1 files changed, 45 insertions, 0 deletions
diff --git a/crates/cargo-util/src/registry.rs b/crates/cargo-util/src/registry.rs
new file mode 100644
index 0000000..6b1ccd2
--- /dev/null
+++ b/crates/cargo-util/src/registry.rs
@@ -0,0 +1,45 @@
+/// Make a path to a dependency, which aligns to
+///
+/// - [index from of Cargo's index on filesystem][1], and
+/// - [index from Crates.io][2].
+///
+/// [1]: https://docs.rs/cargo/latest/cargo/sources/registry/index.html#the-format-of-the-index
+/// [2]: https://github.com/rust-lang/crates.io-index
+pub fn make_dep_path(dep_name: &str, prefix_only: bool) -> String {
+    let (slash, name) = if prefix_only {
+        ("", "")
+    } else {
+        ("/", dep_name)
+    };
+    match dep_name.len() {
+        1 => format!("1{}{}", slash, name),
+        2 => format!("2{}{}", slash, name),
+        3 => format!("3/{}{}{}", &dep_name[..1], slash, name),
+        _ => format!("{}/{}{}{}", &dep_name[0..2], &dep_name[2..4], slash, name),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::make_dep_path;
+
+    #[test]
+    fn prefix_only() {
+        assert_eq!(make_dep_path("a", true), "1");
+        assert_eq!(make_dep_path("ab", true), "2");
+        assert_eq!(make_dep_path("abc", true), "3/a");
+        assert_eq!(make_dep_path("Abc", true), "3/A");
+        assert_eq!(make_dep_path("AbCd", true), "Ab/Cd");
+        assert_eq!(make_dep_path("aBcDe", true), "aB/cD");
+    }
+
+    #[test]
+    fn full() {
+        assert_eq!(make_dep_path("a", false), "1/a");
+        assert_eq!(make_dep_path("ab", false), "2/ab");
+        assert_eq!(make_dep_path("abc", false), "3/a/abc");
+        assert_eq!(make_dep_path("Abc", false), "3/A/Abc");
+        assert_eq!(make_dep_path("AbCd", false), "Ab/Cd/AbCd");
+        assert_eq!(make_dep_path("aBcDe", false), "aB/cD/aBcDe");
+    }
+}