Auto merge of rust-lang#88066 - LeSeulArtichaut:patterns-cleanups, r=nagisa

Use if-let guards in the codebase and various other pattern cleanups

Dogfooding if-let guards as experimentation for the feature.

Tracking issue rust-lang#51114. Conflicts with rust-lang#87937.

Author: bors

core/src/lib.rs

@@ -69,6 +69,7 @@
 #![warn(missing_debug_implementations)]
 #![warn(missing_docs)]
 #![allow(explicit_outlives_requirements)]
+#![cfg_attr(bootstrap, allow(incomplete_features))] // if_let_guard
 //
 // Library features for const fns:
 #![feature(const_align_of_val)]
@@ -134,6 +135,7 @@
 #![feature(exhaustive_patterns)]
 #![feature(extern_types)]
 #![feature(fundamental)]
+#![feature(if_let_guard)]
 #![feature(intra_doc_pointers)]
 #![feature(intrinsics)]
 #![feature(lang_items)]

core/src/num/dec2flt/mod.rs

@@ -236,13 +236,8 @@ pub fn dec2flt<F: RawFloat>(s: &str) -> Result<F, ParseFloatError> {
 
     let num = match parse_number(s, negative) {
         Some(r) => r,
-        None => {
-            if let Some(value) = parse_inf_nan(s, negative) {
-                return Ok(value);
-            } else {
-                return Err(pfe_invalid());
-            }
-        }
+        None if let Some(value) = parse_inf_nan(s, negative) => return Ok(value),
+        None => return Err(pfe_invalid()),
     };
     if let Some(value) = num.try_fast_path::<F>() {
         return Ok(value);