}
+
+const loadCommand: Command = async (args, std) => {
+  if (args.length !== 0) {
+    die(std, "usage: sourcecred load");
+  }
+  const baseDir = process.cwd();
+  const config = await loadInstanceConfig(baseDir);
+  for (const [name, plugin] of config.bundledPlugins) {
+    const dirContext = pluginDirectoryContext(baseDir, name);
+    plugin.load(dirContext);
+  }
+  return 0;
+};
+
+export default loadCommand;

src/cli2/sourcecred.js

@@ -2,9 +2,20 @@
 
 import type {Command} from "./command";
 
+import load from "./load";
+
 const sourcecred: Command = async (args, std) => {
-  std.err("SourceCred CLI v2 not yet implemented");
+  if (args.length === 0) {
-  return 1;
+    std.err("fatal: specify a command");
+    return 1;
+  }
+  switch (args[0]) {
+    case "load":
+      return load(args.slice(1), std);
+    default:
+      std.err("fatal: unknown command: " + JSON.stringify(args[0]));
+      return 1;
+  }
 };
 
 export default sourcecred;

src/plugins/github/cliPlugin.js

@@ -0,0 +1,108 @@
+// @flow
+
+import Database from "better-sqlite3";
+import fs from "fs-extra";
+import {join as pathJoin} from "path";
+
+import fetchGithubRepo, {fetchGithubRepoFromCache} from "./fetchGithubRepo";
+import type {CacheProvider} from "../../backend/cache";
+import type {CliPlugin, PluginDirectoryContext} from "../../cli2/cliPlugin";
+import type {PluginDeclaration} from "../../analysis/pluginDeclaration";
+import type {ReferenceDetector} from "../../core/references/referenceDetector";
+import type {WeightedGraph} from "../../core/weightedGraph";
+import {Graph} from "../../core/graph";
+import {RelationalView} from "./relationalView";
+import {createGraph} from "./createGraph";
+import {declaration} from "./declaration";
+import {fromRelationalViews as referenceDetectorFromRelationalViews} from "./referenceDetector";
+import {parse as parseConfig, type GithubConfig} from "./config";
+import {validateToken, type GithubToken} from "./token";
+import {weightsForDeclaration} from "../../analysis/pluginDeclaration";
+
+const TOKEN_ENV_VAR_NAME = "SOURCECRED_GITHUB_TOKEN";
+
+async function loadConfig(
+  dirContext: PluginDirectoryContext
+): Promise<GithubConfig> {
+  const dirname = dirContext.configDirectory();
+  const path = pathJoin(dirname, "config.json");
+  const contents = await fs.readFile(path);
+  return Promise.resolve(parseConfig(JSON.parse(contents)));
+}
+
+// Shim to interface with `fetchGithubRepo`; TODO: refactor that to just
+// take a directory.
+class CacheProviderImpl implements CacheProvider {
+  _dirContext: PluginDirectoryContext;
+  constructor(dirContext: PluginDirectoryContext) {
+    this._dirContext = dirContext;
+  }
+  database(id: string): Promise<Database> {
+    const path = pathJoin(this._dirContext.cacheDirectory(), `${id}.db`);
+    return Promise.resolve(new Database(path));
+  }
+}
+
+function getTokenFromEnv(): GithubToken {
+  const rawToken = process.env[TOKEN_ENV_VAR_NAME];
+  if (rawToken == null) {
+    throw new Error(`No GitHub token provided: set ${TOKEN_ENV_VAR_NAME}`);
+  }
+  return validateToken(rawToken);
+}
+
+export class GithubCliPlugin implements CliPlugin {
+  declaration(): PluginDeclaration {
+    return declaration;
+  }
+
+  async load(ctx: PluginDirectoryContext): Promise<void> {
+    const cache = new CacheProviderImpl(ctx);
+    const token = getTokenFromEnv();
+    const config = await loadConfig(ctx);
+    for (const repoId of config.repoIds) {
+      await fetchGithubRepo(repoId, {token, cache});
+    }
+  }
+
+  async graph(
+    ctx: PluginDirectoryContext,
+    rd: ReferenceDetector
+  ): Promise<WeightedGraph> {
+    const _ = rd; // TODO(#1808): not yet used
+    const cache = new CacheProviderImpl(ctx);
+    const token = getTokenFromEnv();
+    const config = await loadConfig(ctx);
+
+    const repositories = [];
+    for (const repoId of config.repoIds) {
+      repositories.push(await fetchGithubRepoFromCache(repoId, {token, cache}));
+    }
+    const graph = Graph.merge(
+      repositories.map((r) => {
+        const rv = new RelationalView();
+        rv.addRepository(r);
+        return createGraph(rv);
+      })
+    );
+    const weights = weightsForDeclaration(declaration);
+    return {graph, weights};
+  }
+
+  async referenceDetector(
+    ctx: PluginDirectoryContext
+  ): Promise<ReferenceDetector> {
+    const cache = new CacheProviderImpl(ctx);
+    const token = getTokenFromEnv();
+    const config = await loadConfig(ctx);
+
+    const rvs = [];
+    for (const repoId of config.repoIds) {
+      const repo = await fetchGithubRepoFromCache(repoId, {token, cache});
+      const rv = new RelationalView();
+      rv.addRepository(repo);
+      rvs.push(rv);
+    }
+    return referenceDetectorFromRelationalViews(rvs);
+  }
+}

src/plugins/github/config.js

@@ -0,0 +1,38 @@
+// @flow
+
+import {type RepoId, stringToRepoId} from "./repoId";
+
+export type GithubConfig = {|
+  +repoIds: $ReadOnlyArray<RepoId>,
+|};
+
+// eslint-disable-next-line no-unused-vars
+type SerializedGithubConfig = {|
+  +repositories: $ReadOnlyArray<string>,
+|};
+// (^ for documentation purposes)
+
+type JsonObject =
+  | string
+  | number
+  | boolean
+  | null
+  | JsonObject[]
+  | {[string]: JsonObject};
+
+export function parse(raw: JsonObject): GithubConfig {
+  if (raw == null || typeof raw !== "object" || Array.isArray(raw)) {
+    throw new Error("bad config: " + JSON.stringify(raw));
+  }
+  const {repositories} = raw;
+  if (!Array.isArray(repositories)) {
+    throw new Error("bad repositories: " + JSON.stringify(repositories));
+  }
+  const repoIds = repositories.map((x) => {
+    if (typeof x !== "string") {
+      throw new Error("bad repository: " + JSON.stringify(x));
+    }
+    return stringToRepoId(x);
+  });
+  return {repoIds};
+}