Implement sync subcommand in clippy_dev

Now that JOSH is used to sync, it is much easier to script the sync process.
This introduces the two commands `sync pull` and `sync push`. The first one will
pull changes from the Rust repo, the second one will push the changes to the
Rust repo. For details, see the documentation in the book.

clippy_dev/Cargo.toml

@@ -6,12 +6,15 @@ edition = "2021"
 
 [dependencies]
 aho-corasick = "1.0"
+chrono = { version = "0.4.38", default-features = false, features = ["clock"] }
 clap = { version = "4.4", features = ["derive"] }
+directories = "5"
 indoc = "1.0"
 itertools = "0.12"
 opener = "0.6"
 shell-escape = "0.1"
 walkdir = "2.3"
+xshell = "0.2"
 
 [features]
 deny-warnings = []

clippy_dev/src/lib.rs

@@ -22,5 +22,6 @@ pub mod lint;
 pub mod new_lint;
 pub mod serve;
 pub mod setup;
+pub mod sync;
 pub mod update_lints;
 pub mod utils;

clippy_dev/src/main.rs

@@ -3,7 +3,7 @@
 #![warn(rust_2018_idioms, unused_lifetimes)]
 
 use clap::{Args, Parser, Subcommand};
-use clippy_dev::{dogfood, fmt, lint, new_lint, serve, setup, update_lints, utils};
+use clippy_dev::{dogfood, fmt, lint, new_lint, serve, setup, sync, update_lints, utils};
 use std::convert::Infallible;
 
 fn main() {
@@ -75,6 +75,15 @@ fn main() {
             uplift,
         } => update_lints::rename(&old_name, new_name.as_ref().unwrap_or(&old_name), uplift),
         DevCommand::Deprecate { name, reason } => update_lints::deprecate(&name, reason.as_deref()),
+        DevCommand::Sync(SyncCommand { subcommand }) => match subcommand {
+            SyncSubcommand::Pull => sync::rustc_pull(),
+            SyncSubcommand::Push {
+                repo_path,
+                user,
+                branch,
+                force,
+            } => sync::rustc_push(repo_path, &user, branch, force),
+        },
     }
 }
 
@@ -225,6 +234,8 @@ enum DevCommand {
         /// The reason for deprecation
         reason: Option<String>,
     },
+    /// Sync between the rust repo and the Clippy repo
+    Sync(SyncCommand),
 }
 
 #[derive(Args)]
@@ -291,3 +302,31 @@ enum RemoveSubcommand {
     /// Remove the tasks added with 'cargo dev setup vscode-tasks'
     VscodeTasks,
 }
+
+#[derive(Args)]
+struct SyncCommand {
+    #[command(subcommand)]
+    subcommand: SyncSubcommand,
+}
+
+#[derive(Subcommand)]
+enum SyncSubcommand {
+    /// Pull changes from rustc and update the toolchain
+    Pull,
+    /// Push changes to rustc
+    Push {
+        /// The path to a rustc repo that will be used for pushing changes
+        repo_path: String,
+        #[arg(long)]
+        /// The GitHub username to use for pushing changes
+        user: String,
+        #[arg(long, short, default_value = "clippy-subtree-update")]
+        /// The branch to push to
+        ///
+        /// This is mostly for experimentation and usually the default should be used.
+        branch: String,
+        #[arg(long, short)]
+        /// Force push changes
+        force: bool,
+    },
+}

