perf(linter): allocate strings with some initial capacity

Author: camchenry

crates/oxc_linter/src/rules/eslint/class_methods_use_this.rs

@@ -1,4 +1,4 @@
-use std::{borrow::Cow, ops::Deref};
+use std::ops::Deref;
 
 use itertools::Itertools;
 use oxc_ast::{
@@ -13,10 +13,9 @@ use oxc_span::{CompactStr, GetSpan, Span};
 
 use crate::{LintContext, rule::Rule};
 
-fn class_methods_use_this_diagnostic(span: Span, name: Option<Cow<'_, str>>) -> OxcDiagnostic {
-    let method_name_str = name.map_or(String::new(), |name| format!(" `{name}`"));
-    OxcDiagnostic::warn(format!("Expected method{method_name_str} to have this."))
-        .with_help(format!("Consider converting method{method_name_str} to a static method."))
+fn class_methods_use_this_diagnostic(span: Span, name: &str) -> OxcDiagnostic {
+    OxcDiagnostic::warn(format!("Expected method `{name}` to have this."))
+        .with_help(format!("Consider converting method `{name}` to a static method."))
         .with_label(span)
 }
 
@@ -219,8 +218,10 @@ impl Rule for ClassMethodsUseThis {
         }
         let mut finder = ThisFinder::new();
         finder.visit_function_body(function_body);
-        if !finder.has_this {
-            ctx.diagnostic(class_methods_use_this_diagnostic(name.span(), name.name()));
+        if !finder.has_this
+            && let Some(name_str) = name.name()
+        {
+            ctx.diagnostic(class_methods_use_this_diagnostic(name.span(), &name_str));
         }
     }
 }

crates/oxc_linter/src/rules/eslint/no_loss_of_precision.rs

@@ -370,7 +370,7 @@ pub fn to_precision(mut num: f64, precision: usize) -> String {
     let precision_i32 = precision as i32;
 
     // Handle sign
-    let mut prefix = String::new();
+    let mut prefix = String::with_capacity(8);
     if num < 0.0 {
         prefix.push('-');
         num = -num;

crates/oxc_linter/src/rules/eslint/sort_imports.rs

@@ -322,6 +322,7 @@ impl SortImports {
                     // add a empty string for zip with specifiers
                     paddings.push("");
 
+                    let specifiers_len = specifiers.len();
                     let specifiers = specifiers.iter().sorted_by(|a, b| {
                         let a = a.local.name.as_str();
                         let b = b.local.name.as_str();
@@ -334,7 +335,7 @@ impl SortImports {
                     });
 
                     let sorted_text = specifiers.zip(paddings).fold(
-                        String::new(),
+                        String::with_capacity(specifiers_len * 8),
                         |mut acc, (specifier, padding)| {
                             let _ = acc.write_str(ctx.source_range(specifier.span));
                             let _ = acc.write_str(padding);

crates/oxc_linter/src/rules/eslint/sort_keys.rs

@@ -291,7 +291,7 @@ impl Rule for SortKeys {
                     // trailing comma) to the end, we must remove their trailing comma so
                     // the resulting object doesn't end up with an extra comma before `}`.
                     // Also normalize separators between properties to `, ` for clarity.
-                    let mut sorted_text = String::new();
+                    let mut sorted_text = String::with_capacity(8 * indices.len()); // initialize with avg 8 chars per prop
                     let trim_end_commas = |s: &str| -> String {
                         let s = s.trim_end();
                         let mut trimmed = s.to_string();

crates/oxc_linter/src/rules/import/consistent_type_specifier_style.rs

@@ -115,7 +115,7 @@ impl Rule for ConsistentTypeSpecifierStyle {
                 ctx.diagnostic_with_fix(
                     consistent_type_specifier_style_diagnostic(item.span(), &self.mode),
                     |fixer| {
-                        let mut import_source = String::new();
+                        let mut import_source = String::with_capacity(128);
 
