|
| 1 | +use std::borrow::Cow; |
| 2 | + |
| 3 | +use biome_analyze::{ |
| 4 | + Ast, Rule, RuleDiagnostic, RuleSource, context::RuleContext, declare_lint_rule, |
| 5 | +}; |
| 6 | +use biome_console::markup; |
| 7 | +use biome_js_syntax::{ |
| 8 | + AnyJsExpression, AnyJsFunction, AnyJsLiteralExpression, AnyJsRoot, JsBlockStatement, |
| 9 | + JsExpressionStatement, JsSyntaxNode, JsUnaryOperator, TsModuleBlock, |
| 10 | +}; |
| 11 | +use biome_rowan::{AstNode, SyntaxResult}; |
| 12 | +use biome_rule_options::no_unused_expressions::NoUnusedExpressionsOptions; |
| 13 | + |
| 14 | +declare_lint_rule! { |
| 15 | + /// Disallow expression statements that are neither a function call nor an |
| 16 | + /// assignment. |
| 17 | + /// |
| 18 | + /// When an expression is used as a statement, it should be explicitly clear |
| 19 | + /// what the intention behind the expression is. This is clear for function |
| 20 | + /// calls and assignments, because the call or the assignment itself is the |
| 21 | + /// primary intention behind the statement. For other expression kinds, the |
| 22 | + /// intention is much more ambiguous; it could be the expression contains |
| 23 | + /// side-effects that are not very explicit, but it could also be that it is |
| 24 | + /// an error where the author forgot to use the result of the expression, |
| 25 | + /// such as a forgotten `return` keyword, or it could point to a function |
| 26 | + /// that the author forgot to call. |
| 27 | + /// |
| 28 | + /// ## Examples |
| 29 | + /// |
| 30 | + /// ### Invalid |
| 31 | + /// |
| 32 | + /// ```js,expect_diagnostic |
| 33 | + /// 0 |
| 34 | + /// ``` |
| 35 | + /// |
| 36 | + /// ```js,expect_diagnostic |
| 37 | + /// if(0) 0 |
| 38 | + /// ``` |
| 39 | + /// |
| 40 | + /// ```js,expect_diagnostic |
| 41 | + /// {0} |
| 42 | + /// ``` |
| 43 | + /// |
| 44 | + /// ```js,expect_diagnostic |
| 45 | + /// f(0), {} |
| 46 | + /// ``` |
| 47 | + /// |
| 48 | + /// ```js,expect_diagnostic |
| 49 | + /// a && b() |
| 50 | + /// ``` |
| 51 | + /// |
| 52 | + /// ```js,expect_diagnostic |
| 53 | + /// a, b() |
| 54 | + /// ``` |
| 55 | + /// |
| 56 | + /// ```js,expect_diagnostic |
| 57 | + /// c = a, b |
| 58 | + /// ``` |
| 59 | + /// |
| 60 | + /// ```js,expect_diagnostic |
| 61 | + /// a() && function namedFunctionInExpressionContext () {f();} |
| 62 | + /// ``` |
| 63 | + /// |
| 64 | + /// ```js,expect_diagnostic |
| 65 | + /// (function anIncompleteIIFE () {}); |
| 66 | + /// ``` |
| 67 | + /// |
| 68 | + /// ```js,expect_diagnostic |
| 69 | + /// injectGlobal`body{ color: red; }` |
| 70 | + /// ``` |
| 71 | + /// |
| 72 | + /// ```ts,expect_diagnostic |
| 73 | + /// Set<number> |
| 74 | + /// ``` |
| 75 | + /// |
| 76 | + /// ```ts,expect_diagnostic |
| 77 | + /// 1 as number |
| 78 | + /// ``` |
| 79 | + /// |
| 80 | + /// ```ts,expect_diagnostic |
| 81 | + /// window! |
| 82 | + /// ``` |
| 83 | + /// |
| 84 | + /// JSX expressions are considered invalid when used as a statement too: |
| 85 | + /// |
| 86 | + /// ```jsx,expect_diagnostic |
| 87 | + /// <MyComponent /> |
| 88 | + /// ``` |
| 89 | + /// |
| 90 | + /// ```jsx,expect_diagnostic |
| 91 | + /// <></> |
| 92 | + /// ``` |
| 93 | + /// |
| 94 | + /// ### Valid |
| 95 | + /// |
| 96 | + /// ```js |
| 97 | + /// {} // In this context, this is a block statement, not an object literal |
| 98 | + /// |
| 99 | + /// { myLabel: foo() } // In this context, this is a block statement with a label and expression, not an object literal |
| 100 | + /// |
| 101 | + /// function namedFunctionDeclaration () {} |
| 102 | + /// |
| 103 | + /// (function aGenuineIIFE () {}()); |
| 104 | + /// |
| 105 | + /// f() |
| 106 | + /// |
| 107 | + /// a = 0 |
| 108 | + /// |
| 109 | + /// new C |
| 110 | + /// |
| 111 | + /// delete a.b |
