feat(lint): useCollapsedElseIf (#160)

Co-authored-by: Victorien Elvinger <victorien@elvinger.fr>

crates/rome_diagnostics_categories/src/categories.rs

@@ -103,6 +103,7 @@ define_categories! {
     "lint/nursery/useAriaPropTypes": "https://biomejs.dev/linter/rules/use-aria-prop-types",
     "lint/nursery/useArrowFunction": "https://biomejs.dev/linter/rules/use-arrow-function",
     "lint/nursery/useBiomeSuppressionComment": "https://biomejs.dev/lint/rules/use-biome-suppression-comment",
+    "lint/nursery/useCollapsedElseIf": "https://biomejs.dev/lint/rules/use-collapsed-else-if",
     "lint/nursery/useExhaustiveDependencies": "https://biomejs.dev/linter/rules/use-exhaustive-dependencies",
     "lint/nursery/useGetterReturn": "https://biomejs.dev/linter/rules/use-getter-return",
     "lint/nursery/useGroupedTypeImport": "https://biomejs.dev/linter/rules/use-grouped-type-import",

crates/rome_js_analyze/src/analyzers/nursery/use_collapsed_else_if.rs

@@ -0,0 +1,154 @@
+use crate::JsRuleAction;
+use rome_analyze::{context::RuleContext, declare_rule, ActionCategory, Ast, Rule, RuleDiagnostic};
+use rome_console::markup;
+use rome_diagnostics::Applicability;
+use rome_js_syntax::{AnyJsStatement, JsBlockStatement, JsElseClause, JsIfStatement};
+use rome_rowan::{AstNode, AstNodeList, BatchMutationExt};
+
+declare_rule! {
+    /// Enforce using `else if` instead of nested `if` in `else` clauses.
+    ///
+    /// If an `if` statement is the only statement in the `else` block, it is often clearer to use an `else if` form.
+    ///
+    /// Source: https://eslint.org/docs/latest/rules/no-lonely-if
+    ///
+    /// ## Examples
+    ///
+    /// ### Invalid
+    ///
+    /// ```js,expect_diagnostic
+    /// if (condition) {
+    ///     // ...
+    /// } else {
+    ///     if (anotherCondition) {
+    ///         // ...
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// ```js,expect_diagnostic
+    /// if (condition) {
+    ///     // ...
+    /// } else {
+    ///     if (anotherCondition) {
+    ///         // ...
+    ///     } else {
+    ///         // ...
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// ### Valid
+    ///
+    /// ```js
+    /// if (condition) {
+    ///     // ...
+    /// } else if (anotherCondition) {
+    ///     // ...
+    /// }
+    /// ```
+    ///
+    /// ```js
+    /// if (condition) {
+    ///     // ...
+    /// } else if (anotherCondition) {
+    ///     // ...
+    /// } else {
+    ///     // ...
+    /// }
+    /// ```
+    ///
+    /// ```js
+    /// if (condition) {
+    ///     // ...
+    /// } else {
+    ///     if (anotherCondition) {
+    ///         // ...
+    ///     }
+    ///     doSomething();
+    /// }
+    /// ```
+    ///
+    pub(crate) UseCollapsedElseIf {
+        version: "next",
+        name: "useCollapsedElseIf",
+        recommended: false,
+    }
+}
+
+pub(crate) struct RuleState {
+    block_statement: JsBlockStatement,
+    if_statement: JsIfStatement,
+}
+
+impl Rule for UseCollapsedElseIf {
+    type Query = Ast<JsElseClause>;
+    type State = RuleState;
+    type Signals = Option<Self::State>;
+    type Options = ();
+
+    fn run(ctx: &RuleContext<Self>) -> Self::Signals {
+        let else_clause = ctx.query();
+        let alternate = else_clause.alternate().ok()?;
+        let AnyJsStatement::JsBlockStatement(block_statement) = alternate else {
+            return None;
+        };
+        let statements = block_statement.statements();
+        if statements.len() != 1 {
+            return None;
+        }
+        if let AnyJsStatement::JsIfStatement(if_statement) = statements.first()? {
+            Some(RuleState {
+                block_statement,
+                if_statement,
+            })
+        } else {
+            None
+        }
+    }
+
+    fn diagnostic(_: &RuleContext<Self>, state: &Self::State) -> Option<RuleDiagnostic> {
+        Some(RuleDiagnostic::new(
+            rule_category!(),
+            state.if_statement.syntax().text_range(),
+            markup! {
+                "This "<Emphasis>"if"</Emphasis>" statement can be collapsed into an "<Emphasis>"else if"</Emphasis>" statement."
+            },
+        ))
+    }
+
+    fn action(ctx: &RuleContext<Self>, state: &Self::State) -> Option<JsRuleAction> {
+        let RuleState {
+            block_statement,
+            if_statement,
+        } = state;
+
+        let has_comments = block_statement
+            .l_curly_token()
+            .ok()?
+            .has_trailing_comments()
+            || if_statement.syntax().has_leading_comments()
+            || if_statement.syntax().has_trailing_comments()
+            || block_statement.r_curly_token().ok()?.has_leading_comments();
+
+        let applicability = if has_comments {
+            Applicability::MaybeIncorrect
+        } else {
+            Applicability::Always
+        };
+
+        let mut mutation = ctx.root().begin();
+        mutation.replace_node(
+            AnyJsStatement::from(block_statement.clone()),
+            if_statement.clone().into(),
+        );
+
+        Some(JsRuleAction {
+            category: ActionCategory::QuickFix,
+            applicability,
+            message: markup! { "Use collapsed "<Emphasis>"else if"</Emphasis>" instead." }
+                .to_owned(),
+            mutation,
+        })
+    }
+}

crates/rome_js_analyze/tests/specs/nursery/useCollapsedElseIf/invalid.js

@@ -0,0 +1,101 @@
+/**
+ * Safe fixes:
+ */
+
+if (condition) {
+	// ...
+} else {
+	if (anotherCondition) {
+		// ...
+	}
+}
+
+if (condition) {
+	// ...
+} else {
+	if (anotherCondition) {
+		// ...
+	} else {
+		// ...
+	}
+}
+
+/**
+ * Suggested fixes:
+ */
+
+if (condition) {
+	// ...
+} else { // Comment
+	if (anotherCondition) {
+		// ...
+	}
+}
+
+if (condition) {
+	// ...
+} else {
+	// Comment
+	if (anotherCondition) {
+		// ...
+	}
+}
+
+if (condition) {
+	// ...
+} else {
+	if (anotherCondition) {
+		// ...
+	} // Comment
+}
+
+if (condition) {
+	// ...
+} else {
+	if (anotherCondition) {
+		// ...
+	}
+	// Comment
+}
+
+if (condition) {
+	// ...
+} else { // Comment
+	if (anotherCondition) {
+		// ...
+	} else {
+		// ...
+	}
+}
+
+if (condition) {
+	// ...
+} else {
+	// Comment
+	if (anotherCondition) {
+		// ...
+	} else {
+		// ...
+	}
+}
+
+if (condition) {
+	// ...
+} else {
+	if (anotherCondition) {
+		// ...
+	} else {
+		// ...
+	} // Comment
+}
+
+if (condition) {
+	// ...
+} else {
+	if (anotherCondition) {
+		// ...
+	} else {
+		// ...
+	}
+	// Comment
+}