ci: always try to find a nightly toolchain with rustfmt.

Author: emilio

ci/assert-rustfmt.sh

@@ -3,10 +3,11 @@
 set -xeu
 cd "$(dirname "$0")/.."
 
-rustup update nightly
-rustup component add rustfmt --toolchain nightly
+TOOLCHAIN="nightly-$(curl https://rust-lang.github.io/rustup-components-history/$(rustup target list --installed | tail -1)/rustfmt)"
+rustup update "$TOOLCHAIN"
+rustup component add rustfmt --toolchain "$TOOLCHAIN"
 
 # 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.
-rustup run nightly cargo fmt -- --check
+rustup run "$TOOLCHAIN" cargo fmt -- --check

ci/script.sh

@@ -17,10 +17,10 @@ fi
 case "$BINDGEN_JOB" in
     "test")
         # Need rustfmt to compare the test expectations.
-        rustup update nightly
-        rustup component add rustfmt
-        rustup component add --toolchain nightly rustfmt
-        RUSTFMT="$(rustup which rustfmt)"
+        TOOLCHAIN="nightly-$(curl https://rust-lang.github.io/rustup-components-history/$(rustup target list --installed | tail -1)/rustfmt)"
+        rustup update "$TOOLCHAIN"
+        rustup component add rustfmt --toolchain "$TOOLCHAIN"
+        RUSTFMT="$(rustup which --toolchain "$TOOLCHAIN" rustfmt)"
         export RUSTFMT
         cargo test "$BINDGEN_PROFILE" $NO_DEFAULT_FEATURES --features "$BINDGEN_FEATURES"
         ./ci/assert-no-diff.sh