feat(ops/gerrit-autosubmit): init simple gerrit autosubmitter r/7077

Adds a small Rust program that connects to the Gerrit API and uses a
simple algorithm to figure out which changes should be submitted, and
submits them:

* it fetches all changes the Gerrit query API considers
  submittable (i.e. all requirements fulfilled), and that have the
  `Autosubmit` label set

* it filters these changes down to those that are _actually_
  submittable (in Gerrit API terms: that have an active Submit button)

* it filters out those that would submit ancestors that are *not*
  marked with the `Autosubmit` label

* it submits the longest chain

After that it just loops.

There is no rebasing logic yet for when it "runs out" of submittable
changes, but it will not be difficult to add.

Relates to b/333.

Change-Id: Ib91ecf2c45b178e8c64ff7b2174d617d4c45efe2
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10131
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
Reviewed-by: ezemtsov <eugene.zemtsov@gmail.com>
Autosubmit: tazjin <tazjin@tvl.su>

1 files changed, 193 insertions, 0 deletions

diff --git a/ops/gerrit-autosubmit/src/main.rs b/ops/gerrit-autosubmit/src/main.rs
new file mode 100644
index 000000000000..9d7087d67deb
--- /dev/null
+++ b/ops/gerrit-autosubmit/src/main.rs
@@ -0,0 +1,193 @@
+//! gerrit-autosubmit connects to a Gerrit instance and submits the
+//! longest chain of changes in which all ancestors are ready and
+//! marked for autosubmit.
+//!
+//! It works like this:
+//!
+//! * it fetches all changes the Gerrit query API considers
+//!   submittable (i.e. all requirements fulfilled), and that have the
+//!   `Autosubmit` label set
+//!
+//! * it filters these changes down to those that are _actually_
+//!   submittable (in Gerrit API terms: that have an active Submit button)
+//!
+//! * it filters out those that would submit ancestors that are *not*
+//!   marked with the `Autosubmit` label
+//!
+//! * it submits the longest chain
+//!
+//! After that it just loops.
+
+use anyhow::{Context, Result};
+use std::collections::{BTreeMap, HashMap, HashSet};
+
+mod gerrit {
+    use anyhow::{anyhow, Context, Result};
+    use serde::Deserialize;
+    use serde_json::Value;
+    use std::collections::HashMap;
+    use std::env;
+
+    pub struct Config {
+        gerrit_url: String,
+        username: String,
+        password: String,
+    }
+
+    impl Config {
+        pub fn from_env() -> Result<Self> {
+            Ok(Config {
+                gerrit_url: env::var("GERRIT_URL")
+                    .context("Gerrit base URL (no trailing slash) must be set in GERRIT_URL")?,
+                username: env::var("GERRIT_USERNAME")
+                    .context("Gerrit username must be set in GERRIT_USERNAME")?,
+                password: env::var("GERRIT_PASSWORD")
+                    .context("Gerrit password must be set in GERRIT_PASSWORD")?,
+            })
+        }
+    }
+
+    #[derive(Deserialize)]
+    pub struct ChangeInfo {
+        pub id: String,
+        pub revisions: HashMap<String, Value>,
+    }
+
+    #[derive(Deserialize)]
+    pub struct Action {
+        #[serde(default)]
+        pub enabled: bool,
+    }
+
+    const GERRIT_RESPONSE_PREFIX: &'static str = ")]}'";
+
+    pub fn get<T: serde::de::DeserializeOwned>(cfg: &Config, endpoint: &str) -> Result<T> {
+        let response = crimp::Request::get(&format!("{}/a{}", cfg.gerrit_url, endpoint))
+            .user_agent("gerrit-autosubmit")?
+            .basic_auth(&cfg.username, &cfg.password)?
+            .send()?
+            .error_for_status(|r| anyhow!("request failed with status {}", r.status))?;
+
+        let result: T = serde_json::from_slice(&response.body[GERRIT_RESPONSE_PREFIX.len()..])?;
+        Ok(result)
+    }
+
+    pub fn submit(cfg: &Config, change_id: &str) -> Result<()> {
+        let response = crimp::Request::post(&format!(
+            "{}/a/changes/{}/submit",
+            cfg.gerrit_url, change_id
+        ))
+        .user_agent("gerrit-autosubmit")?
+        .basic_auth(&cfg.username, &cfg.password)?
+        .send()?
+        .error_for_status(|r| anyhow!("submit failed with status {}", r.status))?;
+
+        Ok(())
+    }
+}
+
+#[derive(Debug)]
+struct SubmittableChange {
+    id: String,
+    revision: String,
+}
+
+fn list_submittable(cfg: &gerrit::Config) -> Result<Vec<SubmittableChange>> {
+    let mut out = Vec::new();
+
+    let changes: Vec<gerrit::ChangeInfo> = gerrit::get(
+        &cfg,
+        "/changes/?q=is:submittable+label:Autosubmit+-is:wip+is:open&o=SKIP_DIFFSTAT&o=CURRENT_REVISION",
+    )
+    .context("failed to list submittable changes")?;
+
+    for change in changes.into_iter() {
+        out.push(SubmittableChange {
+            id: change.id,
+            revision: change
+                .revisions
+                .into_keys()
+                .next()
+                .context("change had no current revision")?,
+        });
+    }
+
+    Ok(out)
+}
+
+fn is_submittable(cfg: &gerrit::Config, change: &SubmittableChange) -> Result<bool> {
+    let response: HashMap<String, gerrit::Action> = gerrit::get(
+        cfg,
+        &format!(
+            "/changes/{}/revisions/{}/actions",
+            change.id, change.revision
+        ),
+    )
+    .context("failed to fetch actions for change")?;
+
+    match response.get("submit") {
+        None => Ok(false),
+        Some(action) => Ok(action.enabled),
+    }
+}
+
+fn submitted_with(cfg: &gerrit::Config, change_id: &str) -> Result<HashSet<String>> {
+    let response: Vec<gerrit::ChangeInfo> =
+        gerrit::get(cfg, &format!("/changes/{}/submitted_together", change_id))
+            .context("failed to fetch related change list")?;
+
+    Ok(response.into_iter().map(|c| c.id).collect())
+}
+
+fn autosubmit(cfg: &gerrit::Config) -> Result<bool> {
+    let mut submittable_changes: HashSet<String> = Default::default();
+
+    for change in list_submittable(&cfg)? {
+        if !is_submittable(&cfg, &change)? {
+            continue;
+        }
+
+        submittable_changes.insert(change.id.clone());
+    }
+
+    let mut chains: BTreeMap<usize, String> = Default::default();
+    for change_id in &submittable_changes {
+        let ancestors = submitted_with(&cfg, &change_id)?;
+        if ancestors.is_subset(&submittable_changes) {
+            chains.insert(
+                if ancestors.is_empty() {
+                    1
+                } else {
+                    ancestors.len()
+                },
+                change_id.clone(),
+            );
+        }
+    }
+
+    // BTreeMap::last_key_value gives us the value associated with the
+    // largest key, i.e. with the longest submittable chain of changes.
+    if let Some((count, change_id)) = chains.last_key_value() {
+        println!(
+            "submitting change {} with chain length {}",
+            change_id, count
+        );
+
+        gerrit::submit(cfg, change_id);
+
+        Ok(true)
+    } else {
+        println!("nothing ready for autosubmit, waiting ...");
+        Ok(false)
+    }
+}
+
+fn main() -> Result<()> {
+    let cfg = gerrit::Config::from_env()?;
+
+    loop {
+        if !autosubmit(&cfg)? {
+            std::thread::sleep_ms(30000);
+        }
+    }
+}