arcature-cli 2026.2.0

//! Transactional generator plan (PROGRAM.md AP2.1-11): plan → conflict-detect
//! → dry-run → stage → validate → rollback-on-failure.
//!
//! A [`Plan`] is a small multi-file transaction used by the `arc make`
//! generators. It never silently overwrites user files: every create is
//! conflict-checked before any file is touched, a dry run reports exactly
//! what would happen without touching the filesystem, and a staged write
//! that fails a caller-provided validation step rolls back — removing only
//! the files the plan created and restoring any file it modified.
//!
//! # Why a transaction
//!
//! Before this, [`super::write::write_file`] handled one file at a time with
//! a per-file refuse-overwrite guard. A generator that writes several files
//! (a source file *and* a `pub mod` declaration appended to the module's
//! `mod.rs`) could fail halfway through, leaving the project in a partial
//! state. [`Plan`] makes that multi-file write atomic from the caller's view:
//! either every op lands, or — on conflict or validation failure — the
//! project is left as it was.
//!
//! # Rollback scope
//!
//! Rollback only ever touches files the plan itself created or modified. It
//! never deletes a file the plan did not write, and it restores the exact
//! original content of a file it overwrote or appended to. A pre-existing
//! user file is therefore always recoverable to its pre-plan state.
//!
//! # Validation
//!
//! The optional validation step runs *after* staging, with every planned
//! file on disk, so a validator can compile-check or read back what was
//! written. On failure the plan rolls back and returns
//! [`PlanError::Validation`]. The shipped generators pass `None` (the
//! conflict checks are their safety boundary this wave); the hook is the seam
//! future schema-aware generators (model/crud/api-resource) plug a real
//! compile check into once `#[model]` freezes in AP2.1-6.
//!
//! # Path safety
//!
//! Each operation's path must already be validated by the generator (the
//! [`super::naming`] helpers enforce containment within the project root and
//! reject path traversal). The plan does not re-canonicalize; it owns the
//! transactional write/rollback mechanics, not path validation.

use std::path::{Path, PathBuf};

#[cfg(test)]
use super::naming;

/// One staged filesystem operation in a [`Plan`].
#[derive(Debug, Clone)]
pub(crate) enum PlannedOp {
    /// Create a new file at `path` with `content`.
    Create {
        /// The absolute destination path (already validated by the generator).
        path: PathBuf,
        /// The full file content to write.
        content: String,
    },
    /// Append `declaration` to `path` if it is not already present
    /// (idempotent — the same declaration is never appended twice). Creates
    /// the file if it does not exist. This is how a generator adds a
    /// `pub mod <name>;` line to a module's `mod.rs`.
    Append {
        /// The destination file (e.g. `src/<module>/mod.rs`).
        path: PathBuf,
        /// The line to append if absent (e.g. `pub mod links_mail;`).
        declaration: String,
    },
}

/// The overwrite policy for create operations. Set per execution from the
/// CLI `--force` flag; the shipped generators always use [`Refuse`](Self::Refuse).
#[derive(Debug, Clone, Copy, Eq, PartialEq)]
pub(crate) enum OverwritePolicy {
    /// Refuse to create a file that already exists. The default; user files
    /// are never silently overwritten.
    Refuse,
    /// Overwrite an existing file. Explicit only (CLI `--force`). The
    /// original content is captured before writing so rollback can restore it.
    Overwrite,
}

/// A caller-provided validation step run after staging. Receives the paths
/// the plan just wrote, in stage order. Returning `Err` triggers rollback.
pub(crate) type Validator = Box<dyn FnOnce(&[PathBuf]) -> Result<(), String>>;

/// A typed failure from a [`Plan`] execution (AGENTS.md §18: no raw `String`
/// errors at the API boundary).
#[derive(Debug)]
pub(crate) enum PlanError {
    /// A create operation refused to overwrite an existing file. Carries the
    /// exact conflicting path so the CLI can report it verbatim.
    Conflict(PathBuf),
    /// A filesystem operation (create directory, read, write, remove) failed.
    Io {
        /// The path the operation targeted.
        path: PathBuf,
        /// The underlying error message.
        error: String,
    },
    /// The post-stage validation step failed; the plan rolled back. Carries
    /// the validator's message.
    Validation(String),
}

