Proper treatment of splicing tuples in array literals

Fixes #32465.

src/compiler/checker.ts

@@ -22238,58 +22238,69 @@ namespace ts {
         function checkArrayLiteral(node: ArrayLiteralExpression, checkMode: CheckMode | undefined, forceTuple: boolean | undefined): Type {
             const elements = node.elements;
             const elementCount = elements.length;
-            let hasNonEndingSpreadElement = false;
             const elementTypes: Type[] = [];
-            const inDestructuringPattern = isAssignmentTarget(node);
+            let hasEndingSpreadElement = false;
+            let hasNonEndingSpreadElement = false;
             const contextualType = getApparentTypeOfContextualType(node);
+            const inDestructuringPattern = isAssignmentTarget(node);
             const inConstContext = isConstContext(node);
-            for (let index = 0; index < elementCount; index++) {
-                const e = elements[index];
-                if (inDestructuringPattern && e.kind === SyntaxKind.SpreadElement) {
-                    // Given the following situation:
-                    //    var c: {};
-                    //    [...c] = ["", 0];
-                    //
-                    // c is represented in the tree as a spread element in an array literal.
-                    // But c really functions as a rest element, and its purpose is to provide
-                    // a contextual type for the right hand side of the assignment. Therefore,
-                    // instead of calling checkExpression on "...c", which will give an error
-                    // if c is not iterable/array-like, we need to act as if we are trying to
-                    // get the contextual element type from it. So we do something similar to
-                    // getContextualTypeForElementExpression, which will crucially not error
-                    // if there is no index type / iterated type.
-                    const restArrayType = checkExpression((<SpreadElement>e).expression, checkMode, forceTuple);
-                    const restElementType = getIndexTypeOfType(restArrayType, IndexKind.Number) ||
-                        getIteratedTypeOrElementType(IterationUse.Destructuring, restArrayType, undefinedType, /*errorNode*/ undefined, /*checkAssignability*/ false);
-                    if (restElementType) {
-                        elementTypes.push(restElementType);
+            for (let i = 0; i < elementCount; i++) {
+                const e = elements[i];
+                const spread = e.kind === SyntaxKind.SpreadElement && (<SpreadElement>e).expression;
+                const spreadType = spread && checkExpression(spread, checkMode, forceTuple);
+                if (spreadType && isTupleType(spreadType)) {
+                    elementTypes.push(...getTypeArguments(spreadType));
+                    if (spreadType.target.hasRestElement) {
+                        if (i === elementCount - 1) hasEndingSpreadElement = true;
+                        else hasNonEndingSpreadElement = true;
                     }
                 }
                 else {
-                    const elementContextualType = getContextualTypeForElementExpression(contextualType, index);
-                    const type = checkExpressionForMutableLocation(e, checkMode, elementContextualType, forceTuple);
-                    elementTypes.push(type);
-                }
-                if (index < elementCount - 1 && e.kind === SyntaxKind.SpreadElement) {
-                    hasNonEndingSpreadElement = true;
+                    if (inDestructuringPattern && spreadType) {
+                        // Given the following situation:
+                        //    var c: {};
+                        //    [...c] = ["", 0];
+                        //
+                        // c is represented in the tree as a spread element in an array literal.
+                        // But c really functions as a rest element, and its purpose is to provide
+                        // a contextual type for the right hand side of the assignment. Therefore,
+                        // instead of calling checkExpression on "...c", which will give an error
+                        // if c is not iterable/array-like, we need to act as if we are trying to
+                        // get the contextual element type from it. So we do something similar to
+                        // getContextualTypeForElementExpression, which will crucially not error
+                        // if there is no index type / iterated type.
+                        const restElementType = getIndexTypeOfType(spreadType, IndexKind.Number) ||
+                            getIteratedTypeOrElementType(IterationUse.Destructuring, spreadType, undefinedType, /*errorNode*/ undefined, /*checkAssignability*/ false);
+                        if (restElementType) {
+                            elementTypes.push(restElementType);
+                        }
+                    }
+                    else {
+                        const elementContextualType = getContextualTypeForElementExpression(contextualType, elementTypes.length);
+                        const type = checkExpressionForMutableLocation(e, checkMode, elementContextualType, forceTuple);
+                        elementTypes.push(type);
+                    }
+                    if (spread) { // tuples are done above
+                        if (i === elementCount - 1) hasEndingSpreadElement = true;
+                        else hasNonEndingSpreadElement = true;
+                    }
                 }
             }
             if (!hasNonEndingSpreadElement) {
-                const hasRestElement = elementCount > 0 && elements[elementCount - 1].kind === SyntaxKind.SpreadElement;
-                const minLength = elementCount - (hasRestElement ? 1 : 0);
+                const minLength = elementTypes.length - (hasEndingSpreadElement ? 1 : 0);
                 // If array literal is actually a destructuring pattern, mark it as an implied type. We do this such
                 // that we get the same behavior for "var [x, y] = []" and "[x, y] = []".
                 let tupleResult;
                 if (inDestructuringPattern && minLength > 0) {
-                    const type = cloneTypeReference(<TypeReference>createTupleType(elementTypes, minLength, hasRestElement));
+                    const type = cloneTypeReference(<TypeReference>createTupleType(elementTypes, minLength, hasEndingSpreadElement));
                     type.pattern = node;
                     return type;
                 }
-                else if (tupleResult = getArrayLiteralTupleTypeIfApplicable(elementTypes, contextualType, hasRestElement, elementCount, inConstContext)) {
+                else if (tupleResult = getArrayLiteralTupleTypeIfApplicable(elementTypes, contextualType, hasEndingSpreadElement, elementTypes.length, inConstContext)) {
                     return createArrayLiteralType(tupleResult);
                 }
                 else if (forceTuple) {
-                    return createArrayLiteralType(createTupleType(elementTypes, minLength, hasRestElement));
+                    return createArrayLiteralType(createTupleType(elementTypes, minLength, hasEndingSpreadElement));
                 }
             }
             return createArrayLiteralType(createArrayType(elementTypes.length ?

