Replace spawned git process with git2 bindings (holochain#363)

src/scaffold/app/git.rs

@@ -23,6 +23,13 @@ pub fn setup_git_environment<P: AsRef<Path>>(path: P) -> ScaffoldResult<()> {
     Ok(())
 }
 
+pub fn is_inside_work_tree<P: AsRef<Path>>(dir: P) -> bool {
+    match Repository::open(dir) {
+        Ok(repo) => repo.is_bare(),
+        Err(_) => false,
+    }
+}
+
 pub fn gitignore() -> &'static str {
     include_str!("./gitignore")
 }

src/scaffold/app/nix.rs

@@ -8,6 +8,8 @@ use std::process::{Command, Stdio};
 use crate::error::{ScaffoldError, ScaffoldResult};
 use crate::file_tree::*;
 
+use super::git::is_inside_work_tree;
+
 pub fn flake_nix(holo_enabled: bool) -> FileTree {
     let holo_inputs = holo_enabled
         .then_some(
@@ -74,16 +76,8 @@ pub fn setup_nix_developer_environment(dir: &Path) -> ScaffoldResult<()> {
     // This is here to catch the issue from this thread https://discourse.nixos.org/t/nix-flakes-nix-store-source-no-such-file-or-directory/17836
     // If you run Scaffolding inside a Git repository when the `nix flake update` will fail. At some point Nix should report this so we don't need
     // to worry about it but for now this helps solve a strange error message.
-    if let Ok(output) = Command::new("git")
-        .stdout(Stdio::piped())
-        .stderr(Stdio::null())
-        .current_dir(dir)
-        .args(["rev-parse", "--is-inside-work-tree"])
-        .output()
-    {
-        if output.status.success() && output.stdout == b"true\n" {
-            return Err(ScaffoldError::NixSetupError("- detected that Scaffolding is running inside an existing Git repository, please choose a different location to scaffold".to_string()));
-        }
+    if is_inside_work_tree(dir) {
+        return Err(ScaffoldError::NixSetupError("- detected that Scaffolding is running inside an existing Git repository, please choose a different location to scaffold".to_string()));
     }
 
     println!("Setting up nix development environment...");