impl PlanError {
    fn io(path: PathBuf, error: impl Into<String>) -> Self {
        Self::Io {
            path,
            error: error.into(),
        }
    }
}

impl std::fmt::Display for PlanError {
    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Conflict(path) => write!(
                formatter,
                "refusing to overwrite existing file: {}",
                path.display()
            ),
            Self::Io { path, error } => {
                write!(formatter, "filesystem error at {}: {error}", path.display())
            }
            Self::Validation(message) => {
                write!(formatter, "validation failed; rolled back: {message}")
            }
        }
    }
}

impl std::error::Error for PlanError {}

/// A multi-file generator transaction.
pub(crate) struct Plan {
    ops: Vec<PlannedOp>,
    /// Rollback bookkeeping, populated during [`stage`]. Each entry records
    /// exactly how to undo one op: delete a file the plan created, or restore
    /// the original content of a file the plan modified.
    rollback: Vec<RollbackStep>,
}

/// One undo step captured during staging.
#[derive(Debug)]
enum RollbackStep {
    /// The plan created this file (it did not exist before); rollback deletes it.
    DeleteCreated(PathBuf),
    /// The plan modified or overwrote this file; rollback restores `original`.
    /// `original` is `None` when the plan created the file via an append (the
    /// file did not exist before) — rollback then deletes it.
    Restore {
        path: PathBuf,
        original: Option<String>,
    },
}

impl Plan {
    /// An empty plan.
    pub(crate) fn new() -> Self {
        Self {
            ops: Vec::new(),
            rollback: Vec::new(),
        }
    }

    /// Add a create op. The path must already be validated by the generator.
    pub(crate) fn create(mut self, path: PathBuf, content: String) -> Self {
        self.ops.push(PlannedOp::Create { path, content });
        self
    }

    /// Add an idempotent append op. `declaration` is appended to `path` only
    /// if not already present.
    pub(crate) fn append(mut self, path: PathBuf, declaration: String) -> Self {
        self.ops.push(PlannedOp::Append { path, declaration });
        self
    }

    /// Whether the plan has any operations.
    pub(crate) fn is_empty(&self) -> bool {
        self.ops.is_empty()
    }

    /// The operations in stage order (for inspection / dry-run reporting).
    /// Test-only: the shipped generators call `execute` / `dry_run_report`
    /// directly; this accessor exists so unit tests can assert the plan's
    /// shape before committing it.
    #[cfg(test)]
    pub(crate) fn ops(&self) -> &[PlannedOp] {
        &self.ops
    }

    /// Detect create-op conflicts against the current filesystem. Returns
    /// [`PlanError::Conflict`] with the exact conflicting path on the first
    /// create that would overwrite under [`OverwritePolicy::Refuse`]. Append
    /// ops never conflict (appending is always allowed; idempotency is
    /// resolved at stage time).
    fn detect_conflicts(&self, overwrite: OverwritePolicy) -> Result<(), PlanError> {
        if overwrite == OverwritePolicy::Overwrite {
            return Ok(());
        }
        for op in &self.ops {
            if let PlannedOp::Create { path, .. } = op
                && path.exists()
            {
                return Err(PlanError::Conflict(path.clone()));
            }
        }
        Ok(())
    }

    /// Build a human-readable dry-run report. Touches no files. Conflict
    /// detection runs first so a conflicting dry run reports the exact file
    /// rather than pretending it would succeed.
    pub(crate) fn dry_run_report(&self, overwrite: OverwritePolicy) -> Result<String, PlanError> {
        self.detect_conflicts(overwrite)?;
        let mut lines = Vec::with_capacity(self.ops.len() + 1);
        lines.push("dry run: no files will be written".to_owned());
        for op in &self.ops {
            lines.push(describe_op(op));
        }
        Ok(lines.join("\n"))
    }

