cargo-soothfast 0.3.3

//! `cargo soothfast report render|changelog` — doc fragments produced from
//! recorded data: perf tables, trend charts, badges, llms.txt, and a living
//! CHANGELOG.md whose Unreleased section is regenerated in place.

use std::path::PathBuf;

use serde_json::Value;
use soothfast_report::{badges, changelog, llms, perf_table, trend_chart};

use crate::{docs_support, invoke, workspace};

pub fn run(args: &[String]) -> i32 {
    match args.first().map(String::as_str) {
        Some("render") => render(&args[1..]),
        Some("changelog") => changelog_cmd(&args[1..]),
        _ => {
            eprintln!(
                "soothfast: usage: cargo soothfast report render|changelog -p PKG [-p PKG ...] [--out DIR|FILE] [--against-ref REF]"
            );
            2
        }
    }
}

struct ReportArgs {
    // Repeatable: `report render` accepts multiple `-p PKG` to combine
    // several crates' surfaces into one llms.txt (a facade crate's own
    // surface is typically too thin on its own — see llms.rs docs).
    pkg: Vec<String>,
    baseline: String,
    out: Option<PathBuf>,
    against_ref: Option<String>,
    features: Option<String>,
    bot_author: Option<String>,
}

fn parse(args: &[String]) -> Result<ReportArgs, String> {
    let mut a = ReportArgs {
        pkg: Vec::new(),
        baseline: "base".into(),
        out: None,
        against_ref: None,
        features: None,
        bot_author: None,
    };
    let mut it = args.iter();
    while let Some(arg) = it.next() {
        match arg.as_str() {
            "-p" | "--package" => a
                .pkg
                .push(it.next().cloned().ok_or("-p needs a package name")?),
            "--baseline" => a.baseline = it.next().cloned().ok_or("--baseline needs a name")?,
            "--out" => a.out = it.next().map(PathBuf::from),
            "--against-ref" => a.against_ref = it.next().cloned(),
            "--features" => a.features = it.next().cloned(),
            "--bot-author" => a.bot_author = it.next().cloned(),
            other => return Err(format!("unknown report arg {other:?}")),
        }
    }
    Ok(a)
}

fn load_baseline_required(name: &str) -> Result<Value, String> {
    match invoke::load_baseline(name) {
        Ok(Some(b)) => Ok(b),
        Ok(None) => Err(format!(
            "no baseline {name:?} — run `cargo soothfast measure --save-baseline {name}`"
        )),
        Err(e) => Err(e.to_string()),
    }
}

fn render(args: &[String]) -> i32 {
    let a = match parse(args) {
        Ok(a) => a,
        Err(e) => return err(&e),
    };
    let baseline = match load_baseline_required(&a.baseline) {
        Ok(b) => b,
        Err(e) => return err(&e),
    };
    let root = match invoke::workspace_root() {
        Ok(r) => r,
        Err(e) => return err(&e.to_string()),
    };
    let out_dir = a.out.clone().unwrap_or_else(|| root.join("docs/perf"));
    let _ = std::fs::create_dir_all(&out_dir);
    let _ = std::fs::create_dir_all(out_dir.join("badges"));

    let mut summary =
        String::from("# Performance summary\n\n> Generated by `cargo soothfast report`\n\n");
    summary.push_str(&perf_table::markdown(&baseline));

    // Trend charts from the series, when it exists.
    let trend_path = root.join(".soothfast").join("trend.jsonl");
    if let Ok(text) = std::fs::read_to_string(&trend_path) {
        let points: Vec<Value> = text
            .lines()
            .filter_map(|l| serde_json::from_str(l).ok())
            .collect();
        for (key, name, threshold, rel) in trend_chart::METRICS {
            if let Some(svg) = trend_chart::render(&points, key, name, *threshold, *rel) {
                let file = format!("trend-{name}.svg");
                if std::fs::write(out_dir.join(&file), svg).is_ok() {
                    summary.push_str(&format!("\n![{name} trend]({file})\n"));
                    println!("report: wrote {}", out_dir.join(&file).display());
                }
            }
        }
    }

