Include getCsharpTempDependencyDir in C# caches if FF is enabled

src/dependency-caching.test.ts

@@ -20,6 +20,8 @@ import {
   downloadDependencyCaches,
   CacheHitKind,
   cacheKey,
+  getCsharpDependencyDirs,
+  getCsharpTempDependencyDir,
 } from "./dependency-caching";
 import { Feature } from "./feature-flags";
 import { KnownLanguage } from "./languages";
@@ -38,6 +40,28 @@ function makeAbsolutePatterns(tmpDir: string, patterns: string[]): string[] {
   return patterns.map((pattern) => path.join(tmpDir, pattern));
 }
 
+test("getCsharpDependencyDirs - does not include BMN dir if FF is enabled", async (t) => {
+  await withTmpDir(async (tmpDir) => {
+    process.env["RUNNER_TEMP"] = tmpDir;
+    const codeql = createStubCodeQL({});
+    const features = createFeatures([]);
+
+    const results = await getCsharpDependencyDirs(codeql, features);
+    t.false(results.includes(getCsharpTempDependencyDir()));
+  });
+});
+
+test("getCsharpDependencyDirs - includes BMN dir if FF is enabled", async (t) => {
+  await withTmpDir(async (tmpDir) => {
+    process.env["RUNNER_TEMP"] = tmpDir;
+    const codeql = createStubCodeQL({});
+    const features = createFeatures([Feature.CsharpCacheBuildModeNone]);
+
+    const results = await getCsharpDependencyDirs(codeql, features);
+    t.assert(results.includes(getCsharpTempDependencyDir()));
+  });
+});
+
 test("makePatternCheck - returns undefined if no patterns match", async (t) => {
   await withTmpDir(async (tmpDir) => {
     fs.writeFileSync(path.join(tmpDir, "test.java"), "");
@@ -387,3 +411,28 @@ test("getFeaturePrefix - non-C# - returns '' if CsharpNewCacheKey is enabled", a
     t.deepEqual(result, "", `Expected no feature prefix for ${knownLanguage}`);
   }
 });
+
+test("getFeaturePrefix - C# - returns prefix if CsharpCacheBuildModeNone is enabled", async (t) => {
+  const codeql = createStubCodeQL({});
+  const features = createFeatures([Feature.CsharpCacheBuildModeNone]);
+
+  const result = await getFeaturePrefix(codeql, features, KnownLanguage.csharp);
+  t.notDeepEqual(result, "");
+  t.assert(result.endsWith("-"));
+  // Check the length of the prefix, which should correspond to `cacheKeyHashLength` + 1 for the trailing `-`.
+  t.is(result.length, cacheKeyHashLength + 1);
+});
+
+test("getFeaturePrefix - non-C# - returns '' if CsharpCacheBuildModeNone is enabled", async (t) => {
+  const codeql = createStubCodeQL({});
+  const features = createFeatures([Feature.CsharpCacheBuildModeNone]);
+
+  for (const knownLanguage of Object.values(KnownLanguage)) {
+    // Skip C# since we expect a result for it, which is tested in the previous test.
+    if (knownLanguage === KnownLanguage.csharp) {
+      continue;
+    }
+    const result = await getFeaturePrefix(codeql, features, knownLanguage);
+    t.deepEqual(result, "", `Expected no feature prefix for ${knownLanguage}`);
+  }
+});

src/dependency-caching.ts

@@ -85,8 +85,20 @@ export function getCsharpTempDependencyDir(): string {
  * @returns The paths of directories on the runner that should be included in a dependency cache
  * for a C# analysis.
  */
-export async function getCsharpDependencyDirs(): Promise<string[]> {
-  return [join(os.homedir(), ".nuget", "packages")];
+export async function getCsharpDependencyDirs(
+  codeql: CodeQL,
+  features: FeatureEnablement,
+): Promise<string[]> {
+  const dirs = [
+    // Nuget
+    join(os.homedir(), ".nuget", "packages"),
+  ];
+
+  if (await features.getValue(Feature.CsharpCacheBuildModeNone, codeql)) {
+    dirs.push(getCsharpTempDependencyDir());
+  }
+
+  return dirs;
 }
 
 /**
@@ -512,6 +524,7 @@ export async function getFeaturePrefix(
     }
   } else if (language === KnownLanguage.csharp) {
     await addFeatureIfEnabled(Feature.CsharpNewCacheKey);
+    await addFeatureIfEnabled(Feature.CsharpCacheBuildModeNone);
   }
 
   // If any features that affect the cache are enabled, return a feature prefix by