tests/baselines/reference/arrayLiteralExpressionContextualTyping.errors.txt

@@ -7,9 +7,9 @@ tests/cases/conformance/expressions/contextualTyping/arrayLiteralExpressionConte
 tests/cases/conformance/expressions/contextualTyping/arrayLiteralExpressionContextualTyping.ts(8,5): error TS2322: Type '[number, number, number, string]' is not assignable to type '[number, number, number]'.
   Types of property 'length' are incompatible.
     Type '4' is not assignable to type '3'.
-tests/cases/conformance/expressions/contextualTyping/arrayLiteralExpressionContextualTyping.ts(14,5): error TS2322: Type '[number, number, number, ...number[]]' is not assignable to type '[number, number, number]'.
+tests/cases/conformance/expressions/contextualTyping/arrayLiteralExpressionContextualTyping.ts(14,5): error TS2322: Type '[number, number, number, number, number, number]' is not assignable to type '[number, number, number]'.
   Types of property 'length' are incompatible.
-    Type 'number' is not assignable to type '3'.
+    Type '6' is not assignable to type '3'.
 
 
 ==== tests/cases/conformance/expressions/contextualTyping/arrayLiteralExpressionContextualTyping.ts (4 errors) ====
@@ -40,7 +40,7 @@ tests/cases/conformance/expressions/contextualTyping/arrayLiteralExpressionConte
     var spr1 = [1, 2, 3, ...tup];
     var spr2:[number, number, number] = [1, 2, 3, ...tup];  // Error
         ~~~~
-!!! error TS2322: Type '[number, number, number, ...number[]]' is not assignable to type '[number, number, number]'.
+!!! error TS2322: Type '[number, number, number, number, number, number]' is not assignable to type '[number, number, number]'.
 !!! error TS2322:   Types of property 'length' are incompatible.
-!!! error TS2322:     Type 'number' is not assignable to type '3'.
+!!! error TS2322:     Type '6' is not assignable to type '3'.
 

tests/baselines/reference/arrayLiteralExpressionContextualTyping.types

@@ -62,7 +62,7 @@ var spr1 = [1, 2, 3, ...tup];
 
 var spr2:[number, number, number] = [1, 2, 3, ...tup];  // Error
 >spr2 : [number, number, number]
->[1, 2, 3, ...tup] : [number, number, number, ...number[]]
+>[1, 2, 3, ...tup] : [number, number, number, number, number, number]
 >1 : 1
 >2 : 2
 >3 : 3

tests/baselines/reference/arrayLiterals3.errors.txt

@@ -5,15 +5,14 @@ tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(11,51): erro
 tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(17,5): error TS2322: Type '[number, number, string, boolean]' is not assignable to type '[number, number]'.
   Types of property 'length' are incompatible.
     Type '4' is not assignable to type '2'.
-tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(32,5): error TS2739: Type '(number[] | string[])[]' is missing the following properties from type 'tup': 0, 1
 tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(33,5): error TS2739: Type 'number[]' is missing the following properties from type '[number, number, number]': 0, 1, 2
 tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(34,5): error TS2322: Type '(string | number)[]' is not assignable to type 'myArray'.
   The types returned by 'pop()' are incompatible between these types.
     Type 'string | number' is not assignable to type 'Number'.
       Type 'string' is not assignable to type 'Number'.
 
