Use more slice patterns inside the compiler

3 files changed, 20 insertions, 23 deletions

diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index f844930ad26..6fcb4cfd8ad 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -445,8 +445,8 @@ impl<'a> PathSource<'a> {
                 Some(ExprKind::Call(call_expr, _)) => match &call_expr.kind {
                     // the case of `::some_crate()`
                     ExprKind::Path(_, path)
-                        if path.segments.len() == 2
-                            && path.segments[0].ident.name == kw::PathRoot =>
+                        if let [segment, _] = path.segments.as_slice()
+                            && segment.ident.name == kw::PathRoot =>
                     {
                         "external crate"
                     }
@@ -2395,15 +2395,14 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
     }
 
     fn future_proof_import(&mut self, use_tree: &UseTree) {
-        let segments = &use_tree.prefix.segments;
-        if !segments.is_empty() {
-            let ident = segments[0].ident;
+        if let [segment, rest @ ..] = use_tree.prefix.segments.as_slice() {
+            let ident = segment.ident;
             if ident.is_path_segment_keyword() || ident.span.is_rust_2015() {
                 return;
             }
 
             let nss = match use_tree.kind {
-                UseTreeKind::Simple(..) if segments.len() == 1 => &[TypeNS, ValueNS][..],
+                UseTreeKind::Simple(..) if rest.is_empty() => &[TypeNS, ValueNS][..],
                 _ => &[TypeNS],
             };
             let report_error = |this: &Self, ns| {
@@ -3999,16 +3998,15 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
 
             if this.should_report_errs() {
                 if candidates.is_empty() {
-                    if path.len() == 2 && prefix_path.len() == 1 {
+                    if path.len() == 2
+                        && let [segment] = prefix_path
+                    {
                         // Delay to check whether methond name is an associated function or not
                         // ```
                         // let foo = Foo {};
                         // foo::bar(); // possibly suggest to foo.bar();
                         //```
-                        err.stash(
-                            prefix_path[0].ident.span,
-                            rustc_errors::StashKey::CallAssocMethod,
-                        );
+                        err.stash(segment.ident.span, rustc_errors::StashKey::CallAssocMethod);
                     } else {
                         // When there is no suggested imports, we can just emit the error
                         // and suggestions immediately. Note that we bypass the usually error
diff --git a/compiler/rustc_resolve/src/late/diagnostics.rs b/compiler/rustc_resolve/src/late/diagnostics.rs
index f126563fe58..9031c96027e 100644
--- a/compiler/rustc_resolve/src/late/diagnostics.rs
+++ b/compiler/rustc_resolve/src/late/diagnostics.rs
@@ -650,14 +650,14 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
         let typo_sugg = self
             .lookup_typo_candidate(path, following_seg, source.namespace(), is_expected)
             .to_opt_suggestion();
-        if path.len() == 1
+        if let [segment] = path
             && !matches!(source, PathSource::Delegation)
             && self.self_type_is_available()
         {
             if let Some(candidate) =
                 self.lookup_assoc_candidate(ident, ns, is_expected, source.is_call())
             {
-                let self_is_available = self.self_value_is_available(path[0].ident.span);
+                let self_is_available = self.self_value_is_available(segment.ident.span);
                 // Account for `Foo { field }` when suggesting `self.field` so we result on
                 // `Foo { field: self.field }`.
                 let pre = match source {
@@ -665,7 +665,7 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                         if expr
                             .fields
                             .iter()
-                            .any(|f| f.ident == path[0].ident && f.is_shorthand) =>
+                            .any(|f| f.ident == segment.ident && f.is_shorthand) =>
                     {
                         format!("{path_str}: ")
                     }
@@ -1258,8 +1258,7 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                             )
                         })
                         .collect();
-                if targets.len() == 1 {
-                    let target = targets[0];
+                if let [target] = targets.as_slice() {
                     return Some(TypoSuggestion::single_item_from_ident(target.0.ident, target.1));
                 }
             }
@@ -2104,8 +2103,8 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
         filter_fn: &impl Fn(Res) -> bool,
     ) -> TypoCandidate {
         let mut names = Vec::new();
-        if path.len() == 1 {
-            let mut ctxt = path.last().unwrap().ident.span.ctxt();
+        if let [segment] = path {
+            let mut ctxt = segment.ident.span.ctxt();
 
             // Search in lexical scope.
             // Walk backwards up the ribs in scope and collect candidates.
diff --git a/compiler/rustc_resolve/src/macros.rs b/compiler/rustc_resolve/src/macros.rs
index 64ae0d82952..77808df973c 100644
--- a/compiler/rustc_resolve/src/macros.rs
+++ b/compiler/rustc_resolve/src/macros.rs
@@ -108,8 +108,8 @@ pub(crate) fn sub_namespace_match(
 // `format!("{}", path)`, because that tries to insert
 // line-breaks and is slow.
 fn fast_print_path(path: &ast::Path) -> Symbol {
-    if path.segments.len() == 1 {
-        path.segments[0].ident.name
+    if let [segment] = path.segments.as_slice() {
+        segment.ident.name
     } else {
         let mut path_str = String::with_capacity(64);
         for (i, segment) in path.segments.iter().enumerate() {
@@ -724,10 +724,10 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         // Possibly apply the macro helper hack
         if deleg_impl.is_none()
             && kind == Some(MacroKind::Bang)
-            && path.len() == 1
-            && path[0].ident.span.ctxt().outer_expn_data().local_inner_macros
+            && let [segment] = path.as_slice()
+            && segment.ident.span.ctxt().outer_expn_data().local_inner_macros
         {
-            let root = Ident::new(kw::DollarCrate, path[0].ident.span);
+            let root = Ident::new(kw::DollarCrate, segment.ident.span);
             path.insert(0, Segment::from_ident(root));
         }