    // Badge reflects the last recorded gate verdict, never a hardcoded pass.
    let gate_passed = std::fs::read_to_string(root.join(".soothfast/gate-status.json"))
        .ok()
        .and_then(|t| serde_json::from_str::<Value>(&t).ok())
        .and_then(|v| v["passed"].as_bool());
    let gate = badges::gate_badge(gate_passed);
    let writes: &[(&str, String)] = &[
        ("summary.md", summary),
        ("summary.html", perf_table::html(&baseline)),
        ("badges/gate.json", gate.to_string()),
        ("badges/gate.svg", badges::svg_from(&gate)),
    ];
    for (file, content) in writes {
        if std::fs::write(out_dir.join(file), content).is_err() {
            return err(&format!("cannot write {file}"));
        }
        println!("report: wrote {}", out_dir.join(file).display());
    }

    // llms.txt needs the public surface (nightly rustdoc); skip with a note
    // when no package is given. Multiple -p flags combine into one digest —
    // a single facade crate's own surface is typically too thin alone.
    if a.pkg.is_empty() {
        println!(
            "report: skipped llms.txt (pass -p PKG to generate; repeat -p for multiple crates)"
        );
    } else {
        let mut entries = Vec::new();
        for pkg in &a.pkg {
            match docs_support::surface_entries(pkg, a.features.as_deref()) {
                Ok(e) => entries.extend(e),
                Err(e) => return err(&format!("llms.txt needs the API surface of {pkg}: {e}")),
            }
        }
        let label = if a.pkg.len() == 1 {
            a.pkg[0].clone()
        } else {
            a.pkg.join(", ")
        };
        let text = llms::render(&label, &entries, &baseline);
        let path = out_dir.join("llms.txt");
        if std::fs::write(&path, text).is_err() {
            return err("cannot write llms.txt");
        }
        println!("report: wrote {}", path.display());
    }
    0
}

/// One diff per package, headed by the crate name when there is more than
/// one — an unattributed `ADDED foo::bar` says nothing about where it landed.
fn surface_diffs(pkgs: &[String], refname: &str, features: Option<&str>) -> Result<String, String> {
    let mut out = String::new();
    for pkg in pkgs {
        let text = docs_support::surface_diff_text(pkg, refname, features)?;
        if text.trim().is_empty() {
            continue;
        }
        if pkgs.len() > 1 {
            out.push_str(&format!("# {pkg}\n"));
        }
        out.push_str(text.trim_end());
        out.push_str("\n\n");
    }
    Ok(out)
}

/// Measure every `-p` package that carries a bench target at the merge-base
/// of `refname`, merged into one baseline-shaped document.
///
/// One worktree for all of them; packages without a bench target there are
/// skipped rather than failing the run, since a newly measured crate simply
/// has no earlier side to compare against. `Ok(None)` when that leaves
/// nothing measured, which renders the current-only table as before.
fn measure_ref(a: &ReportArgs, refname: &str) -> Result<Option<Value>, String> {
    let pkgs = a.pkg.clone();
    let features = a.features.clone();
    println!("report: measuring {refname} in a worktree for the perf delta");
    let runs = invoke::with_merge_base_worktree(refname, |wt| {
        let mut runs = Vec::new();
        for pkg in &pkgs {
            if !workspace::has_bench_target(pkg, "soothfast", Some(wt))
                .map_err(|e| e.to_string())?
            {
                continue;
            }
            let common = invoke::CommonArgs {
                pkg: Some(pkg.clone()),
                features: features.clone(),
                ..Default::default()
            };
            let records =
                invoke::run_bench_in(&common, &[], Some(wt)).map_err(|e| e.to_string())?;
            runs.push(invoke::collect(&records));
        }
        Ok(runs)
    })?;
    if runs.is_empty() {
        return Ok(None);
    }
    let mut items = serde_json::Map::new();
    let mut noise: Option<f64> = None;
    for run in &runs {
        if let Some(obj) = invoke::run_to_items_value(run).as_object() {
            items.extend(obj.clone());
        }
        if let Some(n) = run.noise_pct {
            noise = Some(noise.map_or(n, |m: f64| m.max(n)));
        }
    }
    let mut doc = serde_json::json!({ "version": 1, "items": items });
    if let Some(n) = noise {
        doc["noise_pct"] = serde_json::json!(n);
    }
    Ok(Some(doc))
}

fn changelog_cmd(args: &[String]) -> i32 {
    let mut a = match parse(args) {
        Ok(a) => a,
        Err(e) => return err(&e),
    };

