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/bedrock/src/bedrock.rs

@@ -3,7 +3,7 @@ mod models;
 use std::collections::HashMap;
 use std::pin::Pin;
 
-use anyhow::{Error, Result, anyhow};
+use anyhow::{Context as _, Error, Result, anyhow};
 use aws_sdk_bedrockruntime as bedrock;
 pub use aws_sdk_bedrockruntime as bedrock_client;
 pub use aws_sdk_bedrockruntime::types::{
@@ -97,7 +97,7 @@ pub async fn stream_completion(
             }
         })
         .await
-        .map_err(|err| anyhow!("failed to spawn task: {err:?}"))?
+        .context("spawning a task")?
 }
 
 pub fn aws_document_to_value(document: &Document) -> Value {

crates/bedrock/src/models.rs

@@ -1,4 +1,3 @@
-use anyhow::anyhow;
 use serde::{Deserialize, Serialize};
 use strum::EnumIter;
 
@@ -107,7 +106,7 @@ impl Model {
         } else if id.starts_with("claude-3-7-sonnet-thinking") {
             Ok(Self::Claude3_7SonnetThinking)
         } else {
-            Err(anyhow!("invalid model id"))
+            anyhow::bail!("invalid model id {id}");
         }
     }
 
@@ -294,7 +293,7 @@ impl Model {
         }
     }
 
-    pub fn cross_region_inference_id(&self, region: &str) -> Result<String, anyhow::Error> {
+    pub fn cross_region_inference_id(&self, region: &str) -> anyhow::Result<String> {
         let region_group = if region.starts_with("us-gov-") {
             "us-gov"
         } else if region.starts_with("us-") {
@@ -307,8 +306,7 @@ impl Model {
             // Canada and South America regions - default to US profiles
             "us"
         } else {
-            // Unknown region
-            return Err(anyhow!("Unsupported Region"));
+            anyhow::bail!("Unsupported Region {region}");
         };
 
         let model_id = self.id();