clippy_dev/src/sync.rs

@@ -0,0 +1,233 @@
+use std::fmt::Write;
+use std::path::Path;
+use std::process;
+use std::process::exit;
+
+use chrono::offset::Utc;
+use xshell::{cmd, Shell};
+
+use crate::utils::{clippy_project_root, replace_region_in_file, UpdateMode};
+
+const JOSH_FILTER: &str = ":rev(20b085d500dfba5afe0869707bf357af3afe20be:prefix=src/tools/clippy):/src/tools/clippy";
+const JOSH_PORT: &str = "42042";
+
+fn start_josh() -> impl Drop {
+    // Create a wrapper that stops it on drop.
+    struct Josh(process::Child);
+    impl Drop for Josh {
+        fn drop(&mut self) {
+            #[cfg(unix)]
+            {
+                // Try to gracefully shut it down.
+                process::Command::new("kill")
+                    .args(["-s", "INT", &self.0.id().to_string()])
+                    .output()
+                    .expect("failed to SIGINT josh-proxy");
+                // Sadly there is no "wait with timeout"... so we just give it some time to finish.
+                std::thread::sleep(std::time::Duration::from_secs(1));
+                // Now hopefully it is gone.
+                if self.0.try_wait().expect("failed to wait for josh-proxy").is_some() {
+                    return;
+                }
+            }
+            // If that didn't work (or we're not on Unix), kill it hard.
+            eprintln!("I have to kill josh-proxy the hard way, let's hope this does not break anything.");
+            self.0.kill().expect("failed to SIGKILL josh-proxy");
+        }
+    }
+
+    // Determine cache directory.
+    let local_dir = {
+        let user_dirs = directories::ProjectDirs::from("org", "rust-lang", "clippy-josh").unwrap();
+        user_dirs.cache_dir().to_owned()
+    };
+    println!("Using local cache directory: {}", local_dir.display());
+
+    // Start josh, silencing its output.
+    let mut cmd = process::Command::new("josh-proxy");
+    cmd.arg("--local").arg(local_dir);
+    cmd.arg("--remote").arg("https://github.com");
+    cmd.arg("--port").arg(JOSH_PORT);
+    cmd.arg("--no-background");
+    cmd.stdout(process::Stdio::null());
+    cmd.stderr(process::Stdio::null());
+    let josh = cmd
+        .spawn()
+        .expect("failed to start josh-proxy, make sure it is installed");
+    // Give it some time so hopefully the port is open.
+    std::thread::sleep(std::time::Duration::from_secs(1));
+
+    Josh(josh)
+}
+
+fn rustc_hash() -> String {
+    let sh = Shell::new().expect("failed to create shell");
+    // Make sure we pick up the updated toolchain (usually rustup pins the toolchain
+    // inside a single cargo/rustc invocation via this env var).
+    sh.set_var("RUSTUP_TOOLCHAIN", "");
+    cmd!(sh, "rustc --version --verbose")
+        .read()
+        .expect("failed to run `rustc -vV`")
+        .lines()
+        .find(|line| line.starts_with("commit-hash:"))
+        .expect("failed to parse `rustc -vV`")
+        .split_whitespace()
+        .last()
+        .expect("failed to get commit from `rustc -vV`")
+        .to_string()
+}
+
+fn assert_clean_repo(sh: &Shell) {
+    if !cmd!(sh, "git status --untracked-files=no --porcelain")
+        .read()
+        .expect("failed to run git status")
+        .is_empty()
+    {
+        eprintln!("working directory must be clean before running `cargo dev sync pull`");
+        exit(1);
+    }
+}
+
+pub fn rustc_pull() {
+    const MERGE_COMMIT_MESSAGE: &str = "Merge from rustc";
+
+    let sh = Shell::new().expect("failed to create shell");
+    sh.change_dir(clippy_project_root());
+
+    assert_clean_repo(&sh);
+
+    // Update rust-toolchain file
+    let date = Utc::now().format("%Y-%m-%d").to_string();
+    replace_region_in_file(
+        UpdateMode::Change,
+        Path::new("rust-toolchain"),
+        "# begin autogenerated version\n",
+        "# end autogenerated version",
+        |res| {
+            writeln!(res, "channel = \"nightly-{date}\"").unwrap();
+        },
+    );
+
+    let message = format!("Bump nightly version -> {date}");
+    cmd!(sh, "git commit rust-toolchain --no-verify -m {message}")
+        .run()
+        .expect("FAILED to commit rust-toolchain file, something went wrong");
+
+    let commit = rustc_hash();
+
+    // Make sure josh is running in this scope
+    {