    /// Execute the plan as a commit: conflict-detect → stage → validate (if
    /// provided) → rollback on validation failure. Returns the list of paths
    /// the plan wrote, in stage order.
    ///
    /// For a dry run, call [`Plan::dry_run_report`] instead — it reports
    /// conflicts and the planned actions without touching the filesystem.
    ///
    /// # Errors
    ///
    /// [`PlanError::Conflict`] — a create op would overwrite under
    /// [`OverwritePolicy::Refuse`]. [`PlanError::Io`] — a filesystem op
    /// failed (the plan rolls back what it staged so far). [`PlanError::Validation`]
    /// — the validator failed and the plan rolled back.
    pub(crate) fn execute(
        &mut self,
        overwrite: OverwritePolicy,
        validate: Option<Validator>,
    ) -> Result<Vec<PathBuf>, PlanError> {
        self.detect_conflicts(overwrite)?;
        let written = self.stage(overwrite)?;
        if let Some(validator) = validate
            && let Err(message) = validator(&written)
        {
            // Rollback swallows its own IO errors only to surface the
            // validation failure (the primary cause); a rollback IO
            // failure is appended to the returned message so it is not
            // silently lost.
            let rollback_note = match self.rollback() {
                Ok(()) => String::new(),
                Err(PlanError::Io { path, error }) => {
                    format!(" (rollback also failed at {}: {error})", path.display())
                }
                Err(other) => format!(" (rollback also failed: {other})"),
            };
            return Err(PlanError::Validation(format!("{message}{rollback_note}")));
        }
        Ok(written)
    }

    /// Stage every op to disk, recording rollback steps. Returns the paths
    /// written, in stage order. On an IO failure mid-stage, the plan rolls
    /// back what it has staged so far and returns the IO error.
    fn stage(&mut self, overwrite: OverwritePolicy) -> Result<Vec<PathBuf>, PlanError> {
        // Take ownership of the ops so we can call `&mut self` stage helpers
        // without borrowing `self.ops` immutably at the same time. The ops
        // are cheap `Clone`s (path + content strings); correctness matters
        // more than the one allocation here.
        let ops = std::mem::take(&mut self.ops);
        let mut written = Vec::with_capacity(ops.len());
        for op in &ops {
            match op {
                PlannedOp::Create { path, content } => {
                    match self.stage_create(path, content, overwrite) {
                        Ok(()) => written.push(path.clone()),
                        Err(error) => {
                            // Restore the ops so a retry is possible; surface
                            // the primary IO error after rolling back.
                            self.ops = ops;
                            let _ = self.rollback();
                            return Err(error);
                        }
                    }
                }
                PlannedOp::Append { path, declaration } => {
                    match self.stage_append(path, declaration) {
                        Ok(Some(())) => written.push(path.clone()),
                        Ok(None) => {} // idempotent no-op: nothing written
                        Err(error) => {
                            self.ops = ops;
                            let _ = self.rollback();
                            return Err(error);
                        }
                    }
                }
            }
        }
        self.ops = ops;
        Ok(written)
    }

    /// Stage one create op. Captures rollback info: delete if the plan
    /// created the file, restore the original if it overwrote an existing
    /// file (only under [`OverwritePolicy::Overwrite`]).
    fn stage_create(
        &mut self,
        path: &Path,
        content: &str,
        overwrite: OverwritePolicy,
    ) -> Result<(), PlanError> {
        let existed = path.exists();
        if existed && overwrite == OverwritePolicy::Refuse {
            return Err(PlanError::Conflict(path.to_path_buf()));
        }
        if let Some(parent) = path.parent() {
            std::fs::create_dir_all(parent)
                .map_err(|e| PlanError::io(path.to_path_buf(), e.to_string()))?;
        }
        if existed {
            // Overwrite path: capture the original so rollback can restore it.
            let original = std::fs::read_to_string(path)
                .map_err(|e| PlanError::io(path.to_path_buf(), e.to_string()))?;
            self.rollback.push(RollbackStep::Restore {
                path: path.to_path_buf(),
                original: Some(original),
            });
        } else {
            self.rollback
                .push(RollbackStep::DeleteCreated(path.to_path_buf()));
        }
        std::fs::write(path, content)
            .map_err(|e| PlanError::io(path.to_path_buf(), e.to_string()))?;
        Ok(())
    }

