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/context_server/src/client.rs

@@ -1,4 +1,4 @@
-use anyhow::{Context, Result, anyhow};
+use anyhow::{Context as _, Result, anyhow};
 use collections::HashMap;
 use futures::{FutureExt, StreamExt, channel::oneshot, select};
 use gpui::{AppContext as _, AsyncApp, BackgroundExecutor, Task};
@@ -308,7 +308,7 @@ impl Client {
             .response_handlers
             .lock()
             .as_mut()
-            .ok_or_else(|| anyhow!("server shut down"))
+            .context("server shut down")
             .map(|handlers| {
                 handlers.insert(
                     RequestId::Int(id),
@@ -341,7 +341,7 @@ impl Client {
                         } else if let Some(result) = parsed.result {
                             Ok(serde_json::from_str(result.get())?)
                         } else {
-                            Err(anyhow!("Invalid response: no result or error"))
+                            anyhow::bail!("Invalid response: no result or error");
                         }
                     }
                     Err(_) => anyhow::bail!("cancelled")

crates/context_server/src/protocol.rs

@@ -46,12 +46,11 @@ impl ModelContextProtocol {
             .request(types::RequestType::Initialize.as_str(), params)
             .await?;
 
-        if !Self::supported_protocols().contains(&response.protocol_version) {
-            return Err(anyhow::anyhow!(
-                "Unsupported protocol version: {:?}",
-                response.protocol_version
-            ));
-        }
+        anyhow::ensure!(
+            Self::supported_protocols().contains(&response.protocol_version),
+            "Unsupported protocol version: {:?}",
+            response.protocol_version
+        );
 
         log::trace!("mcp server info {:?}", response.server_info);
 
@@ -96,14 +95,11 @@ impl InitializedContextServerProtocol {
     }
 
     fn check_capability(&self, capability: ServerCapability) -> Result<()> {
-        if self.capable(capability) {
-            Ok(())
-        } else {
-            Err(anyhow::anyhow!(
-                "Server does not support {:?} capability",
-                capability
-            ))
-        }
+        anyhow::ensure!(
+            self.capable(capability),
+            "Server does not support {capability:?} capability"
+        );
+        Ok(())
     }
 
     /// List the MCP prompts.