From cd7e30b2c4e890976695494d97f93de43be78140 Mon Sep 17 00:00:00 2001
From: hippietrail <hippytrail@gmail.com>
Date: Fri, 22 Aug 2025 23:00:48 +0900
Subject: [PATCH] =?UTF-8?q?feat:=20(wip)=20in=20(a)=20good=20condition(s)?=
 =?UTF-8?q?=20=E2=86=92=20in=20good=20condition?=
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---
 .../src/linting/in_adjective_condition.rs     | 112 ++++++++++++++++++
 harper-core/src/linting/lint_group.rs         |   2 +
 harper-core/src/linting/mod.rs                |   2 +
 3 files changed, 116 insertions(+)
 create mode 100644 harper-core/src/linting/in_adjective_condition.rs

diff --git a/harper-core/src/linting/in_adjective_condition.rs b/harper-core/src/linting/in_adjective_condition.rs
new file mode 100644
index 000000000..40f77e250
--- /dev/null
+++ b/harper-core/src/linting/in_adjective_condition.rs
@@ -0,0 +1,112 @@
+//! Linter for correcting common errors with the phrase "in [adjective] condition".
+
+use crate::{
+    Token,
+    expr::{Expr, SequenceExpr},
+    linting::{ExprLinter, Lint, LintKind, Suggestion},
+    token_string_ext::TokenStringExt,
+};
+
+/// Linter that corrects common errors with phrases like "in good condition".
+///
+/// Handles two cases:
+/// 1. "in [a/an] [adjective] condition" -> "in [adjective] condition"
+/// 2. "in [adjective] conditions" -> "in [adjective] condition"
+pub struct InAdjectiveCondition {
+    expr: Box<dyn Expr>,
+}
+
+impl Default for InAdjectiveCondition {
+    fn default() -> Self {
+        let singular = SequenceExpr::default()
+            .then_indefinite_article()
+            .t_ws()
+            .then_adjective()
+            .t_ws()
+            .t_aco("condition");
+
+        let plural = SequenceExpr::default()
+            .then_adjective()
+            .t_ws()
+            .t_aco("conditions");
+
+        Self {
+            expr: Box::new(
+                SequenceExpr::default()
+                    .t_aco("in")
+                    .t_ws()
+                    .then_any_of(vec![Box::new(singular), Box::new(plural)]),
+            ),
+        }
+    }
+}
+
+impl ExprLinter for InAdjectiveCondition {
+    fn expr(&self) -> &dyn Expr {
+        self.expr.as_ref()
+    }
+
+    fn match_to_lint(&self, toks: &[Token], src: &[char]) -> Option<Lint> {
+        let (span, sugg, msg) = match toks.len() {
+            5 => (
+                toks.last()?.span,
+                Suggestion::replace_with_match_case(
+                    "condition".chars().collect(),
+                    toks.last()?.span.get_content(src),
+                ),
+                "`Condition` should be singular.",
+            ),
+            7 => (
+                toks[1..3].span()?,
+                Suggestion::Remove,
+                "An indefinite article should not be used here.",
+            ),
+            _ => return None,
+        };
+
+        Some(Lint {
+            span,
+            lint_kind: LintKind::Grammar,
+            suggestions: vec![sugg],
+            message: msg.to_string(),
+            ..Default::default()
+        })
+    }
+
+    fn description(&self) -> &str {
+        "Corrects incorrect variants of `in good condition` with an indefinite article or plural."
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::InAdjectiveCondition;
+    use crate::linting::tests::assert_suggestion_result;
+
+    #[test]
+    fn fix_in_good_conditions() {
+        assert_suggestion_result(
+            "in good conditions",
+            InAdjectiveCondition::default(),
+            "in good condition",
+        );
+    }
+
+    #[test]
+    fn fix_in_a_bad_condition() {
+        assert_suggestion_result(
+            "in a bad condition",
+            InAdjectiveCondition::default(),
+            "in bad condition",
+        );
+    }
+
+    #[test]
+    fn fix_great_condition_all_caps() {
+        assert_suggestion_result(
+            "YEAH IT'S IN GREAT CONDITIONS REALLY!",
+            InAdjectiveCondition::default(),
+            "YEAH IT'S IN GREAT CONDITION REALLY!",
+        )
+    }
+}
diff --git a/harper-core/src/linting/lint_group.rs b/harper-core/src/linting/lint_group.rs
index 641585af5..44878e9bd 100644
--- a/harper-core/src/linting/lint_group.rs
+++ b/harper-core/src/linting/lint_group.rs
@@ -52,6 +52,7 @@ use super::hop_hope::HopHope;
 use super::how_to::HowTo;
 use super::hyphenate_number_day::HyphenateNumberDay;
 use super::i_am_agreement::IAmAgreement;
+use super::in_adjective_condition::InAdjectiveCondition;
 use super::in_on_the_cards::InOnTheCards;
 use super::inflected_verb_after_to::InflectedVerbAfterTo;
 use super::its_contraction::ItsContraction;
@@ -442,6 +443,7 @@ impl LintGroup {
         insert_struct_rule!(HowTo, true);
         insert_expr_rule!(HyphenateNumberDay, true);
         insert_expr_rule!(IAmAgreement, true);
+        insert_expr_rule!(InAdjectiveCondition, true);
         insert_struct_rule!(ItsContraction, true);
         insert_struct_rule!(ItsPossessive, true);
         insert_expr_rule!(LeftRightHand, true);
diff --git a/harper-core/src/linting/mod.rs b/harper-core/src/linting/mod.rs
index de41f8156..ea95c4f04 100644
--- a/harper-core/src/linting/mod.rs
+++ b/harper-core/src/linting/mod.rs
@@ -47,6 +47,7 @@ mod hope_youre;
 mod how_to;
 mod hyphenate_number_day;
 mod i_am_agreement;
+mod in_adjective_condition;
 mod in_on_the_cards;
 mod inflected_verb_after_to;
 mod initialism_linter;
@@ -176,6 +177,7 @@ pub use hop_hope::HopHope;
 pub use how_to::HowTo;
 pub use hyphenate_number_day::HyphenateNumberDay;
 pub use i_am_agreement::IAmAgreement;
+pub use in_adjective_condition::InAdjectiveCondition;
 pub use in_on_the_cards::InOnTheCards;
 pub use inflected_verb_after_to::InflectedVerbAfterTo;
 pub use initialism_linter::InitialismLinter;