    /// Stage one append op, idempotently. If `declaration` is already in the
    /// file, this is a no-op (no rollback step recorded). Otherwise the
    /// original content (or `None` if the file did not exist) is captured for
    /// rollback and the declaration is appended.
    fn stage_append(&mut self, path: &Path, declaration: &str) -> Result<Option<()>, PlanError> {
        let original: Option<String> = std::fs::read_to_string(path).ok();
        let existed = original.is_some();
        if let Some(existing) = &original
            && existing.contains(declaration)
        {
            return Ok(None);
        }
        if let Some(parent) = path.parent() {
            std::fs::create_dir_all(parent)
                .map_err(|e| PlanError::io(path.to_path_buf(), e.to_string()))?;
        }
        // Capture the rollback original (the pre-plan content if the file
        // existed, else `None` to signal "the plan created this file").
        let rollback_original = if existed { original.clone() } else { None };
        let mut content = original.unwrap_or_default();
        if !content.is_empty() && !content.ends_with('\n') {
            content.push('\n');
        }
        content.push_str(declaration);
        content.push('\n');
        std::fs::write(path, content)
            .map_err(|e| PlanError::io(path.to_path_buf(), e.to_string()))?;
        self.rollback.push(RollbackStep::Restore {
            path: path.to_path_buf(),
            original: rollback_original,
        });
        Ok(Some(()))
    }

    /// Roll back every staged op, in reverse stage order. Only touches files
    /// the plan created or modified. A rollback failure does not abort the
    /// remaining undo steps (best-effort full undo) but is returned.
    fn rollback(&mut self) -> Result<(), PlanError> {
        let mut last_err: Option<PlanError> = None;
        while let Some(step) = self.rollback.pop() {
            if let Err(e) = self.undo(step) {
                last_err = Some(e);
            }
        }
        match last_err {
            Some(e) => Err(e),
            None => Ok(()),
        }
    }

    /// Undo one rollback step.
    fn undo(&self, step: RollbackStep) -> Result<(), PlanError> {
        match step {
            RollbackStep::DeleteCreated(path) => {
                // Only delete if the file still exists and matches a file we
                // created. We never delete a path we did not stage.
                std::fs::remove_file(&path).map_err(|e| PlanError::io(path, e.to_string()))
            }
            RollbackStep::Restore { path, original } => match original {
                Some(content) => {
                    std::fs::write(&path, content).map_err(|e| PlanError::io(path, e.to_string()))
                }
                None => {
                    // The plan created the file via an append (it did not
                    // exist before). Remove it to restore the pre-plan state.
                    if path.exists() {
                        std::fs::remove_file(&path).map_err(|e| PlanError::io(path, e.to_string()))
                    } else {
                        Ok(())
                    }
                }
            },
        }
    }
}

impl Default for Plan {
    fn default() -> Self {
        Self::new()
    }
}

/// Describe one op for a dry-run report, touching no files.
fn describe_op(op: &PlannedOp) -> String {
    match op {
        PlannedOp::Create { path, .. } => {
            format!("would create {}", path.display())
        }
        PlannedOp::Append { path, declaration } => {
            let existing = std::fs::read_to_string(path).unwrap_or_default();
            if existing.contains(declaration) {
                format!(
                    "{} already declares `{declaration}` — no change",
                    path.display()
                )
            } else {
                format!("would append `{declaration}` to {}", path.display())
            }
        }
    }
}

/// Append a `pub mod <stem>;` declaration to a module's `mod.rs` as an
/// idempotent [`Plan`] op. The declaration is derived and validated by
/// [`naming`]; this is the transactional counterpart of the direct
/// [`naming::append_mod_declaration`] used by the per-file generators.
///
/// Test-only: the shipped generators build their append ops inline via
/// `Plan::append`; this helper exists so the plan's mod-declaration op is
/// constructable in one place for tests. A future UAG-aware generator may
/// promote it to non-test use.
#[cfg(test)]
pub(crate) fn append_mod_declaration_op(
    root: &Path,
    module: &str,
    file_stem: &str,
) -> Result<PlannedOp, String> {
    let mod_rs = super::write::module_mod_rs(root, module);
    let declaration = naming::mod_declaration(file_stem)?;
    Ok(PlannedOp::Append {
        path: mod_rs,
        declaration,
    })
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::fs;
    use std::path::PathBuf;

    fn temp_root(label: &str) -> PathBuf {
        let root = std::env::temp_dir().join(format!(
            "arcature-cli-plan-{label}-{}-{}",
            std::process::id(),
            unique_suffix()
        ));
        fs::create_dir_all(&root).expect("temp root should be created");
        root
    }

    fn unique_suffix() -> u128 {
        std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .map_or(0, |d| d.as_nanos())
    }

