git: allow fetching tags without prefixing refs/tags/

work around for NixOS/nix#5291

src/fetcher/git.rs

@@ -1,8 +1,6 @@
-use crate::{
-    impl_fetcher,
-    simple::{SimpleFetcher, SimpleFlakeFetcher},
-    GitScheme, Url,
-};
+use anyhow::Result;
+
+use crate::{impl_fetcher, prefetch::git_prefetch, simple::SimpleFetcher, GitScheme, Url};
 
 pub struct Fetchgit(pub GitScheme);
 impl_fetcher!(Fetchgit);
@@ -20,13 +18,18 @@ impl<'a> SimpleFetcher<'a, 1> for Fetchgit {
     }
 }
 
-impl<'a> SimpleFlakeFetcher<'a, 1> for Fetchgit {
-    fn get_flake_ref(&self, [url]: &[&str; 1], rev: &str) -> String {
-        let rev_type = if rev.len() == 40 { "rev" } else { "ref" };
-        if matches!(self.0, GitScheme::Yes) {
-            format!("{url}?{rev_type}={rev}&submodules=1")
+impl<'a> Fetchgit {
+    fn fetch(
+        &'a self,
+        values @ [url]: &[&str; 1],
+        rev: &str,
+        args: &[(String, String)],
+        args_str: &[(String, String)],
+    ) -> Result<String> {
+        if args.is_empty() && args_str.is_empty() {
+            git_prefetch(matches!(self.0, GitScheme::Yes), url, rev)
         } else {
-            format!("git+{url}?{rev_type}={rev}&submodules=1")
+            self.fetch_fod(values, rev, args, args_str)
         }
     }
 }

src/prefetch.rs

@@ -51,6 +51,24 @@ pub fn flake_prefetch(flake_ref: String) -> Result<String> {
     .hash)
 }
 
+// work around for https://github.com/NixOS/nix/issues/5291
+pub fn git_prefetch(git_scheme: bool, url: &str, rev: &str) -> Result<String> {
+    let prefix = if git_scheme { "" } else { "git+" };
+
+    if rev.len() == 40 {
+        flake_prefetch(format!("{prefix}{url}?rev={rev}&submodules=1"))
+    } else {
+        if !rev.starts_with("refs/") {
+            if let hash @ Ok(_) =
+                flake_prefetch(format!("{prefix}{url}?ref=refs/tags/{rev}&submodules=1"))
+            {
+                return hash;
+            }
+        }
+        flake_prefetch(format!("{prefix}{url}?ref={rev}&submodules=1"))
+    }
+}
+
 pub fn url_prefetch(url: String, unpack: bool) -> Result<String> {
     let mut cmd = Command::new("nix-prefetch-url");
     if unpack {

tests/cmd/fetcher/git/basic.stdout

@@ -1,5 +1,5 @@
 fetchgit {
   url = "https://github.com/nix-community/nurl";
-  rev = "refs/tags/v0.3.0";
+  rev = "v0.3.0";
   hash = "sha256-jZ+cCp1THDhfHH5yMmRPjGuthOqsgcF/3OjZ61FMdA4=";
 }

tests/cmd/fetcher/git/basic.toml

@@ -1,6 +1,6 @@
 args = [
     "https://github.com/nix-community/nurl",
-    "refs/tags/v0.3.0",
+    "v0.3.0",
     "--fetcher",
     "fetchgit",
 ]

tests/cmd/fetcher/git/scheme.stdout

@@ -1,5 +1,5 @@
 fetchgit {
   url = "git://git.kernel.org/pub/scm/linux/kernel/git/jejb/efitools.git";
-  rev = "refs/tags/v1.9.0";
+  rev = "v1.9.0";
   hash = "sha256-W38CWoPnkt0+VkVp+uW+sjWjo6MXYq2eTXRxWKyQph8=";
 }

tests/cmd/fetcher/git/scheme.toml

@@ -1,6 +1,6 @@
 args = [
     "git://git.kernel.org/pub/scm/linux/kernel/git/jejb/efitools.git",
-    "refs/tags/v1.9.0",
+    "v1.9.0",
     "--fetcher",
     "fetchgit",
 ]