couple of clippy::perf fixes

compiler/rustc_expand/src/base.rs

@@ -1436,7 +1436,7 @@ fn pretty_printing_compatibility_hack(item: &Item, sess: &ParseSess) -> bool {
                             let crate_matches = if c.starts_with("allsorts-rental") {
                                 true
                             } else {
-                                let mut version = c.trim_start_matches("rental-").split(".");
+                                let mut version = c.trim_start_matches("rental-").split('.');
                                 version.next() == Some("0")
                                     && version.next() == Some("5")
                                     && version

compiler/rustc_lint/src/unused.rs

@@ -584,15 +584,15 @@ trait UnusedDelimLint {
                 let sm = cx.sess().source_map();
                 let lo_replace =
                     if keep_space.0 &&
-                        let Ok(snip) = sm.span_to_prev_source(lo) && !snip.ends_with(" ") {
+                        let Ok(snip) = sm.span_to_prev_source(lo) && !snip.ends_with(' ') {
                         " ".to_string()
                         } else {
                             "".to_string()
                         };
 
                 let hi_replace =
                     if keep_space.1 &&
-                        let Ok(snip) = sm.span_to_next_source(hi) && !snip.starts_with(" ") {
+                        let Ok(snip) = sm.span_to_next_source(hi) && !snip.starts_with(' ') {
                         " ".to_string()
                         } else {
                             "".to_string()

compiler/rustc_macros/src/diagnostics/utils.rs

@@ -830,5 +830,5 @@ pub(super) fn should_generate_set_arg(field: &Field) -> bool {
 }
 
 pub(super) fn is_doc_comment(attr: &Attribute) -> bool {
-    attr.path.segments.last().unwrap().ident.to_string() == "doc"
+    attr.path.segments.last().unwrap().ident == "doc"
 }

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -2194,11 +2194,9 @@ impl<'tcx> FmtPrinter<'_, 'tcx> {
 
         define_scoped_cx!(self);
 
-        let possible_names =
-            ('a'..='z').rev().map(|s| Symbol::intern(&format!("'{s}"))).collect::<Vec<_>>();
+        let possible_names = ('a'..='z').rev().map(|s| Symbol::intern(&format!("'{s}")));
 
         let mut available_names = possible_names
-            .into_iter()
             .filter(|name| !self.used_region_names.contains(&name))
             .collect::<Vec<_>>();
         debug!(?available_names);

compiler/rustc_mir_dataflow/src/value_analysis.rs

@@ -899,7 +899,7 @@ fn debug_with_context_rec<V: Debug + Eq>(
         let info_elem = map.places[child].proj_elem.unwrap();
         let child_place_str = match info_elem {
             TrackElem::Field(field) => {
-                if place_str.starts_with("*") {
+                if place_str.starts_with('*') {
                     format!("({}).{}", place_str, field.index())
                 } else {
                     format!("{}.{}", place_str, field.index())

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -1657,14 +1657,14 @@ impl<'a> Parser<'a> {
                 let left = begin_par_sp;
                 let right = self.prev_token.span;
                 let left_snippet = if let Ok(snip) = sm.span_to_prev_source(left) &&
-                        !snip.ends_with(" ") {
+                        !snip.ends_with(' ') {
                                 " ".to_string()
                             } else {
                                 "".to_string()
                             };
 
                 let right_snippet = if let Ok(snip) = sm.span_to_next_source(right) &&
-                        !snip.starts_with(" ") {
+                        !snip.starts_with(' ') {
                                 " ".to_string()
                             } else {
                                 "".to_string()

compiler/rustc_passes/src/check_attr.rs

@@ -353,7 +353,7 @@ impl CheckAttrVisitor<'_> {
                 attr.span,
                 OnlyHasEffectOn {
                     attr_name: attr.name_or_empty(),
-                    target_name: allowed_target.name().replace(" ", "_"),
+                    target_name: allowed_target.name().replace(' ', "_"),
                 },
             );
         }

compiler/rustc_passes/src/dead.rs

@@ -772,7 +772,7 @@ impl<'tcx> DeadVisitor<'tcx> {
         self.tcx.emit_spanned_lint(
             lint,
             tcx.hir().local_def_id_to_hir_id(first_id),
-            MultiSpan::from_spans(spans.clone()),
+            MultiSpan::from_spans(spans),
             diag,
         );
     }

src/librustdoc/config.rs

@@ -418,7 +418,7 @@ impl Options {
             ) {
                 Ok(p) => p,
                 Err(e) => {
-                    diag.struct_err(&e.to_string()).emit();
+                    diag.struct_err(e).emit();
                     return Err(1);
                 }
             };
@@ -561,7 +561,7 @@ impl Options {
             ) {
                 Ok(p) => p,
                 Err(e) => {
-                    diag.struct_err(&e.to_string()).emit();
+                    diag.struct_err(e).emit();
                     return Err(1);
                 }
             };

src/librustdoc/html/static_files.rs

@@ -58,7 +58,7 @@ pub(crate) fn suffix_path(filename: &str, suffix: &str) -> PathBuf {
 }
 
 pub(crate) fn static_filename(filename: &str, contents: &[u8]) -> PathBuf {
-    let filename = filename.rsplit("/").next().unwrap();
+    let filename = filename.rsplit('/').next().unwrap();
     suffix_path(filename, &static_suffix(contents))
 }
 

src/tools/miropt-test-tools/src/lib.rs

@@ -11,7 +11,7 @@ pub fn files_for_miropt_test(testfile: &std::path::Path, bit_width: u32) -> Vec<
     let test_file_contents = fs::read_to_string(&testfile).unwrap();
 
     let test_dir = testfile.parent().unwrap();
-    let test_crate = testfile.file_stem().unwrap().to_str().unwrap().replace("-", "_");
+    let test_crate = testfile.file_stem().unwrap().to_str().unwrap().replace('-', "_");
 
     let bit_width = if test_file_contents.lines().any(|l| l == "// EMIT_MIR_FOR_EACH_BIT_WIDTH") {
         format!(".{}bit", bit_width)