some minor code simplifications

compiler/rustc_hir_typeck/src/callee.rs

@@ -755,7 +755,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = callee_expr.kind
             && let Res::Local(_) = path.res
-            && let [segment] = &path.segments[..]
+            && let [segment] = &path.segments
         {
             for id in self.tcx.hir().items() {
                 if let Some(node) = self.tcx.hir().get_if_local(id.owner_id.into())

compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs

@@ -401,9 +401,8 @@ pub(super) fn extract_branch_mappings(
             }
             let (span, _) = unexpand_into_body_span_with_visible_macro(raw_span, body_span)?;
 
-            let bcb_from_marker = |marker: BlockMarkerId| {
-                Some(basic_coverage_blocks.bcb_from_bb(block_markers[marker]?)?)
-            };
+            let bcb_from_marker =
+                |marker: BlockMarkerId| basic_coverage_blocks.bcb_from_bb(block_markers[marker]?);
 
             let true_bcb = bcb_from_marker(true_marker)?;
             let false_bcb = bcb_from_marker(false_marker)?;

compiler/rustc_session/src/config.rs

@@ -144,18 +144,12 @@ pub enum InstrumentCoverage {
 }
 
 /// Individual flag values controlled by `-Z coverage-options`.
-#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Default)]
 pub struct CoverageOptions {
     /// Add branch coverage instrumentation.
     pub branch: bool,
 }
 
-impl Default for CoverageOptions {
-    fn default() -> Self {
-        Self { branch: false }
-    }
-}
-
 /// Settings for `-Z instrument-xray` flag.
 #[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Hash)]
 pub struct InstrumentXRay {

src/librustdoc/clean/mod.rs

@@ -1572,7 +1572,7 @@ fn first_non_private<'tcx>(
     path: &hir::Path<'tcx>,
 ) -> Option<Path> {
     let target_def_id = path.res.opt_def_id()?;
-    let (parent_def_id, ident) = match &path.segments[..] {
+    let (parent_def_id, ident) = match &path.segments {
         [] => return None,
         // Relative paths are available in the same scope as the owner.
         [leaf] => (cx.tcx.local_parent(hir_id.owner.def_id), leaf.ident),

src/librustdoc/clean/utils.rs

@@ -598,7 +598,7 @@ pub(crate) fn has_doc_flag(tcx: TyCtxt<'_>, did: DefId, flag: Symbol) -> bool {
 /// Set by `bootstrap::Builder::doc_rust_lang_org_channel` in order to keep tests passing on beta/stable.
 pub(crate) const DOC_RUST_LANG_ORG_CHANNEL: &str = env!("DOC_RUST_LANG_ORG_CHANNEL");
 pub(crate) static DOC_CHANNEL: Lazy<&'static str> =
-    Lazy::new(|| DOC_RUST_LANG_ORG_CHANNEL.rsplit('/').filter(|c| !c.is_empty()).next().unwrap());
+    Lazy::new(|| DOC_RUST_LANG_ORG_CHANNEL.rsplit('/').find(|c| !c.is_empty()).unwrap());
 
 /// Render a sequence of macro arms in a format suitable for displaying to the user
 /// as part of an item declaration.

src/librustdoc/html/render/mod.rs

@@ -150,13 +150,13 @@ impl RenderType {
             string.push('{');
             write_optional_id(self.id, string);
             string.push('{');
-            for generic in &self.generics.as_ref().map(Vec::as_slice).unwrap_or_default()[..] {
+            for generic in &self.generics.as_deref().unwrap_or_default()[..] {
                 generic.write_to_string(string);
             }
             string.push('}');
             if self.bindings.is_some() {
                 string.push('{');
-                for binding in &self.bindings.as_ref().map(Vec::as_slice).unwrap_or_default()[..] {
+                for binding in &self.bindings.as_deref().unwrap_or_default()[..] {
                     string.push('{');
                     binding.0.write_to_string(string);
                     string.push('{');