Add post-merge analysis CI workflow

.github/workflows/post-merge.yml

@@ -0,0 +1,36 @@
+# Workflow that runs after a merge to master, analyses changes in test executions
+# and posts the result to the merged PR.
+
+name: Post merge analysis
+
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  analysis:
+    runs-on: ubuntu-24.04
+    if: github.repository == 'rust-lang/rust'
+    permissions:
+      pull-requests: write
+    steps:
+      - uses: actions/checkout@v4
+      - name: Perform analysis and send PR
+        run: |
+          # Get closest bors merge commit
+          PARENT_COMMIT=`git rev-list --author='bors <[email protected]>' -n1 --first-parent HEAD^1`
+
+          # Find PRs for current and parent commit
+          HEAD_PR=`gh pr list --search "${{ github.sha }}" --state merged --json number --jq '.[0].number'`
+
+          echo "Parent: ${PARENT_COMMIT}"
+          echo "HEAD: ${{ github.sha }} (#${HEAD_PR})"
+
+          cd src/ci/citool
+
+          echo "Post-merge analysis result" > output.log
+          cargo run --release post-merge-analysis ${PARENT_COMMIT} ${{ github.sha }} >> output.log
+          cat output.log
+
+          gh pr comment ${HEAD_PR} -F output.log

src/build_helper/src/metrics.rs

@@ -74,7 +74,7 @@ pub struct Test {
     pub outcome: TestOutcome,
 }
 
-#[derive(Serialize, Deserialize)]
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, Hash)]
 #[serde(tag = "outcome", rename_all = "snake_case")]
 pub enum TestOutcome {
     Passed,

src/ci/citool/src/main.rs

@@ -1,5 +1,6 @@
 mod cpu_usage;
 mod datadog;
+mod merge_report;
 mod metrics;
 mod utils;
 
@@ -13,6 +14,7 @@ use serde_yaml::Value;
 
 use crate::cpu_usage::load_cpu_usage;
 use crate::datadog::upload_datadog_metric;
+use crate::merge_report::post_merge_report;
 use crate::metrics::postprocess_metrics;
 use crate::utils::load_env_var;
 
@@ -373,6 +375,13 @@ enum Args {
         /// Path to a CSV containing the CI job CPU usage.
         cpu_usage_csv: PathBuf,
     },
+    /// Generate a report of test execution changes between two rustc commits.
+    PostMergeReport {
+        /// Parent commit to use as a base of the comparison.
+        parent: String,
+        /// Current commit that will be compared to `parent`.
+        current: String,
+    },
 }
 
 #[derive(clap::ValueEnum, Clone)]
@@ -410,6 +419,9 @@ fn main() -> anyhow::Result<()> {
         Args::PostprocessMetrics { metrics_path, summary_path } => {
             postprocess_metrics(&metrics_path, &summary_path)?;
         }
+        Args::PostMergeReport { current: commit, parent } => {
+            post_merge_report(load_db(default_jobs_file)?, parent, commit)?;
+        }
     }
 
     Ok(())