    let root = match invoke::workspace_root() {
        Ok(r) => r,
        Err(e) => return err(&e.to_string()),
    };
    let cfg = match crate::changelog_config::load(&root) {
        Ok(c) => c,
        Err(e) => return err(&e),
    };
    if a.pkg.is_empty() {
        a.pkg = cfg.packages;
    }
    if a.pkg.is_empty() {
        return err("report changelog needs -p PKG");
    }
    let gate_cfg = match crate::gate_config::load(&root) {
        Ok(g) => g,
        Err(e) => return err(&e),
    };
    a.features = resolve_features(
        a.features.take(),
        cfg.features.as_deref(),
        gate_cfg.features.as_deref(),
    );
    let path = a.out.clone().unwrap_or_else(|| root.join("CHANGELOG.md"));
    let existing = std::fs::read_to_string(&path).unwrap_or_default();

    // A release PR renames the top heading away from "Unreleased" before
    // its own CI run gets here — regenerating on top of that would inject
    // a fresh Unreleased section the PR is already in the middle of
    // retiring, which then has to be hand-deleted after every release.
    if changelog_already_cut(&existing, a.against_ref.as_deref()) {
        println!(
            "report: {} already has a released top section — nothing to regenerate",
            path.display()
        );
        return 0;
    }

    let baseline = match load_baseline_required(&a.baseline) {
        Ok(b) => b,
        Err(e) => return err(&e),
    };

    // Without a reference there is no earlier surface to diff against, so
    // the release is described by what it contains. A facade crate's own
    // surface is thin; pass every crate whose API ships.
    let (diff_text, entries) = match &a.against_ref {
        Some(refname) => match surface_diffs(&a.pkg, refname, a.features.as_deref()) {
            Ok(t) => (t, Vec::new()),
            Err(e) => return err(&e),
        },
        None => {
            let mut all = Vec::new();
            for pkg in &a.pkg {
                match docs_support::surface_entries(pkg, a.features.as_deref()) {
                    Ok(e) => all.extend(e),
                    Err(e) => return err(&e),
                }
            }
            (String::new(), all)
        }
    };
    // Measuring the ref turns the Performance section from a point-in-time
    // snapshot into "what moved", which is what a changelog reader wants and
    // what keeps a no-op merge from rewriting the whole table.
    let ref_baseline = match &a.against_ref {
        Some(refname) => match measure_ref(&a, refname) {
            Ok(b) => b,
            Err(e) => return err(&e),
        },
        None => None,
    };
    let bot_author = resolve_bot_author(a.bot_author.take(), cfg.bot_author.as_deref());
    let changes = match &a.against_ref {
        Some(refname) => match merged_changes(refname, &bot_author) {
            Ok(c) => c,
            Err(e) => return err(&e),
        },
        None => Vec::new(),
    };
    let text = changelog::draft(&changelog::DraftInputs {
        changes: &changes,
        icons: &cfg.icons,
        api: match &a.against_ref {
            Some(refname) => changelog::ApiSection::Diff {
                against: refname,
                text: &diff_text,
            },
            None => changelog::ApiSection::Initial(&entries),
        },
        old_baseline: ref_baseline.as_ref(),
        new_baseline: &baseline,
        thresholds: changelog::PerfThresholds {
            instructions_pct: crate::gate::INSTRUCTIONS_THRESHOLD_PCT,
            allocs_pct: crate::gate::ALLOC_THRESHOLD_PCT as f64,
        },
    });

    if std::fs::write(&path, merge_changelog(&existing, &text)).is_err() {
        return err(&format!("cannot write {}", path.display()));
    }
    println!("report: regenerated {}", path.display());
    0
}

/// The features `report changelog` reads the API surface under: the command
/// line first, then `[changelog] features`, then `[gate] features`.
fn resolve_features(
    cli: Option<String>,
    changelog: Option<&str>,
    gate: Option<&str>,
) -> Option<String> {
    cli.or_else(|| changelog.or(gate).map(str::to_string))
}

/// The author `report changelog` leaves out: the command line first, then
/// `[changelog] bot-author`, then the slug the action ships with.
fn resolve_bot_author(cli: Option<String>, config: Option<&str>) -> String {
    cli.unwrap_or_else(|| config.unwrap_or(DEFAULT_BOT_AUTHOR).to_string())
}

/// Author of the soothfast bot's own commits, as `action/land.sh` commits
/// them under the default `bot-slug`.
const DEFAULT_BOT_AUTHOR: &str = "soothfast-bot[bot]";

