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/lsp/src/input_handler.rs

@@ -1,7 +1,7 @@
 use std::str;
 use std::sync::Arc;
 
-use anyhow::{Result, anyhow};
+use anyhow::{Context as _, Result};
 use collections::HashMap;
 use futures::{
     AsyncBufReadExt, AsyncRead, AsyncReadExt as _,
@@ -35,7 +35,7 @@ where
         }
 
         if reader.read_until(b'\n', buffer).await? == 0 {
-            return Err(anyhow!("cannot read LSP message headers"));
+            anyhow::bail!("cannot read LSP message headers");
         }
     }
 }
@@ -82,7 +82,7 @@ impl LspStdoutHandler {
                 .split('\n')
                 .find(|line| line.starts_with(CONTENT_LEN_HEADER))
                 .and_then(|line| line.strip_prefix(CONTENT_LEN_HEADER))
-                .ok_or_else(|| anyhow!("invalid LSP message header {headers:?}"))?
+                .with_context(|| format!("invalid LSP message header {headers:?}"))?
                 .trim_end()
                 .parse()?;
 

crates/lsp/src/lsp.rs

@@ -352,7 +352,7 @@ impl LanguageServer {
         let stdout = server.stdout.take().unwrap();
         let stderr = server.stderr.take().unwrap();
         let root_uri = Url::from_file_path(&working_dir)
-            .map_err(|_| anyhow!("{} is not a valid URI", working_dir.display()))?;
+            .map_err(|()| anyhow!("{working_dir:?} is not a valid URI"))?;
         let server = Self::new_internal(
             server_id,
             server_name,