populate: refer to flakes as git+file: only with a usable .git

Writing the lock file of a git+file: flake, Nix runs Git, with the
repository's configuration and hooks, which may run commands.  A .git
in a source's directory can come from anywhere, e.g. one planted in a
materialized flake, or one a file source keeps.  So drawing inputs
refers to a flake as git+file: only if git_problems finds nothing wrong
with its .git directory, the way git sources check their work trees,
and else as path:.

lock-foreign-git plants a .git in a materialized flake and in a file
source that keeps it, whose configuration names an fsmonitor command.

1 files changed, 8 insertions, 2 deletions

diff --git a/pkgs/populate/default.nix b/pkgs/populate/default.nix
index b724b23..7b22662 100644
--- a/pkgs/populate/default.nix
+++ b/pkgs/populate/default.nix
@@ -608,14 +608,20 @@ let
           fi
         }
 
-        # Prints the flake URL of the source named $1.
+        ${gitProblems}
+        # Prints the flake URL of the source named $1: git+file: if it has a
+        # .git directory git_problems finds nothing wrong with, else path:.
+        # Nix runs Git in a git+file: flake, with the repository's
+        # configuration and hooks.
         flake_url() {
           path=$(readlink -f ${quote target.path}/"$1")
           if ! test -d "$path"; then
             >&2 printf 'error: source %s is not a directory\n' "$1"
             exit 1
           fi
-          if test -e "$path"/.git; then
+          if ! test -L "$path"/.git && test -d "$path"/.git &&
+              problems=$(git_problems "$path" 2>/dev/null) &&
+              test -z "$problems"; then
             if test -e "$path"/.gitmodules; then
               printf 'git+file:%s?submodules=1' "$(url_path "$path")"
             else