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feat(31388): Destructuring array, ability to explicitly tell the variable is unused #41378

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Merged
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Jan 12, 2021
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feat(31388): Destructuring array, ability to explicitly tell the variable is unused #41378

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15 changes: 9 additions & 6 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -33362,13 +33362,16 @@ namespace ts {
}

function isValidUnusedLocalDeclaration(declaration: Declaration): boolean {
if (isBindingElement(declaration) && isIdentifierThatStartsWithUnderscore(declaration.name)) {
return !!findAncestor(declaration.parent, ancestor =>
isArrayBindingPattern(ancestor) || isVariableDeclaration(ancestor) || isVariableDeclarationList(ancestor) ? false :
isForOfStatement(ancestor) ? true : "quit"
);
if (isBindingElement(declaration)) {
if (isObjectBindingPattern(declaration.parent)) {
/**
* ignore starts with underscore names _
* const { a: _a } = { a: 1 }
*/
return !!(declaration.propertyName && isIdentifierThatStartsWithUnderscore(declaration.name));
}
return isIdentifierThatStartsWithUnderscore(declaration.name);
}

return isAmbientModule(declaration) ||
(isVariableDeclaration(declaration) && isForInOrOfStatement(declaration.parent.parent) || isImportedDeclaration(declaration)) && isIdentifierThatStartsWithUnderscore(declaration.name!);
}
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145 changes: 145 additions & 0 deletions tests/baselines/reference/unusedVariablesWithUnderscoreInBindingElement.errors.txt
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@@ -0,0 +1,145 @@
tests/cases/compiler/unusedVariablesWithUnderscoreInBindingElement.ts(12,17): error TS6133: 'b1' is declared but its value is never read.
tests/cases/compiler/unusedVariablesWithUnderscoreInBindingElement.ts(13,12): error TS6133: 'a2' is declared but its value is never read.
tests/cases/compiler/unusedVariablesWithUnderscoreInBindingElement.ts(14,12): error TS6133: 'a3' is declared but its value is never read.
tests/cases/compiler/unusedVariablesWithUnderscoreInBindingElement.ts(14,16): error TS6133: 'b3' is declared but its value is never read.
tests/cases/compiler/unusedVariablesWithUnderscoreInBindingElement.ts(23,12): error TS6133: 'a3' is declared but its value is never read.
tests/cases/compiler/unusedVariablesWithUnderscoreInBindingElement.ts(23,18): error TS6133: 'b3' is declared but its value is never read.
tests/cases/compiler/unusedVariablesWithUnderscoreInBindingElement.ts(23,22): error TS6133: 'c3' is declared but its value is never read.
tests/cases/compiler/unusedVariablesWithUnderscoreInBindingElement.ts(23,28): error TS6133: 'd3' is declared but its value is never read.
tests/cases/compiler/unusedVariablesWithUnderscoreInBindingElement.ts(23,32): error TS6133: 'e3' is declared but its value is never read.
tests/cases/compiler/unusedVariablesWithUnderscoreInBindingElement.ts(37,22): error TS6133: 'b1' is declared but its value is never read.
tests/cases/compiler/unusedVariablesWithUnderscoreInBindingElement.ts(38,13): error TS6133: 'a2' is declared but its value is never read.
tests/cases/compiler/unusedVariablesWithUnderscoreInBindingElement.ts(39,11): error TS6198: All destructured elements are unused.
tests/cases/compiler/unusedVariablesWithUnderscoreInBindingElement.ts(68,9): error TS6133: 'a3' is declared but its value is never read.
tests/cases/compiler/unusedVariablesWithUnderscoreInBindingElement.ts(70,18): error TS6198: All destructured elements are unused.
tests/cases/compiler/unusedVariablesWithUnderscoreInBindingElement.ts(74,9): error TS6133: 'c3' is declared but its value is never read.
tests/cases/compiler/unusedVariablesWithUnderscoreInBindingElement.ts(75,9): error TS6133: 'd3' is declared but its value is never read.
tests/cases/compiler/unusedVariablesWithUnderscoreInBindingElement.ts(81,11): error TS6198: All destructured elements are unused.


