fix: Enable cache with externalDependencies

.yarnrc.yml

@@ -1 +1,4 @@
 yarnPath: .yarn/releases/yarn-3.2.3.cjs
+enableGlobalCache: true
+nodeLinker: node-modules
+

src/cache.js

@@ -90,9 +90,16 @@
     cacheIdentifier,
     cacheDirectory,
     cacheCompression,
+    cachedDepMtimes,
   } = params;
 
-  const file = path.join(directory, filename(source, cacheIdentifier, options));
+  const file = path.join(
+    directory,
+    filename(source, cacheIdentifier, {
+      options,
+      __cachedDepMtimes: cachedDepMtimes,
+    }),
+  );
 
   try {
     // No errors mean that the file was previously cached
@@ -119,19 +126,15 @@
   // return it to the user asap and write it in cache
   const result = await transform(source, options);
 
-  // Do not cache if there are external dependencies,
-  // since they might change and we cannot control it.
-  if (!result.externalDependencies.length) {
-    try {
-      await write(file, cacheCompression, result);
-    } catch (err) {
-      if (fallback) {
-        // Fallback to tmpdir if node_modules folder not writable
-        return handleCache(os.tmpdir(), params);
-      }
-
-      throw err;
+  try {
+    await write(file, cacheCompression, result);
+  } catch (err) {
+    if (fallback) {
+      // Fallback to tmpdir if node_modules folder not writable
+      return handleCache(os.tmpdir(), params);
     }
+
+    throw err;
   }
 
   return result;

src/index.js

@@ -26,6 +26,7 @@ const injectCaller = require("./injectCaller");
 const schema = require("./schema");
 
 const { isAbsolute } = require("path");
+const fs = require("fs");
 const validateOptions = require("schema-utils").validate;
 
 function subscribe(subscriber, metadata, context) {
@@ -39,19 +40,22 @@ module.exports.custom = makeLoader;
 
 function makeLoader(callback) {
   const overrides = callback ? callback(babel) : undefined;
+  const data = {
+    cachedDepMtimes: { __proto__: null },
+  };
 
   return function (source, inputSourceMap) {
     // Make the loader async
     const callback = this.async();
 
-    loader.call(this, source, inputSourceMap, overrides).then(
+    loader.call(this, source, inputSourceMap, overrides, data).then(
       args => callback(null, ...args),
       err => callback(err),
     );
   };
 }
 
-async function loader(source, inputSourceMap, overrides) {
+async function loader(source, inputSourceMap, overrides, data) {
   const filename = this.resourcePath;
 
   let loaderOptions = this.getOptions();
@@ -185,13 +189,24 @@ async function loader(source, inputSourceMap, overrides) {
 
     let result;
     if (cacheDirectory) {
+      const cachedDepMtimes = [];
+      for (const dep of Object.keys(data.cachedDepMtimes)) {
+        let mtime = 0;
+        try {
+          mtime = fs.statSync(dep).mtimeMs;
+        } catch (error) {}
+        cachedDepMtimes.push(dep + mtime);
+      }
+      cachedDepMtimes.sort();
+
       result = await cache({
         source,
         options,
         transform,
         cacheDirectory,
         cacheIdentifier,
         cacheCompression,
+        cachedDepMtimes,
       });
     } else {
       result = await transform(source, options);
@@ -212,7 +227,17 @@ async function loader(source, inputSourceMap, overrides) {
 
       const { code, map, metadata, externalDependencies } = result;
 
-      externalDependencies?.forEach(dep => this.addDependency(dep));
+      externalDependencies?.forEach(dep => {
+        if (data.cachedDepMtimes[dep] == null) {
+          let mtime = 0;
+          try {
+            mtime = fs.statSync(dep).mtimeMs;
+          } catch (error) {}
+          data.cachedDepMtimes[dep] = mtime;
+        }
+        this.addDependency(dep);
+      });
+
       metadataSubscribers.forEach(subscriber => {
         subscribe(subscriber, metadata, this);
       });

test/cache.test.js

@@ -389,3 +389,90 @@ test.cb("should allow to specify the .babelrc file", t => {
     });
   });
 });
+
+test.cb("should cache external dependencies", t => {
+  const dep = path.join(cacheDir, "externalDependency.txt");
+
+  fs.writeFileSync(dep, "123");
+
+  let counter = 0;
+
+  const config = Object.assign({}, globalConfig, {
+    entry: path.join(__dirname, "fixtures/constant.js"),
+    output: {
+      path: t.context.directory,
+    },
+    module: {
+      rules: [
+        {
+          test: /\.js$/,
+          loader: babelLoader,
+          options: {
+            babelrc: false,
+            configFile: false,
+            cacheDirectory: t.context.cacheDirectory,
+            plugins: [
+              api => {
+                api.cache.never();
+                api.addExternalDependency(dep);
+                return {
+                  visitor: {
+                    BooleanLiteral(path) {
+                      counter++;
+                      path.replaceWith(
+                        api.types.stringLiteral(fs.readFileSync(dep, "utf8")),
+                      );
+                      path.stop();
+                    },
+                  },
+                };
+              },
+            ],
+          },
+        },
+      ],
+    },
+  });
+
+  webpack(config, (err, stats) => {
+    t.deepEqual(stats.compilation.warnings, []);
+    t.deepEqual(stats.compilation.errors, []);
+
+    t.true(stats.compilation.fileDependencies.has(dep));
+
+    t.is(counter, 1);
+
+    webpack(config, (err, stats) => {
+      t.deepEqual(stats.compilation.warnings, []);
+      t.deepEqual(stats.compilation.errors, []);
+
+      t.true(stats.compilation.fileDependencies.has(dep));
+
+      t.is(counter, 2);
+
+      webpack(config, (err, stats) => {
+        t.deepEqual(stats.compilation.warnings, []);
+        t.deepEqual(stats.compilation.errors, []);
+
+        t.true(stats.compilation.fileDependencies.has(dep));
+
+        t.is(counter, 2);
+
+        fs.writeFileSync(dep, "456");
+
+        setTimeout(() => {
+          webpack(config, (err, stats) => {
+            t.deepEqual(stats.compilation.warnings, []);
+            t.deepEqual(stats.compilation.errors, []);
+
+            t.true(stats.compilation.fileDependencies.has(dep));
+
+            t.is(counter, 3);
+
+            t.end();
+          });
+        }, 1000);
+      });
+    });
+  });
+});