Make the pre-commit script pre-push instead

This should make it substantially less annoying, and hopefully more
people will find it useful. In particular, it will no longer run tidy
each time you run `git commit --amend` or rebase a branch.

This also warns if you have the old script in pre-commit; see the HACK
comment for details.

src/bootstrap/bin/main.rs

@@ -30,6 +30,7 @@ fn main() {
         println!("{}", suggestion);
     }
 
+    let pre_commit = config.src.join(".git").join("hooks").join("pre-commit");
     Build::new(config).build();
 
     if suggest_setup {
@@ -42,6 +43,19 @@ fn main() {
         println!("{}", suggestion);
     }
 
+    // Give a warning if the pre-commit script is in pre-commit and not pre-push.
+    // HACK: Since the commit script uses hard links, we can't actually tell if it was installed by x.py setup or not.
+    // We could see if it's identical to src/etc/pre-push.sh, but pre-push may have been modified in the meantime.
+    // Instead, look for this comment, which is almost certainly not in any custom hook.
+    if std::fs::read_to_string(pre_commit).map_or(false, |contents| {
+        contents.contains("https://github.com/rust-lang/rust/issues/77620#issuecomment-705144570")
+    }) {
+        println!(
+            "warning: You have the pre-push script installed to .git/hooks/pre-commit. \
+                  Consider moving it to .git/hooks/pre-push instead, which runs less often."
+        );
+    }
+
     if suggest_setup || changelog_suggestion.is_some() {
         println!("note: this message was printed twice to make it more likely to be seen");
     }

src/bootstrap/setup.rs

@@ -191,9 +191,9 @@ fn install_git_hook_maybe(src_path: &Path) -> io::Result<()> {
     let mut input = String::new();
     println!(
         "Rust's CI will automatically fail if it doesn't pass `tidy`, the internal tool for ensuring code quality.
-If you'd like, x.py can install a git hook for you that will automatically run `tidy --bless` on each commit
-to ensure your code is up to par. If you decide later that this behavior is undesirable,
-simply delete the `pre-commit` file from .git/hooks."
+If you'd like, x.py can install a git hook for you that will automatically run `tidy --bless` before
+pushing your code to ensure your code is up to par. If you decide later that this behavior is
+undesirable, simply delete the `pre-push` file from .git/hooks."
     );
 
     let should_install = loop {
@@ -213,21 +213,21 @@ simply delete the `pre-commit` file from .git/hooks."
     };
 
     if should_install {
-        let src = src_path.join("src").join("etc").join("pre-commit.sh");
+        let src = src_path.join("src").join("etc").join("pre-push.sh");
         let git = t!(Command::new("git").args(&["rev-parse", "--git-common-dir"]).output().map(
             |output| {
                 assert!(output.status.success(), "failed to run `git`");
                 PathBuf::from(t!(String::from_utf8(output.stdout)).trim())
             }
         ));
-        let dst = git.join("hooks").join("pre-commit");
+        let dst = git.join("hooks").join("pre-push");
         match fs::hard_link(src, &dst) {
             Err(e) => println!(
                 "error: could not create hook {}: do you already have the git hook installed?\n{}",
                 dst.display(),
                 e
             ),
-            Ok(_) => println!("Linked `src/etc/pre-commit.sh` to `.git/hooks/pre-commit`"),
+            Ok(_) => println!("Linked `src/etc/pre-commit.sh` to `.git/hooks/pre-push`"),
         };
     } else {
         println!("Ok, skipping installation!");

src/etc/pre-commit.sh → src/etc/pre-push.sh

@@ -16,7 +16,7 @@ if [[ "$OSTYPE" == "msys" || "$OSTYPE" == "win32" ]]; then
   COMMAND="python $COMMAND"
 fi
 
-echo "Running pre-commit script '$COMMAND'"
+echo "Running pre-push script '$COMMAND'"
 
 cd "$ROOT_DIR"