feat(linter) eslint plugin unicorn: no negated condition (#1253)

crates/oxc_linter/src/rules.rs

@@ -152,6 +152,7 @@ mod unicorn {
     pub mod no_empty_file;
     pub mod no_instanceof_array;
     pub mod no_invalid_remove_event_listener;
+    pub mod no_negated_condition;
     pub mod no_new_array;
     pub mod no_new_buffer;
     pub mod no_object_as_default_parameter;
@@ -298,6 +299,7 @@ oxc_macros::declare_all_lint_rules! {
     unicorn::no_empty_file,
     unicorn::no_instanceof_array,
     unicorn::no_invalid_remove_event_listener,
+    unicorn::no_negated_condition,
     unicorn::no_new_array,
     unicorn::no_new_buffer,
     unicorn::no_object_as_default_parameter,

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

@@ -0,0 +1,146 @@
+use oxc_ast::{
+    ast::{Expression, Statement},
+    AstKind,
+};
+use oxc_diagnostics::{
+    miette::{self, Diagnostic},
+    thiserror::Error,
+};
+use oxc_macros::declare_oxc_lint;
+use oxc_span::{GetSpan, Span};
+use oxc_syntax::operator::{BinaryOperator, UnaryOperator};
+
+use crate::{context::LintContext, rule::Rule, AstNode};
+
+#[derive(Debug, Error, Diagnostic)]
+#[error("eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.")]
+#[diagnostic(
+    severity(warning),
+    help("Remove the negation operator and switch the consequent and alternate branches.")
+)]
+struct NoNegatedConditionDiagnostic(#[label] pub Span);
+
+#[derive(Debug, Default, Clone)]
+pub struct NoNegatedCondition;
+
+declare_oxc_lint!(
+    /// ### What it does
+    ///
+    /// Disallow negated conditions.
+    ///
+    /// ### Why is this bad?
+    ///
+    /// Negated conditions are more difficult to understand. Code can be made more readable by inverting the condition.
+    ///
+    /// ### Example
+    /// ```javascript
+    /// // Bad
+    ///
+    /// if (!a) {
+    /// 	doSomethingC();
+    /// } else {
+    /// 	doSomethingB();
+    /// }
+    ///
+    /// !a ? doSomethingC() : doSomethingB()
+    ///
+    /// // Good
+    ///
+    /// if (a) {
+    /// 	doSomethingB();
+    /// } else {
+    /// 	doSomethingC();
+    /// }
+    ///
+    /// a ? doSomethingB() : doSomethingC()
+    /// ```
+    NoNegatedCondition,
+    pedantic
+);
+
+impl Rule for NoNegatedCondition {
+    fn run<'a>(&self, node: &AstNode<'a>, ctx: &LintContext<'a>) {
+        let stmt_test = match node.kind() {
+            AstKind::IfStatement(if_stmt) => {
+                let Some(if_stmt_alternate) = &if_stmt.alternate else { return };
+
+                if matches!(if_stmt_alternate, Statement::IfStatement(_)) {
+                    return;
+                }
+
+                if_stmt.test.without_parenthesized()
+            }
+            AstKind::ConditionalExpression(conditional_expr) => {
+                conditional_expr.test.without_parenthesized()
+            }
+            _ => {
+                return;
+            }
+        };
+
+        match stmt_test {
+            Expression::UnaryExpression(unary_expr) => {
+                if unary_expr.operator != UnaryOperator::LogicalNot {
+                    return;
+                }
+            }
+            Expression::BinaryExpression(binary_expr) => {
+                if !matches!(
+                    binary_expr.operator,
+                    BinaryOperator::Inequality | BinaryOperator::StrictInequality
+                ) {
+                    return;
+                }
+            }
+            _ => {
+                return;
+            }
+        }
+
+        ctx.diagnostic(NoNegatedConditionDiagnostic(stmt_test.span()));
+    }
+}
+
+#[test]
+fn test() {
+    use crate::tester::Tester;
+
+    let pass = vec![
+        r#"if (a) {}"#,
+        r#"if (a) {} else {}"#,
+        r#"if (!a) {}"#,
+        r#"if (!a) {} else if (b) {}"#,
+        r#"if (!a) {} else if (b) {} else {}"#,
+        r#"if (a == b) {}"#,
+        r#"if (a == b) {} else {}"#,
+        r#"if (a != b) {}"#,
+        r#"if (a != b) {} else if (b) {}"#,
+        r#"if (a != b) {} else if (b) {} else {}"#,
+        r#"if (a !== b) {}"#,
+        r#"if (a === b) {} else {}"#,
+        r#"a ? b : c"#,
+    ];
+
+    let fail = vec![
+        r#"if (!a) {;} else {;}"#,
+        r#"if (a != b) {;} else {;}"#,
+        r#"if (a !== b) {;} else {;}"#,
+        r#"!a ? b : c"#,
+        r#"a != b ? c : d"#,
+        r#"a !== b ? c : d"#,
+        r#"(( !a )) ? b : c"#,
+        r#"!(( a )) ? b : c"#,
+        r#"if(!(( a ))) b(); else c();"#,
+        r#"if((( !a ))) b(); else c();"#,
+        r#"function a() {return!a ? b : c}"#,
+        r#"function a() {return!(( a )) ? b : c}"#,
+        r#"!a ? b : c ? d : e"#,
+        r#"!a ? b : (( c ? d : e ))"#,
+        r#"if(!a) b(); else c()"#,
+        r#"if(!a) {b()} else {c()}"#,
+        r#"if(!!a) b(); else c();"#,
+        r#"(!!a) ? b() : c();"#,
+    ];
+
+    Tester::new_without_config(NoNegatedCondition::NAME, pass, fail).test_and_snapshot();
+}

