Use anyhow more idiomatically (#31052)

https://github.com/zed-industries/zed/issues/30972 brought up another
case where our context is not enough to track the actual source of the
issue: we get a general top-level error without inner error.

The reason for this was `.ok_or_else(|| anyhow!("failed to read HEAD
SHA"))?; ` on the top level.

The PR finally reworks the way we use anyhow to reduce such issues (or
at least make it simpler to bubble them up later in a fix).
On top of that, uses a few more anyhow methods for better readability.

* `.ok_or_else(|| anyhow!("..."))`, `map_err` and other similar error
conversion/option reporting cases are replaced with `context` and
`with_context` calls
* in addition to that, various `anyhow!("failed to do ...")` are
stripped with `.context("Doing ...")` messages instead to remove the
parasitic `failed to` text
* `anyhow::ensure!` is used instead of `if ... { return Err(...); }`
calls
* `anyhow::bail!` is used instead of `return Err(anyhow!(...));`

Release Notes:

- N/A

crates/git_ui/src/branch_picker.rs

@@ -1,4 +1,4 @@
-use anyhow::{Context as _, anyhow};
+use anyhow::Context as _;
 use fuzzy::StringMatchCandidate;
 
 use collections::HashSet;
@@ -381,7 +381,7 @@ impl PickerDelegate for BranchListDelegate {
                         .delegate
                         .repo
                         .as_ref()
-                        .ok_or_else(|| anyhow!("No active repository"))?
+                        .context("No active repository")?
                         .clone();
 
                     let mut cx = cx.to_async();

crates/git_ui/src/commit_view.rs

@@ -1,4 +1,4 @@
-use anyhow::{Result, anyhow};
+use anyhow::{Context as _, Result};
 use buffer_diff::{BufferDiff, BufferDiffSnapshot};
 use editor::{Editor, EditorEvent, MultiBuffer};
 use git::repository::{CommitDetails, CommitDiff, CommitSummary, RepoPath};
@@ -172,7 +172,7 @@ impl CommitView {
                             .map(|path| path.worktree_id)
                             .or(first_worktree_id)
                     })?
-                    .ok_or_else(|| anyhow!("project has no worktrees"))?;
+                    .context("project has no worktrees")?;
                 let file = Arc::new(GitBlob {
                     path: file.path.clone(),
                     is_deleted,

crates/git_ui/src/git_panel.rs

@@ -9,7 +9,7 @@ use crate::{branch_picker, picker_prompt, render_remote_button};
 use crate::{
     git_panel_settings::GitPanelSettings, git_status_icon, repository_selector::RepositorySelector,
 };
-use anyhow::Result;
+use anyhow::Context as _;
 use askpass::AskPassDelegate;
 use assistant_settings::AssistantSettings;
 use db::kvp::KEY_VALUE_STORE;
@@ -1626,14 +1626,12 @@ impl GitPanel {
         &mut self,
         window: &mut Window,
         cx: &mut Context<Self>,
-    ) -> impl Future<Output = Result<bool, anyhow::Error>> + use<> {
+    ) -> impl Future<Output = anyhow::Result<bool>> + use<> {
         let repo = self.active_repository.clone();
         let mut cx = window.to_async(cx);
 
         async move {
-            let Some(repo) = repo else {
-                return Err(anyhow::anyhow!("No active repository"));
-            };
+            let repo = repo.context("No active repository")?;
 
             let pushed_to: Vec<SharedString> = repo
                 .update(&mut cx, |repo, _| repo.check_for_pushed_commits())?
@@ -2090,22 +2088,16 @@ impl GitPanel {
         let mut cx = window.to_async(cx);
 
         async move {
-            let Some(repo) = repo else {
-                return Err(anyhow::anyhow!("No active repository"));
-            };
-
+            let repo = repo.context("No active repository")?;
             let mut current_remotes: Vec<Remote> = repo
                 .update(&mut cx, |repo, _| {
-                    let Some(current_branch) = repo.branch.as_ref() else {
-                        return Err(anyhow::anyhow!("No active branch"));
-                    };
-
-                    Ok(repo.get_remotes(Some(current_branch.name().to_string())))
+                    let current_branch = repo.branch.as_ref().context("No active branch")?;
+                    anyhow::Ok(repo.get_remotes(Some(current_branch.name().to_string())))
                 })??
                 .await??;
 
             if current_remotes.len() == 0 {
-                return Err(anyhow::anyhow!("No active remote"));
+                anyhow::bail!("No active remote");
             } else if current_remotes.len() == 1 {
                 return Ok(Some(current_remotes.pop().unwrap()));
             } else {