perf(linter/no-unused-vars): use default IgnorePattern when /^_/ is provided as a pattern (#6697)

Use `IgnorePattern::Default` even when `/^_/` is explicitly provided as a regex. This gives better diagnostic messages and lets us use `starts_with('_')` in more cases.

crates/oxc_linter/src/rules/eslint/no_unused_vars/options.rs

@@ -234,10 +234,10 @@ impl<R> IgnorePattern<R> {
         matches!(self, Self::None)
     }
 
-    /// Returns `true` if the pattern is [`IgnorePattern::Some`].
+    /// Returns `true` if the pattern is [`IgnorePattern::Some`] or [`IgnorePattern::Default`].
     #[inline]
     pub fn is_some(&self) -> bool {
-        matches!(self, Self::Some(_))
+        matches!(self, Self::Some(_) | Self::Default)
     }
 
     /// Returns the inner value if it is [`IgnorePattern::Some`], otherwise
@@ -288,12 +288,16 @@ where
     }
 }
 
-impl From<Option<Regex>> for IgnorePattern<Regex> {
-    #[inline]
-    fn from(value: Option<Regex>) -> Self {
+impl TryFrom<Option<&str>> for IgnorePattern<Regex> {
+    type Error = regex::Error;
+
+    fn try_from(value: Option<&str>) -> Result<Self, Self::Error> {
         match value {
-            None => Self::None,
-            Some(regex) => Self::Some(regex),
+            None => Ok(Self::None),
+            Some("^_") => Ok(Self::Default),
+            Some(pattern) => {
+                regex::RegexBuilder::new(pattern).unicode(true).build().map(Self::Some)
+            }
         }
     }
 }
@@ -488,15 +492,13 @@ impl TryFrom<&Value> for CaughtErrors {
 
 /// Parses a potential pattern into a [`Regex`] that accepts unicode characters.
 fn parse_unicode_rule(value: Option<&Value>, name: &str) -> IgnorePattern<Regex> {
-    IgnorePattern::from(
-        value
-            .and_then(Value::as_str)
-            .map(|pattern| regex::RegexBuilder::new(pattern).unicode(true).build())
-            .transpose()
-            .map_err(|err| panic!("Invalid '{name}' option for no-unused-vars: {err}"))
-            .unwrap(),
-    )
+    IgnorePattern::try_from(value.and_then(Value::as_str))
+        .map_err(|err| {
+            OxcDiagnostic::error(format!("Invalid '{name}' option for no-unused-vars: {err}"))
+        })
+        .unwrap()
 }
+
 impl TryFrom<Value> for NoUnusedVarsOptions {
     type Error = OxcDiagnostic;
     fn try_from(value: Value) -> Result<Self, Self::Error> {
@@ -635,12 +637,12 @@ mod tests {
         .unwrap();
 
         assert_eq!(rule.vars, VarsOption::Local);
-        assert_eq!(rule.vars_ignore_pattern.unwrap().as_str(), "^_");
+        assert!(rule.vars_ignore_pattern.is_default());
         assert_eq!(rule.args, ArgsOption::All);
-        assert_eq!(rule.args_ignore_pattern.unwrap().as_str(), "^_");
+        assert!(rule.args_ignore_pattern.is_default());
         assert_eq!(rule.caught_errors, CaughtErrors::all());
-        assert_eq!(rule.caught_errors_ignore_pattern.unwrap().as_str(), "^_");
-        assert_eq!(rule.destructured_array_ignore_pattern.unwrap().as_str(), "^_");
+        assert!(rule.caught_errors_ignore_pattern.is_default());
+        assert!(rule.destructured_array_ignore_pattern.is_default());
         assert!(rule.ignore_rest_siblings);
         assert!(!rule.ignore_class_with_static_init_block);
         assert!(rule.report_used_ignore_pattern);
@@ -657,7 +659,7 @@ mod tests {
         .unwrap();
         // option object provided, no default varsIgnorePattern
         assert!(rule.vars_ignore_pattern.is_none());
-        assert!(rule.args_ignore_pattern.unwrap().as_str() == "^_");
+        assert!(rule.args_ignore_pattern.is_default());
 
         let rule: NoUnusedVarsOptions = json!([
             {
@@ -668,7 +670,7 @@ mod tests {
         .unwrap();
 
         // option object provided, no default argsIgnorePattern
-        assert!(rule.vars_ignore_pattern.unwrap().as_str() == "^_");
+        assert!(matches!(rule.vars_ignore_pattern, IgnorePattern::Default));
         assert!(rule.args_ignore_pattern.is_none());
     }
 
@@ -708,9 +710,12 @@ mod tests {
 
     #[test]
     fn test_parse_unicode_regex() {
-        let pat = json!("^_");
+        let pat = json!("^[iI]gnore");
         parse_unicode_rule(Some(&pat), "varsIgnorePattern")
             .expect("json strings should get parsed into a regex");
+
+        let pat = json!("^_");
+        assert!(parse_unicode_rule(Some(&pat), "varsIgnorePattern").is_default());
     }
 
