Auto merge of #94987 - Dylan-DPC:rollup-5tssuhi, r=Dylan-DPC

Rollup of 5 pull requests

Successful merges:

 - #94868 (Format core and std macro rules, removing needless surrounding blocks)
 - #94951 (Extend the irrefutable_let_patterns lint to let chains)
 - #94955 (Refactor: Use `format_args_capture` in some parts of `rustc_parse`)
 - #94957 (Improve the explanation about the behaviour of read_line)
 - #94974 (Ensure that `let_else` does not interact with `let_chains`)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

5 files changed, 240 insertions, 96 deletions

diff --git a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
index e2c56df6014..8a3a46c1190 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
@@ -158,7 +158,7 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
         self.check_patterns(pat, Refutable);
         let mut cx = self.new_cx(scrutinee.hir_id);
         let tpat = self.lower_pattern(&mut cx, pat, &mut false);
-        check_let_reachability(&mut cx, pat.hir_id, tpat, span);
+        self.check_let_reachability(&mut cx, pat.hir_id, tpat, span);
     }
 
     fn check_match(
@@ -176,7 +176,7 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
             if let Some(hir::Guard::IfLet(ref pat, _)) = arm.guard {
                 self.check_patterns(pat, Refutable);
                 let tpat = self.lower_pattern(&mut cx, pat, &mut false);
-                check_let_reachability(&mut cx, pat.hir_id, tpat, tpat.span());
+                self.check_let_reachability(&mut cx, pat.hir_id, tpat, tpat.span());
             }
         }
 
@@ -224,6 +224,157 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
         }
     }
 
