cli/commands/build-cache: make max entries configurable and set to 2 in CI

.github/workflows/frontend.yml

@@ -15,6 +15,7 @@ jobs:
     env:
       CI: true
       BACKSTAGE_CACHE_DIR: <repoRoot>/.backstage-build-cache
+      BACKSTAGE_CACHE_MAX_ENTRIES: 2
 
     steps:
       - uses: actions/checkout@v2

.github/workflows/master.yml

@@ -15,6 +15,7 @@ jobs:
     env:
       CI: true
       BACKSTAGE_CACHE_DIR: <repoRoot>/.backstage-build-cache
+      BACKSTAGE_CACHE_MAX_ENTRIES: 2
 
     steps:
       - uses: actions/checkout@v2

packages/cli/src/commands/build-cache/cache.ts

@@ -20,13 +20,12 @@ import { runPlain, runCheck } from '../../helpers/run';
 import { Options } from './options';
 import { extractArchive, createArchive } from './archive';
 
-const MAX_ENTRIES = 10;
 const INFO_FILE = '.backstage-build-cache';
 
 export type CacheQueryResult = {
   hit: boolean;
   copy?: (outputDir: string) => Promise<void>;
-  archive?: (outputDir: string) => Promise<void>;
+  archive?: (outputDir: string, maxEntries: number) => Promise<void>;
 };
 
 export type CacheKey = string[];
@@ -83,7 +82,7 @@ export class Cache {
       return { hit: false };
     }
 
-    const archive = async (outputDir: string) => {
+    const archive = async (outputDir: string, maxEntries: number) => {
       await writeCacheInfo(outputDir, { key });
 
       const timestamp = new Date().toISOString().replace(/-|:|\..*/g, '');
@@ -111,7 +110,7 @@ export class Cache {
       entries.unshift({ key, path: archiveName });
 
       // Remove old cache entries
-      const removedEntries = entries.splice(MAX_ENTRIES);
+      const removedEntries = entries.splice(maxEntries);
       for (const entry of removedEntries) {
         try {
           await fs.remove(resolvePath(location, entry.path));

packages/cli/src/commands/build-cache/index.ts

@@ -48,7 +48,7 @@ export default async (cmd: Command, args: string[]) => {
 
     if (cacheResult.archive) {
       print('caching build output');
-      await cacheResult.archive(options.output);
+      await cacheResult.archive(options.output, options.maxCacheEntries);
     }
   }
 };

packages/cli/src/commands/build-cache/options.ts

@@ -18,10 +18,13 @@ import { resolve as resolvePath } from 'path';
 import { Command } from 'commander';
 import { runPlain } from '../../helpers/run';
 
+const DEFAULT_MAX_ENTRIES = 10;
+
 export type Options = {
   inputs: string[];
   output: string;
   cacheDir: string;
+  maxCacheEntries: number;
   repoRoot: string;
 };
 
@@ -38,5 +41,7 @@ export async function parseOptions(cmd: Command): Promise<Options> {
   const cacheDir = argTransformer(
     process.env.BACKSTAGE_CACHE_DIR || cmd.cacheDir,
   );
-  return { inputs, output, cacheDir, repoRoot };
+  const maxCacheEntries =
+    Number(process.env.BACKSTAGE_CACHE_MAX_ENTRIES) || DEFAULT_MAX_ENTRIES;
+  return { inputs, output, cacheDir, repoRoot, maxCacheEntries };
 }