src/ci/citool/src/merge_report.rs

@@ -0,0 +1,257 @@
+use std::cmp::Reverse;
+use std::collections::HashMap;
+
+use anyhow::Context;
+use build_helper::metrics::{JsonRoot, TestOutcome};
+
+use crate::JobDatabase;
+use crate::metrics::get_test_suites;
+
+type Sha = String;
+type JobName = String;
+
+/// Computes a post merge CI analysis report between the `parent` and `current` commits.
+pub fn post_merge_report(job_db: JobDatabase, parent: Sha, current: Sha) -> anyhow::Result<()> {
+    let jobs = download_all_metrics(&job_db, &parent, &current)?;
+    let diffs = aggregate_test_diffs(&jobs)?;
+    report_test_changes(diffs);
+
+    Ok(())
+}
+
+struct JobMetrics {
+    parent: Option<JsonRoot>,
+    current: JsonRoot,
+}
+
+/// Download before/after metrics for all auto jobs in the job database.
+fn download_all_metrics(
+    job_db: &JobDatabase,
+    parent: &str,
+    current: &str,
+) -> anyhow::Result<HashMap<JobName, JobMetrics>> {
+    let mut jobs = HashMap::default();
+
+    for job in &job_db.auto_jobs {
+        eprintln!("Downloading metrics of job {}", job.name);
+        let metrics_parent = match download_job_metrics(&job.name, parent) {
+            Ok(metrics) => Some(metrics),
+            Err(error) => {
+                eprintln!(
+                    r#"Did not find metrics for job `{}` at `{}`: {error:?}.
+Maybe it was newly added?"#,
+                    job.name, parent
+                );
+                None
+            }
+        };
+        let metrics_current = download_job_metrics(&job.name, current)?;
+        jobs.insert(
+            job.name.clone(),
+            JobMetrics { parent: metrics_parent, current: metrics_current },
+        );
+    }
+    Ok(jobs)
+}
+
+fn download_job_metrics(job_name: &str, sha: &str) -> anyhow::Result<JsonRoot> {
+    let url = get_metrics_url(job_name, sha);
+    let mut response = ureq::get(&url).call()?;
+    if !response.status().is_success() {
+        return Err(anyhow::anyhow!(
+            "Cannot fetch metrics from {url}: {}\n{}",
+            response.status(),
+            response.body_mut().read_to_string()?
+        ));
+    }
+    let data: JsonRoot = response
+        .body_mut()
+        .read_json()
+        .with_context(|| anyhow::anyhow!("cannot deserialize metrics from {url}"))?;
+    Ok(data)
+}
+
+fn get_metrics_url(job_name: &str, sha: &str) -> String {
+    let suffix = if job_name.ends_with("-alt") { "-alt" } else { "" };
+    format!("https://ci-artifacts.rust-lang.org/rustc-builds{suffix}/{sha}/metrics-{job_name}.json")
+}
+
+fn aggregate_test_diffs(
+    jobs: &HashMap<JobName, JobMetrics>,
+) -> anyhow::Result<Vec<AggregatedTestDiffs>> {
+    let mut job_diffs = vec![];
+
+    // Aggregate test suites
+    for (name, metrics) in jobs {
+        if let Some(parent) = &metrics.parent {
+            let tests_parent = aggregate_tests(parent);
+            let tests_current = aggregate_tests(&metrics.current);
+            let test_diffs = calculate_test_diffs(tests_parent, tests_current);
+            if !test_diffs.is_empty() {
+                job_diffs.push((name.clone(), test_diffs));
+            }
+        }
+    }
+
+    // Aggregate jobs with the same diff, as often the same diff will appear in many jobs
+    let job_diffs: HashMap<Vec<(Test, TestOutcomeDiff)>, Vec<String>> =
+        job_diffs.into_iter().fold(HashMap::new(), |mut acc, (job, diffs)| {
+            acc.entry(diffs).or_default().push(job);
+            acc
+        });
+
+    Ok(job_diffs
+        .into_iter()
+        .map(|(test_diffs, jobs)| AggregatedTestDiffs { jobs, test_diffs })
+        .collect())
+}
+
+fn calculate_test_diffs(
+    reference: TestSuiteData,
+    current: TestSuiteData,
+) -> Vec<(Test, TestOutcomeDiff)> {
+    let mut diffs = vec![];
+    for (test, outcome) in &current.tests {
+        match reference.tests.get(test) {
+            Some(before) => {
+                if before != outcome {
+                    diffs.push((
+                        test.clone(),
+                        TestOutcomeDiff::ChangeOutcome {
+                            before: before.clone(),
+                            after: outcome.clone(),
+                        },
+                    ));
+                }
+            }
+            None => diffs.push((test.clone(), TestOutcomeDiff::Added(outcome.clone()))),
+        }
+    }
+    for (test, outcome) in &reference.tests {
+        if !current.tests.contains_key(test) {
+            diffs.push((test.clone(), TestOutcomeDiff::Missing { before: outcome.clone() }));
+        }
+    }
+
+    diffs
+}
+
+/// Represents a difference in the outcome of tests between a base and a current commit.
+#[derive(Debug)]
+struct AggregatedTestDiffs {
+    /// All jobs that had the exact same test diffs.
+    jobs: Vec<String>,
+    test_diffs: Vec<(Test, TestOutcomeDiff)>,
+}
+
+#[derive(Eq, PartialEq, Hash, Debug)]
+enum TestOutcomeDiff {
+    ChangeOutcome { before: TestOutcome, after: TestOutcome },
+    Missing { before: TestOutcome },
+    Added(TestOutcome),
+}
+
+/// Aggregates test suite executions from all bootstrap invocations in a given CI job.
+#[derive(Default)]
+struct TestSuiteData {
+    tests: HashMap<Test, TestOutcome>,
+}
+
+#[derive(Hash, PartialEq, Eq, Debug, Clone)]
+struct Test {
+    name: String,
+}
+
+/// Extracts all tests from the passed metrics and map them to their outcomes.
+fn aggregate_tests(metrics: &JsonRoot) -> TestSuiteData {
+    let mut tests = HashMap::new();
+    let test_suites = get_test_suites(&metrics);
+    for suite in test_suites {
+        for test in &suite.tests {
+            let test_entry = Test { name: normalize_test_name(&test.name) };
+            tests.insert(test_entry, test.outcome.clone());
+        }
+    }
+    TestSuiteData { tests }
+}
+
+/// Normalizes Windows-style path delimiters to Unix-style paths.
+fn normalize_test_name(name: &str) -> String {
+    name.replace('\\', "/")
+}
+
+/// Prints test changes in Markdown format to stdout.
+fn report_test_changes(mut diffs: Vec<AggregatedTestDiffs>) {
+    println!("## Test differences");
+    if diffs.is_empty() {
+        println!("No test diffs found");
+        return;
+    }
+
+    // Sort diffs in decreasing order by diff count
+    diffs.sort_by_key(|entry| Reverse(entry.test_diffs.len()));
+
+    fn format_outcome(outcome: &TestOutcome) -> String {
+        match outcome {
+            TestOutcome::Passed => "pass".to_string(),
+            TestOutcome::Failed => "fail".to_string(),
+            TestOutcome::Ignored { ignore_reason } => {
+                let reason = match ignore_reason {
+                    Some(reason) => format!(" ({reason})"),
+                    None => String::new(),
+                };
+                format!("ignore{reason}")
+            }
+        }
+    }
+
+    fn format_diff(diff: &TestOutcomeDiff) -> String {
+        match diff {
+            TestOutcomeDiff::ChangeOutcome { before, after } => {
+                format!("{} -> {}", format_outcome(before), format_outcome(after))
+            }
+            TestOutcomeDiff::Missing { before } => {
+                format!("{} -> [missing]", format_outcome(before))
+            }
+            TestOutcomeDiff::Added(outcome) => {
+                format!("[missing] -> {}", format_outcome(outcome))
+            }
+        }
+    }
+
+    let max_diff_count = 10;
+    let max_job_count = 5;
+    let max_test_count = 10;
+
+    for diff in diffs.iter().take(max_diff_count) {
+        let mut jobs = diff.jobs.clone();
+        jobs.sort();
+
+        let jobs = jobs.iter().take(max_job_count).map(|j| format!("`{j}`")).collect::<Vec<_>>();
+
+        let extra_jobs = diff.jobs.len().saturating_sub(max_job_count);
+        let suffix = if extra_jobs > 0 {
+            format!(" (and {extra_jobs} {})", pluralize("other", extra_jobs))
+        } else {
+            String::new()
+        };
+        println!("- {}{suffix}", jobs.join(","));
+
+        let extra_tests = diff.test_diffs.len().saturating_sub(max_test_count);
+        for (test, outcome_diff) in diff.test_diffs.iter().take(max_test_count) {
+            println!("  - {}: {}", test.name, format_diff(&outcome_diff));
+        }
+        if extra_tests > 0 {
+            println!("  - (and {extra_tests} additional {})", pluralize("tests", extra_tests));
+        }
+    }
+
+    let extra_diffs = diffs.len().saturating_sub(max_diff_count);
+    if extra_diffs > 0 {
+        println!("\n(and {extra_diffs} additional {})", pluralize("diff", extra_diffs));
+    }
+}
+
+fn pluralize(text: &str, count: usize) -> String {
+    if count == 1 { text.to_string() } else { format!("{text}s") }
+}

