refactor(core): move em and en dash rules to their own linter

harper-core/src/linting/dashes.rs

@@ -0,0 +1,89 @@
+use crate::{
+    patterns::{EitherPattern, Pattern, SequencePattern},
+    Token, TokenStringExt,
+};
+
+use super::{Lint, LintKind, PatternLinter, Suggestion};
+
+pub struct Dashes {
+    pattern: Box<dyn Pattern>,
+}
+
+impl Default for Dashes {
+    fn default() -> Self {
+        let en_dash = SequencePattern::default().then_hyphen().then_hyphen();
+        let em_dash = SequencePattern::default()
+            .then_hyphen()
+            .then_hyphen()
+            .then_hyphen();
+
+        let pattern = EitherPattern::new(vec![Box::new(em_dash), Box::new(en_dash)]);
+
+        Self {
+            pattern: Box::new(pattern),
+        }
+    }
+}
+
+impl PatternLinter for Dashes {
+    fn pattern(&self) -> &dyn Pattern {
+        self.pattern.as_ref()
+    }
+
+    fn match_to_lint(&self, matched_tokens: &[Token], _source: &[char]) -> Lint {
+        let span = matched_tokens.span().unwrap();
+        let lint_kind = LintKind::Formatting;
+
+        match matched_tokens.len() {
+            2 => Lint {
+                span,
+                lint_kind,
+                suggestions: vec![Suggestion::ReplaceWith(vec!['–'])],
+                message: "A sequence of hyphens is not an en dash.".to_owned(),
+                priority: 63,
+            },
+            3 => Lint {
+                span,
+                lint_kind,
+                suggestions: vec![Suggestion::ReplaceWith(vec!['—'])],
+                message: "A sequence of hyphens is not an em dash.".to_owned(),
+                priority: 63,
+            },
+            _ => panic!("Received unexpected number of tokens."),
+        }
+    }
+
+    fn description(&self) -> &'static str {
+        "Rather than outright using an em dash or en dash, authors often use a sequence of hyphens, expecting them to be condensed.\nThis rule does so."
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::linting::tests::{assert_suggestion_count, assert_suggestion_result};
+
+    use super::Dashes;
+
+    #[test]
+    fn catches_en_dash() {
+        assert_suggestion_result(
+            "pre--Industrial Revolution",
+            Dashes::default(),
+            "pre–Industrial Revolution",
+        );
+    }
+
+    #[test]
+    fn catches_em_dash() {
+        assert_suggestion_result(
+            "'There is no box' --- Scott",
+            Dashes::default(),
+            "'There is no box' — Scott",
+        );
+    }
+
+    #[test]
+    fn no_overlaps() {
+        assert_suggestion_count("'There is no box' --- Scott", Dashes::default(), 1);
+    }
+}

harper-core/src/linting/matcher.rs

@@ -190,19 +190,6 @@ impl Matcher {
             "take", "a", "decision" => "make a decision"
         };
 
-        // TODO: Improve the description for this lint specifically.
-        // We need to be more explicit that we are replacing with an Em dash
-        triggers.push(Rule {
-            pattern: vec![pt!(Hyphen), pt!(Hyphen), pt!(Hyphen)],
-            replace_with: vecword!("—"),
-        });
-
-        // Same goes for this En dash
-        triggers.push(Rule {
-            pattern: vec![pt!(Hyphen), pt!(Hyphen)],
-            replace_with: vecword!("–"),
-        });
-
         triggers.push(Rule {
             pattern: vec![pt!("L"), pt!(Period), pt!("L"), pt!(Period), pt!("M")],
             replace_with: vecword!("large language model"),

harper-core/src/linting/mod.rs

@@ -4,6 +4,7 @@ mod boring_words;
 mod capitalize_personal_pronouns;
 mod compound_words;
 mod correct_number_suffix;
+mod dashes;
 mod dot_initialisms;
 mod ellipsis_length;
 mod linking_verbs;