Merge pull request #26070 from ajafff/tuple-rest

Infer array rest as tuple if possible

Author: RyanCavanaugh

src/compiler/checker.ts

@@ -4678,11 +4678,11 @@ namespace ts {
                 const elementType = checkIteratedTypeOrElementType(parentType, pattern, /*allowStringInput*/ false, /*allowAsyncIterables*/ false);
                 const index = pattern.elements.indexOf(declaration);
                 if (declaration.dotDotDotToken) {
-                    // If the parent is a tuple type, the rest element has an array type with a union of the
+                    // If the parent is a tuple type, the rest element has a tuple type of the
                     // remaining tuple element types. Otherwise, the rest element has an array type with same
                     // element type as the parent type.
                     type = isTupleType(parentType) ?
-                        getArrayLiteralType((parentType.typeArguments || emptyArray).slice(index, getTypeReferenceArity(parentType))) :
+                        sliceTupleType(parentType, index) :
                         createArrayType(elementType);
                 }
                 else {
@@ -8725,6 +8725,20 @@ namespace ts {
             return links.resolvedType;
         }
 
+        function sliceTupleType(type: TupleTypeReference, index: number) {
+            const tuple = type.target;
+            if (tuple.hasRestElement) {
+                // don't slice off rest element
+                index = Math.min(index, getTypeReferenceArity(type) - 1);
+            }
+            return createTupleType(
+                (type.typeArguments || emptyArray).slice(index),
+                Math.max(0, tuple.minLength - index),
+                tuple.hasRestElement,
+                tuple.associatedNames && tuple.associatedNames.slice(index),
+            );
+        }
+
         function getTypeFromOptionalTypeNode(node: OptionalTypeNode): Type {
             const type = getTypeFromTypeNode(node.type);
             return strictNullChecks ? getOptionalType(type) : type;
@@ -21691,7 +21705,7 @@ namespace ts {
                         else {
                             checkGrammarForDisallowedTrailingComma(node.elements, Diagnostics.A_rest_parameter_or_binding_pattern_may_not_have_a_trailing_comma);
                             const type = isTupleType(sourceType) ?
-                                getArrayLiteralType((sourceType.typeArguments || emptyArray).slice(elementIndex, getTypeReferenceArity(sourceType))) :
+                                sliceTupleType(sourceType, elementIndex) :
                                 createArrayType(elementType);
                             return checkDestructuringAssignment(restExpression, type, checkMode);
                         }

tests/baselines/reference/declarationEmitDestructuring3.types

@@ -8,7 +8,7 @@ function bar([x, z, ...w]) { }
 function foo([x, ...y] = [1, "string", true]) { }
 >foo : ([x, ...y]?: [number, string, boolean]) => void
 >x : number
->y : (string | boolean)[]
+>y : [string, boolean]
 >[1, "string", true] : [number, string, boolean]
 >1 : 1
 >"string" : "string"

tests/baselines/reference/declarationEmitDestructuringArrayPattern4.js

@@ -22,10 +22,10 @@ var _f = [1, "hello", true], x19 = _f[0], y19 = _f[1], z19 = _f[2], a13 = _f.sli
 
 //// [declarationEmitDestructuringArrayPattern4.d.ts]
 declare var a5: number[];
-declare var x14: number, a6: number[];
-declare var x15: number, y15: number, a7: number[];
-declare var x16: number, y16: number, z16: number, a8: any[];
+declare var x14: number, a6: [number, number];
+declare var x15: number, y15: number, a7: [number];
+declare var x16: number, y16: number, z16: number, a8: [];
 declare var a9: (string | number | boolean)[];
-declare var x17: number, a10: (string | boolean)[];
-declare var x18: number, y18: string, a12: boolean[];
-declare var x19: number, y19: string, z19: boolean, a13: any[];
+declare var x17: number, a10: [string, boolean];
+declare var x18: number, y18: string, a12: [boolean];
+declare var x19: number, y19: string, z19: boolean, a13: [];

tests/baselines/reference/declarationEmitDestructuringArrayPattern4.types

@@ -8,7 +8,7 @@ var [...a5] = [1, 2, 3];
 
 var [x14, ...a6] = [1, 2, 3];
 >x14 : number
->a6 : number[]
+>a6 : [number, number]
 >[1, 2, 3] : [number, number, number]
 >1 : 1
 >2 : 2
@@ -17,7 +17,7 @@ var [x14, ...a6] = [1, 2, 3];
 var [x15, y15, ...a7] = [1, 2, 3];
 >x15 : number
 >y15 : number
->a7 : number[]
+>a7 : [number]
 >[1, 2, 3] : [number, number, number]
 >1 : 1
 >2 : 2
@@ -27,7 +27,7 @@ var [x16, y16, z16, ...a8] = [1, 2, 3];
 >x16 : number
 >y16 : number
 >z16 : number
->a8 : any[]
+>a8 : []
 >[1, 2, 3] : [number, number, number]
 >1 : 1
 >2 : 2
@@ -42,7 +42,7 @@ var [...a9] = [1, "hello", true];
 
