Rollup merge of #69619 - matthiaskrgr:misc, r=eddyb

more cleanups

* use starts_with() instead of chars().next() == Some(x)
* use subsec_micros() instead of subsec_nanos() / 1000
* use for (idx, item) in iter.enumerate() instead of manually counting loop iterations with variables
* use values() or keys() respectively when iterating only over keys or values of maps.

Author: JohnTitor

src/librustc/traits/structural_impls.rs

@@ -234,7 +234,7 @@ impl BoundNamesCollector {
             start = false;
             write!(fmt, "{}", r)?;
         }
-        for (_, t) in &self.types {
+        for t in self.types.values() {
             if !start {
                 write!(fmt, ", ")?;
             }

src/librustc/ty/layout.rs

@@ -1382,10 +1382,8 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
 
         // Write down the order of our locals that will be promoted to the prefix.
         {
-            let mut idx = 0u32;
-            for local in ineligible_locals.iter() {
-                assignments[local] = Ineligible(Some(idx));
-                idx += 1;
+            for (idx, local) in ineligible_locals.iter().enumerate() {
+                assignments[local] = Ineligible(Some(idx as u32));
             }
         }
         debug!("generator saved local assignments: {:?}", assignments);

src/librustc_builtin_macros/format.rs

@@ -188,7 +188,7 @@ fn parse_args<'a>(
                 let mut err = ecx
                     .struct_span_err(e.span, "positional arguments cannot follow named arguments");
                 err.span_label(e.span, "positional arguments must be before named arguments");
-                for (_, pos) in &names {
+                for pos in names.values() {
                     err.span_label(args[*pos].span, "named argument");
                 }
                 err.emit();

src/librustc_errors/emitter.rs

@@ -1574,9 +1574,9 @@ impl EmitterWriter {
 
             let line_start = sm.lookup_char_pos(parts[0].span.lo()).line;
             draw_col_separator_no_space(&mut buffer, 1, max_line_num_len + 1);
-            let mut line_pos = 0;
             let mut lines = complete.lines();
-            for line in lines.by_ref().take(MAX_SUGGESTION_HIGHLIGHT_LINES) {
+            for (line_pos, line) in lines.by_ref().take(MAX_SUGGESTION_HIGHLIGHT_LINES).enumerate()
+            {
                 // Print the span column to avoid confusion
                 buffer.puts(
                     row_num,
@@ -1587,7 +1587,6 @@ impl EmitterWriter {
                 // print the suggestion
                 draw_col_separator(&mut buffer, row_num, max_line_num_len + 1);
                 buffer.append(row_num, line, Style::NoStyle);
-                line_pos += 1;
                 row_num += 1;
             }
 

src/librustc_hir/hir.rs

@@ -679,15 +679,15 @@ impl Crate<'_> {
     where
         V: itemlikevisit::ItemLikeVisitor<'hir>,
     {
-        for (_, item) in &self.items {
+        for item in self.items.values() {
             visitor.visit_item(item);
         }
 
-        for (_, trait_item) in &self.trait_items {
+        for trait_item in self.trait_items.values() {
             visitor.visit_trait_item(trait_item);
         }
 
-        for (_, impl_item) in &self.impl_items {
+        for impl_item in self.impl_items.values() {
             visitor.visit_impl_item(impl_item);
         }
     }

src/librustc_infer/infer/lexical_region_resolve/mod.rs

@@ -751,7 +751,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
         let dummy_source = graph.add_node(());
         let dummy_sink = graph.add_node(());
 
-        for (constraint, _) in &self.data.constraints {
+        for constraint in self.data.constraints.keys() {
             match *constraint {
                 Constraint::VarSubVar(a_id, b_id) => {
                     graph.add_edge(

src/librustc_infer/infer/region_constraints/leak_check.rs

@@ -34,7 +34,7 @@ impl<'tcx> RegionConstraintCollector<'tcx> {
         assert!(self.in_snapshot());
 
         // Go through each placeholder that we created.
-        for (_, &placeholder_region) in placeholder_map {
+        for &placeholder_region in placeholder_map.values() {
             // Find the universe this placeholder inhabits.
             let placeholder = match placeholder_region {
                 ty::RePlaceholder(p) => p,

src/librustc_resolve/late/lifetimes.rs

@@ -347,7 +347,7 @@ fn krate(tcx: TyCtxt<'_>) -> NamedRegionMap {
             lifetime_uses: &mut Default::default(),
             missing_named_lifetime_spots: vec![],
         };
-        for (_, item) in &krate.items {
+        for item in krate.items.values() {
             visitor.visit_item(item);
         }
     }

src/librustc_typeck/astconv.rs

@@ -1652,7 +1652,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         }
 
         for (projection_bound, _) in &bounds.projection_bounds {
-            for (_, def_ids) in &mut associated_types {
+            for def_ids in associated_types.values_mut() {
                 def_ids.remove(&projection_bound.projection_def_id());
             }
         }

src/librustc_typeck/check/demand.rs

@@ -526,7 +526,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // we may want to suggest removing a `&`.
                 if !sm.span_to_filename(expr.span).is_real() {
                     if let Ok(code) = sm.span_to_snippet(sp) {
-                        if code.chars().next() == Some('&') {
+                        if code.starts_with('&') {
                             return Some((
                                 sp,
                                 "consider removing the borrow",