chore: refactor backtrace style in panic

fix: rustfmt

library/std/src/panic.rs

@@ -463,11 +463,10 @@ static SHOULD_CAPTURE: AtomicU8 = AtomicU8::new(0);
 /// environment variable; see the details in [`get_backtrace_style`].
 #[unstable(feature = "panic_backtrace_config", issue = "93346")]
 pub fn set_backtrace_style(style: BacktraceStyle) {
-    if !cfg!(feature = "backtrace") {
-        // If the `backtrace` feature of this crate isn't enabled, skip setting.
-        return;
+    if cfg!(feature = "backtrace") {
+        // If the `backtrace` feature of this crate is enabled, set the backtrace style.
+        SHOULD_CAPTURE.store(style.as_u8(), Ordering::Release);
     }
-    SHOULD_CAPTURE.store(style.as_u8(), Ordering::Release);
 }
 
 /// Checks whether the standard library's panic hook will capture and print a
@@ -499,27 +498,28 @@ pub fn get_backtrace_style() -> Option<BacktraceStyle> {
         // to optimize away callers.
         return None;
     }
-    if let Some(style) = BacktraceStyle::from_u8(SHOULD_CAPTURE.load(Ordering::Acquire)) {
-        return Some(style);
-    }
-
-    let format = crate::env::var_os("RUST_BACKTRACE")
-        .map(|x| {
-            if &x == "0" {
-                BacktraceStyle::Off
-            } else if &x == "full" {
-                BacktraceStyle::Full
-            } else {
-                BacktraceStyle::Short
-            }
-        })
-        .unwrap_or(if crate::sys::FULL_BACKTRACE_DEFAULT {
-            BacktraceStyle::Full
-        } else {
-            BacktraceStyle::Off
+    return BacktraceStyle::from_u8(SHOULD_CAPTURE.load(Ordering::Acquire))
+        .map(Some)
+        .unwrap_or_else(|| {
+            let env_var = crate::env::var_os("RUST_BACKTRACE");
+            let style = env_var
+                .and_then(|var| {
+                    var.to_str().map(|s| match s {
+                        "0" => BacktraceStyle::Off,
+                        "full" => BacktraceStyle::Full,
+                        _ => BacktraceStyle::Short,
+                    })
+                })
+                .unwrap_or_else(|| {
+                    if crate::sys::FULL_BACKTRACE_DEFAULT {
+                        BacktraceStyle::Full
+                    } else {
+                        BacktraceStyle::Short
+                    }
+                });
+            set_backtrace_style(style);
+            Some(style)
         });
-    set_backtrace_style(format);
-    Some(format)
 }
 
 #[cfg(test)]