git: remove git2 from git subprocessing code paths in lib

Currently, the subprocessing code paths in the library were relying on
git2 to figure out if a remote exists. This is because when git errors
out for a remote not existing it outputs the same error as when the
repository is not found.

As the cli tool makes a distinction between the two (e.g., after
cloning, the remote must exist and as such we cannot send out an error
that is shared by `no remote found` and `no repository found`), this was a
hack put in place to sort out the difference.

It calls out to `git remote` to list out the remotes.

lib/src/git.rs

@@ -1601,15 +1601,14 @@ impl<'a> GitFetch<'a> {
         branch_names: &[StringPattern],
         remote_name: &str,
     ) -> Result<Option<String>, GitFetchError> {
-        // check the remote exists
-        // TODO: we should ideally find a way to do this without git2
-        let _remote = self.git_repo.find_remote(remote_name).map_err(|err| {
-            if is_remote_not_found_err(&err) {
-                GitFetchError::NoSuchRemote(remote_name.to_string())
-            } else {
-                GitFetchError::InternalGitError(err)
-            }
-        })?;
+        let git_ctx =
+            GitSubprocessContext::from_git2(self.git_repo, &self.git_settings.executable_path);
+
+        let remotes = git_ctx.spawn_remote()?;
+        if !remotes.contains(remote_name) {
+            return Err(GitFetchError::NoSuchRemote(remote_name.to_string()));
+        }
+
         // At this point, we are only updating Git's remote tracking branches, not the
         // local branches.
         let mut remaining_refspecs: Vec<_> = Self::expand_refspecs(remote_name, branch_names)?;
@@ -1618,9 +1617,6 @@ impl<'a> GitFetch<'a> {
             return Ok(None);
         }
 
-        let git_ctx =
-            GitSubprocessContext::from_git2(self.git_repo, &self.git_settings.executable_path);
-
         let mut branches_to_prune = Vec::new();
         // git unfortunately errors out if one of the many refspecs is not found
         //
@@ -2019,16 +2015,12 @@ fn subprocess_push_refs(
     qualified_remote_refs_expected_locations: &HashMap<&str, Option<&CommitId>>,
     refspecs: &[RefSpec],
 ) -> Result<(), GitPushError> {
-    // check the remote exists
-    // TODO: we should ideally find a way to do this without git2
-    let _remote = git_repo.find_remote(remote_name).map_err(|err| {
-        if is_remote_not_found_err(&err) {
-            GitPushError::NoSuchRemote(remote_name.to_string())
-        } else {
-            GitPushError::InternalGitError(err)
-        }
-    })?;
     let git_ctx = GitSubprocessContext::from_git2(git_repo, git_executable_path);
+    // check the remote exists
+    let remotes = git_ctx.spawn_remote()?;
+    if !remotes.contains(remote_name) {
+        return Err(GitPushError::NoSuchRemote(remote_name.to_string()));
+    }
 
     let mut remaining_remote_refs: HashSet<_> = qualified_remote_refs_expected_locations
         .keys()

lib/src/git_subprocess.rs

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 //
+use std::collections::HashSet;
 use std::num::NonZeroU32;
 use std::path::Path;
 use std::path::PathBuf;
@@ -156,6 +157,20 @@ impl<'a> GitSubprocessContext<'a> {
         Ok(())
     }
 
+    /// List the configured remotes
+    ///
+    /// `git remote`
+    ///
+    /// Prints a remote per line
+    pub(crate) fn spawn_remote(&self) -> Result<HashSet<String>, GitSubprocessError> {
+        let mut command = self.create_command();
+        command.stdout(Stdio::piped());
+        command.arg("remote");
+        let output = self.spawn_cmd(command)?;
+
+        parse_git_remote_output(output)
+    }
+
     /// How we retrieve the remote's default branch:
     ///
     /// `git remote show <remote_name>`
@@ -321,6 +336,18 @@ fn parse_git_branch_prune_output(output: Output) -> Result<(), GitSubprocessErro
     Err(external_git_error(&output.stderr))
 }
 
+fn parse_git_remote_output(output: Output) -> Result<HashSet<String>, GitSubprocessError> {
+    if !output.status.success() {
+        return Err(external_git_error(&output.stderr));
+    }
+
+    Ok(output
+        .stdout
+        .lines()
+        .map(|line| line.to_str_lossy().into_owned())
+        .collect())
+}
+
 fn parse_git_remote_show_output(output: Output) -> Result<Output, GitSubprocessError> {
     if output.status.success() {
         return Ok(output);