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/remote_server/src/headless_project.rs

@@ -1,5 +1,5 @@
 use ::proto::{FromProto, ToProto};
-use anyhow::{Result, anyhow};
+use anyhow::{Context as _, Result, anyhow};
 
 use extension::ExtensionHostProxy;
 use extension_host::headless_host::HeadlessExtensionStore;
@@ -368,7 +368,7 @@ impl HeadlessProject {
                 let mut parent = path
                     .parent()
                     .ok_or(e)
-                    .map_err(|_| anyhow!("{:?} does not exist", path))?;
+                    .with_context(|| format!("{path:?} does not exist"))?;
                 if parent == Path::new("") {
                     parent = util::paths::home_dir();
                 }
@@ -558,11 +558,7 @@ impl HeadlessProject {
         mut cx: AsyncApp,
     ) -> Result<proto::FindSearchCandidatesResponse> {
         let message = envelope.payload;
-        let query = SearchQuery::from_proto(
-            message
-                .query
-                .ok_or_else(|| anyhow!("missing query field"))?,
-        )?;
+        let query = SearchQuery::from_proto(message.query.context("missing query field")?)?;
         let results = this.update(&mut cx, |this, cx| {
             this.buffer_store.update(cx, |buffer_store, cx| {
                 buffer_store.find_search_candidates(&query, message.limit as _, this.fs.clone(), cx)

crates/remote_server/src/unix.rs

@@ -333,7 +333,7 @@ fn start_server(
                             break;
                         };
                         if let Err(error) = incoming_tx.unbounded_send(message) {
-                            log::error!("failed to send message to application: {:?}. exiting.", error);
+                            log::error!("failed to send message to application: {error:?}. exiting.");
                             return Err(anyhow!(error));
                         }
                     }
@@ -390,8 +390,7 @@ fn init_paths() -> anyhow::Result<()> {
     ]
     .iter()
     {
-        std::fs::create_dir_all(path)
-            .map_err(|e| anyhow!("Could not create directory {:?}: {}", path, e))?;
+        std::fs::create_dir_all(path).with_context(|| format!("creating directory {path:?}"))?;
     }
     Ok(())
 }
@@ -542,7 +541,7 @@ pub fn execute_proxy(identifier: String, is_reconnecting: bool) -> Result<()> {
     if is_reconnecting {
         if !server_running {
             log::error!("attempted to reconnect, but no server running");
-            return Err(anyhow!(ProxyLaunchError::ServerNotRunning));
+            anyhow::bail!(ProxyLaunchError::ServerNotRunning);
         }
     } else {
         if let Some(pid) = server_pid {
@@ -573,19 +572,20 @@ pub fn execute_proxy(identifier: String, is_reconnecting: bool) -> Result<()> {
         let mut stream = smol::net::unix::UnixStream::connect(&server_paths.stderr_socket).await?;
         let mut stderr_buffer = vec![0; 2048];
         loop {
-            match stream.read(&mut stderr_buffer).await {
-                Ok(0) => {
+            match stream
+                .read(&mut stderr_buffer)
+                .await
+                .context("reading stderr")?
+            {
+                0 => {
                     let error =
                         std::io::Error::new(std::io::ErrorKind::UnexpectedEof, "stderr closed");
                     Err(anyhow!(error))?;
                 }
-                Ok(n) => {
+                n => {
                     stderr.write_all(&mut stderr_buffer[..n]).await?;
                     stderr.flush().await?;
                 }
-                Err(error) => {
-                    Err(anyhow!("error reading stderr: {error:?}"))?;
-                }
             }
         }
     });
@@ -868,7 +868,7 @@ fn read_proxy_settings(cx: &mut Context<HeadlessProject>) -> Option<Url> {
 }
 
 fn daemonize() -> Result<ControlFlow<()>> {
-    match fork::fork().map_err(|e| anyhow::anyhow!("failed to call fork with error code {}", e))? {
+    match fork::fork().map_err(|e| anyhow!("failed to call fork with error code {e}"))? {
         fork::Fork::Parent(_) => {
             return Ok(ControlFlow::Break(()));
         }