Consistently error when rest element isn't last in tuple type (microsoft#40254)

* Consistently error when rest element isn't last in tuple type

* Add regression test

* Accept new baselines

* Stricter circular recursion check in type inference

* Revert "Stricter circular recursion check in type inference"

This reverts commit 80e6df6.

* Revert "Accept new baselines"

This reverts commit 355706d.

* Accept new baselines

Author: ahejlsberg

src/compiler/checker.ts

@@ -31172,6 +31172,7 @@ namespace ts {
         function checkTupleType(node: TupleTypeNode) {
             const elementTypes = node.elements;
             let seenOptionalElement = false;
+            let seenRestElement = false;
             const hasNamedElement = some(elementTypes, isNamedTupleMember);
             for (let i = 0; i < elementTypes.length; i++) {
                 const e = elementTypes[i];
@@ -31181,16 +31182,17 @@ namespace ts {
                 }
                 const flags = getTupleElementFlags(e);
                 if (flags & ElementFlags.Variadic) {
-                    if (!isArrayLikeType(getTypeFromTypeNode((<RestTypeNode | NamedTupleMember>e).type))) {
+                    const type = getTypeFromTypeNode((<RestTypeNode | NamedTupleMember>e).type);
+                    if (!isArrayLikeType(type)) {
                         error(e, Diagnostics.A_rest_element_type_must_be_an_array_type);
                         break;
                     }
+                    if (isArrayType(type) || isTupleType(type) && type.target.combinedFlags & ElementFlags.Rest) {
+                        seenRestElement = true;
+                    }
                 }
                 else if (flags & ElementFlags.Rest) {
-                    if (i !== elementTypes.length - 1) {
-                        grammarErrorOnNode(e, Diagnostics.A_rest_element_must_be_last_in_a_tuple_type);
-                        break;
-                    }
+                    seenRestElement = true;
                 }
                 else if (flags & ElementFlags.Optional) {
                     seenOptionalElement = true;
@@ -31199,6 +31201,10 @@ namespace ts {
                     grammarErrorOnNode(e, Diagnostics.A_required_element_cannot_follow_an_optional_element);
                     break;
                 }
+                if (seenRestElement && i !== elementTypes.length - 1) {
+                    grammarErrorOnNode(e, Diagnostics.A_rest_element_must_be_last_in_a_tuple_type);
+                    break;
+                }
             }
             forEach(node.elements, checkSourceElement);
         }

tests/baselines/reference/variadicTuples1.errors.txt

@@ -41,9 +41,12 @@ tests/cases/conformance/types/tuple/variadicTuples1.ts(203,5): error TS2322: Typ
   Type '"2"' is not assignable to type 'number | "0" | "length" | "toString" | "toLocaleString" | "pop" | "push" | "concat" | "join" | "reverse" | "shift" | "slice" | "sort" | "splice" | "unshift" | "indexOf" | "lastIndexOf" | "every" | "some" | "forEach" | "map" | "filter" | "reduce" | "reduceRight" | "1"'.
 tests/cases/conformance/types/tuple/variadicTuples1.ts(346,14): error TS7019: Rest parameter 'x' implicitly has an 'any[]' type.
 tests/cases/conformance/types/tuple/variadicTuples1.ts(354,26): error TS2322: Type 'string' is not assignable to type 'number | undefined'.
+tests/cases/conformance/types/tuple/variadicTuples1.ts(393,19): error TS1256: A rest element must be last in a tuple type.
+tests/cases/conformance/types/tuple/variadicTuples1.ts(396,20): error TS1256: A rest element must be last in a tuple type.
+tests/cases/conformance/types/tuple/variadicTuples1.ts(397,12): error TS1256: A rest element must be last in a tuple type.
 
 
-==== tests/cases/conformance/types/tuple/variadicTuples1.ts (20 errors) ====
+==== tests/cases/conformance/types/tuple/variadicTuples1.ts (23 errors) ====
     // Variadics in tuple types
 
     type TV0<T extends unknown[]> = [string, ...T];
@@ -496,4 +499,20 @@ tests/cases/conformance/types/tuple/variadicTuples1.ts(354,26): error TS2322: Ty
 
     callApi(getUser);
     callApi(getOrgUser);
+    
+    // Repro from #40235
+    
+    type Numbers = number[];
+    type Unbounded = [...Numbers, boolean];
+                      ~~~~~~~~~~
+!!! error TS1256: A rest element must be last in a tuple type.
+    const data: Unbounded = [false, false];
+    
+    type U1 = [string, ...Numbers, boolean];
+                       ~~~~~~~~~~
+!!! error TS1256: A rest element must be last in a tuple type.
+    type U2 = [...[string, ...Numbers], boolean];
+               ~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS1256: A rest element must be last in a tuple type.
+    type U3 = [...[string, number], boolean];
 

tests/baselines/reference/variadicTuples1.js

@@ -387,6 +387,16 @@ function callApi<T extends unknown[] = [], U = void>(method: (...args: [...T, ob
 
 callApi(getUser);
 callApi(getOrgUser);
+
+// Repro from #40235
+
+type Numbers = number[];
+type Unbounded = [...Numbers, boolean];
+const data: Unbounded = [false, false];
+
+type U1 = [string, ...Numbers, boolean];
+type U2 = [...[string, ...Numbers], boolean];
+type U3 = [...[string, number], boolean];
 
