feat: migrate out of the flat store layout

src/cli/link.rs

@@ -19,6 +19,15 @@ pub enum Link {
 
     /// List untracked paths a sandbox would still see
     Check(Check),
+
+    /// Move this checkout's paths from the old store layout into its own directory
+    Migrate(Migrate),
+}
+
+#[derive(Args, Debug)]
+pub struct Migrate {
+    #[command(flatten)]
+    pub store: Store,
 }
 
 #[derive(Args, Debug)]

src/commands/link.rs

@@ -170,6 +170,12 @@ enum Stored {
 // the store mirrors the repository layout, so walking it finds every path this
 // repository has put there without asking git anything
 fn stored_paths(repo: &Repo, dir: &Path) -> Result<Vec<(PathBuf, Stored)>> {
+    mirrored_paths(repo, &repo.store, dir)
+}
+
+// the paths under `dir` as the repository would link them, with `mirror` as
+// the directory that stands for the repository root
+fn mirrored_paths(repo: &Repo, mirror: &Path, dir: &Path) -> Result<Vec<(PathBuf, Stored)>> {
     let mut found = Vec::new();
 
     let entries = match read_dir(dir) {
@@ -180,11 +186,11 @@ fn stored_paths(repo: &Repo, dir: &Path) -> Result<Vec<(PathBuf, Stored)>> {
 
     for entry in entries {
         let stored = entry?.path();
-        let rel = stored.strip_prefix(&repo.store).with_context(|| {
+        let rel = stored.strip_prefix(mirror).with_context(|| {
             format!(
                 "{} is not under the store {}",
                 stored.display(),
-                repo.store.display()
+                mirror.display()
             )
         })?;
         let src = repo.root.join(rel);
@@ -204,7 +210,7 @@ fn stored_paths(repo: &Repo, dir: &Path) -> Result<Vec<(PathBuf, Stored)>> {
         if state == Stored::Linked || !holds_dir {
             found.push((src, state));
         } else {
-            found.extend(stored_paths(repo, &stored)?);
+            found.extend(mirrored_paths(repo, mirror, &stored)?);
         }
     }
 
@@ -212,8 +218,29 @@ fn stored_paths(repo: &Repo, dir: &Path) -> Result<Vec<(PathBuf, Stored)>> {
     Ok(found)
 }
 
+// what this repository links into the flat layout above its own directory,
+// from before the store was keyed by checkout
+fn legacy_paths(repo: &Repo) -> Result<Vec<PathBuf>> {
+    let Some(legacy) = repo.store.parent() else {
+        return Ok(Vec::new());
+    };
+
+    Ok(mirrored_paths(repo, legacy, legacy)?
+        .into_iter()
+        .filter(|(_, state)| *state == Stored::Linked)
+        .map(|(src, _)| src)
+        .collect())
+}
+
+pub struct Summary {
+    pub store: PathBuf,
+    pub linked: usize,
+    pub other: usize,
+    pub legacy: usize,
+}
+
 // what the store holds, without the git questions check asks
-pub fn stored_summary(ctx: &Ctx, store: Option<&Path>) -> Result<(PathBuf, usize, usize)> {
+pub fn stored_summary(ctx: &Ctx, store: Option<&Path>) -> Result<Summary> {
     let repo = Repo::discover(ctx, store)?;
     let stored = stored_paths(&repo, &repo.store)?;
 
@@ -222,17 +249,27 @@ pub fn stored_summary(ctx: &Ctx, store: Option<&Path>) -> Result<(PathBuf, usize
         .filter(|(_, state)| *state == Stored::Linked)
         .count();
 
-    Ok((repo.store, linked, stored.len() - linked))
+    let legacy = legacy_paths(&repo)?.len();
+
+    Ok(Summary {
+        store: repo.store,
+        linked,
+        other: stored.len() - linked,
+        legacy,
+    })
 }
 
+pub const MIGRATE_HINT: &str = "run `ahab link migrate` to move them into it";
+
 // list what the store holds for this repository, the inverse of check
 pub fn list(ctx: &Ctx, args: &cli::List) -> Result<()> {
     let repo = Repo::discover(ctx, args.store.root())?;
     let stored = stored_paths(&repo, &repo.store)?;
+    let legacy = legacy_paths(&repo)?;
 
     line!("store: {}", repo.store.display());
 
