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Fix: prefer-const false negative about eslintUsed (fixes #5837) #6971

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merged 1 commit into from
Aug 26, 2016
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Fix: prefer-const false negative about eslintUsed (fixes #5837) #6971

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9 changes: 7 additions & 2 deletions lib/rules/prefer-const.js
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Original file line number Diff line number Diff line change
Expand Up @@ -70,9 +70,14 @@ function canBecomeVariableDeclaration(identifier) {
*
* If the variable should not change to const, this function returns null.
* - If the variable is reassigned.
* - If the variable is never initialized and assigned.
* - If the variable is never initialized nor assigned.
* - If the variable is initialized in a different scope from the declaration.
* - If the unique assignment of the variable cannot change to a declaration.
* e.g. `if (a) b = 1` / `return (b = 1)`
* - If the variable is declared in the global scope and `eslintUsed` is `true`.
* `/*exported foo` directive comment makes such variables. This rule does not
* warn such variables because this rule cannot distinguish whether the
* exported variables are reassigned or not.
*
* @param {escope.Variable} variable - A variable to get.
* @param {boolean} ignoreReadBeforeAssign -
Expand All @@ -82,7 +87,7 @@ function canBecomeVariableDeclaration(identifier) {
* Otherwise, null.
*/
function getIdentifierIfShouldBeConst(variable, ignoreReadBeforeAssign) {
if (variable.eslintUsed) {
if (variable.eslintUsed && variable.scope.type === "global") {
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Can you add a comment in the JSDoc to explain why you're checking for global scope?

return null;
}

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27 changes: 25 additions & 2 deletions tests/lib/rules/prefer-const.js
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Expand Up @@ -18,6 +18,12 @@ const rule = require("../../../lib/rules/prefer-const"),

const ruleTester = new RuleTester();

ruleTester.defineRule("use-x", context => ({
VariableDeclaration() {
context.markVariableAsUsed("x");
}
}));

ruleTester.run("prefer-const", rule, {
valid: [
{ code: "var x = 0;" },
Expand Down Expand Up @@ -63,6 +69,7 @@ ruleTester.run("prefer-const", rule, {
parserOptions: { ecmaVersion: 6 }
},
{ code: "/*exported a*/ let a; function init() { a = foo(); }", parserOptions: { ecmaVersion: 6 } },
{ code: "/*exported a*/ let a = 1", parserOptions: { ecmaVersion: 6 } },
{ code: "let a; if (true) a = 0; foo(a);", parserOptions: { ecmaVersion: 6 } },

// The assignment is located in a different scope.
Expand All @@ -89,7 +96,9 @@ ruleTester.run("prefer-const", rule, {
code: "let x; function foo() { bar(x); } x = 0;",
options: [{ignoreReadBeforeAssign: true}],
parserOptions: {ecmaVersion: 6}
}
},


],
invalid: [
{
Expand Down Expand Up @@ -336,6 +345,20 @@ ruleTester.run("prefer-const", rule, {
output: "let x; function foo() { bar(x); } x = 0;",
parserOptions: {ecmaVersion: 6},
errors: [{ message: "'x' is never reassigned. Use 'const' instead.", type: "Identifier", column: 5}]
}
},

// https://github.com/eslint/eslint/issues/5837
{
code: "/*eslint use-x:error*/ let x = 1",
output: "/*eslint use-x:error*/ const x = 1",
parserOptions: {ecmaVersion: 6, ecmaFeatures: {globalReturn: true}},
errors: [{ message: "'x' is never reassigned. Use 'const' instead.", type: "Identifier"}]
},
{
code: "/*eslint use-x:error*/ { let x = 1 }",
output: "/*eslint use-x:error*/ { const x = 1 }",
parserOptions: {ecmaVersion: 6},
errors: [{ message: "'x' is never reassigned. Use 'const' instead.", type: "Identifier"}]
},
]
});