feat: support TypeScript syntax in no-use-before-define (#19566)

Tanujkanti4441 · web-flow · commit bfd0e7a39535 · 2025-05-29T12:48:55.000+05:30
diff --git a/docs/src/rules/no-use-before-define.md b/docs/src/rules/no-use-before-define.md
@@ -157,6 +157,18 @@ export { foo };
   These references are safe even if the variables are declared later in the code.
   Default is `false`.
 
+This rule additionally supports TypeScript type syntax. The following options enable checking for the references to `type`, `interface` and `enum` declarations:
+
+* `enums` (`boolean`) -
+  If it is `true`, the rule warns every reference to an `enum` before it is defined.
+  Defult is `true`.
+* `typedefs` (`boolean`) -
+  If it is `true`, this rule warns every reference to a type `alias` or `interface` before its declaration. If `false`, the rule allows using type `alias`es and `interface`s before they are defined.
+  Default is `true`.
+* `ignoreTypeReferences` (`boolean`) -
+  If it is `true`, rule will ignore all type references, such as in type annotations and assertions.
+  Default is `true`.
+
 This rule accepts `"nofunc"` string as an option.
 `"nofunc"` is the same as `{ "functions": false, "classes": true, "variables": true, "allowNamedExports": false }`.
 
@@ -350,3 +362,129 @@ const d = 1;
 ```
 
 :::
+
+### enums (TypeScript only)
+
+Examples of **incorrect** code for the `{ "enums": true }` option:
+
+::: incorrect
+
+```ts
+/*eslint no-use-before-define: ["error", { "enums": true }]*/
+
+const x = Foo.FOO;
+
+enum Foo {
+  FOO,
+}
+```
+
+:::
+
+Examples of **correct** code for the `{ "enums": true }` option:
+
+::: correct
+
+```ts
+/*eslint no-use-before-define: ["error", { "enums": true }]*/
+
+enum Foo {
+  FOO,
+}
+
+const x = Foo.FOO;
+```
+
+:::
+
+### typedefs (TypeScript only)
+
+Examples of **incorrect** code for the `{ "enums": true }` with `{ "ignoreTypeReferences": false }` option:
+
+::: incorrect
+
+```ts
+/*eslint no-use-before-define: ["error", { "typedefs": true, "ignoreTypeReferences": false }]*/
+
+let myVar: StringOrNumber;
+
+type StringOrNumber = string | number;
+
+const x: Foo = {};
+
+interface Foo {}
+```
+
+:::
+
+Examples of **correct** code for the `{ "typedefs": true }` with `{ "ignoreTypeReferences": false }` option:
+
+::: correct
+
+```ts
+/*eslint no-use-before-define: ["error", { "typedefs": true, "ignoreTypeReferences": false }]*/
+
+type StringOrNumber = string | number;
+
+let myVar: StringOrNumber;
+
+interface Foo {}
+
+const x: Foo = {};
+```
+
+:::
+
+### ignoreTypeReferences (TypeScript only)
+
+Examples of **incorrect** code for the `{ "ignoreTypeReferences": false }` option:
+
+::: incorrect
+
+```ts
+/*eslint no-use-before-define: ["error", { "ignoreTypeReferences": false }]*/
+
+let var1: StringOrNumber;
+
+type StringOrNumber = string | number;
+
+let var2: Enum;
+
+enum Enum {}
+```
+
+:::
+
+Examples of **correct** code for the `{ "ignoreTypeReferences": false }` option:
+
+::: correct
+
+```ts
+/*eslint no-use-before-define: ["error", { "ignoreTypeReferences": false }]*/
+
+type StringOrNumber = string | number;
+
+let myVar: StringOrNumber;
+
+enum Enum {}
+
+let var2: Enum;
+```
+
+Examples of **correct** code for the `{ "ignoreTypeReferences": false }` with `{ "typedefs": false }` option:
+
+::: correct
+
+```ts
+/*eslint no-use-before-define: ["error", { "ignoreTypeReferences": false, "typedefs": false, }]*/
+
+let myVar: StringOrNumber;
+
+type StringOrNumber = string | number;
+
+const x: Foo = {};
+
+interface Foo {}
+```
+
+:::
diff --git a/lib/rules/no-use-before-define.js b/lib/rules/no-use-before-define.js
@@ -30,6 +30,9 @@ function parseOptions(options) {
 		classes: true,
 		variables: true,
 		allowNamedExports: false,
+		enums: true,
+		typedefs: true,
+		ignoreTypeReferences: true,
 	};
 }
 
@@ -208,6 +211,57 @@ function isEvaluatedDuringInitialization(reference) {