+    fn check_let_reachability(
+        &mut self,
+        cx: &mut MatchCheckCtxt<'p, 'tcx>,
+        pat_id: HirId,
+        pat: &'p DeconstructedPat<'p, 'tcx>,
+        span: Span,
+    ) {
+        if self.check_let_chain(cx, pat_id) {
+            return;
+        }
+
+        if is_let_irrefutable(cx, pat_id, pat) {
+            irrefutable_let_pattern(cx.tcx, pat_id, span);
+        }
+    }
+
+    fn check_let_chain(&mut self, cx: &mut MatchCheckCtxt<'p, 'tcx>, pat_id: HirId) -> bool {
+        let hir = self.tcx.hir();
+        let parent = hir.get_parent_node(pat_id);
+
+        // First, figure out if the given pattern is part of a let chain,
+        // and if so, obtain the top node of the chain.
+        let mut top = parent;
+        let mut part_of_chain = false;
+        loop {
+            let new_top = hir.get_parent_node(top);
+            if let hir::Node::Expr(
+                hir::Expr {
+                    kind: hir::ExprKind::Binary(Spanned { node: hir::BinOpKind::And, .. }, lhs, rhs),
+                    ..
+                },
+                ..,
+            ) = hir.get(new_top)
+            {
+                // If this isn't the first iteration, we need to check
+                // if there is a let expr before us in the chain, so
+                // that we avoid doubly checking the let chain.
+
+                // The way a chain of &&s is encoded is ((let ... && let ...) && let ...) && let ...
+                // as && is left-to-right associative. Thus, we need to check rhs.
+                if part_of_chain && matches!(rhs.kind, hir::ExprKind::Let(..)) {
+                    return true;
+                }
+                // If there is a let at the lhs, and we provide the rhs, we don't do any checking either.
+                if !part_of_chain && matches!(lhs.kind, hir::ExprKind::Let(..)) && rhs.hir_id == top
+                {
+                    return true;
+                }
+            } else {
+                // We've reached the top.
+                break;
+            }
+
+            // Since this function is called within a let context, it is reasonable to assume that any parent
+            // `&&` infers a let chain
+            part_of_chain = true;
+            top = new_top;
+        }
+        if !part_of_chain {
+            return false;
+        }
+
+        // Second, obtain the refutabilities of all exprs in the chain,
+        // and record chain members that aren't let exprs.
+        let mut chain_refutabilities = Vec::new();
+        let hir::Node::Expr(top_expr) = hir.get(top) else {
+            // We ensure right above that it's an Expr
+            unreachable!()
+        };
+        let mut cur_expr = top_expr;
+        loop {
+            let mut add = |expr: &hir::Expr<'tcx>| {
+                let refutability = match expr.kind {
+                    hir::ExprKind::Let(hir::Let { pat, init, span, .. }) => {
+                        let mut ncx = self.new_cx(init.hir_id);
+                        let tpat = self.lower_pattern(&mut ncx, pat, &mut false);
+
+                        let refutable = !is_let_irrefutable(&mut ncx, pat.hir_id, tpat);
+                        Some((*span, refutable))
+                    }
+                    _ => None,
+                };
+                chain_refutabilities.push(refutability);
+            };
+            if let hir::Expr {
+                kind: hir::ExprKind::Binary(Spanned { node: hir::BinOpKind::And, .. }, lhs, rhs),
+                ..
+            } = cur_expr
+            {
+                add(rhs);
+                cur_expr = lhs;
+            } else {
+                add(cur_expr);
+                break;
+            }
+        }
+        chain_refutabilities.reverse();
+
+        // Third, emit the actual warnings.
+
+        if chain_refutabilities.iter().all(|r| matches!(*r, Some((_, false)))) {
+            // The entire chain is made up of irrefutable `let` statements
+            let let_source = let_source_parent(self.tcx, top, None);
+            irrefutable_let_patterns(
+                cx.tcx,
+                top,
+                let_source,
+                chain_refutabilities.len(),
+                top_expr.span,
+            );
+            return true;
+        }
+        let lint_affix = |affix: &[Option<(Span, bool)>], kind, suggestion| {
+            let span_start = affix[0].unwrap().0;
+            let span_end = affix.last().unwrap().unwrap().0;
+            let span = span_start.to(span_end);
+            let cnt = affix.len();
+            cx.tcx.struct_span_lint_hir(IRREFUTABLE_LET_PATTERNS, top, span, |lint| {
+                let s = pluralize!(cnt);
+                let mut diag = lint.build(&format!("{kind} irrefutable pattern{s} in let chain"));
+                diag.note(&format!(
+                    "{these} pattern{s} will always match",
+                    these = pluralize!("this", cnt),
+                ));
+                diag.help(&format!(
+                    "consider moving {} {suggestion}",
+                    if cnt > 1 { "them" } else { "it" }
+                ));
+                diag.emit()
+            });
+        };
+        if let Some(until) = chain_refutabilities.iter().position(|r| !matches!(*r, Some((_, false)))) && until > 0 {
+            // The chain has a non-zero prefix of irrefutable `let` statements.
+
+            // Check if the let source is while, for there is no alternative place to put a prefix,
+            // and we shouldn't lint.
+            let let_source = let_source_parent(self.tcx, top, None);
+            if !matches!(let_source, LetSource::WhileLet) {
+                // Emit the lint
+                let prefix = &chain_refutabilities[..until];
+                lint_affix(prefix, "leading", "outside of the construct");
+            }
+        }
+        if let Some(from) = chain_refutabilities.iter().rposition(|r| !matches!(*r, Some((_, false)))) && from != (chain_refutabilities.len() - 1) {
+            // The chain has a non-empty suffix of irrefutable `let` statements
+            let suffix = &chain_refutabilities[from + 1..];
+            lint_affix(suffix, "trailing", "into the body");
+        }
+        true
+    }
+
     fn check_irrefutable(&self, pat: &'tcx Pat<'tcx>, origin: &str, sp: Option<Span>) {
         let mut cx = self.new_cx(pat.hir_id);
 
@@ -453,6 +604,17 @@ fn unreachable_pattern(tcx: TyCtxt<'_>, span: Span, id: HirId, catchall: Option<
 }
 
 fn irrefutable_let_pattern(tcx: TyCtxt<'_>, id: HirId, span: Span) {
+    let source = let_source(tcx, id);
+    irrefutable_let_patterns(tcx, id, source, 1, span);
+}
+
+fn irrefutable_let_patterns(
+    tcx: TyCtxt<'_>,
+    id: HirId,
+    source: LetSource,
+    count: usize,
+    span: Span,
+) {
     macro_rules! emit_diag {
         (
             $lint:expr,
@@ -460,14 +622,15 @@ fn irrefutable_let_pattern(tcx: TyCtxt<'_>, id: HirId, span: Span) {
             $note_sufix:expr,
             $help_sufix:expr
         ) => {{
-            let mut diag = $lint.build(concat!("irrefutable ", $source_name, " pattern"));
-            diag.note(concat!("this pattern will always match, so the ", $note_sufix));
+            let s = pluralize!(count);
+            let these = pluralize!("this", count);
+            let mut diag = $lint.build(&format!("irrefutable {} pattern{s}", $source_name));
+            diag.note(&format!("{these} pattern{s} will always match, so the {}", $note_sufix));
             diag.help(concat!("consider ", $help_sufix));
             diag.emit()
         }};
     }
 