crates/oxc_linter/src/snapshots/no_negated_condition.snap

@@ -0,0 +1,131 @@
+---
+source: crates/oxc_linter/src/tester.rs
+expression: no_negated_condition
+---
+  ⚠ eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.
+   ╭─[no_negated_condition.tsx:1:1]
+ 1 │ if (!a) {;} else {;}
+   ·     ──
+   ╰────
+  help: Remove the negation operator and switch the consequent and alternate branches.
+
+  ⚠ eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.
+   ╭─[no_negated_condition.tsx:1:1]
+ 1 │ if (a != b) {;} else {;}
+   ·     ──────
+   ╰────
+  help: Remove the negation operator and switch the consequent and alternate branches.
+
+  ⚠ eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.
+   ╭─[no_negated_condition.tsx:1:1]
+ 1 │ if (a !== b) {;} else {;}
+   ·     ───────
+   ╰────
+  help: Remove the negation operator and switch the consequent and alternate branches.
+
+  ⚠ eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.
+   ╭─[no_negated_condition.tsx:1:1]
+ 1 │ !a ? b : c
+   · ──
+   ╰────
+  help: Remove the negation operator and switch the consequent and alternate branches.
+
+  ⚠ eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.
+   ╭─[no_negated_condition.tsx:1:1]
+ 1 │ a != b ? c : d
+   · ──────
+   ╰────
+  help: Remove the negation operator and switch the consequent and alternate branches.
+
+  ⚠ eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.
+   ╭─[no_negated_condition.tsx:1:1]
+ 1 │ a !== b ? c : d
+   · ───────
+   ╰────
+  help: Remove the negation operator and switch the consequent and alternate branches.
+
+  ⚠ eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.
+   ╭─[no_negated_condition.tsx:1:1]
+ 1 │ (( !a )) ? b : c
+   ·    ──
+   ╰────
+  help: Remove the negation operator and switch the consequent and alternate branches.
+
+  ⚠ eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.
+   ╭─[no_negated_condition.tsx:1:1]
+ 1 │ !(( a )) ? b : c
+   · ────────
+   ╰────
+  help: Remove the negation operator and switch the consequent and alternate branches.
+
+  ⚠ eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.
+   ╭─[no_negated_condition.tsx:1:1]
+ 1 │ if(!(( a ))) b(); else c();
+   ·    ────────
+   ╰────
+  help: Remove the negation operator and switch the consequent and alternate branches.
+
+  ⚠ eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.
+   ╭─[no_negated_condition.tsx:1:1]
+ 1 │ if((( !a ))) b(); else c();
+   ·       ──
+   ╰────
+  help: Remove the negation operator and switch the consequent and alternate branches.
+
+  ⚠ eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.
+   ╭─[no_negated_condition.tsx:1:1]
+ 1 │ function a() {return!a ? b : c}
+   ·                     ──
+   ╰────
+  help: Remove the negation operator and switch the consequent and alternate branches.
+
+  ⚠ eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.
+   ╭─[no_negated_condition.tsx:1:1]
+ 1 │ function a() {return!(( a )) ? b : c}
+   ·                     ────────
+   ╰────
+  help: Remove the negation operator and switch the consequent and alternate branches.
+
+  ⚠ eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.
+   ╭─[no_negated_condition.tsx:1:1]
+ 1 │ !a ? b : c ? d : e
+   · ──
+   ╰────
+  help: Remove the negation operator and switch the consequent and alternate branches.
+
+  ⚠ eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.
+   ╭─[no_negated_condition.tsx:1:1]
+ 1 │ !a ? b : (( c ? d : e ))
+   · ──
+   ╰────
+  help: Remove the negation operator and switch the consequent and alternate branches.
+
+  ⚠ eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.
+   ╭─[no_negated_condition.tsx:1:1]
+ 1 │ if(!a) b(); else c()
+   ·    ──
+   ╰────
+  help: Remove the negation operator and switch the consequent and alternate branches.
+
+  ⚠ eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.
+   ╭─[no_negated_condition.tsx:1:1]
+ 1 │ if(!a) {b()} else {c()}
+   ·    ──
+   ╰────
+  help: Remove the negation operator and switch the consequent and alternate branches.
+
+  ⚠ eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.
+   ╭─[no_negated_condition.tsx:1:1]
+ 1 │ if(!!a) b(); else c();
+   ·    ───
+   ╰────
+  help: Remove the negation operator and switch the consequent and alternate branches.
+
+  ⚠ eslint-plugin-unicorn(no-negated-condition): Unexpected negated condition.
+   ╭─[no_negated_condition.tsx:1:1]
+ 1 │ (!!a) ? b() : c();
+   ·  ───
+   ╰────
+  help: Remove the negation operator and switch the consequent and alternate branches.
+
+