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/lmstudio/src/lmstudio.rs

@@ -1,4 +1,4 @@
-use anyhow::{Context as _, Result, anyhow};
+use anyhow::{Context as _, Result};
 use futures::{AsyncBufReadExt, AsyncReadExt, StreamExt, io::BufReader, stream::BoxStream};
 use http_client::{AsyncBody, HttpClient, Method, Request as HttpRequest, http};
 use serde::{Deserialize, Serialize};
@@ -25,7 +25,7 @@ impl TryFrom<String> for Role {
             "assistant" => Ok(Self::Assistant),
             "system" => Ok(Self::System),
             "tool" => Ok(Self::Tool),
-            _ => Err(anyhow!("invalid role '{value}'")),
+            _ => anyhow::bail!("invalid role '{value}'"),
         }
     }
 }
@@ -253,11 +253,11 @@ pub async fn complete(
         let mut body = Vec::new();
         response.body_mut().read_to_end(&mut body).await?;
         let body_str = std::str::from_utf8(&body)?;
-        Err(anyhow!(
+        anyhow::bail!(
             "Failed to connect to API: {} {}",
             response.status(),
             body_str
-        ))
+        );
     }
 }
 
@@ -304,12 +304,11 @@ pub async fn stream_chat_completion(
     } else {
         let mut body = String::new();
         response.body_mut().read_to_string(&mut body).await?;
-
-        Err(anyhow!(
+        anyhow::bail!(
             "Failed to connect to LM Studio API: {} {}",
             response.status(),
             body,
-        ))
+        );
     }
 }
 
@@ -331,17 +330,15 @@ pub async fn get_models(
     let mut body = String::new();
     response.body_mut().read_to_string(&mut body).await?;
 
-    if response.status().is_success() {
-        let response: ListModelsResponse =
-            serde_json::from_str(&body).context("Unable to parse LM Studio models response")?;
-        Ok(response.data)
-    } else {
-        Err(anyhow!(
-            "Failed to connect to LM Studio API: {} {}",
-            response.status(),
-            body,
-        ))
-    }
+    anyhow::ensure!(
+        response.status().is_success(),
+        "Failed to connect to LM Studio API: {} {}",
+        response.status(),
+        body,
+    );
+    let response: ListModelsResponse =
+        serde_json::from_str(&body).context("Unable to parse LM Studio models response")?;
+    Ok(response.data)
 }
 
 /// Sends an empty request to LM Studio to trigger loading the model
@@ -367,11 +364,10 @@ pub async fn preload_model(client: Arc<dyn HttpClient>, api_url: &str, model: &s
     } else {
         let mut body = String::new();
         response.body_mut().read_to_string(&mut body).await?;
-
-        Err(anyhow!(
+        anyhow::bail!(
             "Failed to connect to LM Studio API: {} {}",
             response.status(),
             body,
-        ))
+        );
     }
 }