-    let source = let_source(tcx, id);
     let span = match source {
         LetSource::LetElse(span) => span,
         _ => span,
@@ -511,16 +674,11 @@ fn irrefutable_let_pattern(tcx: TyCtxt<'_>, id: HirId, span: Span) {
     });
 }
 
-fn check_let_reachability<'p, 'tcx>(
+fn is_let_irrefutable<'p, 'tcx>(
     cx: &mut MatchCheckCtxt<'p, 'tcx>,
     pat_id: HirId,
     pat: &'p DeconstructedPat<'p, 'tcx>,
-    span: Span,
-) {
-    if is_let_chain(cx.tcx, pat_id) {
-        return;
-    }
-
+) -> bool {
     let arms = [MatchArm { pat, hir_id: pat_id, has_guard: false }];
     let report = compute_match_usefulness(&cx, &arms, pat_id, pat.ty());
 
@@ -529,10 +687,9 @@ fn check_let_reachability<'p, 'tcx>(
     // `is_uninhabited` check.
     report_arm_reachability(&cx, &report);
 
-    if report.non_exhaustiveness_witnesses.is_empty() {
-        // The match is exhaustive, i.e. the `if let` pattern is irrefutable.
-        irrefutable_let_pattern(cx.tcx, pat_id, span);
-    }
+    // If the list of witnesses is empty, the match is exhaustive,
+    // i.e. the `if let` pattern is irrefutable.
+    report.non_exhaustiveness_witnesses.is_empty()
 }
 
 /// Report unreachable arms, if any.
@@ -941,13 +1098,19 @@ fn let_source(tcx: TyCtxt<'_>, pat_id: HirId) -> LetSource {
     let hir = tcx.hir();
 
     let parent = hir.get_parent_node(pat_id);
+    let_source_parent(tcx, parent, Some(pat_id))
+}
+
+fn let_source_parent(tcx: TyCtxt<'_>, parent: HirId, pat_id: Option<HirId>) -> LetSource {
+    let hir = tcx.hir();
+
     let parent_node = hir.get(parent);
 
     match parent_node {
         hir::Node::Arm(hir::Arm {
             guard: Some(hir::Guard::IfLet(&hir::Pat { hir_id, .. }, _)),
             ..
-        }) if hir_id == pat_id => {
+        }) if Some(hir_id) == pat_id => {
             return LetSource::IfLetGuard;
         }
         hir::Node::Expr(hir::Expr { kind: hir::ExprKind::Let(..), span, .. }) => {
@@ -980,21 +1143,3 @@ fn let_source(tcx: TyCtxt<'_>, pat_id: HirId) -> LetSource {
 
     LetSource::GenericLet
 }
-
-// Since this function is called within a let context, it is reasonable to assume that any parent
-// `&&` infers a let chain
-fn is_let_chain(tcx: TyCtxt<'_>, pat_id: HirId) -> bool {
-    let hir = tcx.hir();
-    let parent = hir.get_parent_node(pat_id);
-    let parent_parent = hir.get_parent_node(parent);
-    matches!(
-        hir.get(parent_parent),
-        hir::Node::Expr(
-            hir::Expr {
-                kind: hir::ExprKind::Binary(Spanned { node: hir::BinOpKind::And, .. }, ..),
-                ..
-            },
-            ..
-        )
-    )
-}
diff --git a/compiler/rustc_parse/src/parser/attr.rs b/compiler/rustc_parse/src/parser/attr.rs
index 379e47077ea..8f759ae84fa 100644
--- a/compiler/rustc_parse/src/parser/attr.rs
+++ b/compiler/rustc_parse/src/parser/attr.rs
@@ -139,7 +139,7 @@ impl<'a> Parser<'a> {
                 Ok(attr::mk_attr_from_item(item, None, style, attr_sp))
             } else {
                 let token_str = pprust::token_to_string(&this.token);
-                let msg = &format!("expected `#`, found `{}`", token_str);
+                let msg = &format!("expected `#`, found `{token_str}`");
                 Err(this.struct_span_err(this.token.span, msg))
             }
         })
@@ -421,7 +421,7 @@ impl<'a> Parser<'a> {
         }
 