 
 //// [variadicTuples1.js]
@@ -609,6 +619,7 @@ function callApi(method) {
 }
 callApi(getUser);
 callApi(getOrgUser);
+var data = [false, false];
 
 
 //// [variadicTuples1.d.ts]
@@ -774,3 +785,9 @@ declare function getOrgUser(id: string, orgId: number, options?: {
     z?: boolean;
 }): void;
 declare function callApi<T extends unknown[] = [], U = void>(method: (...args: [...T, object]) => U): (...args_0: T) => U;
+declare type Numbers = number[];
+declare type Unbounded = [...Numbers, boolean];
+declare const data: Unbounded;
+declare type U1 = [string, ...Numbers, boolean];
+declare type U2 = [...[string, ...Numbers], boolean];
+declare type U3 = [...[string, number], boolean];

tests/baselines/reference/variadicTuples1.symbols

@@ -1327,3 +1327,27 @@ callApi(getOrgUser);
 >callApi : Symbol(callApi, Decl(variadicTuples1.ts, 380, 100))
 >getOrgUser : Symbol(getOrgUser, Decl(variadicTuples1.ts, 378, 71))
 
+// Repro from #40235
+
+type Numbers = number[];
+>Numbers : Symbol(Numbers, Decl(variadicTuples1.ts, 387, 20))
+
+type Unbounded = [...Numbers, boolean];
+>Unbounded : Symbol(Unbounded, Decl(variadicTuples1.ts, 391, 24))
+>Numbers : Symbol(Numbers, Decl(variadicTuples1.ts, 387, 20))
+
+const data: Unbounded = [false, false];
+>data : Symbol(data, Decl(variadicTuples1.ts, 393, 5))
+>Unbounded : Symbol(Unbounded, Decl(variadicTuples1.ts, 391, 24))
+
+type U1 = [string, ...Numbers, boolean];
+>U1 : Symbol(U1, Decl(variadicTuples1.ts, 393, 39))
+>Numbers : Symbol(Numbers, Decl(variadicTuples1.ts, 387, 20))
+
+type U2 = [...[string, ...Numbers], boolean];
+>U2 : Symbol(U2, Decl(variadicTuples1.ts, 395, 40))
+>Numbers : Symbol(Numbers, Decl(variadicTuples1.ts, 387, 20))
+
+type U3 = [...[string, number], boolean];
+>U3 : Symbol(U3, Decl(variadicTuples1.ts, 396, 45))
+

tests/baselines/reference/variadicTuples1.types

@@ -1383,3 +1383,26 @@ callApi(getOrgUser);
 >callApi : <T extends unknown[] = [], U = void>(method: (...args_0: T, args_1: object) => U) => (...args_0: T) => U
 >getOrgUser : (id: string, orgId: number, options?: { y?: number | undefined; z?: boolean | undefined; } | undefined) => void
 
+// Repro from #40235
+
+type Numbers = number[];
+>Numbers : Numbers
+
+type Unbounded = [...Numbers, boolean];
+>Unbounded : (number | boolean)[]
+
+const data: Unbounded = [false, false];
+>data : (number | boolean)[]
+>[false, false] : false[]
+>false : false
+>false : false
+
+type U1 = [string, ...Numbers, boolean];
+>U1 : [string, ...(number | boolean)[]]
+
+type U2 = [...[string, ...Numbers], boolean];
+>U2 : [string, ...(number | boolean)[]]
+
+type U3 = [...[string, number], boolean];
+>U3 : [string, number, boolean]
+

tests/cases/conformance/types/tuple/variadicTuples1.ts

@@ -389,3 +389,13 @@ function callApi<T extends unknown[] = [], U = void>(method: (...args: [...T, ob
 
 callApi(getUser);
 callApi(getOrgUser);
+
+// Repro from #40235
+
+type Numbers = number[];
+type Unbounded = [...Numbers, boolean];
+const data: Unbounded = [false, false];
+
+type U1 = [string, ...Numbers, boolean];
+type U2 = [...[string, ...Numbers], boolean];
+type U3 = [...[string, number], boolean];