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/repl/src/kernels/native_kernel.rs

@@ -351,14 +351,7 @@ impl RunningKernel for NativeRunningKernel {
     fn force_shutdown(&mut self, _window: &mut Window, _cx: &mut App) -> Task<anyhow::Result<()>> {
         self._process_status_task.take();
         self.request_tx.close_channel();
-
-        Task::ready(match self.process.kill() {
-            Ok(_) => Ok(()),
-            Err(error) => Err(anyhow::anyhow!(
-                "Failed to kill the kernel process: {}",
-                error
-            )),
-        })
+        Task::ready(self.process.kill().context("killing the kernel process"))
     }
 }
 

crates/repl/src/kernels/remote_kernels.rs

@@ -54,7 +54,7 @@ pub async fn launch_remote_kernel(
     if !response.status().is_success() {
         let mut body = String::new();
         response.into_body().read_to_string(&mut body).await?;
-        return Err(anyhow::anyhow!("Failed to launch kernel: {}", body));
+        anyhow::bail!("Failed to launch kernel: {body}");
     }
 
     let mut body = String::new();
@@ -79,36 +79,31 @@ pub async fn list_remote_kernelspecs(
 
     let response = http_client.send(request).await?;
 
-    if response.status().is_success() {
-        let mut body = response.into_body();
+    anyhow::ensure!(
+        response.status().is_success(),
+        "Failed to fetch kernel specs: {}",
+        response.status()
+    );
+    let mut body = response.into_body();
 
-        let mut body_bytes = Vec::new();
-        body.read_to_end(&mut body_bytes).await?;
+    let mut body_bytes = Vec::new();
+    body.read_to_end(&mut body_bytes).await?;
 
-        let kernel_specs: KernelSpecsResponse = serde_json::from_slice(&body_bytes)?;
+    let kernel_specs: KernelSpecsResponse = serde_json::from_slice(&body_bytes)?;
 
-        let remote_kernelspecs = kernel_specs
-            .kernelspecs
-            .into_iter()
-            .map(|(name, spec)| RemoteKernelSpecification {
-                name: name.clone(),
-                url: remote_server.base_url.clone(),
-                token: remote_server.token.clone(),
-                kernelspec: spec.spec,
-            })
-            .collect::<Vec<RemoteKernelSpecification>>();
+    let remote_kernelspecs = kernel_specs
+        .kernelspecs
+        .into_iter()
+        .map(|(name, spec)| RemoteKernelSpecification {
+            name: name.clone(),
+            url: remote_server.base_url.clone(),
+            token: remote_server.token.clone(),
+            kernelspec: spec.spec,
+        })
+        .collect::<Vec<RemoteKernelSpecification>>();
 
-        if remote_kernelspecs.is_empty() {
-            Err(anyhow::anyhow!("No kernel specs found"))
-        } else {
-            Ok(remote_kernelspecs.clone())
-        }
-    } else {
-        Err(anyhow::anyhow!(
-            "Failed to fetch kernel specs: {}",
-            response.status()
-        ))
-    }
+    anyhow::ensure!(!remote_kernelspecs.is_empty(), "No kernel specs found");
+    Ok(remote_kernelspecs.clone())
 }
 
 impl PartialEq for RemoteKernelSpecification {
@@ -288,14 +283,12 @@ impl RunningKernel for RemoteRunningKernel {
 
             let response = http_client.send(request).await?;
 
-            if response.status().is_success() {
-                Ok(())
-            } else {
-                Err(anyhow::anyhow!(
-                    "Failed to shutdown kernel: {}",
-                    response.status()
-                ))
-            }
+            anyhow::ensure!(
+                response.status().is_success(),
+                "Failed to shutdown kernel: {}",
+                response.status()
+            );
+            Ok(())
         })
     }
 }