refactor(git_status): simplify git status with once-cell (starship#2150)

I simplified the code in the git status module by moving everything from RwLock<_> to OnceCell<_>. I think this should also get rid of any remaining race conditions that remained after starship#1777.

src/modules/git_status.rs

@@ -1,12 +1,13 @@
 use git2::{Repository, Status};
+use once_cell::sync::OnceCell;
 
 use super::{Context, Module, RootModuleConfig};
 
 use crate::configs::git_status::GitStatusConfig;
 use crate::context::Repo;
 use crate::formatter::StringFormatter;
 use crate::segment::Segment;
-use std::sync::{Arc, RwLock};
+use std::sync::Arc;
 
 const ALL_STATUS_FORMAT: &str = "$conflicted$stashed$deleted$renamed$modified$staged$untracked";
 
@@ -108,18 +109,18 @@ pub fn module<'a>(context: &'a Context) -> Option<Module<'a>> {
 
 struct GitStatusInfo<'a> {
     repo: &'a Repo,
-    ahead_behind: RwLock<Option<Result<(usize, usize), git2::Error>>>,
-    repo_status: RwLock<Option<Result<RepoStatus, git2::Error>>>,
-    stashed_count: RwLock<Option<Result<usize, git2::Error>>>,
+    ahead_behind: OnceCell<Option<(usize, usize)>>,
+    repo_status: OnceCell<Option<RepoStatus>>,
+    stashed_count: OnceCell<Option<usize>>,
 }
 
 impl<'a> GitStatusInfo<'a> {
     pub fn load(repo: &'a Repo) -> Self {
         Self {
             repo,
-            ahead_behind: RwLock::new(None),
-            repo_status: RwLock::new(None),
-            stashed_count: RwLock::new(None),
+            ahead_behind: OnceCell::new(),
+            repo_status: OnceCell::new(),
+            stashed_count: OnceCell::new(),
         }
     }
 
@@ -137,89 +138,47 @@ impl<'a> GitStatusInfo<'a> {
         Repository::open(repo_root).ok()
     }
 
-    pub fn get_ahead_behind(&self) -> Option<(usize, usize)> {
-        {
-            let data = self.ahead_behind.read().unwrap();
-            if let Some(result) = data.as_ref() {
-                return match result.as_ref() {
-                    Ok(ahead_behind) => Some(*ahead_behind),
-                    Err(error) => {
-                        log::debug!("get_ahead_behind: {}", error);
-                        None
-                    }
-                };
-            };
-        }
-
-        {
-            let mut data = self.ahead_behind.write().unwrap();
+    pub fn get_ahead_behind(&self) -> &Option<(usize, usize)> {
+        self.ahead_behind.get_or_init(|| {
             let repo = self.get_repository()?;
             let branch_name = self.get_branch_name();
-            *data = Some(get_ahead_behind(&repo, &branch_name));
-            match data.as_ref().unwrap() {
-                Ok(ahead_behind) => Some(*ahead_behind),
+
+            match get_ahead_behind(&repo, &branch_name) {
+                Ok(ahead_behind) => Some(ahead_behind),
                 Err(error) => {
                     log::debug!("get_ahead_behind: {}", error);
                     None
                 }
             }
-        }
+        })
     }
 
-    pub fn get_repo_status(&self) -> Option<RepoStatus> {
-        {
-            let data = self.repo_status.read().unwrap();
-            if let Some(result) = data.as_ref() {
-                return match result.as_ref() {
-                    Ok(repo_status) => Some(*repo_status),
-                    Err(error) => {
-                        log::debug!("get_repo_status: {}", error);
-                        None
-                    }
-                };
-            };
-        }
-
-        {
-            let mut data = self.repo_status.write().unwrap();
+    pub fn get_repo_status(&self) -> &Option<RepoStatus> {
+        self.repo_status.get_or_init(|| {
             let mut repo = self.get_repository()?;
-            *data = Some(get_repo_status(&mut repo));
-            match data.as_ref().unwrap() {
-                Ok(repo_status) => Some(*repo_status),
+
+            match get_repo_status(&mut repo) {
+                Ok(repo_status) => Some(repo_status),
                 Err(error) => {
-                    log::debug!(" get_repo_status: {}", error);
+                    log::debug!("get_repo_status: {}", error);
                     None
                 }
             }
-        }
+        })
     }
 
-    pub fn get_stashed(&self) -> Option<usize> {
-        {
-            let data = self.stashed_count.read().unwrap();
-            if let Some(result) = data.as_ref() {
-                return match result.as_ref() {
-                    Ok(stashed_count) => Some(*stashed_count),
-                    Err(error) => {
-                        log::debug!("get_stashed_count: {}", error);
-                        None
-                    }
-                };
-            };
-        }
-
-        {
-            let mut data = self.stashed_count.write().unwrap();
+    pub fn get_stashed(&self) -> &Option<usize> {
+        self.stashed_count.get_or_init(|| {
             let mut repo = self.get_repository()?;
-            *data = Some(get_stashed_count(&mut repo));
-            match data.as_ref().unwrap() {
-                Ok(stashed_count) => Some(*stashed_count),
+
+            match get_stashed_count(&mut repo) {
+                Ok(stashed_count) => Some(stashed_count),
                 Err(error) => {
                     log::debug!("get_stashed_count: {}", error);
                     None
                 }
             }
-        }
+        })
     }
 
     pub fn get_conflicted(&self) -> Option<usize> {