No speculative inferences for variadic tuples

src/compiler/checker.ts

@@ -18457,7 +18457,7 @@ namespace ts {
         }
 
         function getEndLengthOfType(type: Type) {
-            return isTupleType(type) ? getTypeReferenceArity(type) - findLastIndex(type.target.elementFlags, f => !!(f & ElementFlags.Variable)) - 1 : 0;
+            return isTupleType(type) ? getTypeReferenceArity(type) - findLastIndex(type.target.elementFlags, f => !(f & ElementFlags.Required)) - 1 : 0;
         }
 
         function getElementTypeOfSliceOfTupleType(type: TupleTypeReference, index: number, endSkipCount = 0, writing = false) {

tests/baselines/reference/variadicTuples1.errors.txt

@@ -40,9 +40,11 @@ tests/cases/conformance/types/tuple/variadicTuples1.ts(191,5): error TS2322: Typ
 tests/cases/conformance/types/tuple/variadicTuples1.ts(203,5): error TS2322: Type 'string' is not assignable to type 'keyof [1, 2, ...T]'.
   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(333,14): error TS7019: Rest parameter 'x' implicitly has an 'any[]' type.
+tests/cases/conformance/types/tuple/variadicTuples1.ts(341,19): error TS2322: Type 'string' is not assignable to type 'number | undefined'.
+tests/cases/conformance/types/tuple/variadicTuples1.ts(342,19): error TS2322: Type 'string' is not assignable to type 'number | undefined'.
 
 
-==== tests/cases/conformance/types/tuple/variadicTuples1.ts (19 errors) ====
+==== tests/cases/conformance/types/tuple/variadicTuples1.ts (21 errors) ====
     // Variadics in tuple types
 
     type TV0<T extends unknown[]> = [string, ...T];
@@ -438,4 +440,27 @@ tests/cases/conformance/types/tuple/variadicTuples1.ts(333,14): error TS7019: Re
     call(...sa, (...x) => 42);
                  ~~~~
 !!! error TS7019: Rest parameter 'x' implicitly has an 'any[]' type.
+
+    // No inference to ending optional elements (except with identical structure)
+
+    declare function f20<T extends unknown[] = []>(args: [...T, number?]): T;
+
+    function f21<U extends string[]>(args: [...U, number?]) {
+        let v1 = f20(args);  // U
+        let v2 = f20(["foo", "bar"]);  // []
+                      ~~~~~
+!!! error TS2322: Type 'string' is not assignable to type 'number | undefined'.
+        let v3 = f20(["foo", 42]);  // []
+                      ~~~~~
+!!! error TS2322: Type 'string' is not assignable to type 'number | undefined'.
+    }
+
+    declare function f22<T extends unknown[] = []>(args: [...T, number]): T;
+    declare function f22<T extends unknown[] = []>(args: [...T]): T;
+
+    function f23<U extends string[]>(args: [...U, number]) {
+        let v1 = f22(args);  // U
+        let v2 = f22(["foo", "bar"]);  // [string, string]
+        let v3 = f22(["foo", 42]);  // [string]
+    }
 

tests/baselines/reference/variadicTuples1.js

@@ -332,6 +332,25 @@ call('hello', 32, (a, b) => 42);
 // Requires [starting-fixed-part, ...rest-part, ending-fixed-part] tuple structure
 
 call(...sa, (...x) => 42);
+
+// No inference to ending optional elements (except with identical structure)
+
+declare function f20<T extends unknown[] = []>(args: [...T, number?]): T;
+
+function f21<U extends string[]>(args: [...U, number?]) {
+    let v1 = f20(args);  // U
+    let v2 = f20(["foo", "bar"]);  // []
+    let v3 = f20(["foo", 42]);  // []
+}
+
+declare function f22<T extends unknown[] = []>(args: [...T, number]): T;
+declare function f22<T extends unknown[] = []>(args: [...T]): T;
+
+function f23<U extends string[]>(args: [...U, number]) {
+    let v1 = f22(args);  // U
+    let v2 = f22(["foo", "bar"]);  // [string, string]
+    let v3 = f22(["foo", 42]);  // [string]
+}
 
 
 //// [variadicTuples1.js]
@@ -528,6 +547,16 @@ call.apply(void 0, __spreadArrays(sa, [function () {
         }
         return 42;
     }]));
+function f21(args) {
+    var v1 = f20(args); // U
+    var v2 = f20(["foo", "bar"]); // []
+    var v3 = f20(["foo", 42]); // []
+}
+function f23(args) {
+    var v1 = f22(args); // U
+    var v2 = f22(["foo", "bar"]); // [string, string]
+    var v3 = f22(["foo", 42]); // [string]
+}
 
