Rollup merge of #128762 - fmease:use-more-slice-pats, r=compiler-errors

Use more slice patterns inside the compiler

Nothing super noteworthy. Just replacing the common 'fragile' pattern of "length check followed by indexing or unwrap" with slice patterns for legibility and 'robustness'.

r? ghost

4 files changed, 10 insertions, 10 deletions

diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index ccf8dcdf0b6..cf5d65708ab 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -694,12 +694,12 @@ impl<'a> Parser<'a> {
                         // `foo: `
                         ExprKind::Path(None, ast::Path { segments, .. }),
                         token::Ident(kw::For | kw::Loop | kw::While, IdentIsRaw::No),
-                    ) if segments.len() == 1 => {
+                    ) if let [segment] = segments.as_slice() => {
                         let snapshot = self.create_snapshot_for_diagnostic();
                         let label = Label {
                             ident: Ident::from_str_and_span(
-                                &format!("'{}", segments[0].ident),
-                                segments[0].ident.span,
+                                &format!("'{}", segment.ident),
+                                segment.ident.span,
                             ),
                         };
                         match self.parse_expr_labeled(label, false) {
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index baa5eb2df63..8775d792c3d 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -471,9 +471,8 @@ impl<'a> Parser<'a> {
             Err(mut err) => {
                 // Maybe the user misspelled `macro_rules` (issue #91227)
                 if self.token.is_ident()
-                    && path.segments.len() == 1
-                    && edit_distance("macro_rules", &path.segments[0].ident.to_string(), 2)
-                        .is_some()
+                    && let [segment] = path.segments.as_slice()
+                    && edit_distance("macro_rules", &segment.ident.to_string(), 2).is_some()
                 {
                     err.span_suggestion(
                         path.span,
diff --git a/compiler/rustc_parse/src/parser/path.rs b/compiler/rustc_parse/src/parser/path.rs
index 70d2c98d4f1..6f82d6b9826 100644
--- a/compiler/rustc_parse/src/parser/path.rs
+++ b/compiler/rustc_parse/src/parser/path.rs
@@ -826,7 +826,8 @@ impl<'a> Parser<'a> {
             // We can only resolve single-segment paths at the moment, because multi-segment paths
             // require type-checking: see `visit_generic_arg` in `src/librustc_resolve/late.rs`.
             ast::ExprKind::Path(None, path)
-                if path.segments.len() == 1 && path.segments[0].args.is_none() =>
+                if let [segment] = path.segments.as_slice()
+                    && segment.args.is_none() =>
             {
                 true
             }
diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
index a3b782d651d..b206f134f0e 100644
--- a/compiler/rustc_parse/src/parser/stmt.rs
+++ b/compiler/rustc_parse/src/parser/stmt.rs
@@ -676,7 +676,7 @@ impl<'a> Parser<'a> {
 
                             match &expr.kind {
                                 ExprKind::Path(None, ast::Path { segments, .. })
-                                    if segments.len() == 1 =>
+                                    if let [segment] = segments.as_slice() =>
                                 {
                                     if self.token == token::Colon
                                         && self.look_ahead(1, |token| {
@@ -693,8 +693,8 @@ impl<'a> Parser<'a> {
                                         let snapshot = self.create_snapshot_for_diagnostic();
                                         let label = Label {
                                             ident: Ident::from_str_and_span(
-                                                &format!("'{}", segments[0].ident),
-                                                segments[0].ident.span,
+                                                &format!("'{}", segment.ident),
+                                                segment.ident.span,
                                             ),
                                         };
                                         match self.parse_expr_labeled(label, false) {