src/ci/citool/src/metrics.rs

@@ -105,17 +105,21 @@ struct TestSuiteRecord {
     failed: u64,
 }
 
+fn test_metadata_name(metadata: &TestSuiteMetadata) -> String {
+    match metadata {
+        TestSuiteMetadata::CargoPackage { crates, stage, .. } => {
+            format!("{} (stage {stage})", crates.join(", "))
+        }
+        TestSuiteMetadata::Compiletest { suite, stage, .. } => {
+            format!("{suite} (stage {stage})")
+        }
+    }
+}
+
 fn aggregate_test_suites(suites: &[&TestSuite]) -> BTreeMap<String, TestSuiteRecord> {
     let mut records: BTreeMap<String, TestSuiteRecord> = BTreeMap::new();
     for suite in suites {
-        let name = match &suite.metadata {
-            TestSuiteMetadata::CargoPackage { crates, stage, .. } => {
-                format!("{} (stage {stage})", crates.join(", "))
-            }
-            TestSuiteMetadata::Compiletest { suite, stage, .. } => {
-                format!("{suite} (stage {stage})")
-            }
-        };
+        let name = test_metadata_name(&suite.metadata);
         let record = records.entry(name).or_default();
         for test in &suite.tests {
             match test.outcome {
@@ -134,7 +138,7 @@ fn aggregate_test_suites(suites: &[&TestSuite]) -> BTreeMap<String, TestSuiteRec
     records
 }
 
-fn get_test_suites(metrics: &JsonRoot) -> Vec<&TestSuite> {
+pub fn get_test_suites(metrics: &JsonRoot) -> Vec<&TestSuite> {
     fn visit_test_suites<'a>(nodes: &'a [JsonNode], suites: &mut Vec<&'a TestSuite>) {
         for node in nodes {
             match node {