         let found = pprust::token_to_string(&self.token);
-        let msg = format!("expected unsuffixed literal or identifier, found `{}`", found);
+        let msg = format!("expected unsuffixed literal or identifier, found `{found}`");
         Err(self.struct_span_err(self.token.span, &msg))
     }
 }
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index 21d5bec65f0..1909e9ee749 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -327,8 +327,8 @@ impl<'a> Parser<'a> {
                 expect.clone()
             };
             (
-                format!("expected one of {}, found {}", expect, actual),
-                (self.prev_token.span.shrink_to_hi(), format!("expected one of {}", short_expect)),
+                format!("expected one of {expect}, found {actual}"),
+                (self.prev_token.span.shrink_to_hi(), format!("expected one of {short_expect}")),
             )
         } else if expected.is_empty() {
             (
@@ -337,8 +337,8 @@ impl<'a> Parser<'a> {
             )
         } else {
             (
-                format!("expected {}, found {}", expect, actual),
-                (self.prev_token.span.shrink_to_hi(), format!("expected {}", expect)),
+                format!("expected {expect}, found {actual}"),
+                (self.prev_token.span.shrink_to_hi(), format!("expected {expect}")),
             )
         };
         self.last_unexpected_token_span = Some(self.token.span);
@@ -421,7 +421,7 @@ impl<'a> Parser<'a> {
                     String::new(),
                     Applicability::MachineApplicable,
                 );
-                err.note(&format!("the raw string started with {} `#`s", n_hashes));
+                err.note(&format!("the raw string started with {n_hashes} `#`s"));
                 true
             }
             _ => false,
@@ -1191,7 +1191,7 @@ impl<'a> Parser<'a> {
                     _ => None,
                 };
                 if let Some(name) = previous_item_kind_name {
-                    err.help(&format!("{} declarations are not followed by a semicolon", name));
+                    err.help(&format!("{name} declarations are not followed by a semicolon"));
                 }
             }
             err.emit();
@@ -1226,12 +1226,12 @@ impl<'a> Parser<'a> {
             "expected `{}`, found {}",
             token_str,
             match (&self.token.kind, self.subparser_name) {
-                (token::Eof, Some(origin)) => format!("end of {}", origin),
+                (token::Eof, Some(origin)) => format!("end of {origin}"),
                 _ => this_token_str,
             },
         );
         let mut err = self.struct_span_err(sp, &msg);
-        let label_exp = format!("expected `{}`", token_str);
+        let label_exp = format!("expected `{token_str}`");
         match self.recover_closing_delimiter(&[t.clone()], err) {
             Err(e) => err = e,
             Ok(recovered) => {
@@ -1368,7 +1368,7 @@ impl<'a> Parser<'a> {
                     Applicability::MachineApplicable,
                 );
             }
-            err.span_suggestion(lo.shrink_to_lo(), &format!("{}you can still access the deprecated `try!()` macro using the \"raw identifier\" syntax", prefix), "r#".to_string(), Applicability::MachineApplicable);
+            err.span_suggestion(lo.shrink_to_lo(), &format!("{prefix}you can still access the deprecated `try!()` macro using the \"raw identifier\" syntax"), "r#".to_string(), Applicability::MachineApplicable);
             err.emit();
             Ok(self.mk_expr_err(lo.to(hi)))
         } else {
@@ -1504,7 +1504,7 @@ impl<'a> Parser<'a> {
                 delim.retain(|c| c != '`');
                 err.span_suggestion_short(
                     self.prev_token.span.shrink_to_hi(),
-                    &format!("`{}` may belong here", delim),
+                    &format!("`{delim}` may belong here"),
                     delim,
                     Applicability::MaybeIncorrect,
                 );
@@ -1698,7 +1698,7 @@ impl<'a> Parser<'a> {
                                 (
                                     ident,
                                     "self: ".to_string(),
-                                    format!("{}: &{}TypeName", ident, mutab),
+                                    format!("{ident}: &{mutab}TypeName"),
                                     "_: ".to_string(),
                                     pat.span.shrink_to_lo(),
                                     pat.span,
@@ -1826,7 +1826,7 @@ impl<'a> Parser<'a> {
         let (span, msg) = match (&self.token.kind, self.subparser_name) {
             (&token::Eof, Some(origin)) => {
                 let sp = self.sess.source_map().next_point(self.prev_token.span);
-                (sp, format!("expected expression, found end of {}", origin))
+                (sp, format!("expected expression, found end of {origin}"))
             }
             _ => (
                 self.token.span,
@@ -1975,8 +1975,8 @@ impl<'a> Parser<'a> {
             (ty_generics, self.sess.source_map().span_to_snippet(param.span()))
         {
             let (span, sugg) = match &generics.params[..] {
-                [] => (generics.span, format!("<{}>", snippet)),
-                [.., generic] => (generic.span().shrink_to_hi(), format!(", {}", snippet)),
+                [] => (generics.span, format!("<{snippet}>")),
+                [.., generic] => (generic.span().shrink_to_hi(), format!(", {snippet}")),
             };
             err.multipart_suggestion(
                 "`const` parameters must be declared for the `impl`",
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index b993d48c995..550d79a898c 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -223,7 +223,7 @@ impl<'a> Parser<'a> {
                     AssocOp::NotEqual => "!=",
                     _ => unreachable!(),
                 };
-                self.struct_span_err(sp, &format!("invalid comparison operator `{}=`", sugg))
+                self.struct_span_err(sp, &format!("invalid comparison operator `{sugg}=`"))
                     .span_suggestion_short(
                         sp,
                         &format!("`{s}=` is not a valid comparison operator, use `{s}`", s = sugg),
@@ -441,10 +441,10 @@ impl<'a> Parser<'a> {
 