| 112 | + /// |
| 113 | + /// void a |
| 114 | + /// ``` |
| 115 | + /// |
| 116 | + /// ### Handling of Directives |
| 117 | + /// |
| 118 | + /// Any stand-alone string at the start of a script, module, or function is |
| 119 | + /// considered a directive and is therefore allowed. |
| 120 | + /// |
| 121 | + /// ```js |
| 122 | + /// "use strict"; |
| 123 | + /// "use asm" |
| 124 | + /// "use stricter"; |
| 125 | + /// "use babel" |
| 126 | + /// "any other strings like this in the directive prologue"; |
| 127 | + /// "this is still the directive prologue"; |
| 128 | + /// |
| 129 | + /// function foo() { |
| 130 | + /// "bar"; |
| 131 | + /// } |
| 132 | + /// |
| 133 | + /// class Foo { |
| 134 | + /// someMethod() { |
| 135 | + /// "use strict"; |
| 136 | + /// } |
| 137 | + /// } |
| 138 | + /// ``` |
| 139 | + /// |
| 140 | + /// The following are **not** considered valid directives: |
| 141 | + /// |
| 142 | + /// ```js,expect_diagnostic |
| 143 | + /// doSomething(); |
| 144 | + /// "use strict"; // this isn't in a directive prologue, because there is a non-directive statement before it |
| 145 | + /// ``` |
| 146 | + /// |
| 147 | + /// ```js,expect_diagnostic |
| 148 | + /// function foo() { |
| 149 | + /// "bar" + 1; |
| 150 | + /// } |
| 151 | + /// ``` |
| 152 | + /// |
| 153 | + /// ```js,expect_diagnostic |
| 154 | + /// class Foo { |
| 155 | + /// static { |
| 156 | + /// "use strict"; // class static blocks do not have directive prologues |
| 157 | + /// } |
| 158 | + /// } |
| 159 | + /// ``` |
| 160 | + pub NoUnusedExpressions { |
| 161 | + version: "next", |
| 162 | + name: "noUnusedExpressions", |
| 163 | + language: "js", |
| 164 | + sources: &[RuleSource::Eslint("no-unused-expressions").same()], |
| 165 | + recommended: false, |
| 166 | + } |
| 167 | +} |
| 168 | + |
| 169 | +impl Rule for NoUnusedExpressions { |
| 170 | + type Query = Ast<JsExpressionStatement>; |
| 171 | + type State = (); |
| 172 | + type Signals = Option<Self::State>; |
| 173 | + type Options = NoUnusedExpressionsOptions; |
| 174 | + |
| 175 | + fn run(ctx: &RuleContext<Self>) -> Self::Signals { |
| 176 | + let node = ctx.query(); |
| 177 | + |
| 178 | + if is_directive(node) { |
| 179 | + return None; |
| 180 | + } |
| 181 | + |
| 182 | + is_disallowed(&node.expression().ok()?).ok()?.then_some(()) |
| 183 | + } |
| 184 | + |
| 185 | + fn diagnostic(ctx: &RuleContext<Self>, _state: &Self::State) -> Option<RuleDiagnostic> { |
| 186 | + let node = ctx.query(); |
| 187 | + Some( |
| 188 | + RuleDiagnostic::new( |
| 189 | + rule_category!(), |
| 190 | + node.range(), |
| 191 | + markup! { |
| 192 | + "Expected an assignment or function call but found an expression instead." |
| 193 | + }, |
| 194 | + ) |
| 195 | + .note(markup! { |
| 196 | + "This expression may be unintentionally unused or it might be a function that you forgot to call." |
| 197 | + }), |
| 198 | + ) |
| 199 | + } |
| 200 | +} |
| 201 | + |
| 202 | +/// Determines if a node should be treated as a directive. |
| 203 | +/// |
| 204 | +/// Only string literals are treated as directives, and only if they are not |
| 205 | +/// preceeded by any non-directive nodes. |
| 206 | +fn is_directive(node: &JsExpressionStatement) -> bool { |
| 207 | + if node |
| 208 | + .syntax() |
| 209 | + .parent() |
| 210 | + .is_some_and(|parent| !is_at_top_level(&parent)) |
| 211 | + { |
| 212 | + return false; |
| 213 | + } |
| 214 | + |
| 215 | + let mut node = Cow::Borrowed(node); |
| 216 | + loop { |
| 217 | + if !looks_like_directive(&node) { |
| 218 | + break false; |
| 219 | + } |
| 220 | + |
| 221 | + let Some(prev_node) = node.syntax().prev_sibling() else { |
| 222 | + break true; |
| 223 | + }; |
| 224 | + match JsExpressionStatement::cast(prev_node) { |
| 225 | + Some(prev_expr) => node = Cow::Owned(prev_expr), |
