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/ollama/src/ollama.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};
@@ -242,11 +242,11 @@ pub async fn complete(
         Ok(response_message)
     } else {
         let body_str = std::str::from_utf8(&body)?;
-        Err(anyhow!(
+        anyhow::bail!(
             "Failed to connect to API: {} {}",
             response.status(),
             body_str
-        ))
+        );
     }
 }
 
@@ -276,12 +276,11 @@ 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 Ollama API: {} {}",
             response.status(),
             body,
-        ))
+        );
     }
 }
 
@@ -303,18 +302,15 @@ 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: LocalModelsResponse =
-            serde_json::from_str(&body).context("Unable to parse Ollama tag listing")?;
-
-        Ok(response.models)
-    } else {
-        Err(anyhow!(
-            "Failed to connect to Ollama API: {} {}",
-            response.status(),
-            body,
-        ))
-    }
+    anyhow::ensure!(
+        response.status().is_success(),
+        "Failed to connect to Ollama API: {} {}",
+        response.status(),
+        body,
+    );
+    let response: LocalModelsResponse =
+        serde_json::from_str(&body).context("Unable to parse Ollama tag listing")?;
+    Ok(response.models)
 }
 
 /// Fetch details of a model, used to determine model capabilities
@@ -332,16 +328,14 @@ pub async fn show_model(client: &dyn HttpClient, api_url: &str, model: &str) ->
     let mut body = String::new();
     response.body_mut().read_to_string(&mut body).await?;
 
-    if response.status().is_success() {
-        let details: ModelShow = serde_json::from_str(body.as_str())?;
-        Ok(details)
-    } else {
-        Err(anyhow!(
-            "Failed to connect to Ollama API: {} {}",
-            response.status(),
-            body,
-        ))
-    }
+    anyhow::ensure!(
+        response.status().is_success(),
+        "Failed to connect to Ollama API: {} {}",
+        response.status(),
+        body,
+    );
+    let details: ModelShow = serde_json::from_str(body.as_str())?;
+    Ok(details)
 }
 
 /// Sends an empty request to Ollama to trigger loading the model
@@ -366,12 +360,11 @@ 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 Ollama API: {} {}",
             response.status(),
             body,
-        ))
+        );
     }
 }