     /// Error on `and` and `or` suggesting `&&` and `||` respectively.
     fn error_bad_logical_op(&self, bad: &str, good: &str, english: &str) {
-        self.struct_span_err(self.token.span, &format!("`{}` is not a logical operator", bad))
+        self.struct_span_err(self.token.span, &format!("`{bad}` is not a logical operator"))
             .span_suggestion_short(
                 self.token.span,
-                &format!("use `{}` to perform logical {}", good, english),
+                &format!("use `{good}` to perform logical {english}"),
                 good.to_string(),
                 Applicability::MachineApplicable,
             )
@@ -766,9 +766,9 @@ impl<'a> Parser<'a> {
                                 self.look_ahead(1, |t| t.span).to(span_after_type),
                                 "interpreted as generic arguments",
                             )
-                            .span_label(self.token.span, format!("not interpreted as {}", op_noun))
+                            .span_label(self.token.span, format!("not interpreted as {op_noun}"))
                             .multipart_suggestion(
-                                &format!("try {} the cast value", op_verb),
+                                &format!("try {op_verb} the cast value"),
                                 vec![
                                     (expr.span.shrink_to_lo(), "(".to_string()),
                                     (expr.span.shrink_to_hi(), ")".to_string()),
@@ -970,7 +970,7 @@ impl<'a> Parser<'a> {
     fn error_unexpected_after_dot(&self) {
         // FIXME Could factor this out into non_fatal_unexpected or something.
         let actual = pprust::token_to_string(&self.token);
-        self.struct_span_err(self.token.span, &format!("unexpected token: `{}`", actual)).emit();
+        self.struct_span_err(self.token.span, &format!("unexpected token: `{actual}`")).emit();
     }
 
     // We need an identifier or integer, but the next token is a float.
@@ -1151,7 +1151,7 @@ impl<'a> Parser<'a> {
                             mem::replace(err, replacement_err).cancel();
 
