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feat(linter): implement noUnusedExpressions
#7511
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,29 @@ | ||
| --- | ||
| "@biomejs/biome": patch | ||
| --- | ||
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| Added nursery rule [`noUnusedExpressions`](https://biomejs.dev/linter/rules/no-unused-expressions/) to flag expressions used as a statement that is neither an assignment nor a function call. | ||
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| #### Invalid examples | ||
|
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| ```js | ||
| f // intended to call `f()` instead | ||
| ``` | ||
|
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| ```js | ||
| function foo() { | ||
| 0 // intended to `return 0` instead | ||
| } | ||
| ``` | ||
|
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| #### Valid examples | ||
|
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| ```js | ||
| f() | ||
| ``` | ||
|
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| ```js | ||
| function foo() { | ||
| return 0; | ||
| } | ||
| ``` |
12 changes: 12 additions & 0 deletions
12
crates/biome_cli/src/execute/migrate/eslint_any_rule_to_biome.rs
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301 changes: 301 additions & 0 deletions
301
crates/biome_js_analyze/src/lint/nursery/no_unused_expressions.rs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,301 @@ | ||
| use std::borrow::Cow; | ||
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| use biome_analyze::{ | ||
| Ast, Rule, RuleDiagnostic, RuleSource, context::RuleContext, declare_lint_rule, | ||
| }; | ||
| use biome_console::markup; | ||
| use biome_js_syntax::{ | ||
| AnyJsExpression, AnyJsFunction, AnyJsLiteralExpression, AnyJsRoot, JsBlockStatement, | ||
| JsExpressionStatement, JsSyntaxNode, JsUnaryOperator, TsModuleBlock, | ||
| }; | ||
| use biome_rowan::{AstNode, SyntaxResult}; | ||
| use biome_rule_options::no_unused_expressions::NoUnusedExpressionsOptions; | ||
|
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| declare_lint_rule! { | ||
| /// Disallow expression statements that are neither a function call nor an | ||
| /// assignment. | ||
| /// | ||
| /// When an expression is used as a statement, it should be explicitly clear | ||
| /// what the intention behind the expression is. This is clear for function | ||
| /// calls and assignments, because the call or the assignment itself is the | ||
| /// primary intention behind the statement. For other expression kinds, the | ||
| /// intention is much more ambiguous; it could be the expression contains | ||
| /// side-effects that are not very explicit, but it could also be that it is | ||
| /// an error where the author forgot to use the result of the expression, | ||
| /// such as a forgotten `return` keyword, or it could point to a function | ||
| /// that the author forgot to call. | ||
| /// | ||
| /// ## Examples | ||
| /// | ||
| /// ### Invalid | ||
| /// | ||
| /// ```js,expect_diagnostic | ||
| /// 0 | ||
| /// ``` | ||
| /// | ||
| /// ```js,expect_diagnostic | ||
| /// if(0) 0 | ||
| /// ``` | ||
| /// | ||
| /// ```js,expect_diagnostic | ||
| /// {0} | ||
| /// ``` | ||
| /// | ||
| /// ```js,expect_diagnostic | ||
| /// f(0), {} | ||
| /// ``` | ||
| /// | ||
| /// ```js,expect_diagnostic | ||
| /// a && b() | ||
| /// ``` | ||
| /// | ||
| /// ```js,expect_diagnostic | ||
| /// a, b() | ||
| /// ``` | ||
| /// | ||
| /// ```js,expect_diagnostic | ||
| /// c = a, b | ||
| /// ``` | ||
| /// | ||
| /// ```js,expect_diagnostic | ||
| /// a() && function namedFunctionInExpressionContext () {f();} | ||
| /// ``` | ||
| /// | ||
| /// ```js,expect_diagnostic | ||
| /// (function anIncompleteIIFE () {}); | ||
| /// ``` | ||
| /// | ||
| /// ```js,expect_diagnostic | ||
| /// injectGlobal`body{ color: red; }` | ||
| /// ``` | ||
| /// | ||
| /// ```ts,expect_diagnostic | ||
| /// Set<number> | ||
| /// ``` | ||
| /// | ||
| /// ```ts,expect_diagnostic | ||
| /// 1 as number | ||
| /// ``` | ||
| /// | ||
| /// ```ts,expect_diagnostic | ||
| /// window! | ||
| /// ``` | ||
| /// | ||
| /// JSX expressions are considered invalid when used as a statement too: | ||
| /// | ||