     #[test]

crates/oxc_linter/src/rules/eslint/no_unused_vars/tests/oxc.rs

@@ -6,12 +6,18 @@ use super::NoUnusedVars;
 use crate::{tester::Tester, FixKind, RuleMeta as _};
 
 // uncomment to only run a single test. useful for step-through debugging.
-// #[test]
-// fn test_debug() {
-//     let pass: Vec<&str> = vec![];
-//     let fail = vec![];
-//     Tester::new(NoUnusedVars::NAME, pass, fail).intentionally_allow_no_fix_tests().test();
-// }
+#[test]
+fn test_debug() {
+    let pass = vec![
+        (
+            "const [ a, _b, c ] = items;
+			console.log(a+c);",
+            Some(serde_json::json!([{ "destructuredArrayIgnorePattern": "^_" }])),
+        ), // { "ecmaVersion": 6 },
+    ];
+    let fail = vec![];
+    Tester::new(NoUnusedVars::NAME, pass, fail).intentionally_allow_no_fix_tests().test();
+}
 
 #[test]
 fn test_vars_simple() {

crates/oxc_linter/src/snapshots/no_unused_vars@eslint.snap

@@ -316,7 +316,7 @@ source: crates/oxc_linter/src/tester.rs
    ╰────
   help: Consider removing this declaration.
 
-  ⚠ eslint(no-unused-vars): Variable 'b' is declared but never used. Unused variables should match /^_/.
+  ⚠ eslint(no-unused-vars): Variable 'b' is declared but never used. Unused variables should start with a '_'.
    ╭─[no_unused_vars.tsx:1:13]
  1 │ var _a; var b;
    ·             ┬
@@ -324,7 +324,7 @@ source: crates/oxc_linter/src/tester.rs
    ╰────
   help: Consider removing this declaration.
 
-  ⚠ eslint(no-unused-vars): Variable 'c_' is declared but never used. Unused variables should match /^_/.
+  ⚠ eslint(no-unused-vars): Variable 'c_' is declared but never used. Unused variables should start with a '_'.
    ╭─[no_unused_vars.tsx:1:37]
  1 │ var a; function foo() { var _b; var c_; } foo();
    ·                                     ─┬
@@ -332,7 +332,7 @@ source: crates/oxc_linter/src/tester.rs
    ╰────
   help: Consider removing this declaration.
 
-  ⚠ eslint(no-unused-vars): Parameter 'a' is declared but never used. Unused parameters should match /^_/.
+  ⚠ eslint(no-unused-vars): Parameter 'a' is declared but never used. Unused parameters should start with a '_'.
    ╭─[no_unused_vars.tsx:1:14]
  1 │ function foo(a, _b) { } foo();
    ·              ┬
@@ -340,7 +340,7 @@ source: crates/oxc_linter/src/tester.rs
    ╰────
   help: Consider removing this parameter.
 
-  ⚠ eslint(no-unused-vars): Parameter 'c' is declared but never used. Unused parameters should match /^_/.
+  ⚠ eslint(no-unused-vars): Parameter 'c' is declared but never used. Unused parameters should start with a '_'.
    ╭─[no_unused_vars.tsx:1:21]
  1 │ function foo(a, _b, c) { return a; } foo();
    ·                     ┬
@@ -1376,7 +1376,7 @@ source: crates/oxc_linter/src/tester.rs
    ·       ─┬
    ·        ╰── '_a' is declared here
    ╰────
-  help: Consider renaming this variable to match the pattern /^_/.
+  help: Consider renaming this variable to 'a'.
 
   ⚠ eslint(no-unused-vars): Variable '_a' is marked as ignored but is used.
    ╭─[no_unused_vars.tsx:1:7]
@@ -1384,7 +1384,7 @@ source: crates/oxc_linter/src/tester.rs
    ·       ─┬
    ·        ╰── '_a' is declared here
    ╰────
-  help: Consider renaming this variable to match the pattern /^_/.
+  help: Consider renaming this variable to 'a'.
 
   ⚠ eslint(no-unused-vars): Variable '_a' is marked as ignored but is used.
    ╭─[no_unused_vars.tsx:1:15]

crates/oxc_linter/src/snapshots/no_unused_vars@oxc-vars-simple.snap

@@ -32,7 +32,7 @@ source: crates/oxc_linter/src/tester.rs
    ·     ─┬
    ·      ╰── '_a' is declared here
    ╰────
-  help: Consider renaming this variable to match the pattern /^_/.
+  help: Consider renaming this variable to 'a'.
 
   ⚠ eslint(no-unused-vars): Variable 'fooBar' is declared but never used. Unused variables should start with a '_'.
    ╭─[no_unused_vars.tsx:1:14]