                             err.multipart_suggestion(
-                                &format!("if `{}` is a struct, use braces as delimiters", name),
+                                &format!("if `{name}` is a struct, use braces as delimiters"),
                                 vec![
                                     (open_paren, " { ".to_string()),
                                     (close_paren, " }".to_string()),
@@ -1159,7 +1159,7 @@ impl<'a> Parser<'a> {
                                 Applicability::MaybeIncorrect,
                             );
                             err.multipart_suggestion(
-                                &format!("if `{}` is a function, use the arguments directly", name),
+                                &format!("if `{name}` is a function, use the arguments directly"),
                                 fields
                                     .into_iter()
                                     .map(|field| (field.span.until(field.expr.span), String::new()))
@@ -1776,9 +1776,9 @@ impl<'a> Parser<'a> {
                         )
                         .emit();
                 } else {
-                    let msg = format!("invalid suffix `{}` for number literal", suf);
+                    let msg = format!("invalid suffix `{suf}` for number literal");
                     self.struct_span_err(span, &msg)
-                        .span_label(span, format!("invalid suffix `{}`", suf))
+                        .span_label(span, format!("invalid suffix `{suf}`"))
                         .help("the suffix must be one of the numeric types (`u32`, `isize`, `f32`, etc.)")
                         .emit();
                 }
@@ -1791,9 +1791,9 @@ impl<'a> Parser<'a> {
                     let msg = format!("invalid width `{}` for float literal", &suf[1..]);
                     self.struct_span_err(span, &msg).help("valid widths are 32 and 64").emit();
                 } else {
-                    let msg = format!("invalid suffix `{}` for float literal", suf);
+                    let msg = format!("invalid suffix `{suf}` for float literal");
                     self.struct_span_err(span, &msg)
-                        .span_label(span, format!("invalid suffix `{}`", suf))
+                        .span_label(span, format!("invalid suffix `{suf}`"))
                         .help("valid suffixes are `f32` and `f64`")
                         .emit();
                 }
@@ -1805,7 +1805,7 @@ impl<'a> Parser<'a> {
                     2 => "binary",
                     _ => unreachable!(),
                 };
-                self.struct_span_err(span, &format!("{} float literal is not supported", descr))
+                self.struct_span_err(span, &format!("{descr} float literal is not supported"))
                     .span_label(span, "not supported")
                     .emit();
             }
@@ -1825,7 +1825,7 @@ impl<'a> Parser<'a> {
                 let mut err = self
                     .sess
                     .span_diagnostic
-                    .struct_span_warn(sp, &format!("suffixes on {} are invalid", kind));
+                    .struct_span_warn(sp, &format!("suffixes on {kind} are invalid"));
                 err.note(&format!(
                     "`{}` is *temporarily* accepted on tuple index fields as it was \
                         incorrectly accepted on stable for a few releases",
@@ -1842,10 +1842,10 @@ impl<'a> Parser<'a> {
                 );
                 err
             } else {
-                self.struct_span_err(sp, &format!("suffixes on {} are invalid", kind))
+                self.struct_span_err(sp, &format!("suffixes on {kind} are invalid"))
                     .forget_guarantee()
             };
-            err.span_label(sp, format!("invalid suffix `{}`", suf));
+            err.span_label(sp, format!("invalid suffix `{suf}`"));
             err.emit();
         }
     }
@@ -2211,7 +2211,7 @@ impl<'a> Parser<'a> {
         let ctx = if is_ctx_else { "else" } else { "if" };
         self.struct_span_err(last, "outer attributes are not allowed on `if` and `else` branches")
             .span_label(branch_span, "the attributes are attached to this branch")
-            .span_label(ctx_span, format!("the branch belongs to this `{}`", ctx))
+            .span_label(ctx_span, format!("the branch belongs to this `{ctx}`"))
             .span_suggestion(
                 span,
                 "remove the attributes",
@@ -2391,7 +2391,7 @@ impl<'a> Parser<'a> {
             err.span_label(arrow_span, "while parsing the `match` arm starting here");
             if stmts.len() > 1 {
                 err.multipart_suggestion(
-                    &format!("surround the statement{} with a body", s),
+                    &format!("surround the statement{s} with a body"),
                     vec![
                         (span.shrink_to_lo(), "{ ".to_string()),
                         (span.shrink_to_hi(), " }".to_string()),
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index 178bb62e0b2..b582f060395 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -66,7 +66,7 @@ impl<'a> Parser<'a> {
         if !self.eat(term) {
             let token_str = super::token_descr(&self.token);
             if !self.maybe_consume_incorrect_semicolon(&items) {
-                let msg = &format!("expected item, found {}", token_str);
+                let msg = &format!("expected item, found {token_str}");
                 let mut err = self.struct_span_err(self.token.span, msg);
                 err.span_label(self.token.span, "expected item");
                 return Err(err);
@@ -163,9 +163,9 @@ impl<'a> Parser<'a> {
         }
         let vs = pprust::vis_to_string(&vis);
         let vs = vs.trim_end();
-        self.struct_span_err(vis.span, &format!("visibility `{}` is not followed by an item", vs))
+        self.struct_span_err(vis.span, &format!("visibility `{vs}` is not followed by an item"))
             .span_label(vis.span, "the visibility")
-            .help(&format!("you likely meant to define an item, e.g., `{} fn foo() {{}}`", vs))
+            .help(&format!("you likely meant to define an item, e.g., `{vs} fn foo() {{}}`"))
             .emit();
     }
 