                         if !value_specifiers.is_empty() {
                             let value_import_declaration =

crates/oxc_linter/src/rules/react/jsx_fragments.rs

@@ -130,7 +130,12 @@ impl Rule for JsxFragments {
                             closing_element.span().end,
                             jsx_elem.span().end,
                         ));
-                        let mut replacement = String::new();
+                        let mut replacement = String::with_capacity(
+                            before_opening_tag.len()
+                                + between_opening_tag_and_closing_tag.len()
+                                + after_closing_tag.len()
+                                + "<></>".len(),
+                        );
                         replacement.push_str(before_opening_tag);
                         replacement.push_str("<>");
                         replacement.push_str(between_opening_tag_and_closing_tag);
@@ -156,7 +161,12 @@ impl Rule for JsxFragments {
                             jsx_frag.closing_fragment.span().end,
                             jsx_frag.span().end,
                         ));
-                        let mut replacement = String::new();
+                        let mut replacement = String::with_capacity(
+                            before_opening_tag.len()
+                                + between_opening_tag_and_closing_tag.len()
+                                + after_closing_tag.len()
+                                + "<React.Fragment></React.Fragment>".len(),
+                        );
                         replacement.push_str(before_opening_tag);
                         replacement.push_str("<React.Fragment>");
                         replacement.push_str(between_opening_tag_and_closing_tag);

crates/oxc_linter/src/rules/typescript/consistent_type_definitions.rs

@@ -174,18 +174,18 @@ impl Rule for ConsistentTypeDefinitions {
                     let body_span = &decl.body.span;
                     let body = &ctx.source_text()[body_span.start as usize..body_span.end as usize];
 
-                    let mut extends = String::new();
-                    for exp in &decl.extends {
-                        write!(extends, " & {}", exp.span.source_text(ctx.source_text())).unwrap();
-                    }
-
                     ctx.diagnostic_with_fix(
                         consistent_type_definitions_diagnostic(
                             "type",
                             "interface",
                             Span::sized(decl.span.start, 9),
                         ),
                         |fixer| {
+                            let mut extends = String::with_capacity(8 * decl.extends.len());
+                            for exp in &decl.extends {
+                                write!(extends, " & {}", exp.span.source_text(ctx.source_text()))
+                                    .unwrap();
+                            }
                             fixer.replace(
                                 exp.span,
                                 format!("type {name} = {body}{extends}\nexport default {name}"),
@@ -220,18 +220,18 @@ impl Rule for ConsistentTypeDefinitions {
                 let body_span = &decl.body.span;
                 let body = &ctx.source_text()[body_span.start as usize..body_span.end as usize];
 
-                let mut extends = String::new();
-                for exp in &decl.extends {
-                    write!(extends, " & {}", exp.span.source_text(ctx.source_text())).unwrap();
-                }
-
                 ctx.diagnostic_with_fix(
                     consistent_type_definitions_diagnostic(
                         "type",
                         "interface",
                         Span::sized(start, 9),
                     ),
                     |fixer| {
+                        let mut extends = String::with_capacity(8 * decl.extends.len());
+                        for exp in &decl.extends {
+                            write!(extends, " & {}", exp.span.source_text(ctx.source_text()))
+                                .unwrap();
+                        }
                         fixer.replace(
                             Span::new(start, decl.span.end),
                             format!("type {name} = {body}{extends}"),

crates/oxc_linter/src/rules/unicorn/prefer_modern_math_apis.rs

@@ -262,7 +262,7 @@ fn is_pow_2_expression(expression: &Expression, ctx: &LintContext<'_>) -> bool {
 /// removes any newlines from the string
 /// removes any duplicate spaces
 fn clean_string(input: &str) -> String {
-    let mut result = String::new();
+    let mut result = String::with_capacity(input.len());
     let mut prev_char = ' ';
 
     for c in input.chars() {