From 43b01b6790af2070e6162472bbfa5bbe3bb3ff61 Mon Sep 17 00:00:00 2001
From: Graham Dennis <graham.dennis@gmail.com>
Date: Fri, 10 Oct 2025 14:54:03 +1100
Subject: [PATCH 1/2] Improved backwards compatibility hack for git URLs using
 dir=... attribute

---
 src/libfetchers/git.cc | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/src/libfetchers/git.cc b/src/libfetchers/git.cc
index 7c1630167..a8a52ef30 100644
--- a/src/libfetchers/git.cc
+++ b/src/libfetchers/git.cc
@@ -496,6 +496,36 @@ struct GitInputScheme : InputScheme
                    Git interprets them as part of the file name. So get
                    rid of them. */
                 url.query.clear();
+            /* Backward compatibility hack: In old versions of Nix, if you had
+               a flake input like
+
+                 inputs.foo.url = "git+https://foo/bar?dir=subdir";
+
+               it would result in a lock file entry like
+
+                 "original": {
+                   "dir": "subdir",
+                   "type": "git",
+                   "url": "https://foo/bar?dir=subdir"
+                 }
+
+               New versions of Nix remove `?dir=subdir` from the `url` field,
+               since the subdirectory is intended for `FlakeRef`, not the
+               fetcher (and specifically the remote server), that is, the
+               flakeref is parsed into
+
+                 "original": {
+                   "dir": "subdir",
+                   "type": "git",
+                   "url": "https://foo/bar"
+                 }
+
+               However, new versions of nix parsing old flake.lock files would pass the dir=
+               query parameter in the "url" attribute to git, which will then complain.
+
+               For this reason, we filtering the `dir` query parameter from the URL
+               before passing it to git. */
+            url.query.erase("dir");
             repoInfo.location = url;
         }
 

From 8d9e9bc400433faeb9a6edc49327f7700b93b1c2 Mon Sep 17 00:00:00 2001
From: Graham Dennis <gdennis@anduril.com>
Date: Fri, 10 Oct 2025 15:00:10 +1100
Subject: [PATCH 2/2] Improve comment

---
 src/libfetchers/git.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libfetchers/git.cc b/src/libfetchers/git.cc
index a8a52ef30..9334dc1cb 100644
--- a/src/libfetchers/git.cc
+++ b/src/libfetchers/git.cc
@@ -523,7 +523,7 @@ struct GitInputScheme : InputScheme
                However, new versions of nix parsing old flake.lock files would pass the dir=
                query parameter in the "url" attribute to git, which will then complain.
 
-               For this reason, we filtering the `dir` query parameter from the URL
+               For this reason, we are filtering the `dir` query parameter from the URL
                before passing it to git. */
             url.query.erase("dir");
             repoInfo.location = url;