fix: improve parsing of --env flag

packages/webpack-cli/src/webpack-cli.ts

@@ -756,13 +756,13 @@ class WebpackCLI implements IWebpackCLI {
           value: string,
           previous: Record<string, BasicPrimitive | object> = {},
         ): Record<string, BasicPrimitive | object> => {
-          // for https://github.com/webpack/webpack-cli/issues/2642
-          if (value.endsWith("=")) {
-            value.concat('""');
-          }
-
           // This ensures we're only splitting by the first `=`
-          const [allKeys, val] = value.split(/=(.+)/, 2);
+          let [allKeys, val] = value.split(/=(.+)/, 2);
+          if (typeof val === "undefined" && allKeys.endsWith("=")) {
+            // remove '=' from key
+            allKeys = allKeys.slice(0, -1);
+            val = "undefined";
+          }
           const splitKeys = allKeys.split(/\.(?!$)/);
 
           let prevRef = previous;
@@ -777,8 +777,11 @@ class WebpackCLI implements IWebpackCLI {
             }
 
             if (index === splitKeys.length - 1) {
-              if (typeof val === "string") {
+              if (typeof val === "string" && val !== "undefined") {
                 prevRef[someKey] = val;
+              } else if (val === "undefined") {
+                // @ts-expect-error we explicitly want to set it to undefined
+                prevRef[someKey] = undefined;
               } else {
                 prevRef[someKey] = true;
               }

test/build/config/type/function-with-env/function-with-env.test.js

@@ -142,9 +142,19 @@ describe("function configuration", () => {
 
     expect(exitCode).toBe(0);
     expect(stderr).toBeFalsy();
-    expect(stdout).toBeTruthy();
-    // Should generate the appropriate files
-    expect(existsSync(resolve(__dirname, "./dist/equal-at-the-end.js"))).toBeTruthy();
+    // should log foo: undefined
+    expect(stdout).toContain("foo: undefined");
+  });
+
+  it('Supports env variable with "=$NON_EXISTENT_VAR" at the end', async () => {
+    const { exitCode, stderr, stdout } = await run(__dirname, ["--env", `foo=$NON_EXISTENT_VAR`], {
+      shell: true,
+    });
+
+    expect(exitCode).toBe(0);
+    expect(stderr).toBeFalsy();
+    // should log foo: undefined
+    expect(stdout).toContain("foo: undefined");
   });
 
   it("is able to understand multiple env flags", async () => {

test/build/config/type/function-with-env/webpack.config.js

@@ -1,6 +1,7 @@
 const { DefinePlugin } = require("webpack");
 
 module.exports = (env) => {
+  console.log(env);
   if (env.isProd) {
     return {
       entry: "./a.js",
@@ -25,14 +26,6 @@ module.exports = (env) => {
       },
     };
   }
-  if (env["foo="]) {
-    return {
-      entry: "./a.js",
-      output: {
-        filename: "equal-at-the-end.js",
-      },
-    };
-  }
   return {
     entry: "./a.js",
     mode: "development",