Add tag namespace collision test

Confirm that tags with names that could possibly collide with tag namespace
names are really distinct and don't collide.

Signed-off-by: J Robert Ray <jrray@jrray.org>

crates/spfs/src/fixtures.rs

@@ -273,3 +273,10 @@ fn generate_subtree(root: &std::path::Path, max_depth: i32) {
         }
     }
 }
+
+#[fixture]
+pub fn random_digest() -> spfs_encoding::Digest {
+    let mut thread_rng = rand::thread_rng();
+    let random_bytes: [u8; spfs_encoding::DIGEST_SIZE] = thread_rng.gen();
+    spfs_encoding::Digest::from_bytes(&random_bytes).unwrap()
+}

crates/spfs/src/storage/tag_test.rs

@@ -366,3 +366,53 @@ async fn test_tag_in_namespace(
         }]
     );
 }
+
+#[rstest]
+#[case::fs(tmprepo("fs"))]
+#[tokio::test]
+async fn test_tag_in_namespace_name_collision(
+    #[case]
+    #[future]
+    tmprepo: TempRepo,
+) {
+    init_logging();
+    let tmprepo = tmprepo.await;
+
+    // It should be possible to have these distinct tags at the same time:
+    //
+    // | namespace | tag name    |
+    // | --------- | ----------- |
+    // | none      | foo/bar/baz |
+    // | foo       | bar/baz     |
+    // | foo/bar   | baz         |
+
+    let repo_in_foo = tmprepo.with_tag_namespace("foo").await;
+    let repo_in_foo_bar = tmprepo.with_tag_namespace("foo/bar").await;
+
+    let foo_bar_baz = random_digest();
+    let bar_baz = random_digest();
+    let baz = random_digest();
+
+    let spec_foo_bar_baz = tracking::TagSpec::parse("foo/bar/baz").unwrap();
+    tmprepo
+        .push_tag(&spec_foo_bar_baz, &foo_bar_baz)
+        .await
+        .unwrap();
+
+    let spec_bar_baz = tracking::TagSpec::parse("bar/baz").unwrap();
+    repo_in_foo.push_tag(&spec_bar_baz, &bar_baz).await.unwrap();
+
+    let spec_baz = tracking::TagSpec::parse("baz").unwrap();
+    repo_in_foo_bar.push_tag(&spec_baz, &baz).await.unwrap();
+
+    // Now confirm these can be read back.
+
+    let tag = repo_in_foo_bar.resolve_tag(&spec_baz).await.unwrap();
+    assert_eq!(tag.target, baz);
+
+    let tag = repo_in_foo.resolve_tag(&spec_bar_baz).await.unwrap();
+    assert_eq!(tag.target, bar_baz);
+
+    let tag = tmprepo.resolve_tag(&spec_foo_bar_baz).await.unwrap();
+    assert_eq!(tag.target, foo_bar_baz);
+}