feat(31388): allow variables starting with an underscore in array des…

…tructuring

src/compiler/checker.ts

@@ -33363,10 +33363,7 @@ 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"
-                );
+                return isArrayBindingPattern(declaration.parent);
             }
 
             return isAmbientModule(declaration) ||

tests/baselines/reference/unusedVariablesWithUnderscoreInDestructuringArray1.js

@@ -0,0 +1,20 @@
+//// [unusedVariablesWithUnderscoreInDestructuringArray1.ts]
+function test() {
+    const [_a1, b1] = [1, 2];
+    console.log(b1);
+
+    const [a2, _b2] = [1, 2];
+    console.log(a2);
+
+    const [_a3, _b3] = [1, 2];
+}
+
+
+//// [unusedVariablesWithUnderscoreInDestructuringArray1.js]
+function test() {
+    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];
+}

tests/baselines/reference/unusedVariablesWithUnderscoreInDestructuringArray1.symbols

@@ -0,0 +1,29 @@
+=== tests/cases/compiler/unusedVariablesWithUnderscoreInDestructuringArray1.ts ===
+function test() {
+>test : Symbol(test, Decl(unusedVariablesWithUnderscoreInDestructuringArray1.ts, 0, 0))
+
+    const [_a1, b1] = [1, 2];
+>_a1 : Symbol(_a1, Decl(unusedVariablesWithUnderscoreInDestructuringArray1.ts, 1, 11))
+>b1 : Symbol(b1, Decl(unusedVariablesWithUnderscoreInDestructuringArray1.ts, 1, 15))
+
+    console.log(b1);
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>b1 : Symbol(b1, Decl(unusedVariablesWithUnderscoreInDestructuringArray1.ts, 1, 15))
+
+    const [a2, _b2] = [1, 2];
+>a2 : Symbol(a2, Decl(unusedVariablesWithUnderscoreInDestructuringArray1.ts, 4, 11))
+>_b2 : Symbol(_b2, Decl(unusedVariablesWithUnderscoreInDestructuringArray1.ts, 4, 14))
+
+    console.log(a2);
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>a2 : Symbol(a2, Decl(unusedVariablesWithUnderscoreInDestructuringArray1.ts, 4, 11))
+
+    const [_a3, _b3] = [1, 2];
+>_a3 : Symbol(_a3, Decl(unusedVariablesWithUnderscoreInDestructuringArray1.ts, 7, 11))
+>_b3 : Symbol(_b3, Decl(unusedVariablesWithUnderscoreInDestructuringArray1.ts, 7, 15))
+}
+

tests/baselines/reference/unusedVariablesWithUnderscoreInDestructuringArray1.types

@@ -0,0 +1,40 @@
+=== tests/cases/compiler/unusedVariablesWithUnderscoreInDestructuringArray1.ts ===
+function test() {
+>test : () => void
+
+    const [_a1, b1] = [1, 2];
+>_a1 : number
+>b1 : number
+>[1, 2] : [number, number]
+>1 : 1
+>2 : 2
+
+    console.log(b1);
+>console.log(b1) : void
+>console.log : (...data: any[]) => void
+>console : Console
+>log : (...data: any[]) => void
+>b1 : number
+
+    const [a2, _b2] = [1, 2];
+>a2 : number
+>_b2 : number
+>[1, 2] : [number, number]
+>1 : 1
+>2 : 2
+
+    console.log(a2);
+>console.log(a2) : void
+>console.log : (...data: any[]) => void
+>console : Console
+>log : (...data: any[]) => void
+>a2 : number
+
+    const [_a3, _b3] = [1, 2];
+>_a3 : number
+>_b3 : number
+>[1, 2] : [number, number]
+>1 : 1
+>2 : 2
+}
+

tests/baselines/reference/unusedVariablesWithUnderscoreInDestructuringArray2.errors.txt

@@ -0,0 +1,21 @@
+tests/cases/compiler/unusedVariablesWithUnderscoreInDestructuringArray2.ts(2,17): error TS6133: 'b1' is declared but its value is never read.
+tests/cases/compiler/unusedVariablesWithUnderscoreInDestructuringArray2.ts(3,12): error TS6133: 'a2' is declared but its value is never read.
+tests/cases/compiler/unusedVariablesWithUnderscoreInDestructuringArray2.ts(4,12): error TS6133: 'a3' is declared but its value is never read.
+tests/cases/compiler/unusedVariablesWithUnderscoreInDestructuringArray2.ts(4,16): error TS6133: 'b3' is declared but its value is never read.
+
+
+==== tests/cases/compiler/unusedVariablesWithUnderscoreInDestructuringArray2.ts (4 errors) ====
+    function f() {
+        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.
+    }
+

tests/baselines/reference/unusedVariablesWithUnderscoreInDestructuringArray2.js

@@ -0,0 +1,14 @@
+//// [unusedVariablesWithUnderscoreInDestructuringArray2.ts]
+function f() {
+    const [_a1, b1] = [1, 2];
+    const [a2, _b2] = [1, 2];
+    const [a3, b3] = [1, 2];
+}
+
+
+//// [unusedVariablesWithUnderscoreInDestructuringArray2.js]
+function f() {
+    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];
+}

tests/baselines/reference/unusedVariablesWithUnderscoreInDestructuringArray2.symbols

