Suppress error with --allow-dirty and add a test

Signed-off-by: hi-rustin <rustin.liu@gmail.com>

Author: 0xPoe

crates/cargo-test-support/src/git.rs

@@ -175,6 +175,20 @@ where
     (git_project, repo)
 }
 
+/// Create a new git repository with a project.
+/// Returns both the Project and the git Repository but does not commit.
+pub fn new_repo_without_add_and_commit<F>(name: &str, callback: F) -> (Project, git2::Repository)
+where
+    F: FnOnce(ProjectBuilder) -> ProjectBuilder,
+{
+    let mut git_project = project().at(name);
+    git_project = callback(git_project);
+    let git_project = git_project.build();
+
+    let repo = init(&git_project.root());
+    (git_project, repo)
+}
+
 /// Add all files in the working directory to the git index.
 pub fn add(repo: &git2::Repository) {
     // FIXME(libgit2/libgit2#2514): apparently, `add_all` will add all submodules

src/cargo/ops/fix.rs

@@ -154,11 +154,11 @@ fn check_version_control(config: &Config, opts: &FixOptions) -> CargoResult<()>
     if let Ok(repo) = git2::Repository::discover(config.cwd()) {
         let mut repo_opts = git2::StatusOptions::new();
         repo_opts.include_ignored(false);
-        if repo.is_empty()? {
+        if repo.is_empty()? && !opts.allow_dirty {
             bail!(
                 "no commits found in the git repository, and \
                 `cargo fix` can potentially perform destructive changes; if you'd \
-                like to suppress this error pass `--allow-dirty`, `--allow-staged`, \
+                like to suppress this error pass `--allow-dirty`, \
                 or commit your changes"
             )
         }

tests/testsuite/fix.rs

@@ -771,6 +771,25 @@ commit the changes to these files:
     p.cargo("fix --allow-staged").run();
 }
 
+#[cargo_test]
+fn errors_on_empty_repo() {
+    let (p, _) =
+        git::new_repo_without_add_and_commit("foo", |p| p.file("src/lib.rs", "pub fn foo() {}"));
+
+    p.cargo("fix")
+        .with_status(101)
+        .with_stderr(
+            "\
+error: no commits found in the git repository, \
+and `cargo fix` can potentially perform destructive changes; \
+if you'd like to suppress this error pass `--allow-dirty`, \
+or commit your changes
+",
+        )
+        .run();
+    p.cargo("fix --allow-dirty").run();
+}
+
 #[cargo_test]
 fn does_not_warn_about_clean_working_directory() {
     let p = git::new("foo", |p| p.file("src/lib.rs", "pub fn foo() {}"));
@@ -1715,7 +1734,7 @@ fn fix_with_run_cargo_in_proc_macros() {
             "src/lib.rs",
             r#"
                 use proc_macro::*;
-    
+
                 #[proc_macro]
                 pub fn foo(_input: TokenStream) -> TokenStream {
                     let output = std::process::Command::new(env!("CARGO"))
@@ -1725,7 +1744,7 @@ fn fix_with_run_cargo_in_proc_macros() {
                     eprintln!("{}", std::str::from_utf8(&output.stderr).unwrap());
                     println!("{}", std::str::from_utf8(&output.stdout).unwrap());
                     "".parse().unwrap()
-                }                    
+                }
             "#,
         )
         .file(