@@ -327,7 +327,7 @@ impl<'a> Parser<'a> {
         if self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace)) {
             // possible public struct definition where `struct` was forgotten
             let ident = self.parse_ident().unwrap();
-            let msg = format!("add `struct` here to parse `{}` as a public struct", ident);
+            let msg = format!("add `struct` here to parse `{ident}` as a public struct");
             let mut err = self.struct_span_err(sp, "missing `struct` for struct definition");
             err.span_suggestion_short(
                 sp,
@@ -355,16 +355,16 @@ impl<'a> Parser<'a> {
                 ("fn` or `struct", "function or struct", true)
             };
 
-            let msg = format!("missing `{}` for {} definition", kw, kw_name);
+            let msg = format!("missing `{kw}` for {kw_name} definition");
             let mut err = self.struct_span_err(sp, &msg);
             if !ambiguous {
                 self.consume_block(token::Brace, ConsumeClosingDelim::Yes);
                 let suggestion =
-                    format!("add `{}` here to parse `{}` as a public {}", kw, ident, kw_name);
+                    format!("add `{kw}` here to parse `{ident}` as a public {kw_name}");
                 err.span_suggestion_short(
                     sp,
                     &suggestion,
-                    format!(" {} ", kw),
+                    format!(" {kw} "),
                     Applicability::MachineApplicable,
                 );
             } else if let Ok(snippet) = self.span_to_snippet(ident_sp) {
@@ -393,12 +393,12 @@ impl<'a> Parser<'a> {
             } else {
                 ("fn` or `struct", "function or struct", true)
             };
-            let msg = format!("missing `{}` for {} definition", kw, kw_name);
+            let msg = format!("missing `{kw}` for {kw_name} definition");
             let mut err = self.struct_span_err(sp, &msg);
             if !ambiguous {
                 err.span_suggestion_short(
                     sp,
-                    &format!("add `{}` here to parse `{}` as a public {}", kw, ident, kw_name),
+                    &format!("add `{kw}` here to parse `{ident}` as a public {kw_name}"),
                     format!(" {} ", kw),
                     Applicability::MachineApplicable,
                 );
@@ -1031,8 +1031,8 @@ impl<'a> Parser<'a> {
     fn error_bad_item_kind<T>(&self, span: Span, kind: &ItemKind, ctx: &str) -> Option<T> {
         let span = self.sess.source_map().guess_head_span(span);
         let descr = kind.descr();
-        self.struct_span_err(span, &format!("{} is not supported in {}", descr, ctx))
-            .help(&format!("consider moving the {} out to a nearby module scope", descr))
+        self.struct_span_err(span, &format!("{descr} is not supported in {ctx}"))
+            .help(&format!("consider moving the {descr} out to a nearby module scope"))
             .emit();
         None
     }
@@ -1161,11 +1161,11 @@ impl<'a> Parser<'a> {
             Some(Mutability::Not) => "static",
             None => "const",
         };
-        let mut err = self.struct_span_err(id.span, &format!("missing type for `{}` item", kind));
+        let mut err = self.struct_span_err(id.span, &format!("missing type for `{kind}` item"));
         err.span_suggestion(
             id.span,
             "provide a type for the item",
-            format!("{}: <type>", id),
+            format!("{id}: <type>"),
             Applicability::HasPlaceholders,
         );
         err.stash(id.span, StashKey::ItemNoType);
@@ -1282,8 +1282,7 @@ impl<'a> Parser<'a> {
         } else {
             let token_str = super::token_descr(&self.token);
             let msg = &format!(
-                "expected `where`, `{{`, `(`, or `;` after struct name, found {}",
-                token_str
+                "expected `where`, `{{`, `(`, or `;` after struct name, found {token_str}"
             );
             let mut err = self.struct_span_err(self.token.span, msg);
             err.span_label(self.token.span, "expected `where`, `{`, `(`, or `;` after struct name");
@@ -1310,7 +1309,7 @@ impl<'a> Parser<'a> {
             VariantData::Struct(fields, recovered)
         } else {
             let token_str = super::token_descr(&self.token);
-            let msg = &format!("expected `where` or `{{` after union name, found {}", token_str);
+            let msg = &format!("expected `where` or `{{` after union name, found {token_str}");
             let mut err = self.struct_span_err(self.token.span, msg);
             err.span_label(self.token.span, "expected `where` or `{` after union name");
             return Err(err);
@@ -1591,7 +1590,7 @@ impl<'a> Parser<'a> {
                 }
                 let mut err = self.struct_span_err(
                     lo.to(self.prev_token.span),
-                    &format!("functions are not allowed in {} definitions", adt_ty),
+                    &format!("functions are not allowed in {adt_ty} definitions"),
                 );
                 err.help("unlike in C++, Java, and C#, functions are declared in `impl` blocks");
                 err.help("see https://doc.rust-lang.org/book/ch05-03-method-syntax.html for more information");
@@ -1706,7 +1705,7 @@ impl<'a> Parser<'a> {
         let vstr = pprust::vis_to_string(vis);
         let vstr = vstr.trim_end();
         if macro_rules {
-            let msg = format!("can't qualify macro_rules invocation with `{}`", vstr);
+            let msg = format!("can't qualify macro_rules invocation with `{vstr}`");
             self.struct_span_err(vis.span, &msg)
                 .span_suggestion(
                     vis.span,
@@ -1723,7 +1722,7 @@ impl<'a> Parser<'a> {
                     String::new(),
                     Applicability::MachineApplicable,
                 )
-                .help(&format!("try adjusting the macro to put `{}` inside the invocation", vstr))
+                .help(&format!("try adjusting the macro to put `{vstr}` inside the invocation"))
                 .emit();
         }
     }
@@ -1781,11 +1780,11 @@ impl<'a> Parser<'a> {
 