-    if stored.is_empty() {
+    if stored.is_empty() && legacy.is_empty() {
         line!("nothing in the store for this repository");
         return Ok(());
     }
@@ -248,6 +285,67 @@ pub fn list(ctx: &Ctx, args: &cli::List) -> Result<()> {
         entry(verb, rel);
     }
 
+    for path in &legacy {
+        entry("legacy", path.strip_prefix(&repo.root).unwrap_or(path));
+    }
+    if !legacy.is_empty() {
+        line!(
+            "{} path{} in the old layout, {MIGRATE_HINT}",
+            legacy.len(),
+            plural(legacy.len())
+        );
+    }
+
+    Ok(())
+}
+
+// move this checkout's paths from the old layout into its own directory
+pub fn migrate(ctx: &Ctx, args: &cli::Migrate) -> Result<()> {
+    let repo = Repo::discover(ctx, args.store.root())?;
+    let report = Report::new(&repo);
+    let legacy = legacy_paths(&repo)?;
+
+    if legacy.is_empty() {
+        note!(ctx, "nothing in the old layout for this repository");
+        return Ok(());
+    }
+
+    each(&legacy, |src| migrate_one(ctx, &repo, src, &report))
+}
+
+fn migrate_one(ctx: &Ctx, repo: &Repo, src: &Path, report: &Report) -> Result<()> {
+    let rel = repo.relative(src)?;
+    let old = read_link(src)?;
+    let target = repo.store.join(&rel);
+
+    if symlink_metadata_opt(&target)?.is_some() {
+        bail!(
+            "{} already exists; restore {} and add it again instead",
+            target.display(),
+            rel.display()
+        );
+    }
+
+    stays_in_store(repo, &rel)?;
+    ctx.fs().ensure_private_parent(&repo.base, &target)?;
+    ctx.fs().move_path(&old, &target)?;
+
+    // the link still names the old place until it is repointed, so a failure
+    // here puts the payload back where it points
+    if let Err(e) = ctx.fs().place_link(src, &target) {
+        ctx.fs().move_path(&target, &old).with_context(|| {
+            format!(
+                "could not put {} back after failing to link {} to it",
+                old.display(),
+                rel.display()
+            )
+        })?;
+
+        return Err(e);
+    }
+
+    ctx.fs().prune_empty(old.parent(), &repo.base);
+    report.line("migrated", &rel);
     Ok(())
 }
 

src/commands/status.rs

@@ -32,12 +32,15 @@ pub fn status(ctx: &Ctx, store: Option<&Path>) -> Result<()> {
 fn stored(ctx: &Ctx, store: Option<&Path>) {
     match link::stored_summary(ctx, store) {
         Err(e) => line!("store: {e:#}"),
-        Ok((store, linked, other)) => {
-            line!("store: {}", store.display());
-            line!("\tlinked:    {linked}");
+        Ok(summary) => {
+            line!("store: {}", summary.store.display());
+            line!("\tlinked:    {}", summary.linked);
 
-            if other > 0 {
-                line!("\tnot linked: {other} (see `ahab link list`)");
+            if summary.other > 0 {
+                line!("\tnot linked: {} (see `ahab link list`)", summary.other);
+            }
+            if summary.legacy > 0 {
+                line!("\tlegacy:    {} ({})", summary.legacy, link::MIGRATE_HINT);
             }
 
             line!("\t`ahab link check` lists what a sandbox can still read");

src/main.rs

@@ -94,6 +94,7 @@ fn run(ctx: &Ctx, command: cli::Commands) -> Result<ExitCode> {
             cli::Link::Add(args) => commands::link::add(ctx, &args).map(|()| done),
             cli::Link::List(args) => commands::link::list(ctx, &args).map(|()| done),
             cli::Link::Restore(args) => commands::link::restore(ctx, &args).map(|()| done),
+            cli::Link::Migrate(args) => commands::link::migrate(ctx, &args).map(|()| done),
             // the one command with something to say through its exit code
             cli::Link::Check(args) => match commands::link::check(ctx, &args)? && args.exit_code {
                 true => Ok(ExitCode::from(FINDINGS)),