| /// ```jsx,expect_diagnostic | ||
| /// <MyComponent /> | ||
| /// ``` | ||
| /// | ||
| /// ```jsx,expect_diagnostic | ||
| /// <></> | ||
| /// ``` | ||
| /// | ||
| /// ### Valid | ||
| /// | ||
| /// ```js | ||
| /// {} // In this context, this is a block statement, not an object literal | ||
| /// | ||
| /// { myLabel: foo() } // In this context, this is a block statement with a label and expression, not an object literal | ||
| /// | ||
| /// function namedFunctionDeclaration () {} | ||
| /// | ||
| /// (function aGenuineIIFE () {}()); | ||
| /// | ||
| /// f() | ||
| /// | ||
| /// a = 0 | ||
| /// | ||
| /// new C | ||
| /// | ||
| /// delete a.b | ||
| /// | ||
| /// void a | ||
| /// ``` | ||
| /// | ||
| /// ### Handling of Directives | ||
| /// | ||
| /// Any stand-alone string at the start of a script, module, or function is | ||
| /// considered a directive and is therefore allowed. | ||
| /// | ||
| /// ```js | ||
| /// "use strict"; | ||
| /// "use asm" | ||
| /// "use stricter"; | ||
| /// "use babel" | ||
| /// "any other strings like this in the directive prologue"; | ||
| /// "this is still the directive prologue"; | ||
| /// | ||
| /// function foo() { | ||
| /// "bar"; | ||
| /// } | ||
| /// | ||
| /// class Foo { | ||
| /// someMethod() { | ||
| /// "use strict"; | ||
| /// } | ||
| /// } | ||
| /// ``` | ||
| /// | ||
| /// The following are **not** considered valid directives: | ||
| /// | ||
| /// ```js,expect_diagnostic | ||
| /// doSomething(); | ||
| /// "use strict"; // this isn't in a directive prologue, because there is a non-directive statement before it | ||
| /// ``` | ||
| /// | ||
| /// ```js,expect_diagnostic | ||
| /// function foo() { | ||
| /// "bar" + 1; | ||
| /// } | ||
| /// ``` | ||
| /// | ||
| /// ```js,expect_diagnostic | ||
| /// class Foo { | ||
| /// static { | ||
| /// "use strict"; // class static blocks do not have directive prologues | ||
| /// } | ||
| /// } | ||
| /// ``` | ||
| pub NoUnusedExpressions { | ||
| version: "next", | ||
| name: "noUnusedExpressions", | ||
| language: "js", | ||
| sources: &[RuleSource::Eslint("no-unused-expressions").same()], | ||
| recommended: false, | ||
| } | ||
| } | ||
|
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| impl Rule for NoUnusedExpressions { | ||
| type Query = Ast<JsExpressionStatement>; | ||
| type State = (); | ||
| type Signals = Option<Self::State>; | ||
| type Options = NoUnusedExpressionsOptions; | ||
|
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| fn run(ctx: &RuleContext<Self>) -> Self::Signals { | ||
| let node = ctx.query(); | ||
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| if is_directive(node) { | ||
| return None; | ||
| } | ||
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| is_disallowed(&node.expression().ok()?).ok()?.then_some(()) | ||
| } | ||
|
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| fn diagnostic(ctx: &RuleContext<Self>, _state: &Self::State) -> Option<RuleDiagnostic> { | ||
| let node = ctx.query(); | ||
| Some( | ||
| RuleDiagnostic::new( | ||
| rule_category!(), | ||
| node.range(), | ||
| markup! { | ||
| "Expected an assignment or function call but found an expression instead." | ||
| }, | ||
| ) | ||
| .note(markup! { | ||
| "This expression may be unintentionally unused or it might be a function that you forgot to call." | ||
| }), | ||
| ) | ||
| } | ||
| } | ||
|
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| /// Determines if a node should be treated as a directive. | ||
| /// | ||
| /// Only string literals are treated as directives, and only if they are not | ||
| /// preceeded by any non-directive nodes. | ||
| fn is_directive(node: &JsExpressionStatement) -> bool { | ||
| if node | ||
| .syntax() | ||
| .parent() | ||
| .is_some_and(|parent| !is_at_top_level(&parent)) | ||
| { | ||
| return false; | ||
| } | ||
|
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| let mut node = Cow::Borrowed(node); | ||
| loop { | ||
| if !looks_like_directive(&node) { | ||
| break false; | ||
| } | ||
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| let Some(prev_node) = node.syntax().prev_sibling() else { | ||
| break true; | ||
| }; | ||
| match JsExpressionStatement::cast(prev_node) { | ||
