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/zlog/src/env_config.rs

@@ -1,4 +1,4 @@
-use anyhow::{Result, anyhow};
+use anyhow::Result;
 
 pub struct EnvFilter {
     pub level_global: Option<log::LevelFilter>,
@@ -14,9 +14,7 @@ pub fn parse(filter: &str) -> Result<EnvFilter> {
     for directive in filter.split(',') {
         match directive.split_once('=') {
             Some((name, level)) => {
-                if level.contains('=') {
-                    return Err(anyhow!("Invalid directive: {}", directive));
-                }
+                anyhow::ensure!(!level.contains('='), "Invalid directive: {directive}");
                 let level = parse_level(level.trim())?;
                 directive_names.push(name.trim().trim_end_matches(".rs").to_string());
                 directive_levels.push(level);
@@ -27,9 +25,7 @@ pub fn parse(filter: &str) -> Result<EnvFilter> {
                     directive_levels.push(log::LevelFilter::max() /* Enable all levels */);
                     continue;
                 };
-                if max_level.is_some() {
-                    return Err(anyhow!("Cannot set multiple max levels"));
-                }
+                anyhow::ensure!(max_level.is_none(), "Cannot set multiple max levels");
                 max_level.replace(level);
             }
         };
@@ -61,7 +57,7 @@ fn parse_level(level: &str) -> Result<log::LevelFilter> {
     if level.eq_ignore_ascii_case("OFF") || level.eq_ignore_ascii_case("NONE") {
         return Ok(log::LevelFilter::Off);
     }
-    Err(anyhow!("Invalid level: {}", level))
+    anyhow::bail!("Invalid level: {level}")
 }
 
 #[cfg(test)]

crates/zlog/src/sink.rs

@@ -234,10 +234,7 @@ fn rotate_log_file<PathRef>(
             .map(|err| anyhow::anyhow!(err)),
     };
     if let Some(err) = rotation_error {
-        eprintln!(
-            "Log file rotation failed. Truncating log file anyways: {}",
-            err,
-        );
+        eprintln!("Log file rotation failed. Truncating log file anyways: {err}",);
     }
     _ = file.set_len(0);