"lint/nursery/noUnassignedVariables": "https://biomejs.dev/linter/rules/no-unassigned-variables",

pub mod no_unassigned_variables;

declare_lint_group! { pub Nursery { name : "nursery" , rules : [self :: no_await_in_loop :: NoAwaitInLoop , self :: no_bitwise_operators :: NoBitwiseOperators , self :: no_constant_binary_expression :: NoConstantBinaryExpression , self :: no_destructured_props :: NoDestructuredProps , self :: no_excessive_lines_per_function :: NoExcessiveLinesPerFunction , self :: no_floating_promises :: NoFloatingPromises , self :: no_global_dirname_filename :: NoGlobalDirnameFilename , self :: no_import_cycles :: NoImportCycles , self :: no_nested_component_definitions :: NoNestedComponentDefinitions , self :: no_noninteractive_element_interactions :: NoNoninteractiveElementInteractions , self :: no_process_global :: NoProcessGlobal , self :: no_react_prop_assign :: NoReactPropAssign , self :: no_restricted_elements :: NoRestrictedElements , self :: no_secrets :: NoSecrets , self :: no_shadow :: NoShadow , self :: no_ts_ignore :: NoTsIgnore , self :: no_unassigned_variables :: NoUnassignedVariables , self :: no_unresolved_imports :: NoUnresolvedImports , self :: no_unwanted_polyfillio :: NoUnwantedPolyfillio , self :: no_useless_backref_in_regex :: NoUselessBackrefInRegex , self :: no_useless_escape_in_string :: NoUselessEscapeInString , self :: no_useless_undefined :: NoUselessUndefined , self :: use_adjacent_getter_setter :: UseAdjacentGetterSetter , self :: use_consistent_object_definition :: UseConsistentObjectDefinition , self :: use_consistent_response :: UseConsistentResponse , self :: use_exhaustive_switch_cases :: UseExhaustiveSwitchCases , self :: use_explicit_type :: UseExplicitType , self :: use_exports_last :: UseExportsLast , self :: use_for_component :: UseForComponent , self :: use_google_font_preconnect :: UseGoogleFontPreconnect , self :: use_index_of :: UseIndexOf , self :: use_iterable_callback_return :: UseIterableCallbackReturn , self :: use_json_import_attribute :: UseJsonImportAttribute , self :: use_numeric_separators :: UseNumericSeparators , self :: use_object_spread :: UseObjectSpread , self :: use_parse_int_radix :: UseParseIntRadix , self :: use_readonly_class_properties :: UseReadonlyClassProperties , self :: use_single_js_doc_asterisk :: UseSingleJsDocAsterisk , self :: use_sorted_classes :: UseSortedClasses , self :: use_symbol_description :: UseSymbolDescription , self :: use_unique_element_ids :: UseUniqueElementIds ,] } }

use biome_analyze::{Rule, RuleDiagnostic, RuleSource, context::RuleContext, declare_lint_rule};

use biome_console::markup;

use biome_js_semantic::ReferencesExtensions;

use biome_js_syntax::{

AnyJsBinding, AnyJsBindingPattern, JsIdentifierBinding, JsVariableDeclaration,

JsVariableDeclarationClause, JsVariableDeclarator, JsVariableDeclaratorList,

TsDeclareStatement,

use biome_rowan::AstNode;

use crate::services::semantic::Semantic;

declare_lint_rule! {

/// Disallow `let` or `var` variables that are read but never assigned.

///

/// This rule flags let or var declarations that are never assigned a value but are still read or used in the code.

/// Since these variables will always be undefined, their usage is likely a programming mistake.

///

/// ## Examples

///

/// ### Invalid

///

/// ```js,expect_diagnostic

/// let status;

/// if (status === 'ready') {

/// console.log('Status is ready');

/// }

/// ```

///

/// ```ts,expect_diagnostic

/// let value: number | undefined;

/// console.log(value);

/// ```

///

/// ### Valid

///

/// ```js

/// let message = "hello";

/// console.log(message);

///

/// let user;

/// user = getUser();

/// console.log(user.name);

///

/// let count;

/// count = 0;

/// count++;

/// ```

///

/// ```ts

/// declare let value: number | undefined;

/// console.log(value);

///

/// declare module "my-module" {

/// let value: string;

/// export = value;

/// }

/// ```

///

pub NoUnassignedVariables {

version: "next",

name: "noUnassignedVariables",

language: "js",

sources: &[RuleSource::Eslint("no-unassigned-vars")],

recommended: false,

}

impl Rule for NoUnassignedVariables {

type Query = Semantic<JsVariableDeclarator>;

type State = JsIdentifierBinding;

type Signals = Option<Self::State>;

type Options = ();

fn run(ctx: &RuleContext<Self>) -> Self::Signals {

let declarator = ctx.query();

let Ok(AnyJsBindingPattern::AnyJsBinding(AnyJsBinding::JsIdentifierBinding(id))) =

declarator.id()

else {

return None;

};

let declaration = declarator

.parent::<JsVariableDeclaratorList>()?

.parent::<JsVariableDeclaration>()?;

if declaration.is_const() || declarator.initializer().is_some() {

return None;

}

// e.g. `declare let value: number | undefined;`

if declaration

.parent::<JsVariableDeclarationClause>()

.is_some_and(|clause| clause.parent::<TsDeclareStatement>().is_some())

{

return None;

}

// check if the variable is declared in a function or module

// e.g. `declare module "my-module" { let value: string; export = value; }`

if is_inside_ts_declare_statement(&declaration) {

return None;

}

let model = ctx.model();

if id.all_writes(model).next().is_some() {

return None;

}

if id.all_reads(model).next().is_some() {

return Some(id);

}

None

}

fn diagnostic(ctx: &RuleContext<Self>, state: &Self::State) -> Option<RuleDiagnostic> {

// let state = state.to_trimmed_text();

let node = ctx.query();

let name_token = state.name_token().ok()?;

let name = name_token.text_trimmed();

Some(

RuleDiagnostic::new(

rule_category!(),

node.range(),

markup! {

"The variable '"<Emphasis>{name}</Emphasis>"' is declared but never assigned a value."

},

)

.note(markup! {

"Variable declared without assignment. Either assign a value or remove the declaration."

}),

)

}

fn is_inside_ts_declare_statement(node: &JsVariableDeclaration) -> bool {

node.syntax()

.ancestors()

.skip(1)

.any(|ancestor| TsDeclareStatement::can_cast(ancestor.kind()))

let status;

if (status === 'ready') {

console.log('Ready!');

let user;

function test() {

let error;

return error || "Unknown error";

let options;

const { debug } = options || {};

let flag;

while (!flag) {

// Do something...

let config;

function init() {

return config?.enabled;

source: crates/biome_js_analyze/tests/spec_tests.rs

expression: invalid.js

# Input

let value: number | undefined;