    fn cleanup(root: &Path) {
        let _ = fs::remove_dir_all(root);
    }

    #[test]
    fn dry_run_writes_nothing_and_reports() {
        let root = temp_root("dry-run");
        let target = root.join("src").join("links").join("links_mail.rs");
        let plan = Plan::new().create(target.clone(), "pub fn x() {}".to_owned());
        let report = plan
            .dry_run_report(OverwritePolicy::Refuse)
            .expect("dry-run report should succeed");
        assert!(report.contains("dry run: no files will be written"));
        assert!(report.contains("would create"));
        assert!(report.contains(&target.display().to_string()));
        assert!(!target.exists(), "dry run must not create the file");
        assert!(
            !root.join("src").exists(),
            "dry run must not create directories"
        );
        cleanup(&root);
    }

    #[test]
    fn commit_creates_file_and_dirs() {
        let root = temp_root("commit");
        let target = root.join("src").join("links").join("links_mail.rs");
        let mut plan = Plan::new().create(target.clone(), "pub fn x() {}".to_owned());
        let written = plan
            .execute(OverwritePolicy::Refuse, None)
            .expect("commit should succeed");
        assert_eq!(written, vec![target.clone()]);
        assert!(target.is_file());
        assert_eq!(fs::read_to_string(&target).unwrap(), "pub fn x() {}");
        cleanup(&root);
    }

    #[test]
    fn conflict_reports_exact_file_and_writes_nothing() {
        let root = temp_root("conflict");
        let target = root.join("src").join("existing.rs");
        fs::create_dir_all(target.parent().unwrap()).unwrap();
        fs::write(&target, "user content").unwrap();
        let mut plan = Plan::new().create(target.clone(), "generated".to_owned());
        let err = plan
            .execute(OverwritePolicy::Refuse, None)
            .expect_err("should refuse to overwrite");
        assert!(matches!(err, PlanError::Conflict(p) if p == target));
        // The user file is untouched.
        assert_eq!(fs::read_to_string(&target).unwrap(), "user content");
        cleanup(&root);
    }

    #[test]
    fn dry_run_on_conflict_reports_exact_file() {
        let root = temp_root("dry-conflict");
        let target = root.join("existing.rs");
        fs::write(&target, "user content").unwrap();
        let plan = Plan::new().create(target.clone(), "generated".to_owned());
        let report_result = plan.dry_run_report(OverwritePolicy::Refuse);
        let err = report_result.expect_err("dry-run on conflict should error");
        assert!(matches!(err, PlanError::Conflict(p) if p == target));
        assert_eq!(fs::read_to_string(&target).unwrap(), "user content");
        cleanup(&root);
    }

    #[test]
    fn force_overwrites_and_rollback_restores() {
        let root = temp_root("force");
        let target = root.join("existing.rs");
        fs::write(&target, "user content").unwrap();
        let mut plan = Plan::new().create(target.clone(), "generated".to_owned());
        let _ = plan
            .execute(OverwritePolicy::Overwrite, None)
            .expect("force should overwrite");
        assert_eq!(fs::read_to_string(&target).unwrap(), "generated");
        // Rollback restores the original content (not deletes the file).
        plan.rollback().expect("rollback should restore");
        assert_eq!(fs::read_to_string(&target).unwrap(), "user content");
        cleanup(&root);
    }

    #[test]
    fn validation_failure_rolls_back_leaving_no_partial_files() {
        let root = temp_root("validation-rollback");
        let a = root.join("src").join("a.rs");
        let b = root.join("src").join("b.rs");
        let mut plan = Plan::new()
            .create(a.clone(), "a".to_owned())
            .create(b.clone(), "b".to_owned());
        let result = plan.execute(
            OverwritePolicy::Refuse,
            Some(Box::new(|_| Err("simulated compile failure".to_owned()))),
        );
        let err = result.expect_err("validator failure should error");
        assert!(matches!(err, PlanError::Validation(m) if m.contains("simulated compile failure")));
        assert!(!a.exists(), "rolled-back file must not remain");
        assert!(!b.exists(), "rolled-back file must not remain");
        cleanup(&root);
    }

