Added utility to generate "_redirects" file (#677)

.changeset/many-rats-mate.md

@@ -0,0 +1,5 @@
+---
+'guild-docs': minor
+---
+
+Added utility to generate "\_redirects" file

packages/docs/src/underscore-redirects.ts

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+import { writeFile } from 'fs/promises';
+import { join } from 'path';
+
+class RunPromiseWebpackPlugin {
+  asyncHook;
+
+  constructor(asyncHook: () => Promise<void>) {
+    this.asyncHook = asyncHook;
+  }
+
+  apply(compiler: any) {
+    compiler.hooks.beforeCompile.tapPromise('RunPromiseWebpackPlugin', this.asyncHook);
+  }
+}
+
+export function applyUnderscoreRedirects(config: any, meta: any) {
+  config.plugins.push(
+    new RunPromiseWebpackPlugin(async () => {
+      const outDir = meta.dir;
+      const outFile = join(outDir, './public/_redirects');
+
+      try {
+        const redirects: any[] = meta.config.redirects
+          ? Array.isArray(typeof meta.config.redirects)
+            ? typeof meta.config.redirects
+            : await meta.config.redirects()
+          : [];
+
+        if (redirects.length > 0) {
+          const redirectsTxt = redirects
+            .map(r => `${r.source} ${r.destination} ${r.permanent ? '301' : '302'}`)
+            .join('\n');
+          await writeFile(outFile, redirectsTxt);
+        } else {
+          console.warn(`No redirects defined, no "_redirect" file is created!`);
+        }
+      } catch (e) {
+        console.error('Error while generating redirects file: ', e);
+        throw new Error(`Failed to generate "_redirects" file during build: ${(e as Error).message}`);
+      }
+    })
+  );
+}