Rollup merge of #94146 - est31:let_else, r=cjgillot

Adopt let else in more places

Continuation of #89933, #91018, #91481, #93046, #93590, #94011.

I have extended my clippy lint to also recognize tuple passing and match statements. The diff caused by fixing it is way above 1 thousand lines. Thus, I split it up into multiple pull requests to make reviewing easier. This is the biggest of these PRs and handles the changes outside of rustdoc, rustc_typeck, rustc_const_eval, rustc_trait_selection, which were handled in PRs #94139, #94142, #94143, #94144.

compiler/rustc_parse/src/lexer/unicode_chars.rs

@@ -338,20 +338,16 @@ pub(super) fn check_for_substitution<'a>(
     ch: char,
     err: &mut DiagnosticBuilder<'a>,
 ) -> Option<token::TokenKind> {
-    let (u_name, ascii_char) = match UNICODE_ARRAY.iter().find(|&&(c, _, _)| c == ch) {
-        Some(&(_u_char, u_name, ascii_char)) => (u_name, ascii_char),
-        None => return None,
+    let Some(&(_u_char, u_name, ascii_char)) = UNICODE_ARRAY.iter().find(|&&(c, _, _)| c == ch) else {
+        return None;
     };
 
     let span = Span::with_root_ctxt(pos, pos + Pos::from_usize(ch.len_utf8()));
 
-    let (ascii_name, token) = match ASCII_ARRAY.iter().find(|&&(c, _, _)| c == ascii_char) {
-        Some((_ascii_char, ascii_name, token)) => (ascii_name, token),
-        None => {
-            let msg = format!("substitution character not found for '{}'", ch);
-            reader.sess.span_diagnostic.span_bug_no_panic(span, &msg);
-            return None;
-        }
+    let Some((_ascii_char, ascii_name, token)) = ASCII_ARRAY.iter().find(|&&(c, _, _)| c == ascii_char) else {
+        let msg = format!("substitution character not found for '{}'", ch);
+        reader.sess.span_diagnostic.span_bug_no_panic(span, &msg);
+        return None;
     };
 
     // special help suggestion for "directed" double quotes

compiler/rustc_parse/src/parser/expr.rs

@@ -1667,9 +1667,8 @@ impl<'a> Parser<'a> {
             Err(LitError::NotLiteral) => None,
             Err(err) => {
                 let span = token.span;
-                let lit = match token.kind {
-                    token::Literal(lit) => lit,
-                    _ => unreachable!(),
+                let token::Literal(lit) = token.kind else {
+                    unreachable!();
                 };
                 self.bump();
                 self.report_lit_error(err, lit, span);

compiler/rustc_parse/src/parser/item.rs

@@ -439,9 +439,8 @@ impl<'a> Parser<'a> {
 
     /// Recover if we parsed attributes and expected an item but there was none.
     fn recover_attrs_no_item(&mut self, attrs: &[Attribute]) -> PResult<'a, ()> {
-        let (start, end) = match attrs {
-            [] => return Ok(()),
-            [x0 @ xn] | [x0, .., xn] => (x0, xn),
+        let ([start @ end] | [start, .., end]) = attrs else {
+            return Ok(());
         };
         let msg = if end.is_doc_comment() {
             "expected item after doc comment"

compiler/rustc_parse/src/parser/stmt.rs

@@ -524,9 +524,8 @@ impl<'a> Parser<'a> {
         // Skip looking for a trailing semicolon when we have an interpolated statement.
         maybe_whole!(self, NtStmt, |x| Some(x));
 
-        let mut stmt = match self.parse_stmt_without_recovery(true, ForceCollect::No)? {
-            Some(stmt) => stmt,
-            None => return Ok(None),
+        let Some(mut stmt) = self.parse_stmt_without_recovery(true, ForceCollect::No)? else {
+            return Ok(None);
         };
 
         let mut eat_semi = true;