add test and some documentation for custom extra options passed to build command

docs/src/commands/build.md

@@ -90,6 +90,17 @@ wasm-pack build examples/js-hello-world --mode no-install
 | `no-install`  | `wasm-pack init` implicitly and create wasm binding  without installing `wasm-bindgen`.  |
 | `normal`      | do all the stuffs of `no-install` with installed `wasm-bindgen`.                         |
 
+## Extra options
+
+The `build` command can pass extra options straight to `cargo build` even if they are not
+supported in wasm-pack. To use them you should add standalone `--` argument at the very
+end of your command, and all the arguments you want to pass to cargo should go after.
+For example to build previous example using unstable cargo offline feature:
+
+```
+wasm-pack build examples/js-hello-world --mode no-install -- -Z offline
+```
+
 <hr style="font-size: 1.5em; margin-top: 2.5em"/>
 
 <sup id="footnote-0">0</sup> If you need to include additional assets in the pkg

tests/all/build.rs

@@ -248,3 +248,19 @@ fn it_format_out_dir_on_windows() {
         "directories in wasm-pack.log should be well formatted",
     );
 }
+
+#[test]
+fn build_with_arbitrary_cargo_options() {
+    let fixture = utils::fixture::js_hello_world();
+    fixture.install_local_wasm_bindgen();
+
+    let cli = Cli::from_iter_safe(vec![
+        "wasm-pack",
+        "build",
+        &fixture.path.display().to_string(),
+        "--",
+        "--no-default-features",
+    ])
+    .unwrap();
+    fixture.run(cli.cmd).unwrap();
+}