 var [x17, ...a10] = [1, "hello", true];
 >x17 : number
->a10 : (string | boolean)[]
+>a10 : [string, boolean]
 >[1, "hello", true] : [number, string, boolean]
 >1 : 1
 >"hello" : "hello"
@@ -51,7 +51,7 @@ var [x17, ...a10] = [1, "hello", true];
 var [x18, y18, ...a12] = [1, "hello", true];
 >x18 : number
 >y18 : string
->a12 : boolean[]
+>a12 : [boolean]
 >[1, "hello", true] : [number, string, boolean]
 >1 : 1
 >"hello" : "hello"
@@ -61,7 +61,7 @@ var [x19, y19, z19, ...a13] = [1, "hello", true];
 >x19 : number
 >y19 : string
 >z19 : boolean
->a13 : any[]
+>a13 : []
 >[1, "hello", true] : [number, string, boolean]
 >1 : 1
 >"hello" : "hello"

tests/baselines/reference/declarationsAndAssignments.errors.txt

@@ -219,37 +219,39 @@ tests/cases/conformance/es6/destructuring/declarationsAndAssignments.ts(138,9):
         var x = ([a, b] = [1, 2]);
     }
 
-    function f20() {
+    function f20(v: [number, number, number]) {
         var x: number;
         var y: number;
         var z: number;
-        var a: number[];
-        var a3: any[];
-        var [...a] = [1, 2, 3];
-        var [x, ...a] = [1, 2, 3];
-        var [x, y, ...a] = [1, 2, 3];
-        var [x, y, z, ...a3] = [1, 2, 3];
-        [...a] = [1, 2, 3];
-        [x, ...a] = [1, 2, 3];
-        [x, y, ...a] = [1, 2, 3];
-        [x, y, z, ...a3] = [1, 2, 3];
-    }
-    
-    function f21() {
+        var a0: [];
+        var a1: [number];
+        var a2: [number, number];
+        var a3: [number, number, number];
+        var [...a3] = v;
+        var [x, ...a2] = v;
+        var [x, y, ...a1] = v;
+        var [x, y, z, ...a0] = v;
+        [...a3] = v;
+        [x, ...a2] = v;
+        [x, y, ...a1] = v;
+        [x, y, z, ...a0] = v;
+    }
+    
+    function f21(v: [number, string, boolean]) {
         var x: number;
         var y: string;
         var z: boolean;
-        var a0: (number | string | boolean)[];
-        var a1: (string | boolean)[];
-        var a2: boolean[];
-        var a3: any[];
-        var [...a0] = [1, "hello", true];
-        var [x, ...a1] = [1, "hello", true];
-        var [x, y, ...a2] = [1, "hello", true];
-        var [x, y, z, ...a3] = [1, "hello", true];
-        [...a0] = [1, "hello", true];
-        [x, ...a1] = [1, "hello", true];
-        [x, y, ...a2] = [1, "hello", true];
-        [x, y, z, ...a3] = [1, "hello", true];
+        var a0: [number, string, boolean];
+        var a1: [string, boolean];
+        var a2: [boolean];
+        var a3: [];
+        var [...a0] = v;
+        var [x, ...a1] = v;
+        var [x, y, ...a2] = v;
+        var [x, y, z, ...a3] = v;
+        [...a0] = v;
+        [x, ...a1] = v;
+        [x, y, ...a2] = v;
+        [x, y, z, ...a3] = v;
     }
 

tests/baselines/reference/declarationsAndAssignments.js

@@ -149,38 +149,40 @@ function f19() {
     var x = ([a, b] = [1, 2]);
 }
 
-function f20() {
+function f20(v: [number, number, number]) {
     var x: number;
     var y: number;
     var z: number;
-    var a: number[];
-    var a3: any[];
-    var [...a] = [1, 2, 3];
-    var [x, ...a] = [1, 2, 3];
-    var [x, y, ...a] = [1, 2, 3];
-    var [x, y, z, ...a3] = [1, 2, 3];
-    [...a] = [1, 2, 3];
-    [x, ...a] = [1, 2, 3];
-    [x, y, ...a] = [1, 2, 3];
-    [x, y, z, ...a3] = [1, 2, 3];
+    var a0: [];
+    var a1: [number];
+    var a2: [number, number];
+    var a3: [number, number, number];
+    var [...a3] = v;
+    var [x, ...a2] = v;
+    var [x, y, ...a1] = v;
+    var [x, y, z, ...a0] = v;
+    [...a3] = v;
+    [x, ...a2] = v;
+    [x, y, ...a1] = v;
+    [x, y, z, ...a0] = v;
 }
 
