omni_dev/coverage/

merge.rs

//! Checks on the per-shard reports of a sharded coverage run.
//!
//! The union itself is [`CoverageReport::merge`]. What lives here is the part
//! that keeps a merge honest: a shard that silently produced nothing, or was
//! measured under a different workspace root, would otherwise lower the merged
//! coverage — or simply not line up with the diff — without anyone noticing.

use std::path::Path;

use anyhow::{bail, Result};

use super::model::CoverageReport;

/// Fails when `report` has no executable lines.
///
/// A shard that ran instrumented tests lists every instrumented line, covered
/// or not, so a shard with none means the run failed or its report was lost.
/// Merging it in would not change the result — a union ignores an empty side —
/// so the failure would never surface; this is where it has to.
///
/// `label` names the shard in the message (normally its path). Call this on the
/// freshly parsed report, **before** path filtering: a shard whose files an
/// `--ignore-filename-regex` happens to exclude is not broken.
pub fn require_executable_lines(label: &str, report: &CoverageReport) -> Result<()> {
    if report.total_lines() == 0 {
        bail!(
            "coverage shard {label} has no executable lines; \
             a failed or empty shard would silently lower the merged coverage"
        );
    }
    Ok(())
}

/// Describes a shard measured under a different workspace root, or `None` when
/// it looks fine.
///
/// Report paths are made repo-relative by stripping one prefix, and a path
/// outside it keeps its directory components as if they were relative. A shard
/// from a runner with another workspace root therefore keys every file under a
/// path that exists nowhere in the repository, and its coverage merges in as
/// extra files rather than against the diff.
///
/// The signal is that the shard has absolute paths and **none** starts with
/// `prefix`. A shard with some in-tree paths is left alone, since reports
/// legitimately name a few out-of-tree files (the standard library, vendored
/// sources). Call this on the freshly parsed report, **before** the prefix is
/// stripped.
pub fn prefix_mismatch(label: &str, report: &CoverageReport, prefix: &Path) -> Option<String> {
    let prefix = prefix.to_string_lossy();
    let prefix_slash = format!("{}/", prefix.trim_end_matches('/'));
    let mut absolute = 0_usize;
    for path in report.files.keys() {
        if path.starts_with(&prefix_slash) {
            return None;
        }
        if path.starts_with('/') {
            absolute += 1;
        }
    }
    (absolute > 0).then(|| {
        format!(
            "coverage shard {label}: none of its {absolute} absolute file path(s) is under \
             `{}`, so it was probably measured under a different workspace root and its \
             files will not line up with the diff; pass --strip-prefix with that root, or \
             run every shard under the same one",
            prefix.trim_end_matches('/')
        )
    })
}

#[cfg(test)]
#[allow(clippy::unwrap_used, clippy::expect_used)]
mod tests {
    use super::*;
    use crate::coverage::model::FileCoverage;

    fn report(files: &[(&str, &[(u32, u64)])]) -> CoverageReport {
        let mut report = CoverageReport::new();
        for (path, lines) in files {
            let mut file = FileCoverage::new(*path);
            for &(line, hits) in *lines {
                file.record(line, hits);
            }
            report.insert(file);
        }
        report
    }

    #[test]
    fn an_empty_report_is_rejected_by_name() {
        let message = require_executable_lines("shard-2.lcov", &CoverageReport::new())
            .unwrap_err()
            .to_string();
        assert!(message.contains("shard-2.lcov"), "{message}");
        assert!(message.contains("no executable lines"), "{message}");
    }

    #[test]
    fn a_report_whose_files_have_no_lines_is_rejected() {
        // A parsed `SF:` block with no `DA:` records yields a file with no lines.
        let report = report(&[("src/a.rs", &[])]);
        assert!(require_executable_lines("s", &report).is_err());
    }

    #[test]
    fn a_report_with_executable_lines_passes() {
        let report = report(&[("src/a.rs", &[(1, 0)])]);
        require_executable_lines("s", &report).unwrap();
    }

    #[test]
    fn a_shard_under_another_root_is_flagged() {
        let report = report(&[
            ("/Users/dev/work/repo/src/a.rs", &[(1, 1)]),
            ("/Users/dev/work/repo/src/b.rs", &[(1, 1)]),
        ]);
        let message =
            prefix_mismatch("shard-2.lcov", &report, Path::new("/home/runner/work/repo")).unwrap();
        assert!(message.contains("shard-2.lcov"), "{message}");
        assert!(message.contains("2 absolute file path(s)"), "{message}");
        assert!(message.contains("`/home/runner/work/repo`"), "{message}");
        assert!(message.contains("--strip-prefix"), "{message}");
    }

    #[test]
    fn a_shard_with_some_in_tree_paths_is_not_flagged() {
        // The standard library and vendored sources are out of tree in every
        // llvm-cov report; they must not make an ordinary shard look wrong.
        let report = report(&[
            ("/home/runner/work/repo/src/a.rs", &[(1, 1)]),
            ("/rustc/abc123/library/core/src/option.rs", &[(1, 1)]),
        ]);
        assert_eq!(
            prefix_mismatch("s", &report, Path::new("/home/runner/work/repo")),
            None
        );
    }

    #[test]
    fn relative_paths_are_not_flagged() {
        let report = report(&[("src/a.rs", &[(1, 1)])]);
        assert_eq!(
            prefix_mismatch("s", &report, Path::new("/home/runner/work/repo")),
            None
        );
    }

    #[test]
    fn a_prefix_that_is_only_a_string_prefix_does_not_match() {
        // `/work/repo-two/…` shares the string prefix `/work/repo` but is a
        // different directory.
        let report = report(&[("/work/repo-two/src/a.rs", &[(1, 1)])]);
        assert!(prefix_mismatch("s", &report, Path::new("/work/repo")).is_some());
    }

    #[test]
    fn a_trailing_slash_on_the_prefix_is_ignored() {
        let report = report(&[("/work/repo/src/a.rs", &[(1, 1)])]);
        assert_eq!(
            prefix_mismatch("s", &report, Path::new("/work/repo/")),
            None
        );
    }
}