/// Separates author from subject in the log format below. A unit separator
/// occurs in neither field.
const LOG_FIELD_SEP: char = '\u{1f}';

/// Subjects from `%an%x1f%s` log lines, minus the ones `bot_author` wrote.
/// That one author and no other: `dependabot[bot]` writes real changelog
/// entries, and a rule matching every `[bot]` would delete them all.
fn subjects_excluding_author(log: &str, bot_author: &str) -> Vec<String> {
    log.lines()
        .filter_map(|line| line.split_once(LOG_FIELD_SEP))
        .filter(|(author, _)| *author != bot_author)
        .map(|(_, subject)| subject.to_string())
        .collect()
}

/// Conventional-commit subjects merged since `refname`, newest first, with
/// the soothfast bot's own regeneration commits left out. Read from the log
/// rather than a forge API: every merge lands as a squash whose subject
/// already carries its pull request number, and whose author survives it.
fn merged_changes(refname: &str, bot_author: &str) -> Result<Vec<changelog::Change>, String> {
    let range = format!("{refname}..HEAD");
    let log = invoke::git(&["log", "--format=%an%x1f%s", &range]).map_err(|e| e.to_string())?;
    let subjects = subjects_excluding_author(&log, bot_author);
    let unparsed = changelog::unparsed_subjects(&subjects);
    if !unparsed.is_empty() {
        println!(
            "report: {} subject(s) since {refname} are not conventional commits and are left out:",
            unparsed.len()
        );
        for subject in unparsed {
            println!("  {subject}");
        }
    }
    Ok(changelog::changes_from_subjects(&subjects))
}

/// True only for the specific race the guard exists to catch: a release PR
/// that has renamed the top heading away from "Unreleased" in its own
/// branch, running before the matching tag exists. That PR's own CI still
/// diffs against the *previous* release's tag, so regenerating would inject
/// a fresh Unreleased section duplicating the one it's mid-flight retiring.
///
/// A normal PR sometime after that release has the same top heading, but by
/// then `against_ref` (the latest tag reachable from HEAD) has caught up to
/// match it — that's the signal a new Unreleased section is legitimately
/// due, not a race, so this returns false and regeneration proceeds.
///
/// A file with no `## ` heading yet, or one still under "Unreleased", is
/// never "already cut".
fn changelog_already_cut(existing: &str, against_ref: Option<&str>) -> bool {
    let Some(heading) = existing.lines().find_map(|l| l.strip_prefix("## ")) else {
        return false;
    };
    let heading = heading.trim_start();
    if heading.starts_with("Unreleased") || heading.starts_with("[Unreleased]") {
        return false;
    }
    let heading_version = heading
        .split_whitespace()
        .next()
        .unwrap_or("")
        .trim_start_matches('[')
        .split(']')
        .next()
        .unwrap_or("");
    match against_ref {
        Some(r) => heading_version != r.trim_start_matches('v'),
        // No tag at all reachable from HEAD only happens for a repo's very
        // first release, still mid-flight in its own PR — the same race,
        // just without a previous tag to compare against. Stay conservative.
        None => true,
    }
}

const NOTES_START: &str = "<!-- soothfast:notes -->";
const NOTES_END: &str = "<!-- /soothfast:notes -->";

/// Prompts for the sections a reader wants and no measurement can supply.
/// Commented out so an unfilled block renders as nothing.
const NOTES_SCAFFOLD: &str = "\
<!-- ### Overview -->
<!-- What this release means for someone using it. One paragraph. -->

<!-- ### Upgrade notes -->
<!-- What a consumer has to do. \"Nothing\" is a useful answer. -->
";

/// A maintainer's hand-written prose survives regeneration by living inside
/// a `soothfast:notes` marker pair in the Unreleased section; everything
/// else there is bot-owned and gets replaced. Malformed markers (missing or
/// out-of-order) are treated as no notes, rather than guessing.
fn extract_notes(unreleased: &str) -> Option<&str> {
    let start = unreleased.find(NOTES_START)? + NOTES_START.len();
    let end = unreleased[start..].find(NOTES_END)? + start;
    Some(unreleased[start..end].trim())
}