-function f21() {
+function f21(v: [number, string, boolean]) {
     var x: number;
     var y: string;
     var z: boolean;
-    var a0: (number | string | boolean)[];
-    var a1: (string | boolean)[];
-    var a2: boolean[];
-    var a3: any[];
-    var [...a0] = [1, "hello", true];
-    var [x, ...a1] = [1, "hello", true];
-    var [x, y, ...a2] = [1, "hello", true];
-    var [x, y, z, ...a3] = [1, "hello", true];
-    [...a0] = [1, "hello", true];
-    [x, ...a1] = [1, "hello", true];
-    [x, y, ...a2] = [1, "hello", true];
-    [x, y, z, ...a3] = [1, "hello", true];
+    var a0: [number, string, boolean];
+    var a1: [string, boolean];
+    var a2: [boolean];
+    var a3: [];
+    var [...a0] = v;
+    var [x, ...a1] = v;
+    var [x, y, ...a2] = v;
+    var [x, y, z, ...a3] = v;
+    [...a0] = v;
+    [x, ...a1] = v;
+    [x, y, ...a2] = v;
+    [x, y, z, ...a3] = v;
 }
 
 
@@ -320,37 +322,37 @@ function f19() {
     _d = [[2, 3]][0], _e = _d === void 0 ? [1, 2] : _d, a = _e[0], b = _e[1];
     var x = (_f = [1, 2], a = _f[0], b = _f[1], _f);
 }
-function f20() {
-    var _a, _b, _c;
+function f20(v) {
     var x;
     var y;
     var z;
-    var a;
+    var a0;
+    var a1;
+    var a2;
     var a3;
-    var a = [1, 2, 3].slice(0);
-    var _d = [1, 2, 3], x = _d[0], a = _d.slice(1);
-    var _e = [1, 2, 3], x = _e[0], y = _e[1], a = _e.slice(2);
-    var _f = [1, 2, 3], x = _f[0], y = _f[1], z = _f[2], a3 = _f.slice(3);
-    a = [1, 2, 3].slice(0);
-    _a = [1, 2, 3], x = _a[0], a = _a.slice(1);
-    _b = [1, 2, 3], x = _b[0], y = _b[1], a = _b.slice(2);
-    _c = [1, 2, 3], x = _c[0], y = _c[1], z = _c[2], a3 = _c.slice(3);
+    var a3 = v.slice(0);
+    var x = v[0], a2 = v.slice(1);
+    var x = v[0], y = v[1], a1 = v.slice(2);
+    var x = v[0], y = v[1], z = v[2], a0 = v.slice(3);
+    a3 = v.slice(0);
+    x = v[0], a2 = v.slice(1);
+    x = v[0], y = v[1], a1 = v.slice(2);
+    x = v[0], y = v[1], z = v[2], a0 = v.slice(3);
 }
-function f21() {
-    var _a, _b, _c;
+function f21(v) {
     var x;
     var y;
     var z;
     var a0;
     var a1;
     var a2;
     var a3;
-    var a0 = [1, "hello", true].slice(0);
-    var _d = [1, "hello", true], x = _d[0], a1 = _d.slice(1);
-    var _e = [1, "hello", true], x = _e[0], y = _e[1], a2 = _e.slice(2);
-    var _f = [1, "hello", true], x = _f[0], y = _f[1], z = _f[2], a3 = _f.slice(3);
-    a0 = [1, "hello", true].slice(0);
-    _a = [1, "hello", true], x = _a[0], a1 = _a.slice(1);
-    _b = [1, "hello", true], x = _b[0], y = _b[1], a2 = _b.slice(2);
-    _c = [1, "hello", true], x = _c[0], y = _c[1], z = _c[2], a3 = _c.slice(3);
+    var a0 = v.slice(0);
+    var x = v[0], a1 = v.slice(1);
+    var x = v[0], y = v[1], a2 = v.slice(2);
+    var x = v[0], y = v[1], z = v[2], a3 = v.slice(3);
+    a0 = v.slice(0);
+    x = v[0], a1 = v.slice(1);
+    x = v[0], y = v[1], a2 = v.slice(2);
+    x = v[0], y = v[1], z = v[2], a3 = v.slice(3);
 }