| Some(prev_expr) => node = Cow::Owned(prev_expr), | ||
| None => break false, | ||
| } | ||
| } | ||
| } | ||
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| /// Determines if a node exists at the top-level based on its `parent` node. | ||
| fn is_at_top_level(parent: &JsSyntaxNode) -> bool { | ||
| AnyJsRoot::can_cast(parent.kind()) | ||
| || TsModuleBlock::can_cast(parent.kind()) | ||
| || JsBlockStatement::cast_ref(parent).is_some_and(|block| { | ||
| block | ||
| .syntax() | ||
| .parent() | ||
| .is_some_and(|parent: JsSyntaxNode| AnyJsFunction::can_cast(parent.kind())) | ||
| }) | ||
| } | ||
|
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| fn looks_like_directive(node: &JsExpressionStatement) -> bool { | ||
| matches!( | ||
| node.expression(), | ||
| Ok(AnyJsExpression::AnyJsLiteralExpression( | ||
| AnyJsLiteralExpression::JsStringLiteralExpression(_) | ||
| )) | ||
| ) | ||
| } | ||
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| fn is_disallowed(expr: &AnyJsExpression) -> SyntaxResult<bool> { | ||
| let is_disallowed = match expr { | ||
| AnyJsExpression::AnyJsLiteralExpression(_) | ||
| | AnyJsExpression::JsArrayExpression(_) | ||
| | AnyJsExpression::JsArrowFunctionExpression(_) | ||
| | AnyJsExpression::JsBinaryExpression(_) | ||
| | AnyJsExpression::JsClassExpression(_) | ||
| | AnyJsExpression::JsComputedMemberExpression(_) | ||
| | AnyJsExpression::JsConditionalExpression(_) | ||
| | AnyJsExpression::JsFunctionExpression(_) | ||
| | AnyJsExpression::JsIdentifierExpression(_) | ||
| | AnyJsExpression::JsImportMetaExpression(_) | ||
| | AnyJsExpression::JsInExpression(_) | ||
| | AnyJsExpression::JsInstanceofExpression(_) | ||
| | AnyJsExpression::JsLogicalExpression(_) | ||
| | AnyJsExpression::JsNewTargetExpression(_) | ||
| | AnyJsExpression::JsObjectExpression(_) | ||
| | AnyJsExpression::JsSequenceExpression(_) | ||
| | AnyJsExpression::JsStaticMemberExpression(_) | ||
| | AnyJsExpression::JsSuperExpression(_) | ||
| | AnyJsExpression::JsTemplateExpression(_) | ||
| | AnyJsExpression::JsThisExpression(_) | ||
| | AnyJsExpression::JsxTagExpression(_) => true, | ||
| AnyJsExpression::JsAwaitExpression(_) | ||
| | AnyJsExpression::JsAssignmentExpression(_) | ||
| | AnyJsExpression::JsCallExpression(_) | ||
| | AnyJsExpression::JsImportCallExpression(_) | ||
| | AnyJsExpression::JsNewExpression(_) | ||
| | AnyJsExpression::JsYieldExpression(_) | ||
| | AnyJsExpression::JsPostUpdateExpression(_) | ||
| | AnyJsExpression::JsPreUpdateExpression(_) | ||
| | AnyJsExpression::JsBogusExpression(_) | ||
| | AnyJsExpression::JsMetavariable(_) => false, | ||
| AnyJsExpression::JsParenthesizedExpression(expr) => is_disallowed(&expr.expression()?)?, | ||
| AnyJsExpression::JsUnaryExpression(expr) => match expr.operator()? { | ||
| JsUnaryOperator::BitwiseNot | ||
| | JsUnaryOperator::LogicalNot | ||
| | JsUnaryOperator::Minus | ||
| | JsUnaryOperator::Plus | ||
| | JsUnaryOperator::Typeof => true, | ||
| JsUnaryOperator::Delete | JsUnaryOperator::Void => false, | ||
| }, | ||
| AnyJsExpression::TsAsExpression(expr) => is_disallowed(&expr.expression()?)?, | ||
| AnyJsExpression::TsInstantiationExpression(expr) => is_disallowed(&expr.expression()?)?, | ||
| AnyJsExpression::TsNonNullAssertionExpression(expr) => is_disallowed(&expr.expression()?)?, | ||
| AnyJsExpression::TsSatisfiesExpression(expr) => is_disallowed(&expr.expression()?)?, | ||
| AnyJsExpression::TsTypeAssertionExpression(expr) => is_disallowed(&expr.expression()?)?, | ||
| }; | ||
| Ok(is_disallowed) | ||
| } | ||
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Don’t treat TS namespace/module blocks as directive contexts.
Directive prologues exist only for Script/Module roots and Function bodies. Allowing them inside
TsModuleBlockdeviates from JS semantics and can hide unused string expressions innamespace/modulebodies.Apply this diff:
fn is_at_top_level(parent: &JsSyntaxNode) -> bool { AnyJsRoot::can_cast(parent.kind()) - || TsModuleBlock::can_cast(parent.kind()) || JsBlockStatement::cast_ref(parent).is_some_and(|block| { block .syntax() .parent() .is_some_and(|parent: JsSyntaxNode| AnyJsFunction::can_cast(parent.kind())) }) }📝 Committable suggestion
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