/// Replace the previous Unreleased section with the fresh draft, keeping
/// released sections — regeneration is idempotent, one Unreleased at a time.
/// Keep-a-Changelog files are respected: the preamble prose before the first
/// section survives, and a bracketed `## [Unreleased]` heading counts as the
/// Unreleased section to replace. A `soothfast:notes` block inside the old
/// Unreleased section rides along into the new one (see `extract_notes`).
fn merge_changelog(existing: &str, draft: &str) -> String {
    let mut preamble = String::new();
    let mut released = String::new();
    let mut unreleased = String::new();
    let mut seen_section = false;
    let mut keep = false;
    for line in existing.lines() {
        if let Some(h) = line.strip_prefix("## ") {
            seen_section = true;
            let h = h.trim_start();
            keep = !(h.starts_with("Unreleased") || h.starts_with("[Unreleased]"));
        }
        if !seen_section {
            // The title is re-emitted below; keep any other preamble prose.
            if line.trim() != "# Changelog" {
                preamble.push_str(line);
                preamble.push('\n');
            }
        } else if keep {
            released.push_str(line);
            released.push('\n');
        } else {
            unreleased.push_str(line);
            unreleased.push('\n');
        }
    }
    let mut doc = String::from("# Changelog\n");
    let pre = preamble.trim();
    if !pre.is_empty() {
        doc.push('\n');
        doc.push_str(pre);
        doc.push('\n');
    }
    doc.push('\n');
    match extract_notes(&unreleased).filter(|n| !n.is_empty()) {
        Some(notes) => {
            // Splice right after the heading line, ahead of the bot's own
            // API-surface/Performance sections.
            let (heading, rest) = draft.split_once('\n').unwrap_or((draft, ""));
            doc.push_str(heading);
            doc.push('\n');
            doc.push('\n');
            doc.push_str(NOTES_START);
            doc.push('\n');
            doc.push_str(notes);
            doc.push('\n');
            doc.push_str(NOTES_END);
            doc.push('\n');
            doc.push('\n');
            doc.push_str(rest.trim_start_matches('\n'));
        }
        None => {
            let (heading, rest) = draft.split_once('\n').unwrap_or((draft, ""));
            doc.push_str(heading);
            doc.push_str("\n\n");
            doc.push_str(NOTES_START);
            doc.push('\n');
            doc.push_str(NOTES_SCAFFOLD);
            doc.push_str(NOTES_END);
            doc.push_str("\n\n");
            doc.push_str(rest.trim_start_matches('\n'));
        }
    }
    doc.push('\n');
    if !released.is_empty() {
        doc.push('\n');
        doc.push_str(released.trim_end());
        doc.push('\n');
    }
    doc
}

fn err(msg: &str) -> i32 {
    eprintln!("soothfast: {msg}");
    2
}

#[cfg(test)]
mod tests {
    use super::{
        DEFAULT_BOT_AUTHOR, changelog_already_cut, merge_changelog, resolve_bot_author,
        resolve_features, subjects_excluding_author,
    };

    #[test]
    fn a_release_pr_still_diffing_against_the_previous_tag_is_already_cut() {
        // The race the guard exists for: top heading says 0.1.3, but the
        // ref this run would diff against (v0.1.2, since v0.1.3 isn't
        // tagged yet) is one release behind it.
        assert!(changelog_already_cut(
            "# Changelog\n\n## 0.1.3 - 2026-08-09\n\n- shipped\n",
            Some("v0.1.2")
        ));
        assert!(changelog_already_cut(
            "# Changelog\n\n## [2.8.0] - 2026-07-10\n\n- shipped\n",
            Some("v2.7.0")
        ));
    }

    #[test]
    fn a_release_pr_with_no_prior_tag_at_all_is_already_cut() {
        // A repo's very first release has no earlier tag to compare
        // against; stay conservative rather than guess.
        assert!(changelog_already_cut(
            "# Changelog\n\n## 0.1.0 - 2026-08-01\n\n- shipped\n",
            None
        ));
    }

    #[test]
    fn a_normal_pr_after_the_tag_catches_up_is_not_already_cut() {
        // Once v0.1.3 is tagged, a later PR's `against_ref` matches the top
        // heading exactly — that's not a race, it's a new cycle legitimately
        // starting, so regeneration should proceed and prepend a fresh
        // Unreleased section.
        assert!(!changelog_already_cut(
            "# Changelog\n\n## 0.1.3 - 2026-08-09\n\n- shipped\n",
            Some("v0.1.3")
        ));
        // Keep-a-Changelog repos bracket the version in the heading.
        assert!(!changelog_already_cut(
            "# Changelog\n\n## [3.0.0] - 2026-08-30\n\n- shipped\n",
            Some("v3.0.0")
        ));
        // Generators that link the version to a compare view close the
        // bracket mid-token, so the version has to be cut at the `]`.
        assert!(!changelog_already_cut(
            "# Changelog\n\n## [3.0.0](https://github.com/o/r/compare/v2.9.0...v3.0.0) - 2026-08-30\n\n- shipped\n",
            Some("v3.0.0")
        ));
    }

