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192
crates/biome_js_analyze/src/analyzers/nursery/no_useless_else.rs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,192 @@ | ||
| use biome_analyze::{ | ||
| context::RuleContext, declare_rule, ActionCategory, Ast, Rule, RuleDiagnostic, | ||
| }; | ||
| use biome_console::markup; | ||
| use biome_diagnostics::Applicability; | ||
| use biome_js_factory::make; | ||
| use biome_js_syntax::{AnyJsStatement, JsElseClause, JsIfStatement, JsStatementList}; | ||
| use biome_rowan::{AstNode, AstNodeList, BatchMutationExt}; | ||
|
|
||
| use crate::JsRuleAction; | ||
|
|
||
| declare_rule! { | ||
| /// Disallow `else` block when the `if` block breaks early. | ||
| /// | ||
| /// If an `if` block breaks early using a breaking statement (`return`, `break`, `continue`, or `throw`), | ||
| /// then the `else` block becomes useless. | ||
| /// Its contents can be placed outside of the block. | ||
| /// | ||
| /// ## Examples | ||
| /// | ||
| /// ### Invalid | ||
| /// | ||
| /// ```js,expect_diagnostic | ||
| /// while (x > 0) { | ||
| /// if (f(x)) { | ||
| /// break; | ||
| /// } else { | ||
| /// x++ | ||
| /// } | ||
| /// } | ||
| /// ``` | ||
| /// | ||
| /// ```js,expect_diagnostic | ||
| /// function f() { | ||
| /// if (x < 0) { | ||
| /// return 0; | ||
| /// } else { | ||
| /// return x; | ||
| /// } | ||
| /// } | ||
| /// ``` | ||
| /// | ||
| /// ```js,expect_diagnostic | ||
| /// function f() { | ||
| /// if (x < 0) { | ||
| /// throw new RangeError(); | ||
| /// } else { | ||
| /// return x; | ||
| /// } | ||
| /// } | ||
| /// ``` | ||
| /// | ||
| /// ## Valid | ||
| /// | ||
| /// ```js | ||
| /// function f() { | ||
| /// if (x < 0) { | ||
| /// return 0; | ||
| /// } | ||
| /// return x; | ||
| /// } | ||
| /// ``` | ||
| pub(crate) NoUselessElse { | ||
| version: "next", | ||
| name: "noUselessElse", | ||
| recommended: false, | ||
| } | ||
| } | ||
|
|
||
| impl Rule for NoUselessElse { | ||
| type Query = Ast<JsElseClause>; | ||
| type State = (); | ||
| type Signals = Option<Self::State>; | ||
| type Options = (); | ||
|
|
||
| fn run(ctx: &RuleContext<Self>) -> Self::Signals { | ||
| let else_clause = ctx.query(); | ||
| let if_stmt = else_clause.parent::<JsIfStatement>()?; | ||
| let mut stmt_stack = vec![(if_stmt.consequent().ok()?, ScopeMetadata::default())]; | ||
| while let Some((stmt, metadata)) = stmt_stack.pop() { | ||
| match stmt { | ||
| AnyJsStatement::JsBlockStatement(block_stmt) => { | ||
| let Some(last) = block_stmt.statements().iter().last() else { | ||
| // empty statement block | ||
| return None; | ||
| }; | ||
| stmt_stack.push((last, metadata)); | ||
| } | ||
| AnyJsStatement::JsBreakStatement(_) => { | ||
| if metadata.is_breakable { | ||
| // We are inside a breakable structure (switch statement) | ||
| // that we saw in a previous iteration. | ||
| return None; | ||
| } | ||
| } | ||
| AnyJsStatement::JsContinueStatement(_) | ||
| | AnyJsStatement::JsReturnStatement(_) | ||
| | AnyJsStatement::JsThrowStatement(_) => {} | ||
| AnyJsStatement::JsIfStatement(if_stmt) => { | ||
| let Some(else_clause) = if_stmt.else_clause() else { | ||
| // No else clause | ||
| return None; | ||
| }; | ||
| stmt_stack.push((if_stmt.consequent().ok()?, metadata)); | ||
| stmt_stack.push((else_clause.alternate().ok()?, metadata)); | ||
| } | ||
| AnyJsStatement::JsSwitchStatement(switch_stmt) => { | ||
| // To simplify, We do not tale fallthoughs into account. | ||
| // Thus, this can miss some useless else. | ||
| let cases = switch_stmt.cases(); | ||
| let Some(last_case) = cases.last() else { | ||
| // Empty switch | ||
| return None; | ||
| }; | ||
| if last_case.consequent().is_empty() { | ||
| return None; | ||
| } | ||
| for switch_clause in cases.iter() { | ||
| if let Some(last) = switch_clause.consequent().last() { | ||
| stmt_stack.push((last, ScopeMetadata { is_breakable: true })); | ||
| } | ||
| } | ||
| } | ||
| _ => { | ||
| // labeled statements, loops, try-catch, with statement, and others | ||
| return None; | ||
| } | ||
