Improve the script to enforce rustfmt on automation.

ci/assert-rustfmt.sh

@@ -3,14 +3,10 @@
 set -xeu
 cd "$(dirname "$0")/.."
 
-# Ensure we have the most up-to-date `rustfmt`.
-cargo install -f rustfmt
+rustup update nightly
+rustup component add rustfmt --toolchain nightly
 
 # Run `rustfmt` on the crate! If `rustfmt` can't make a long line shorter, it
 # prints an error and exits non-zero, so tell it to kindly shut its yapper and
 # make sure it doesn't cause us to exit this whole script non-zero.
-cargo fmt --quiet || true
-
-# Exit non-zero if this resulted in any diffs.
-./ci/assert-no-diff.sh
-
+rustup run nightly cargo fmt -- --check

ci/script.sh

@@ -45,8 +45,7 @@ case "$BINDGEN_JOB" in
         ./ci/assert-docs.sh
         ./ci/test-book.sh
         ./ci/no-includes.sh
-        # `rustfmt` isn't reaching a fixed point on bindgen
-        # code... https://github.com/rust-lang/rustfmt/issues/1376
+        # Disabled because https://github.com/rust-lang/rustfmt/issues/3799.
         # ./ci/assert-rustfmt.sh
         ;;
 

src/lib.rs

@@ -1958,7 +1958,10 @@ impl Bindings {
             }
         }
         #[cfg(not(feature = "which-rustfmt"))]
-        Err(io::Error::new(io::ErrorKind::Other, "which wasn't enabled, and no rustfmt binary specified"))
+        Err(io::Error::new(
+            io::ErrorKind::Other,
+            "which wasn't enabled, and no rustfmt binary specified",
+        ))
     }
 
     /// Checks if rustfmt_bindings is set and runs rustfmt on the string