| 226 | + None => break false, |
| 227 | + } |
| 228 | + } |
| 229 | +} |
| 230 | + |
| 231 | +/// Determines if a node exists at the top-level based on its `parent` node. |
| 232 | +fn is_at_top_level(parent: &JsSyntaxNode) -> bool { |
| 233 | + AnyJsRoot::can_cast(parent.kind()) |
| 234 | + || TsModuleBlock::can_cast(parent.kind()) |
| 235 | + || JsBlockStatement::cast_ref(parent).is_some_and(|block| { |
| 236 | + block |
| 237 | + .syntax() |
| 238 | + .parent() |
| 239 | + .is_some_and(|parent: JsSyntaxNode| AnyJsFunction::can_cast(parent.kind())) |
| 240 | + }) |
| 241 | +} |
| 242 | + |
| 243 | +fn looks_like_directive(node: &JsExpressionStatement) -> bool { |
| 244 | + matches!( |
| 245 | + node.expression(), |
| 246 | + Ok(AnyJsExpression::AnyJsLiteralExpression( |
| 247 | + AnyJsLiteralExpression::JsStringLiteralExpression(_) |
| 248 | + )) |
| 249 | + ) |
| 250 | +} |
| 251 | + |
| 252 | +fn is_disallowed(expr: &AnyJsExpression) -> SyntaxResult<bool> { |
| 253 | + let is_disallowed = match expr { |
| 254 | + AnyJsExpression::AnyJsLiteralExpression(_) |
| 255 | + | AnyJsExpression::JsArrayExpression(_) |
| 256 | + | AnyJsExpression::JsArrowFunctionExpression(_) |
| 257 | + | AnyJsExpression::JsBinaryExpression(_) |
| 258 | + | AnyJsExpression::JsClassExpression(_) |
| 259 | + | AnyJsExpression::JsComputedMemberExpression(_) |
| 260 | + | AnyJsExpression::JsConditionalExpression(_) |
| 261 | + | AnyJsExpression::JsFunctionExpression(_) |
| 262 | + | AnyJsExpression::JsIdentifierExpression(_) |
| 263 | + | AnyJsExpression::JsImportMetaExpression(_) |
| 264 | + | AnyJsExpression::JsInExpression(_) |
| 265 | + | AnyJsExpression::JsInstanceofExpression(_) |
| 266 | + | AnyJsExpression::JsLogicalExpression(_) |
| 267 | + | AnyJsExpression::JsNewTargetExpression(_) |
| 268 | + | AnyJsExpression::JsObjectExpression(_) |
| 269 | + | AnyJsExpression::JsSequenceExpression(_) |
| 270 | + | AnyJsExpression::JsStaticMemberExpression(_) |
| 271 | + | AnyJsExpression::JsSuperExpression(_) |
| 272 | + | AnyJsExpression::JsTemplateExpression(_) |
| 273 | + | AnyJsExpression::JsThisExpression(_) |
| 274 | + | AnyJsExpression::JsxTagExpression(_) => true, |
| 275 | + AnyJsExpression::JsAwaitExpression(_) |
| 276 | + | AnyJsExpression::JsAssignmentExpression(_) |
| 277 | + | AnyJsExpression::JsCallExpression(_) |
| 278 | + | AnyJsExpression::JsImportCallExpression(_) |
| 279 | + | AnyJsExpression::JsNewExpression(_) |
| 280 | + | AnyJsExpression::JsYieldExpression(_) |
| 281 | + | AnyJsExpression::JsPostUpdateExpression(_) |
| 282 | + | AnyJsExpression::JsPreUpdateExpression(_) |
| 283 | + | AnyJsExpression::JsBogusExpression(_) |
| 284 | + | AnyJsExpression::JsMetavariable(_) => false, |
| 285 | + AnyJsExpression::JsParenthesizedExpression(expr) => is_disallowed(&expr.expression()?)?, |
| 286 | + AnyJsExpression::JsUnaryExpression(expr) => match expr.operator()? { |
| 287 | + JsUnaryOperator::BitwiseNot |
| 288 | + | JsUnaryOperator::LogicalNot |
| 289 | + | JsUnaryOperator::Minus |
| 290 | + | JsUnaryOperator::Plus |
| 291 | + | JsUnaryOperator::Typeof => true, |
| 292 | + JsUnaryOperator::Delete | JsUnaryOperator::Void => false, |
| 293 | + }, |
| 294 | + AnyJsExpression::TsAsExpression(expr) => is_disallowed(&expr.expression()?)?, |
| 295 | + AnyJsExpression::TsInstantiationExpression(expr) => is_disallowed(&expr.expression()?)?, |
| 296 | + AnyJsExpression::TsNonNullAssertionExpression(expr) => is_disallowed(&expr.expression()?)?, |
| 297 | + AnyJsExpression::TsSatisfiesExpression(expr) => is_disallowed(&expr.expression()?)?, |
| 298 | + AnyJsExpression::TsTypeAssertionExpression(expr) => is_disallowed(&expr.expression()?)?, |
| 299 | + }; |
| 300 | + Ok(is_disallowed) |
| 301 | +} |
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