 
-==== tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts (8 errors) ====
+==== tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts (7 errors) ====
     // Each element expression in a non-empty array literal is processed as follows:
     //    - If the array literal contains no spread elements, and if the array literal is contextually typed (section 4.19)
     //      by a type T and T has a property with the numeric name N, where N is the index of the element expression in the array literal,
@@ -58,8 +57,6 @@ tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(34,5): error
     interface myArray extends Array<Number> { }
     interface myArray2 extends Array<Number|String> { }
     var c0: tup = [...temp2];                         // Error
-        ~~
-!!! error TS2739: Type '(number[] | string[])[]' is missing the following properties from type 'tup': 0, 1
     var c1: [number, number, number] = [...temp1];    // Error cannot assign number[] to [number, number, number]
         ~~
 !!! error TS2739: Type 'number[]' is missing the following properties from type '[number, number, number]': 0, 1, 2

tests/baselines/reference/arrayLiterals3.types

@@ -71,7 +71,7 @@ interface myArray extends Array<Number> { }
 interface myArray2 extends Array<Number|String> { }
 var c0: tup = [...temp2];                         // Error
 >c0 : tup
->[...temp2] : (number[] | string[])[]
+>[...temp2] : [number[], string[]]
 >...temp2 : number[] | string[]
 >temp2 : [number[], string[]]
 

tests/baselines/reference/constAssertions.js

@@ -143,7 +143,7 @@ declare let vc1: "abc";
 declare let a1: readonly [];
 declare let a2: readonly [1, 2, 3];
 declare let a3: readonly [10, "hello", true];
-declare let a4: readonly (1 | 2 | 3)[];
+declare let a4: readonly [1, 2, 3];
 declare let a5: number[];
 declare let a6: readonly number[];
 declare let a7: number[];

tests/baselines/reference/constAssertions.types

@@ -125,9 +125,9 @@ let a3 = [10, 'hello', true] as const;
 >true : true
 
 let a4 = [...[1, 2, 3]] as const;
->a4 : readonly (1 | 2 | 3)[]
->[...[1, 2, 3]] as const : readonly (1 | 2 | 3)[]
->[...[1, 2, 3]] : readonly (1 | 2 | 3)[]
+>a4 : readonly [1, 2, 3]
+>[...[1, 2, 3]] as const : readonly [1, 2, 3]
+>[...[1, 2, 3]] : readonly [1, 2, 3]
 >...[1, 2, 3] : 1 | 2 | 3
 >[1, 2, 3] : readonly [1, 2, 3]
 >1 : 1

tests/baselines/reference/declarationsAndAssignments.types

@@ -727,22 +727,22 @@ function f20(v: [number, number, number]) {
 
     [...a3] = v;
 >[...a3] = v : [number, number, number]
->[...a3] : number[]
+>[...a3] : [number, number, number]
 >...a3 : number
 >a3 : [number, number, number]
 >v : [number, number, number]
 
     [x, ...a2] = v;
 >[x, ...a2] = v : [number, number, number]
->[x, ...a2] : [number, ...number[]]
+>[x, ...a2] : [number, number, number]
 >x : number
 >...a2 : number
 >a2 : [number, number]
 >v : [number, number, number]
 
     [x, y, ...a1] = v;
 >[x, y, ...a1] = v : [number, number, number]
->[x, y, ...a1] : [number, number, ...number[]]
+>[x, y, ...a1] : [number, number, number]
 >x : number
 >y : number
 >...a1 : number
@@ -751,7 +751,7 @@ function f20(v: [number, number, number]) {
 
     [x, y, z, ...a0] = v;
 >[x, y, z, ...a0] = v : [number, number, number]
->[x, y, z, ...a0] : [number, number, number, ...never[]]
+>[x, y, z, ...a0] : [number, number, number]
 >x : number
 >y : number
 >z : number
@@ -809,22 +809,22 @@ function f21(v: [number, string, boolean]) {
 
     [...a0] = v;
 >[...a0] = v : [number, string, boolean]
->[...a0] : (string | number | boolean)[]
+>[...a0] : [number, string, boolean]
 >...a0 : string | number | boolean
 >a0 : [number, string, boolean]
 >v : [number, string, boolean]
 
     [x, ...a1] = v;
 >[x, ...a1] = v : [number, string, boolean]
->[x, ...a1] : [number, ...(string | boolean)[]]
+>[x, ...a1] : [number, string, boolean]
 >x : number
 >...a1 : string | boolean
 >a1 : [string, boolean]
 >v : [number, string, boolean]
 
     [x, y, ...a2] = v;
 >[x, y, ...a2] = v : [number, string, boolean]
->[x, y, ...a2] : [number, string, ...boolean[]]
+>[x, y, ...a2] : [number, string, boolean]
 >x : number
 >y : string
 >...a2 : boolean
@@ -833,7 +833,7 @@ function f21(v: [number, string, boolean]) {
 