+        let _josh = start_josh();
+
+        // Fetch given rustc commit.
+        cmd!(
+            sh,
+            "git fetch http://localhost:{JOSH_PORT}/rust-lang/rust.git@{commit}{JOSH_FILTER}.git"
+        )
+        .run()
+        .expect("FAILED to fetch new commits, something went wrong");
+    }
+
+    // This should not add any new root commits. So count those before and after merging.
+    let num_roots = || -> u32 {
+        cmd!(sh, "git rev-list HEAD --max-parents=0 --count")
+            .read()
+            .expect("failed to determine the number of root commits")
+            .parse::<u32>()
+            .unwrap()
+    };
+    let num_roots_before = num_roots();
+
+    // Merge the fetched commit.
+    cmd!(sh, "git merge FETCH_HEAD --no-verify --no-ff -m {MERGE_COMMIT_MESSAGE}")
+        .run()
+        .expect("FAILED to merge new commits, something went wrong");
+
+    // Check that the number of roots did not increase.
+    if num_roots() != num_roots_before {
+        eprintln!("Josh created a new root commit. This is probably not the history you want.");
+        exit(1);
+    }
+}
+
+pub(crate) const PUSH_PR_DESCRIPTION: &str = "Sync from Clippy commit:";
+
+pub fn rustc_push(rustc_path: String, github_user: &str, branch: String, force: bool) {
+    let sh = Shell::new().expect("failed to create shell");
+    sh.change_dir(clippy_project_root());
+
+    assert_clean_repo(&sh);
+
+    // Prepare the branch. Pushing works much better if we use as base exactly
+    // the commit that we pulled from last time, so we use the `rustc --version`
+    // to find out which commit that would be.
+    let base = rustc_hash();
+
+    println!("Preparing {github_user}/rust (base: {base})...");
+    sh.change_dir(rustc_path);
+    if !force
+        && cmd!(sh, "git fetch https://github.com/{github_user}/rust {branch}")
+            .ignore_stderr()
+            .read()
+            .is_ok()
+    {
+        eprintln!(
+            "The branch '{branch}' seems to already exist in 'https://github.com/{github_user}/rust'. Please delete it and try again."
+        );
+        exit(1);
+    }
+    cmd!(sh, "git fetch https://github.com/rust-lang/rust {base}")
+        .run()
+        .expect("failed to fetch base commit");
+    let force_flag = if force { "--force" } else { "" };
+    cmd!(
+        sh,
+        "git push https://github.com/{github_user}/rust {base}:refs/heads/{branch} {force_flag}"
+    )
+    .ignore_stdout()
+    .ignore_stderr() // silence the "create GitHub PR" message
+    .run()
+    .expect("failed to push base commit to the new branch");
+
+    // Make sure josh is running in this scope
+    {
+        let _josh = start_josh();
+
+        // Do the actual push.
+        sh.change_dir(clippy_project_root());
+        println!("Pushing Clippy changes...");
+        cmd!(
+            sh,
+            "git push http://localhost:{JOSH_PORT}/{github_user}/rust.git{JOSH_FILTER}.git HEAD:{branch}"
+        )
+        .run()
+        .expect("failed to push changes to Josh");
+
+        // Do a round-trip check to make sure the push worked as expected.
+        cmd!(
+            sh,
+            "git fetch http://localhost:{JOSH_PORT}/{github_user}/rust.git{JOSH_FILTER}.git {branch}"
+        )
+        .ignore_stderr()
+        .read()
+        .expect("failed to fetch the branch from Josh");
+    }
+
+    let head = cmd!(sh, "git rev-parse HEAD")
+        .read()
+        .expect("failed to get HEAD commit");
+    let fetch_head = cmd!(sh, "git rev-parse FETCH_HEAD")
+        .read()
+        .expect("failed to get FETCH_HEAD");
+    if head != fetch_head {
+        eprintln!("Josh created a non-roundtrip push! Do NOT merge this into rustc!");
+        exit(1);
+    }
+    println!("Confirmed that the push round-trips back to Clippy properly. Please create a rustc PR:");
+    let description = format!("{}+rust-lang/rust-clippy@{head}", PUSH_PR_DESCRIPTION.replace(" ", "+"));
+    println!(
+        // Open PR with `subtree update` title to silence the `no-merges` triagebot check
+        // See https://github.com/rust-lang/rust/pull/114157
+        "    https://github.com/rust-lang/rust/compare/{github_user}:{branch}?quick_pull=1&title=Clippy+subtree+update&body=r?+@ghost%0A%0A{description}"
+    );
+}