| } | ||
| } | ||
| Some(()) | ||
| } | ||
|
|
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| fn diagnostic(ctx: &RuleContext<Self>, _: &Self::State) -> Option<RuleDiagnostic> { | ||
| let else_clause = ctx.query(); | ||
| Some( | ||
| RuleDiagnostic::new( | ||
| rule_category!(), | ||
| else_clause.range(), | ||
| markup! { | ||
| "This "<Emphasis>"else"</Emphasis>" clause can be omitted." | ||
| }, | ||
| ) | ||
| .detail( | ||
| else_clause.syntax().parent()?.text_trimmed_range(), | ||
| markup! { | ||
| "This "<Emphasis>"if"</Emphasis>" statement uses an early breaking statement." | ||
| }, | ||
| ), | ||
| ) | ||
| } | ||
|
|
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| fn action(ctx: &RuleContext<Self>, _: &Self::State) -> Option<JsRuleAction> { | ||
| let else_clause = ctx.query(); | ||
| let if_stmt = else_clause.parent::<JsIfStatement>()?; | ||
| if let Some(stmts_list) = JsStatementList::cast(if_stmt.syntax().parent()?) { | ||
| // We assume that the last statement is the `if` statement. | ||
| if stmts_list.last()?.syntax() != if_stmt.syntax() { | ||
| return None; | ||
| } | ||
| let else_alternative = else_clause.alternate().ok()?; | ||
| let new_if_stmt = AnyJsStatement::JsIfStatement(if_stmt.clone().with_else_clause(None)) | ||
| .with_trailing_trivia_pieces([])?; | ||
| // We collect teh statements because `chain` is no table to produce an `ExactSizeIterator`. | ||
| let mut new_stmts = stmts_list | ||
| .iter() | ||
| .take(stmts_list.len() - 1) | ||
| .chain([new_if_stmt]) | ||
| .collect::<Vec<_>>(); | ||
| if let AnyJsStatement::JsBlockStatement(else_block_stmts) = else_alternative { | ||
| new_stmts.extend(else_block_stmts.statements().iter()); | ||
| } else { | ||
| new_stmts.push(else_alternative); | ||
| }; | ||
| let new_stmts_list = make::js_statement_list(new_stmts); | ||
| let mut mutation = ctx.root().begin(); | ||
| mutation.replace_node_discard_trivia(stmts_list, new_stmts_list); | ||
| return Some(JsRuleAction { | ||
| category: ActionCategory::QuickFix, | ||
| applicability: Applicability::MaybeIncorrect, | ||
| message: markup! { "Omit the "<Emphasis>"else"</Emphasis>" clause." }.to_owned(), | ||
| mutation, | ||
| }); | ||
| } | ||
| None | ||
| } | ||
| } | ||
|
|
||
| #[derive(Debug, Copy, Clone, Default)] | ||
| struct ScopeMetadata { | ||
| // We are inside a breakable structure | ||
| is_breakable: bool, | ||
| } |
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84 changes: 84 additions & 0 deletions
84
crates/biome_js_analyze/tests/specs/nursery/noUselessElse/invalid.js
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,84 @@ | ||
| function f (x) { | ||
| if (x < 0) { | ||
| throw new RangeError(); | ||
| } else { | ||
| return x; | ||
| } | ||
| } | ||
|
|
||
| function f (x) { | ||
| if (x < 0) { | ||
| throw new RangeError(); | ||
| } else return x; | ||
| } | ||
|
|
||
| function f (x) { | ||
| if (x < 0) | ||
| throw new RangeError(); | ||
| else | ||
| return x; | ||
| } | ||
|
|
||
| function f (x) { | ||
| if (x < 0) { | ||
| throw new RangeError(); | ||
| } else if (x === 0) { | ||
| return 1; | ||
| } else { | ||
| return x; | ||
| } | ||
| } | ||
|
|
||
| function f (x) { | ||
| while (true) { | ||
| if (x < 0) { | ||
| break; | ||
| } else { | ||
| x -= g(x) | ||
| } | ||
| } | ||
| return x; | ||
| } | ||
|
|
||
| function f (x) { | ||
| while (true) { | ||
| if (x < 0) { | ||
| break; | ||
| } else { | ||
| x -= g(x) | ||
| } | ||
| } | ||
| return x; | ||
| } | ||
|
|
||
| function f (x) { | ||
| if (x > 0 && x < 5) { | ||
| switch (x) { | ||
| case 0: | ||
| case 1: | ||
| return 0; | ||
| default: | ||
| return x; | ||
| } | ||
| } else { | ||
| return x; | ||
| } | ||
| } | ||
|
|
||
| function f (x) { // 0 | ||
| // 1 | ||
| if (x > 0 && x < 5) { | ||
| switch (x) { | ||
| case 0: | ||
| case 1: | ||
| return 0; | ||
| default: | ||
| return x; | ||
| } | ||
| } /*a*/ else /*b*/ { // c | ||
| // d | ||
| return x; // e | ||
| // f | ||
| } // g | ||
| // 2 | ||
| } // 3 |
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