Do not create an used and group on macos

Docker desktop for macos already set the right user and group for the
generated files.

Trying to create an group conflicts with an already existing group
inside the container and the generation was failing.

Closes #12.

Dockerfile

@@ -1,9 +1,5 @@
 ARG RUBY_VERSION=3.2.3
 FROM ruby:${RUBY_VERSION}
-ARG USER_ID=1000
-ARG GROUP_ID=1000
-RUN groupadd -g $GROUP_ID app && useradd -u $USER_ID -g app -m app
-USER app
 ARG RAILS_VERSION
 # Install Rails based on the version specified but if not specified, install the latest version.
 RUN if [ -z "$RAILS_VERSION" ] ; then gem install rails ; else gem install rails -v $RAILS_VERSION ; fi

Dockerfile.windows → Dockerfile.unix

@@ -1,5 +1,9 @@
 ARG RUBY_VERSION=3.2.3
 FROM ruby:${RUBY_VERSION}
+ARG USER_ID=1000
+ARG GROUP_ID=1000
+RUN groupadd -g $GROUP_ID app && useradd -u $USER_ID -g app -m app
+USER app
 ARG RAILS_VERSION
 # Install Rails based on the version specified but if not specified, install the latest version.
 RUN if [ -z "$RAILS_VERSION" ] ; then gem install rails ; else gem install rails -v $RAILS_VERSION ; fi

src/main.rs

@@ -10,8 +10,8 @@ use clap::Parser;
 
 use crate::docker_client::DockerClient;
 
-#[cfg_attr(unix, path = "unix.rs")]
-#[cfg_attr(windows, path = "windows.rs")]
+#[cfg_attr(all(unix, not(target_os = "macos")), path = "unix.rs")]
+#[cfg_attr(any(windows, target_os = "macos"), path = "windows.rs")]
 mod os_specific;
 
 fn main() {

src/unix.rs

@@ -1,5 +1,5 @@
 pub fn dockerfile_content() -> &'static [u8] {
-    include_bytes!("../Dockerfile")
+    include_bytes!("../Dockerfile.unix")
 }
 
 pub fn get_user_id() -> Option<u32> {

src/windows.rs

@@ -1,5 +1,5 @@
 pub fn dockerfile_content() -> &'static [u8] {
-    include_bytes!("../Dockerfile.windows")
+    include_bytes!("../Dockerfile")
 }
 
 pub fn get_user_id() -> Option<u32> {