==== tests/cases/compiler/unusedVariablesWithUnderscoreInBindingElement.ts (17 errors) ====
function t1() {
const [_a1, b1] = [1, 2];
console.log(b1);

const [a2, _b2] = [1, 2];
console.log(a2);

const [_a3, _b3] = [1, 2];
}

function t2() {
const [_a1, b1] = [1, 2];
~~
!!! error TS6133: 'b1' is declared but its value is never read.
const [a2, _b2] = [1, 2];
~~
!!! error TS6133: 'a2' is declared but its value is never read.
const [a3, b3] = [1, 2];
~~
!!! error TS6133: 'a3' is declared but its value is never read.
~~
!!! error TS6133: 'b3' is declared but its value is never read.
}

function t3() {
const [_a1, [[_b1, c1]], d1, _e1] = [1, [[2, 3]], 4, 5];
console.log(c1, d1);

const [_a2, [[_b2, _c2]], _d2, _e2] = [1, [[2, 3]], 4, 5];

const [a3, [[b3, c3]], d3, e3] = [1, [[2, 3]], 4, 5];
~~
!!! error TS6133: 'a3' is declared but its value is never read.
~~
!!! error TS6133: 'b3' is declared but its value is never read.
~~
!!! error TS6133: 'c3' is declared but its value is never read.
~~
!!! error TS6133: 'd3' is declared but its value is never read.
~~
!!! error TS6133: 'e3' is declared but its value is never read.
}

function t4() {
const { a1: _a1, b1 } = { a1: 1, b1: 1 };
console.log(b1);

const { a2, b2: _b2 } = { a2: 1, b2: 1 };
console.log(a2);

const { a3: _a3, b3: _b3 } = { a3: 1, b3: 1 };
}

function t5() {
const { a1: _a1, b1 } = { a1: 1, b1: 1 };
~~
!!! error TS6133: 'b1' is declared but its value is never read.
const { a2, b2: _b2 } = { a2: 1, b2: 1 };
~~
!!! error TS6133: 'a2' is declared but its value is never read.
const { a3, b3 } = { a3: 1, b3: 1 };
~~~~~~~~~~
!!! error TS6198: All destructured elements are unused.
}

function t6() {
const {
a1: _a1,
b1: {
b11: {
b111: _b111,
b112
}
},
c1,
d1: _d1
} = { a1: 1, b1: { b11: { b111: 1, b112: 1 } }, c1: 1, d1: 1 };
console.log(b112, c1);

const {
a2: _a2,
b2: {
b21: {
b211: _b211, b212: _b212
}
},
c2: _c2,
d2: _d2
} = { a2: 1, b2: { b21: { b211: 1, b212: 1 } }, c2: 1, d2: 1 };

const {
a3,
~~
!!! error TS6133: 'a3' is declared but its value is never read.
b3: {
b31: {
~
b311, b312
~~~~~~~~~~~~~~~~~~~~~~~~~~
}
~~~~~~~~~~~~~
!!! error TS6198: All destructured elements are unused.
},
c3,
~~
!!! error TS6133: 'c3' is declared but its value is never read.
d3
~~
!!! error TS6133: 'd3' is declared but its value is never read.
} = { a3: 1, b3: { b31: { b311: 1, b312: 1 } }, c3: 1, d3: 1 };
}

function t7() {
// error
const { _a1, _b1 } = { _a1: 1, _b1: 1 };
~~~~~~~~~~~~
!!! error TS6198: All destructured elements are unused.

// ok
const { a2: _a2, b2: _b2 } = { a2: 1, b2: 1 };

// ok
const { _a3: _ignoreA3, _b3: _ignoreB3 } = { _a3: 1, _b3: 1 };
}

136 changes: 136 additions & 0 deletions tests/baselines/reference/unusedVariablesWithUnderscoreInBindingElement.js
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//// [unusedVariablesWithUnderscoreInBindingElement.ts]
function t1() {
const [_a1, b1] = [1, 2];
console.log(b1);

const [a2, _b2] = [1, 2];
console.log(a2);

const [_a3, _b3] = [1, 2];
}

function t2() {
const [_a1, b1] = [1, 2];
const [a2, _b2] = [1, 2];
const [a3, b3] = [1, 2];
}

function t3() {
const [_a1, [[_b1, c1]], d1, _e1] = [1, [[2, 3]], 4, 5];
console.log(c1, d1);

const [_a2, [[_b2, _c2]], _d2, _e2] = [1, [[2, 3]], 4, 5];

const [a3, [[b3, c3]], d3, e3] = [1, [[2, 3]], 4, 5];
}

function t4() {
const { a1: _a1, b1 } = { a1: 1, b1: 1 };
console.log(b1);

const { a2, b2: _b2 } = { a2: 1, b2: 1 };
console.log(a2);

