Add support for snapshot reference recording (mitsuhiko#136)

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changelog
 
+## 1.1.0
+
+* Added the `INSTA_SNAPSHOT_REFERENCES_FILE` environment variable to support
+  deletions of unreferenced snapshot files. (#136)
+
 ## 1.0.0
 
 * Globs now follow links (#132)

src/lib.rs

@@ -353,6 +353,23 @@
 //! ```text
 //! $ cargo insta test --accept --force-update-snapshots
 //! ```
+//!
+//! # Deleting Unused Snapshots
+//!
+//! Insta cannot detect unused snapshot files.  The reason for this is that
+//! insta does not control the execution of the entirety of the tests so it
+//! cannot spot which files are actually unreferenced.  However you can use
+//! the `INSTA_SNAPSHOT_REFERENCES_FILE` environment variable to
+//! instruct insta to append all referenced files into a list.  This can then
+//! be used to delete all files not referenced.  For instance one could use
+//! [`ripgrep`](https://github.com/BurntSushi/ripgrep) like this:
+//!
+//! ```text
+//! export INSTA_SNAPSHOT_REFERENCES_FILE="$(mktemp)"
+//! cargo test
+//! rg --files -lg '*.snap' "$(pwd)" | grep -vFf "$INSTA_SNAPSHOT_REFERENCES_FILE" | xargs rm
+//! rm -f $INSTA_SNAPSHOT_REFERENCES_FILE
+//! ```
 #[macro_use]
 mod macros;
 mod content;

src/runtime.rs

@@ -117,6 +117,19 @@ fn update_snapshot_behavior(unseen: bool) -> UpdateBehavior {
     }
 }
 
+fn memoize_snapshot_file(snapshot_file: &Path) {
+    if let Ok(path) = env::var("INSTA_SNAPSHOT_REFERENCES_FILE") {
+        let mut f = fs::OpenOptions::new()
+            .write(true)
+            .append(true)
+            .create(true)
+            .open(path)
+            .unwrap();
+        f.write_all(format!("{}\n", snapshot_file.display()).as_bytes())
+            .unwrap();
+    }
+}
+
 fn output_snapshot_behavior() -> OutputBehavior {
     match env::var("INSTA_OUTPUT").ok().as_deref() {
         None | Some("") | Some("diff") => OutputBehavior::Diff,
@@ -921,6 +934,11 @@ pub fn assert_snapshot(
         new_snapshot_contents,
     );
 
+    // memoize the snapshot file if requested.
+    if let Some(ref snapshot_file) = snapshot_file {
+        memoize_snapshot_file(snapshot_file);
+    }
+
     // if the snapshot matches we're done.
     if let Some(ref old_snapshot) = old {
         if old_snapshot.contents() == new.contents() {