     [x, y, z, ...a3] = v;
 >[x, y, z, ...a3] = v : [number, string, boolean]
->[x, y, z, ...a3] : [number, string, boolean, ...never[]]
+>[x, y, z, ...a3] : [number, string, boolean]
 >x : number
 >y : string
 >z : boolean

tests/baselines/reference/destructuringTuple.types

@@ -15,7 +15,7 @@ declare var receiver: typeof tuple;
 
 [...receiver] = tuple;
 >[...receiver] = tuple : [boolean, number, ...string[]]
->[...receiver] : (string | number | boolean)[]
+>[...receiver] : [boolean, number, ...string[]]
 >...receiver : string | number | boolean
 >receiver : [boolean, number, ...string[]]
 >tuple : [boolean, number, ...string[]]

tests/baselines/reference/for-of49.types

@@ -13,7 +13,7 @@ var map = new Map([["", true]]);
 >true : true
 
 for ([k, ...[v]] of map) {
->[k, ...[v]] : [string, ...boolean[]]
+>[k, ...[v]] : [string, boolean]
 >k : string
 >...[v] : boolean
 >[v] : [boolean]

tests/baselines/reference/literalFreshnessPropagationOnNarrowing.errors.txt

@@ -1,6 +1,5 @@
 tests/cases/compiler/literalFreshnessPropagationOnNarrowing.ts(37,5): error TS2322: Type '"y"' is not assignable to type '"x"'.
-tests/cases/compiler/literalFreshnessPropagationOnNarrowing.ts(60,5): error TS2322: Type 'string[]' is not assignable to type 'XY[]'.
-  Type 'string' is not assignable to type 'XY'.
+tests/cases/compiler/literalFreshnessPropagationOnNarrowing.ts(60,12): error TS2322: Type 'string' is not assignable to type 'XY'.
 
 
 ==== tests/cases/compiler/literalFreshnessPropagationOnNarrowing.ts (2 errors) ====
@@ -66,7 +65,6 @@ tests/cases/compiler/literalFreshnessPropagationOnNarrowing.ts(60,5): error TS23
         // Desired: OK
         // Error in all extant branches
         arr = [...['y']];
-        ~~~
-!!! error TS2322: Type 'string[]' is not assignable to type 'XY[]'.
-!!! error TS2322:   Type 'string' is not assignable to type 'XY'.
+               ~~~~~~~~
+!!! error TS2322: Type 'string' is not assignable to type 'XY'.
     }

tests/baselines/reference/restElementMustBeLast.types

@@ -8,12 +8,12 @@ var [...a, x] = [1, 2, 3];  // Error, rest must be last element
 >3 : 3
 
 [...a, x] = [1, 2, 3];      // Error, rest must be last element
->[...a, x] = [1, 2, 3] : number[]
->[...a, x] : number[]
+>[...a, x] = [1, 2, 3] : [number, number, number]
+>[...a, x] : [number, number, number, number]
 >...a : number
 >a : [number, number, number]
 >x : number
->[1, 2, 3] : number[]
+>[1, 2, 3] : [number, number, number]
 >1 : 1
 >2 : 2
 >3 : 3

tests/baselines/reference/restElementWithAssignmentPattern1.types

@@ -4,15 +4,15 @@ var a: string, b: number;
 >b : number
 
 [...[a, b = 0]] = ["", 1];
->[...[a, b = 0]] = ["", 1] : (string | number)[]
->[...[a, b = 0]] : (string | number)[]
+>[...[a, b = 0]] = ["", 1] : [string, number]
+>[...[a, b = 0]] : [string, number]
 >...[a, b = 0] : string | number
 >[a, b = 0] : [string, number]
 >a : string
 >b = 0 : 0
 >b : number
 >0 : 0
->["", 1] : (string | number)[]
+>["", 1] : [string, number]
 >"" : ""
 >1 : 1
 

tests/baselines/reference/restElementWithAssignmentPattern3.types

@@ -11,7 +11,7 @@ var tuple: [string, number] = ["", 1];
 
 [...[a, b = 0]] = tuple;
 >[...[a, b = 0]] = tuple : [string, number]
->[...[a, b = 0]] : (string | number)[]
+>[...[a, b = 0]] : [string, number]
 >...[a, b = 0] : string | number
 >[a, b = 0] : [string, number]
 >a : string

tests/baselines/reference/restElementWithAssignmentPattern5.types

@@ -4,13 +4,13 @@ var s: string, s2: string;
 >s2 : string
 
 [...[s, s2]] = ["", ""];
->[...[s, s2]] = ["", ""] : string[]
->[...[s, s2]] : string[]
+>[...[s, s2]] = ["", ""] : [string, string]
+>[...[s, s2]] : [string, string]
 >...[s, s2] : string
 >[s, s2] : [string, string]
 >s : string
 >s2 : string
->["", ""] : string[]
+>["", ""] : [string, string]
 >"" : ""
 >"" : ""