const { a3: _a3, b3: _b3 } = { a3: 1, b3: 1 };
}

function t5() {
const { a1: _a1, b1 } = { a1: 1, b1: 1 };
const { a2, b2: _b2 } = { a2: 1, b2: 1 };
const { a3, b3 } = { a3: 1, b3: 1 };
}

function t6() {
const {
a1: _a1,
b1: {
b11: {
b111: _b111,
b112
}
},
c1,
d1: _d1
} = { a1: 1, b1: { b11: { b111: 1, b112: 1 } }, c1: 1, d1: 1 };
console.log(b112, c1);

const {
a2: _a2,
b2: {
b21: {
b211: _b211, b212: _b212
}
},
c2: _c2,
d2: _d2
} = { a2: 1, b2: { b21: { b211: 1, b212: 1 } }, c2: 1, d2: 1 };

const {
a3,
b3: {
b31: {
b311, b312
}
},
c3,
d3
} = { a3: 1, b3: { b31: { b311: 1, b312: 1 } }, c3: 1, d3: 1 };
}

function t7() {
// error
const { _a1, _b1 } = { _a1: 1, _b1: 1 };

// ok
const { a2: _a2, b2: _b2 } = { a2: 1, b2: 1 };

// ok
const { _a3: _ignoreA3, _b3: _ignoreB3 } = { _a3: 1, _b3: 1 };
}


//// [unusedVariablesWithUnderscoreInBindingElement.js]
function t1() {
var _a = [1, 2], _a1 = _a[0], b1 = _a[1];
console.log(b1);
var _b = [1, 2], a2 = _b[0], _b2 = _b[1];
console.log(a2);
var _c = [1, 2], _a3 = _c[0], _b3 = _c[1];
}
function t2() {
var _a = [1, 2], _a1 = _a[0], b1 = _a[1];
var _b = [1, 2], a2 = _b[0], _b2 = _b[1];
var _c = [1, 2], a3 = _c[0], b3 = _c[1];
}
function t3() {
var _a = [1, [[2, 3]], 4, 5], _a1 = _a[0], _b = _a[1][0], _b1 = _b[0], c1 = _b[1], d1 = _a[2], _e1 = _a[3];
console.log(c1, d1);
var _c = [1, [[2, 3]], 4, 5], _a2 = _c[0], _d = _c[1][0], _b2 = _d[0], _c2 = _d[1], _d2 = _c[2], _e2 = _c[3];
var _e = [1, [[2, 3]], 4, 5], a3 = _e[0], _f = _e[1][0], b3 = _f[0], c3 = _f[1], d3 = _e[2], e3 = _e[3];
}
function t4() {
var _a = { a1: 1, b1: 1 }, _a1 = _a.a1, b1 = _a.b1;
console.log(b1);
var _b = { a2: 1, b2: 1 }, a2 = _b.a2, _b2 = _b.b2;
console.log(a2);
var _c = { a3: 1, b3: 1 }, _a3 = _c.a3, _b3 = _c.b3;
}
function t5() {
var _a = { a1: 1, b1: 1 }, _a1 = _a.a1, b1 = _a.b1;
var _b = { a2: 1, b2: 1 }, a2 = _b.a2, _b2 = _b.b2;
var _c = { a3: 1, b3: 1 }, a3 = _c.a3, b3 = _c.b3;
}
function t6() {
var _a = { a1: 1, b1: { b11: { b111: 1, b112: 1 } }, c1: 1, d1: 1 }, _a1 = _a.a1, _b = _a.b1.b11, _b111 = _b.b111, b112 = _b.b112, c1 = _a.c1, _d1 = _a.d1;
console.log(b112, c1);
var _c = { a2: 1, b2: { b21: { b211: 1, b212: 1 } }, c2: 1, d2: 1 }, _a2 = _c.a2, _d = _c.b2.b21, _b211 = _d.b211, _b212 = _d.b212, _c2 = _c.c2, _d2 = _c.d2;
var _e = { a3: 1, b3: { b31: { b311: 1, b312: 1 } }, c3: 1, d3: 1 }, a3 = _e.a3, _f = _e.b3.b31, b311 = _f.b311, b312 = _f.b312, c3 = _e.c3, d3 = _e.d3;
}
function t7() {
// error
var _a = { _a1: 1, _b1: 1 }, _a1 = _a._a1, _b1 = _a._b1;
// ok
var _b = { a2: 1, b2: 1 }, _a2 = _b.a2, _b2 = _b.b2;
// ok
var _c = { _a3: 1, _b3: 1 }, _ignoreA3 = _c._a3, _ignoreB3 = _c._b3;
}
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