fix clippy::single_char_pattern perf findings

Author: matthiaskrgr

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -2226,8 +2226,8 @@ fn add_upstream_rust_crates<'a, B: ArchiveBuilder<'a>>(
                     continue;
                 }
 
-                let canonical = f.replace("-", "_");
-                let canonical_name = name.replace("-", "_");
+                let canonical = f.replace('-', "_");
+                let canonical_name = name.replace('-', "_");
 
                 let is_rust_object =
                     canonical.starts_with(&canonical_name) && looks_like_rust_object_file(&f);

compiler/rustc_driver/src/lib.rs

@@ -872,7 +872,7 @@ Available lint options:
 
     let print_lints = |lints: Vec<&Lint>| {
         for lint in lints {
-            let name = lint.name_lower().replace("_", "-");
+            let name = lint.name_lower().replace('_', "-");
             println!(
                 "    {}  {:7.7}  {}",
                 padded(&name),
@@ -908,10 +908,10 @@ Available lint options:
 
     let print_lint_groups = |lints: Vec<(&'static str, Vec<LintId>)>| {
         for (name, to) in lints {
-            let name = name.to_lowercase().replace("_", "-");
+            let name = name.to_lowercase().replace('_', "-");
             let desc = to
                 .into_iter()
-                .map(|x| x.to_string().replace("_", "-"))
+                .map(|x| x.to_string().replace('_', "-"))
                 .collect::<Vec<String>>()
                 .join(", ");
             println!("    {}  {}", padded(&name), desc);
@@ -960,7 +960,7 @@ fn print_flag_list<T>(
         println!(
             "    {} {:>width$}=val -- {}",
             cmdline_opt,
-            name.replace("_", "-"),
+            name.replace('_', "-"),
             desc,
             width = max_len
         );
@@ -1015,7 +1015,7 @@ pub fn handle_options(args: &[String]) -> Option<getopts::Matches> {
                 .iter()
                 .map(|&(name, ..)| ('C', name))
                 .chain(DB_OPTIONS.iter().map(|&(name, ..)| ('Z', name)))
-                .find(|&(_, name)| *opt == name.replace("_", "-"))
+                .find(|&(_, name)| *opt == name.replace('_', "-"))
                 .map(|(flag, _)| format!("{}. Did you mean `-{} {}`?", e, flag, opt)),
             _ => None,
         };

compiler/rustc_graphviz/src/lib.rs

@@ -472,7 +472,7 @@ pub trait Labeller<'a> {
 /// Escape tags in such a way that it is suitable for inclusion in a
 /// Graphviz HTML label.
 pub fn escape_html(s: &str) -> String {
-    s.replace("&", "&amp;").replace("\"", "&quot;").replace("<", "&lt;").replace(">", "&gt;")
+    s.replace('&', "&amp;").replace('\"', "&quot;").replace('<', "&lt;").replace('>', "&gt;")
 }
 
 impl<'a> LabelText<'a> {

compiler/rustc_interface/src/passes.rs

@@ -584,7 +584,7 @@ fn output_conflicts_with_dir(output_paths: &[PathBuf]) -> Option<PathBuf> {
 fn escape_dep_filename(filename: &str) -> String {
     // Apparently clang and gcc *only* escape spaces:
     // https://llvm.org/klaus/clang/commit/9d50634cfc268ecc9a7250226dd5ca0e945240d4
-    filename.replace(" ", "\\ ")
+    filename.replace(' ', "\\ ")
 }
 
 // Makefile comments only need escaping newlines and `\`.

compiler/rustc_middle/src/lint.rs

@@ -295,7 +295,7 @@ pub fn struct_lint_level<'s, 'd>(
                     Level::Allow => "-A",
                     Level::ForceWarn => "--force-warn",
                 };
-                let hyphen_case_lint_name = name.replace("_", "-");
+                let hyphen_case_lint_name = name.replace('_', "-");
                 if lint_flag_val.as_str() == name {
                     sess.diag_note_once(
                         &mut err,
@@ -306,7 +306,7 @@ pub fn struct_lint_level<'s, 'd>(
                         ),
                     );
                 } else {
-                    let hyphen_case_flag_val = lint_flag_val.as_str().replace("_", "-");
+                    let hyphen_case_flag_val = lint_flag_val.as_str().replace('_', "-");
                     sess.diag_note_once(
                         &mut err,
                         DiagnosticMessageId::from(lint),

compiler/rustc_middle/src/mir/generic_graphviz.rs

@@ -126,7 +126,7 @@ impl<
             write!(
                 w,
                 r#"<tr><td align="left" balign="left">{}</td></tr>"#,
-                dot::escape_html(&section).replace("\n", "<br/>")
+                dot::escape_html(&section).replace('\n', "<br/>")
             )?;
         }
 
@@ -147,7 +147,7 @@ impl<
             let src = self.node(source);
             let trg = self.node(target);
             let escaped_edge_label = if let Some(edge_label) = edge_labels.get(index) {
-                dot::escape_html(edge_label).replace("\n", r#"<br align="left"/>"#)
+                dot::escape_html(edge_label).replace('\n', r#"<br align="left"/>"#)
             } else {
                 "".to_owned()
             };

compiler/rustc_middle/src/mir/spanview.rs

@@ -681,13 +681,13 @@ fn hir_body<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Option<&'tcx rustc_hir::B
 }
 
 fn escape_html(s: &str) -> String {
-    s.replace("&", "&amp;").replace("<", "&lt;").replace(">", "&gt;")
+    s.replace('&', "&amp;").replace('<', "&lt;").replace('>', "&gt;")
 }
 
 fn escape_attr(s: &str) -> String {
-    s.replace("&", "&amp;")
-        .replace("\"", "&quot;")
-        .replace("'", "&#39;")
-        .replace("<", "&lt;")
-        .replace(">", "&gt;")
+    s.replace('&', "&amp;")
+        .replace('\"', "&quot;")
+        .replace('\'', "&#39;")
+        .replace('<', "&lt;")
+        .replace('>', "&gt;")
 }

compiler/rustc_mir_transform/src/coverage/debug.rs

@@ -148,7 +148,7 @@ impl DebugOptions {
         let mut counter_format = ExpressionFormat::default();
 
         if let Ok(env_debug_options) = std::env::var(RUSTC_COVERAGE_DEBUG_OPTIONS) {
-            for setting_str in env_debug_options.replace(" ", "").replace("-", "_").split(',') {
+            for setting_str in env_debug_options.replace(' ', "").replace('-', "_").split(',') {
                 let (option, value) = match setting_str.split_once('=') {
                     None => (setting_str, None),
                     Some((k, v)) => (k, Some(v)),

compiler/rustc_mir_transform/src/coverage/spans.rs

@@ -155,7 +155,7 @@ impl CoverageSpan {
         format!(
             "{}\n    {}",
             source_range_no_file(tcx, &self.span),
-            self.format_coverage_statements(tcx, mir_body).replace("\n", "\n    "),
+            self.format_coverage_statements(tcx, mir_body).replace('\n', "\n    "),
         )
     }
 

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -2236,7 +2236,7 @@ impl<'a> Parser<'a> {
             err.span_suggestion(
                 seq_span,
                 "...or a vertical bar to match on multiple alternatives",
-                seq_snippet.replace(",", " |"),
+                seq_snippet.replace(',', " |"),
                 Applicability::MachineApplicable,
             );
         }