    #[test]
    fn a_normal_pr_with_an_unreleased_section_is_not_already_cut() {
        assert!(!changelog_already_cut(
            "# Changelog\n\n## Unreleased (draft vs v0.1.1)\n\nold\n",
            Some("v0.1.1")
        ));
        assert!(!changelog_already_cut(
            "# Changelog\n\n## [Unreleased]\n\nold\n",
            None
        ));
    }

    #[test]
    fn a_file_with_no_sections_yet_is_not_already_cut() {
        assert!(!changelog_already_cut("", None));
        assert!(!changelog_already_cut("# Changelog\n", Some("v0.1.0")));
    }

    #[test]
    fn merge_replaces_unreleased_and_keeps_released() {
        let existing =
            "# Changelog\n\n## Unreleased (draft vs abc)\n\nold\n\n## 0.1.0\n\n- shipped\n";
        let merged = merge_changelog(existing, "## Unreleased (draft vs def)\n\nnew");
        assert!(merged.contains("draft vs def"));
        assert!(!merged.contains("old"));
        assert!(merged.contains("## 0.1.0"));
        assert!(merged.contains("- shipped"));
        // Idempotent: merging the same draft again changes nothing.
        assert_eq!(
            merged,
            merge_changelog(&merged, "## Unreleased (draft vs def)\n\nnew")
        );
    }

    #[test]
    fn merge_into_empty_file() {
        let merged = merge_changelog("", "## Unreleased (draft vs abc)\n\nnew");
        assert!(merged.starts_with("# Changelog\n\n## Unreleased"));
    }

    #[test]
    fn merge_respects_keep_a_changelog_files() {
        let existing = "# Changelog\n\nAll notable changes are documented here.\n\n\
            ## [Unreleased]\n\nstale\n\n## [2.8.0] - 2026-07-10\n\n- shipped\n";
        let merged = merge_changelog(existing, "## Unreleased (draft vs v2.8.0)\n\nnew");
        // Preamble prose survives; the bracketed Unreleased section is replaced.
        assert!(merged.contains("All notable changes are documented here."));
        assert!(!merged.contains("stale"));
        assert!(!merged.contains("## [Unreleased]"));
        assert!(merged.contains("## [2.8.0] - 2026-07-10"));
        assert_eq!(
            merged,
            merge_changelog(&merged, "## Unreleased (draft vs v2.8.0)\n\nnew")
        );
    }

    #[test]
    fn hand_written_notes_survive_regeneration() {
        let existing = "# Changelog\n\n## Unreleased (draft vs abc)\n\n\
            <!-- soothfast:notes -->\nDomain handles gain chart/history.\n\
            <!-- /soothfast:notes -->\n\n### API surface\n\nold\n";
        let draft = "## Unreleased (draft vs def)\n\n### API surface\n\nnew";
        let merged = merge_changelog(existing, draft);
        assert!(merged.contains("Domain handles gain chart/history."));
        assert!(merged.contains("### API surface\n\nnew"));
        // A blank line separates the closing marker from the next section.
        assert!(merged.contains("<!-- /soothfast:notes -->\n\n### API surface"));
        // Notes land ahead of the bot's own sections, right after the heading.
        let notes_pos = merged.find("Domain handles").unwrap();
        let surface_pos = merged.find("### API surface").unwrap();
        assert!(notes_pos < surface_pos);
        // Idempotent: re-merging with the same draft carries the notes forward again.
        assert_eq!(merged, merge_changelog(&merged, draft));
    }

    #[test]
    fn a_section_with_no_notes_yet_gets_the_scaffold() {
        let existing = "# Changelog\n\n## Unreleased (draft vs abc)\n\nold\n";
        let merged = merge_changelog(existing, "## Unreleased (draft vs def)\n\nnew");
        assert!(!merged.contains("old"), "{merged}");
        assert!(merged.contains("new"), "{merged}");
        assert!(merged.contains("<!-- ### Overview -->"), "{merged}");
        assert!(merged.contains("<!-- ### Upgrade notes -->"), "{merged}");
        let notes = merged.find("<!-- soothfast:notes -->").unwrap();
        assert!(notes < merged.find("new").unwrap(), "{merged}");
    }

