Fixed webidl output formatting on Windows (#4335)

Author: RunDevelopment

crates/web-sys/README.md

@@ -32,9 +32,6 @@ If you don't see a particular web API in `web-sys`, here is how to add it.
 2. Annotate the functions that can throw with `[Throws]`
 3. `cd crates/web-sys`
 4. Run `cargo run --release --package wasm-bindgen-webidl -- webidls src/features ./Cargo.toml`
-
-   If formatting fails, you can run `cargo fmt` in the `crates/web-sys` directory. On Windows, you might also want to run `cargo fmt -- --config newline_style=Unix` depending on your git configuration.
-
 5. Run `git add .` to add all the generated files into git.
 6. Add an entry in CHANGELOG.md like the following
 

crates/webidl/src/lib.rs

@@ -997,14 +997,21 @@ pub fn generate(from: &Path, to: &Path, options: Options) -> Result<String> {
 
     fn rustfmt(paths: impl IntoIterator<Item = PathBuf>) -> Result<()> {
         // run rustfmt on the generated file - really handy for debugging
-        let result = Command::new("rustfmt")
-            .arg("--edition")
-            .arg("2021")
-            .args(paths)
-            .status()
-            .context("rustfmt failed")?;
-
-        assert!(result.success(), "rustfmt failed");
+
+        // On Windows, the command line length is limited to 32k characters, so
+        // we need to split the command into multiple invocations. I've
+        // arbitrarily chosen to format 400 files at a time, because it works.
+        let paths: Vec<_> = paths.into_iter().collect();
+        for chunk in paths.chunks(400) {
+            let result = Command::new("rustfmt")
+                .arg("--edition")
+                .arg("2021")
+                .args(chunk)
+                .status()
+                .context("rustfmt failed")?;
+
+            assert!(result.success(), "rustfmt failed");
+        }
 
         Ok(())
     }