 
 //// [variadicTuples1.d.ts]
@@ -669,3 +698,8 @@ declare const c22: (...b: string[]) => number;
 declare function curry2<T extends unknown[], U extends unknown[], R>(f: (...args: [...T, ...U]) => R, t: [...T], u: [...U]): R;
 declare function fn10(a: string, b: number, c: boolean): string[];
 declare function call<T extends unknown[], R>(...args: [...T, (...args: T) => R]): [T, R];
+declare function f20<T extends unknown[] = []>(args: [...T, number?]): T;
+declare function f21<U extends string[]>(args: [...U, number?]): void;
+declare function f22<T extends unknown[] = []>(args: [...T, number]): T;
+declare function f22<T extends unknown[] = []>(args: [...T]): T;
+declare function f23<U extends string[]>(args: [...U, number]): void;

tests/baselines/reference/variadicTuples1.symbols

@@ -1141,3 +1141,66 @@ call(...sa, (...x) => 42);
 >sa : Symbol(sa, Decl(variadicTuples1.ts, 29, 13))
 >x : Symbol(x, Decl(variadicTuples1.ts, 332, 13))
 
+// No inference to ending optional elements (except with identical structure)
+
+declare function f20<T extends unknown[] = []>(args: [...T, number?]): T;
+>f20 : Symbol(f20, Decl(variadicTuples1.ts, 332, 26))
+>T : Symbol(T, Decl(variadicTuples1.ts, 336, 21))
+>args : Symbol(args, Decl(variadicTuples1.ts, 336, 47))
+>T : Symbol(T, Decl(variadicTuples1.ts, 336, 21))
+>T : Symbol(T, Decl(variadicTuples1.ts, 336, 21))
+
+function f21<U extends string[]>(args: [...U, number?]) {
+>f21 : Symbol(f21, Decl(variadicTuples1.ts, 336, 73))
+>U : Symbol(U, Decl(variadicTuples1.ts, 338, 13))
+>args : Symbol(args, Decl(variadicTuples1.ts, 338, 33))
+>U : Symbol(U, Decl(variadicTuples1.ts, 338, 13))
+
+    let v1 = f20(args);  // U
+>v1 : Symbol(v1, Decl(variadicTuples1.ts, 339, 7))
+>f20 : Symbol(f20, Decl(variadicTuples1.ts, 332, 26))
+>args : Symbol(args, Decl(variadicTuples1.ts, 338, 33))
+
+    let v2 = f20(["foo", "bar"]);  // []
+>v2 : Symbol(v2, Decl(variadicTuples1.ts, 340, 7))
+>f20 : Symbol(f20, Decl(variadicTuples1.ts, 332, 26))
+
+    let v3 = f20(["foo", 42]);  // []
+>v3 : Symbol(v3, Decl(variadicTuples1.ts, 341, 7))
+>f20 : Symbol(f20, Decl(variadicTuples1.ts, 332, 26))
+}
+
+declare function f22<T extends unknown[] = []>(args: [...T, number]): T;
+>f22 : Symbol(f22, Decl(variadicTuples1.ts, 342, 1), Decl(variadicTuples1.ts, 344, 72))
+>T : Symbol(T, Decl(variadicTuples1.ts, 344, 21))
+>args : Symbol(args, Decl(variadicTuples1.ts, 344, 47))
+>T : Symbol(T, Decl(variadicTuples1.ts, 344, 21))
+>T : Symbol(T, Decl(variadicTuples1.ts, 344, 21))
+
+declare function f22<T extends unknown[] = []>(args: [...T]): T;
+>f22 : Symbol(f22, Decl(variadicTuples1.ts, 342, 1), Decl(variadicTuples1.ts, 344, 72))
+>T : Symbol(T, Decl(variadicTuples1.ts, 345, 21))
+>args : Symbol(args, Decl(variadicTuples1.ts, 345, 47))
+>T : Symbol(T, Decl(variadicTuples1.ts, 345, 21))
+>T : Symbol(T, Decl(variadicTuples1.ts, 345, 21))
+
+function f23<U extends string[]>(args: [...U, number]) {
+>f23 : Symbol(f23, Decl(variadicTuples1.ts, 345, 64))
+>U : Symbol(U, Decl(variadicTuples1.ts, 347, 13))
+>args : Symbol(args, Decl(variadicTuples1.ts, 347, 33))
+>U : Symbol(U, Decl(variadicTuples1.ts, 347, 13))
+
+    let v1 = f22(args);  // U
+>v1 : Symbol(v1, Decl(variadicTuples1.ts, 348, 7))
+>f22 : Symbol(f22, Decl(variadicTuples1.ts, 342, 1), Decl(variadicTuples1.ts, 344, 72))
+>args : Symbol(args, Decl(variadicTuples1.ts, 347, 33))
+
+    let v2 = f22(["foo", "bar"]);  // [string, string]
+>v2 : Symbol(v2, Decl(variadicTuples1.ts, 349, 7))
+>f22 : Symbol(f22, Decl(variadicTuples1.ts, 342, 1), Decl(variadicTuples1.ts, 344, 72))
+
+    let v3 = f22(["foo", 42]);  // [string]
+>v3 : Symbol(v3, Decl(variadicTuples1.ts, 350, 7))
+>f22 : Symbol(f22, Decl(variadicTuples1.ts, 342, 1), Decl(variadicTuples1.ts, 344, 72))
+}
+

