Add './miri fmt' and use it in CI

.github/workflows/ci.yml

@@ -95,15 +95,9 @@ jobs:
         # We need a toolchain that can actually build Miri, just a nightly won't do.
         run: |
           cargo install rustup-toolchain-install-master # TODO: cache this?
-          ./rustup-toolchain "" -c clippy -c rustfmt
-      - name: rustfmt (miri, ui_test)
-        run: cargo fmt --all --check
-      - name: rustfmt (everything else)
-        # TODO: Add `tests` (work in progress).
-        # Maybe change to `find . -name '*.rs'`, superseding the previous step.
-        run: |
-          find bench-cargo-miri benches cargo-miri test-cargo-miri -name '*.rs' \
-            | xargs rustfmt --edition=2021 --config-path ./rustfmt.toml --check
+          ./rustup-toolchain "" -c clippy
+      - name: rustfmt
+        run: ./miri fmt --check
       - name: clippy (miri)
         run: cargo clippy --all-targets -- -D warnings
       #- name: Clippy (ui_test)

miri

@@ -21,10 +21,13 @@ to the final `cargo test` invocation.
 ./miri run <flags>:
 Build miri, set up a sysroot and then run the driver with the given <flags>.
 
-All commands also exist in a "-debug" variant (e.g. "./miri run-debug
+The commands above also exist in a "-debug" variant (e.g. "./miri run-debug
 <flags>") which uses debug builds instead of release builds, for faster build
 times and slower execution times.
 
+./miri fmt <flags>:
+Format all sources and tests.  <flags> are passed to `rustfmt`.
+
   ENVIRONMENT VARIABLES
 
 MIRI_SYSROOT:
@@ -156,6 +159,10 @@ run|run-debug)
     # Then run the actual command.
     exec cargo run $CARGO_BUILD_FLAGS -- --sysroot "$MIRI_SYSROOT" "$@"
     ;;
+fmt)
+    find "$MIRIDIR" -not \( -name target -prune \) -name '*.rs' \
+        | xargs rustfmt --edition=2021 --config-path "$MIRIDIR/rustfmt.toml" "$@"
+    ;;
 *)
     if [ -n "$COMMAND" ]; then
       echo "Unknown command: $COMMAND"

rustup-toolchain

@@ -42,7 +42,7 @@ fi
 
 # Install and setup new toolchain.
 rustup toolchain uninstall miri
-rustup-toolchain-install-master -n miri -c cargo -c rust-src -c rustc-dev -c llvm-tools "$@" -- "$NEW_COMMIT"
+rustup-toolchain-install-master -n miri -c cargo -c rust-src -c rustc-dev -c llvm-tools -c rustfmt "$@" -- "$NEW_COMMIT"
 rustup override set miri
 
 # Cleanup.