@@ -0,0 +1,17 @@
+=== tests/cases/compiler/unusedVariablesWithUnderscoreInDestructuringArray2.ts ===
+function f() {
+>f : Symbol(f, Decl(unusedVariablesWithUnderscoreInDestructuringArray2.ts, 0, 0))
+
+    const [_a1, b1] = [1, 2];
+>_a1 : Symbol(_a1, Decl(unusedVariablesWithUnderscoreInDestructuringArray2.ts, 1, 11))
+>b1 : Symbol(b1, Decl(unusedVariablesWithUnderscoreInDestructuringArray2.ts, 1, 15))
+
+    const [a2, _b2] = [1, 2];
+>a2 : Symbol(a2, Decl(unusedVariablesWithUnderscoreInDestructuringArray2.ts, 2, 11))
+>_b2 : Symbol(_b2, Decl(unusedVariablesWithUnderscoreInDestructuringArray2.ts, 2, 14))
+
+    const [a3, b3] = [1, 2];
+>a3 : Symbol(a3, Decl(unusedVariablesWithUnderscoreInDestructuringArray2.ts, 3, 11))
+>b3 : Symbol(b3, Decl(unusedVariablesWithUnderscoreInDestructuringArray2.ts, 3, 14))
+}
+

tests/baselines/reference/unusedVariablesWithUnderscoreInDestructuringArray2.types

@@ -0,0 +1,26 @@
+=== tests/cases/compiler/unusedVariablesWithUnderscoreInDestructuringArray2.ts ===
+function f() {
+>f : () => void
+
+    const [_a1, b1] = [1, 2];
+>_a1 : number
+>b1 : number
+>[1, 2] : [number, number]
+>1 : 1
+>2 : 2
+
+    const [a2, _b2] = [1, 2];
+>a2 : number
+>_b2 : number
+>[1, 2] : [number, number]
+>1 : 1
+>2 : 2
+
+    const [a3, b3] = [1, 2];
+>a3 : number
+>b3 : number
+>[1, 2] : [number, number]
+>1 : 1
+>2 : 2
+}
+

tests/baselines/reference/unusedVariablesWithUnderscoreInForOfLoop1.js

@@ -1,22 +1,28 @@
 //// [unusedVariablesWithUnderscoreInForOfLoop1.ts]
 function f() {
-    for (const [_a, b] of [['key', 1]]) {}
+    for (const [_a, b] of [['key', 1]]) {
+        console.log(b);
+    }
 
-    for (const [a, _b] of [['key', 1]]) {}
+    for (const [a, _b] of [['key', 1]]) {
+        console.log(a);
+    }
 
-    for (const [a, b] of [['key', 1]]) {}
+    for (const [_a, _b] of [['key', 1]]) {}
 }
 
 
 //// [unusedVariablesWithUnderscoreInForOfLoop1.js]
 function f() {
     for (var _i = 0, _c = [['key', 1]]; _i < _c.length; _i++) {
         var _d = _c[_i], _a = _d[0], b = _d[1];
+        console.log(b);
     }
     for (var _e = 0, _f = [['key', 1]]; _e < _f.length; _e++) {
         var _g = _f[_e], a = _g[0], _b = _g[1];
+        console.log(a);
     }
     for (var _h = 0, _j = [['key', 1]]; _h < _j.length; _h++) {
-        var _k = _j[_h], a = _k[0], b = _k[1];
+        var _k = _j[_h], _a = _k[0], _b = _k[1];
     }
 }

tests/baselines/reference/unusedVariablesWithUnderscoreInForOfLoop1.symbols

@@ -2,16 +2,30 @@
 function f() {
 >f : Symbol(f, Decl(unusedVariablesWithUnderscoreInForOfLoop1.ts, 0, 0))
 
-    for (const [_a, b] of [['key', 1]]) {}
+    for (const [_a, b] of [['key', 1]]) {
 >_a : Symbol(_a, Decl(unusedVariablesWithUnderscoreInForOfLoop1.ts, 1, 16))
 >b : Symbol(b, Decl(unusedVariablesWithUnderscoreInForOfLoop1.ts, 1, 19))
 
-    for (const [a, _b] of [['key', 1]]) {}
->a : Symbol(a, Decl(unusedVariablesWithUnderscoreInForOfLoop1.ts, 3, 16))
->_b : Symbol(_b, Decl(unusedVariablesWithUnderscoreInForOfLoop1.ts, 3, 18))
+        console.log(b);
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>b : Symbol(b, Decl(unusedVariablesWithUnderscoreInForOfLoop1.ts, 1, 19))
+    }
+
+    for (const [a, _b] of [['key', 1]]) {
+>a : Symbol(a, Decl(unusedVariablesWithUnderscoreInForOfLoop1.ts, 5, 16))
+>_b : Symbol(_b, Decl(unusedVariablesWithUnderscoreInForOfLoop1.ts, 5, 18))
 
-    for (const [a, b] of [['key', 1]]) {}
+        console.log(a);
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
 >a : Symbol(a, Decl(unusedVariablesWithUnderscoreInForOfLoop1.ts, 5, 16))
->b : Symbol(b, Decl(unusedVariablesWithUnderscoreInForOfLoop1.ts, 5, 18))
+    }
+
+    for (const [_a, _b] of [['key', 1]]) {}
+>_a : Symbol(_a, Decl(unusedVariablesWithUnderscoreInForOfLoop1.ts, 9, 16))
+>_b : Symbol(_b, Decl(unusedVariablesWithUnderscoreInForOfLoop1.ts, 9, 19))
 }