             self.struct_span_err(
                 kw_token.span,
-                &format!("`{}` definition cannot be nested inside `{}`", kw_str, keyword),
+                &format!("`{kw_str}` definition cannot be nested inside `{keyword}`"),
             )
             .span_suggestion(
                 item.unwrap().span,
-                &format!("consider creating a new `{}` definition instead of nesting", kw_str),
+                &format!("consider creating a new `{kw_str}` definition instead of nesting"),
                 String::new(),
                 Applicability::MaybeIncorrect,
             )
@@ -2045,11 +2044,11 @@ impl<'a> Parser<'a> {
 
                         err.span_suggestion(
                             self.token.uninterpolated_span(),
-                            &format!("`{}` already used earlier, remove this one", original_kw),
+                            &format!("`{original_kw}` already used earlier, remove this one"),
                             "".to_string(),
                             Applicability::MachineApplicable,
                         )
-                        .span_note(original_sp, &format!("`{}` first seen here", original_kw));
+                        .span_note(original_sp, &format!("`{original_kw}` first seen here"));
                     }
                     // The keyword has not been seen yet, suggest correct placement in the function front matter
                     else if let Some(WrongKw::Misplaced(correct_pos_sp)) = wrong_kw {
@@ -2060,8 +2059,8 @@ impl<'a> Parser<'a> {
 
                             err.span_suggestion(
                                     correct_pos_sp.to(misplaced_qual_sp),
-                                    &format!("`{}` must come before `{}`", misplaced_qual, current_qual),
-                                    format!("{} {}", misplaced_qual, current_qual),
+                                    &format!("`{misplaced_qual}` must come before `{current_qual}`"),
+                                    format!("{misplaced_qual} {current_qual}"),
                                     Applicability::MachineApplicable,
                                 ).note("keyword order for functions declaration is `default`, `pub`, `const`, `async`, `unsafe`, `extern`");
                         }
@@ -2084,8 +2083,8 @@ impl<'a> Parser<'a> {
                             if matches!(orig_vis.kind, VisibilityKind::Inherited) {
                                 err.span_suggestion(
                                     sp_start.to(self.prev_token.span),
-                                    &format!("visibility `{}` must come before `{}`", vs, snippet),
-                                    format!("{} {}", vs, snippet),
+                                    &format!("visibility `{vs}` must come before `{snippet}`"),
+                                    format!("{vs} {snippet}"),
                                     Applicability::MachineApplicable,
                                 );
                             }