 	return false;
 }
 
+/**
+ * check whether the reference contains a type query.
+ * @param {ASTNode} node Identifier node to check.
+ * @returns {boolean} true if reference contains type query.
+ */
+function referenceContainsTypeQuery(node) {
+	switch (node.type) {
+		case "TSTypeQuery":
+			return true;
+
+		case "TSQualifiedName":
+		case "Identifier":
+			return referenceContainsTypeQuery(node.parent);
+
+		default:
+			// if we find a different node, there's no chance that we're in a TSTypeQuery
+			return false;
+	}
+}
+
+/**
+ * Decorators are transpiled such that the decorator is placed after the class declaration
+ * So it is considered safe
+ * @param {Variable} variable The variable to check.
+ * @param {Reference} reference The reference to check.
+ * @returns {boolean} `true` if the reference is in a class decorator.
+ */
+function isClassRefInClassDecorator(variable, reference) {
+	if (variable.defs[0].type !== "ClassName") {
+		return false;
+	}
+
+	if (
+		!variable.defs[0].node.decorators ||
+		variable.defs[0].node.decorators.length === 0
+	) {
+		return false;
+	}
+
+	for (const deco of variable.defs[0].node.decorators) {
+		if (
+			reference.identifier.range[0] >= deco.range[0] &&
+			reference.identifier.range[1] <= deco.range[1]
+		) {
+			return true;
+		}
+	}
+
+	return false;
+}
+
 //------------------------------------------------------------------------------
 // Rule Definition
 //------------------------------------------------------------------------------
@@ -237,6 +291,9 @@ module.exports = {
 							classes: { type: "boolean" },
 							variables: { type: "boolean" },
 							allowNamedExports: { type: "boolean" },
+							enums: { type: "boolean" },
+							typedefs: { type: "boolean" },
+							ignoreTypeReferences: { type: "boolean" },
 						},
 						additionalProperties: false,
 					},
@@ -250,6 +307,9 @@ module.exports = {
 				functions: true,
 				variables: true,
 				allowNamedExports: false,
+				enums: true,
+				typedefs: true,
+				ignoreTypeReferences: true,
 			},
 		],
 
@@ -310,6 +370,41 @@ module.exports = {
 				return false;
 			}
 
+			if (!options.enums && definitionType === "TSEnumName") {
+				return false;
+			}
+
+			if (!options.typedefs && definitionType === "Type") {
+				return false;
+			}
+
+			if (
+				options.ignoreTypeReferences &&
+				(referenceContainsTypeQuery(identifier) ||
+					identifier.parent.type === "TSTypeReference")
+			) {
+				return false;
+			}
+
+			// skip nested namespace aliases as variable references
+			if (identifier.parent.type === "TSQualifiedName") {
+				let currentNode = identifier.parent;
+
+				while (currentNode.type === "TSQualifiedName") {
+					currentNode = currentNode.left;
+				}
+
+				if (currentNode === identifier) {
+					return true;
+				}
+
+				return false;
+			}
+
+			if (isClassRefInClassDecorator(variable, reference)) {
+				return false;
+			}
+
 			return true;
 		}
 
@@ -326,7 +421,8 @@ module.exports = {
 				if (
 					reference.identifier.range[1] <
 						definitionIdentifier.range[1] ||
-					isEvaluatedDuringInitialization(reference)
+					(isEvaluatedDuringInitialization(reference) &&
+						reference.identifier.parent.type !== "TSTypeReference")
 				) {
 					context.report({
 						node: reference.identifier,
diff --git a/lib/types/rules.d.ts b/lib/types/rules.d.ts
@@ -4090,6 +4090,18 @@ export interface ESLintRules extends Linter.RulesRecord {
 					 * @default false
 					 */
 					allowNamedExports: boolean;
+					/**
+					 * @default true
+					 */
+					enums: boolean;
+					/**
+					 * @default true
+					 */
+					typedefs: boolean;
+					/**
+					 * @default true
+					 */
+					ignoreTypeReferences: boolean;
 			  }>
 			| "nofunc",
 		]
diff --git a/tests/lib/rules/no-use-before-define.js b/tests/lib/rules/no-use-before-define.js