    #[test]
    fn validation_failure_rolls_back_appends_restoring_original() {
        let root = temp_root("append-rollback");
        let mod_rs = root.join("src").join("links").join("mod.rs");
        fs::create_dir_all(mod_rs.parent().unwrap()).unwrap();
        fs::write(&mod_rs, "pub mod existing;\n").unwrap();
        let original = fs::read_to_string(&mod_rs).unwrap();
        let mut plan = Plan::new()
            .create(
                root.join("src").join("links").join("links_mail.rs"),
                "x".to_owned(),
            )
            .append(mod_rs.clone(), "pub mod links_mail;".to_owned());
        let _ = plan
            .execute(
                OverwritePolicy::Refuse,
                Some(Box::new(|_| Err("fail".to_owned()))),
            )
            .expect_err("validator should fail");
        // The append is undone: mod.rs restored to its original content.
        assert_eq!(fs::read_to_string(&mod_rs).unwrap(), original);
        // The created file is gone.
        assert!(
            !root
                .join("src")
                .join("links")
                .join("links_mail.rs")
                .exists()
        );
        cleanup(&root);
    }

    #[test]
    fn append_is_idempotent_and_creates_file_if_missing() {
        let root = temp_root("append-idempotent");
        let mod_rs = root.join("src").join("fresh").join("mod.rs");
        let mut plan = Plan::new().append(mod_rs.clone(), "pub mod fresh;".to_owned());
        let written = plan
            .execute(OverwritePolicy::Refuse, None)
            .expect("first append should create mod.rs");
        assert_eq!(written, vec![mod_rs.clone()]);
        assert_eq!(fs::read_to_string(&mod_rs).unwrap(), "pub mod fresh;\n");

        // Second append of the same declaration is a no-op (idempotent).
        let mut plan2 = Plan::new().append(mod_rs.clone(), "pub mod fresh;".to_owned());
        let written2 = plan2
            .execute(OverwritePolicy::Refuse, None)
            .expect("second append should succeed");
        assert!(written2.is_empty(), "idempotent append writes nothing");
        assert_eq!(
            fs::read_to_string(&mod_rs).unwrap(),
            "pub mod fresh;\n",
            "declaration appears exactly once"
        );
        cleanup(&root);
    }

    #[test]
    fn rollback_of_created_append_deletes_the_file() {
        let root = temp_root("append-delete-rollback");
        let mod_rs = root.join("src").join("fresh").join("mod.rs");
        // The file does not exist; an append would create it.
        let mut plan = Plan::new().append(mod_rs.clone(), "pub mod fresh;".to_owned());
        let _ = plan
            .execute(
                OverwritePolicy::Refuse,
                Some(Box::new(|_| Err("fail".to_owned()))),
            )
            .expect_err("validator should fail");
        assert!(
            !mod_rs.exists(),
            "created-by-append file must be removed on rollback"
        );
        cleanup(&root);
    }

    #[test]
    fn empty_plan_is_empty_and_commits_nothing() {
        let mut plan = Plan::new();
        assert!(plan.is_empty());
        let written = plan
            .execute(OverwritePolicy::Refuse, None)
            .expect("empty plan commits cleanly");
        assert!(written.is_empty());
    }

    #[test]
    fn multi_file_transaction_is_atomic_on_success() {
        let root = temp_root("multi");
        let file = root.join("src").join("links").join("links_mail.rs");
        let mod_rs = root.join("src").join("links").join("mod.rs");
        let mut plan = Plan::new()
            .create(file.clone(), "pub fn build() {}".to_owned())
            .append(mod_rs.clone(), "pub mod links_mail;".to_owned());
        let written = plan
            .execute(OverwritePolicy::Refuse, None)
            .expect("multi-file commit should succeed");
        assert_eq!(written.len(), 2);
        assert!(file.is_file());
        assert!(mod_rs.is_file());
        assert!(
            fs::read_to_string(&mod_rs)
                .unwrap()
                .contains("pub mod links_mail;")
        );
        cleanup(&root);
    }

    #[test]
    fn append_mod_declaration_op_builds_valid_op() {
        let root = temp_root("mod-op");
        let op = append_mod_declaration_op(&root.join("src"), "links", "links_mail")
            .expect("op should build");
        match op {
            PlannedOp::Append { path, declaration } => {
                assert_eq!(path, root.join("src").join("links").join("mod.rs"));
                assert_eq!(declaration, "pub mod links_mail;");
            }
            PlannedOp::Create { .. } => panic!("expected an Append op"),
        }
        cleanup(&root);
    }
}