tests/baselines/reference/variadicTuples1.types

@@ -1186,3 +1186,71 @@ call(...sa, (...x) => 42);
 >x : any[]
 >42 : 42
 
+// No inference to ending optional elements (except with identical structure)
+
+declare function f20<T extends unknown[] = []>(args: [...T, number?]): T;
+>f20 : <T extends unknown[] = []>(args: [...T, number?]) => T
+>args : [...T, (number | undefined)?]
+
+function f21<U extends string[]>(args: [...U, number?]) {
+>f21 : <U extends string[]>(args: [...U, number?]) => void
+>args : [...U, (number | undefined)?]
+
+    let v1 = f20(args);  // U
+>v1 : U
+>f20(args) : U
+>f20 : <T extends unknown[] = []>(args: [...T, (number | undefined)?]) => T
+>args : [...U, (number | undefined)?]
+
+    let v2 = f20(["foo", "bar"]);  // []
+>v2 : []
+>f20(["foo", "bar"]) : []
+>f20 : <T extends unknown[] = []>(args: [...T, (number | undefined)?]) => T
+>["foo", "bar"] : [string, string]
+>"foo" : "foo"
+>"bar" : "bar"
+
+    let v3 = f20(["foo", 42]);  // []
+>v3 : []
+>f20(["foo", 42]) : []
+>f20 : <T extends unknown[] = []>(args: [...T, (number | undefined)?]) => T
+>["foo", 42] : [string, number]
+>"foo" : "foo"
+>42 : 42
+}
+
+declare function f22<T extends unknown[] = []>(args: [...T, number]): T;
+>f22 : { <T extends unknown[] = []>(args: [...T, number]): T; <T extends unknown[] = []>(args: [...T]): T; }
+>args : [...T, number]
+
+declare function f22<T extends unknown[] = []>(args: [...T]): T;
+>f22 : { <T extends unknown[] = []>(args: [...T, number]): T; <T extends unknown[] = []>(args: [...T]): T; }
+>args : [...T]
+
+function f23<U extends string[]>(args: [...U, number]) {
+>f23 : <U extends string[]>(args: [...U, number]) => void
+>args : [...U, number]
+
+    let v1 = f22(args);  // U
+>v1 : U
+>f22(args) : U
+>f22 : { <T extends unknown[] = []>(args: [...T, number]): T; <T extends unknown[] = []>(args: [...T]): T; }
+>args : [...U, number]
+
+    let v2 = f22(["foo", "bar"]);  // [string, string]
+>v2 : [string, string]
+>f22(["foo", "bar"]) : [string, string]
+>f22 : { <T extends unknown[] = []>(args: [...T, number]): T; <T extends unknown[] = []>(args: [...T]): T; }
+>["foo", "bar"] : [string, string]
+>"foo" : "foo"
+>"bar" : "bar"
+
+    let v3 = f22(["foo", 42]);  // [string]
+>v3 : [string]
+>f22(["foo", 42]) : [string]
+>f22 : { <T extends unknown[] = []>(args: [...T, number]): T; <T extends unknown[] = []>(args: [...T]): T; }
+>["foo", 42] : [string, number]
+>"foo" : "foo"
+>42 : 42
+}
+

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

@@ -334,3 +334,22 @@ call('hello', 32, (a, b) => 42);
 // Requires [starting-fixed-part, ...rest-part, ending-fixed-part] tuple structure
 
 call(...sa, (...x) => 42);
+
+// No inference to ending optional elements (except with identical structure)
+
+declare function f20<T extends unknown[] = []>(args: [...T, number?]): T;
+
+function f21<U extends string[]>(args: [...U, number?]) {
+    let v1 = f20(args);  // U
+    let v2 = f20(["foo", "bar"]);  // []
+    let v3 = f20(["foo", 42]);  // []
+}
+
+declare function f22<T extends unknown[] = []>(args: [...T, number]): T;
+declare function f22<T extends unknown[] = []>(args: [...T]): T;
+
+function f23<U extends string[]>(args: [...U, number]) {
+    let v1 = f22(args);  // U
+    let v2 = f22(["foo", "bar"]);  // [string, string]
+    let v3 = f22(["foo", 42]);  // [string]
+}