Add a scheme for always using the default toolchain, running clippy and fmt before running any other command

Author: oli-obk

.gitignore

@@ -8,3 +8,4 @@ tex/*/out
 perf.data
 perf.data.old
 flamegraph.svg
+.auto-*

CONTRIBUTING.md

@@ -28,6 +28,11 @@ install that exact version of rustc as a toolchain:
 This will set up a rustup toolchain called `miri` and set it as an override for
 the current directory.
 
+You can also create a `.auto-everything` file (contents don't matter, can be empty), which
+will cause any `./miri` command to automatically call `rustup-toolchain`, `clippy` and `rustfmt`
+for you. If you don't want all of these to happen, you can add individual `.auto-toolchain`,
+`.auto-clippy` and `.auto-fmt` files respectively.
+
 [`rustup-toolchain-install-master`]: https://github.com/kennytm/rustup-toolchain-install-master
 
 ## Building and testing Miri
@@ -244,6 +249,14 @@ rustup toolchain link stage2 build/x86_64-unknown-linux-gnu/stage2
 rustup override set stage2
 ```
 
+Note: When you are working with a locally built rustc or any other toolchain that
+is not the same as the one in `rust-version`, you should not have `.auto-everything` or
+`.auto-toolchain` as that will keep resetting your toolchain.
+
+```
+rm -f .auto-everything .auto-toolchain
+```
+
 Important: You need to delete the Miri cache when you change the stdlib; otherwise the
 old, chached version will be used. On Linux, the cache is located at `~/.cache/miri`,
 and on Windows, it is located at `%LOCALAPPDATA%\rust-lang\miri\cache`; the exact

miri

@@ -48,6 +48,25 @@ Pass extra flags to all cargo invocations.
 EOF
 )
 
+## Run the subcommands that the user requested to always run first
+if [ -z "$AUTO_OPS" ]; then
+    export AUTO_OPS=42
+
+    # Run this first, so that the toolchain doesn't change after
+    # other code has run.
+    if [ -f ".auto-everything" ] || [ -f ".auto-toolchain" ] ; then
+        "$MIRIDIR"/rustup-toolchain
+    fi
+
+    if [ -f ".auto-everything" ] || [ -f ".auto-fmt" ] ; then
+        $0 fmt
+    fi
+
+    if [ -f ".auto-everything" ] || [ -f ".auto-clippy" ] ; then
+        $0 clippy -- -D warnings
+    fi
+fi
+
 ## Preparation
 # macOS does not have a useful readlink/realpath so we have to use Python instead...
 MIRIDIR=$(python3 -c 'import os, sys; print(os.path.dirname(os.path.realpath(sys.argv[1])))' "$0")