Configure sourcemap file

`webpack` will by default emit a sourcemap that maps to a `main.js`
file. However, the worker runtime will create the script with a
`worker.js` name. In some cases (like devtools) it doesn't matter
because it resolves the source infos based on the sourcemap `sources`
key. In Sentry for instance, that would fail.

Fixes #681

tests/build.rs

@@ -3,6 +3,7 @@ extern crate lazy_static;
 
 pub mod fixture;
 
+use std::fs;
 use std::process::Command;
 use std::str;
 
@@ -313,6 +314,35 @@ fn it_builds_with_webpack_target_webworker() {
     build_creates_assets(&fixture, vec!["script.js"]);
 }
 
+#[test]
+fn it_builds_with_webpack_name_output() {
+    let fixture = Fixture::new();
+    fixture.scaffold_webpack();
+
+    fixture.create_file(
+        "webpack.config.js",
+        r#"
+        module.exports = {
+            "entry": "./index.js",
+            "devtool": "cheap-module-source-map"
+        }
+    "#,
+    );
+    fixture.create_file("index.js", "");
+
+    let wrangler_toml = WranglerToml::webpack_std_config("test-build-webpack-name-output");
+    fixture.create_wrangler_toml(wrangler_toml);
+
+    build_creates_assets(&fixture, vec!["script.js"]);
+
+    let out = fs::read_to_string(fixture.get_output_path().join("script.js")).unwrap();
+    let sourcemap = out.split("\n").last().unwrap();
+    assert_eq!(
+        sourcemap,
+        r#"//# sourceMappingURL=worker.js.map{"version":3,"file":"worker.js","sources":["webpack:///worker.js"],"mappings":"AAAA","sourceRoot":""}"#
+    );
+}
+
 fn build_creates_assets(fixture: &Fixture, script_names: Vec<&str>) {
     let _lock = fixture.lock();
     let mut build = Command::cargo_bin(env!("CARGO_PKG_NAME")).unwrap();

wranglerjs/index.js

@@ -54,6 +54,18 @@ function filterByExtension(ext) {
   }
   config.target = "webworker";
 
+  // The worker runtime will set the name of the script to `worker.js`,
+  // regardless of what's specified in the sourcemap.
+  // We can tell webpack to name the generated worker by configuring the output.
+  // It's also safe to force that configuration because it mirrors what the
+  // runtime does.
+  // https://github.com/cloudflare/wrangler/issues/681
+  if (config.output === undefined) {
+    config.output = {};
+  }
+  config.output.filename = 'worker.js';
+  config.output.sourceMapFilename = 'worker.js.map';
+
   const compiler = webpack(config);
   const fullConfig = compiler.options;