    #[test]
    fn the_scaffold_is_not_written_over_prose_that_exists() {
        let existing = "# Changelog\n\n## Unreleased (draft vs abc)\n\n\
            <!-- soothfast:notes -->\n### Overview\n\nwhat shipped\n\
            <!-- /soothfast:notes -->\n\nold\n";
        let merged = merge_changelog(existing, "## Unreleased (draft vs def)\n\nnew");
        assert!(merged.contains("what shipped"), "{merged}");
        assert!(!merged.contains("<!-- ### Overview -->"), "{merged}");
    }

    #[test]
    fn unclosed_notes_marker_is_treated_as_absent() {
        let existing = "# Changelog\n\n## Unreleased (draft vs abc)\n\n\
            <!-- soothfast:notes -->\nnever closed\n";
        let merged = merge_changelog(existing, "## Unreleased (draft vs def)\n\nnew");
        assert!(!merged.contains("never closed"));
        assert!(merged.contains("new"));
    }
    #[test]
    fn an_explicit_features_flag_beats_both_tables() {
        let got = resolve_features(Some("cli".into()), Some("changelog"), Some("gate"));
        assert_eq!(got.as_deref(), Some("cli"));
    }

    #[test]
    fn changelog_features_beat_gate_features() {
        let got = resolve_features(None, Some("changelog"), Some("gate"));
        assert_eq!(got.as_deref(), Some("changelog"));
    }

    #[test]
    fn gate_features_fill_in_when_nothing_else_does() {
        assert_eq!(
            resolve_features(None, None, Some("gate")).as_deref(),
            Some("gate")
        );
        assert_eq!(resolve_features(None, None, None), None);
    }

    #[test]
    fn the_bot_s_own_regeneration_commits_are_left_out() {
        let log = "soothfast-bot[bot]\u{1f}chore: regenerate soothfast outputs (#474)\n\
                   Harvey Tseng\u{1f}feat: read gate features from soothfast.toml (#475)\n";
        assert_eq!(
            subjects_excluding_author(log, DEFAULT_BOT_AUTHOR),
            ["feat: read gate features from soothfast.toml (#475)"]
        );
    }

    #[test]
    fn dependabot_commits_survive_the_filter() {
        let log = "dependabot[bot]\u{1f}chore(deps): bump serde from 1.0.2 to 1.0.3 (#476)\n\
                   soothfast-bot[bot]\u{1f}docs: regenerate CHANGELOG.md (#477)\n";
        assert_eq!(
            subjects_excluding_author(log, DEFAULT_BOT_AUTHOR),
            ["chore(deps): bump serde from 1.0.2 to 1.0.3 (#476)"]
        );
    }

    #[test]
    fn a_renamed_bot_author_filters_in_place_of_the_default() {
        let log = "acme-bot[bot]\u{1f}chore: regenerate soothfast outputs (#12)\n\
                   soothfast-bot[bot]\u{1f}feat: ship a thing (#13)\n";
        assert_eq!(
            subjects_excluding_author(log, "acme-bot[bot]"),
            ["feat: ship a thing (#13)"]
        );
    }

    #[test]
    fn an_explicit_bot_author_flag_beats_the_table() {
        assert_eq!(
            resolve_bot_author(Some("cli[bot]".into()), Some("toml[bot]")),
            "cli[bot]"
        );
    }

    #[test]
    fn the_table_fills_in_for_a_repo_that_renamed_the_slug() {
        assert_eq!(resolve_bot_author(None, Some("toml[bot]")), "toml[bot]");
    }

    #[test]
    fn the_shipped_slug_is_the_last_resort() {
        assert_eq!(resolve_bot_author(None, None), DEFAULT_BOT_AUTHOR);
    }

    #[test]
    fn a_subject_the_bot_did_not_write_is_kept_verbatim() {
        let log = "Harvey Tseng\u{1f}fix(server): drop a cache (#478)\n";
        assert_eq!(
            subjects_excluding_author(log, DEFAULT_BOT_AUTHOR),
            ["fix(server): drop a cache (#478)"]
        );
    }
}