Port "Fix of #58996" (#1802)

Author: Andarist

internal/checker/checker.go

@@ -19746,7 +19746,7 @@ func (c *Checker) checkIfExpressionRefinesParameter(fn *ast.Node, expr *ast.Node
 	// "x is T" means that x is T if and only if it returns true. If it returns false then x is not T.
 	// This means that if the function is called with an argument of type trueType, there can't be anything left in the `else` branch. It must reduce to `never`.
 	falseCondition := &ast.FlowNode{Flags: ast.FlowFlagsFalseCondition, Node: expr, Antecedent: antecedent}
-	falseSubtype := c.getFlowTypeOfReferenceEx(param.Name(), initType, trueType, fn, falseCondition)
+	falseSubtype := c.getReducedType(c.getFlowTypeOfReferenceEx(param.Name(), initType, trueType, fn, falseCondition))
 	if falseSubtype.flags&TypeFlagsNever != 0 {
 		return trueType
 	}

testdata/baselines/reference/submodule/compiler/inferTypePredicates.js

@@ -648,4 +648,4 @@ type Rock = {
 type Something = Animal | Rock;
 declare function isAnimal(something: Something): something is Animal;
 declare function positive(t: Something): t is Animal;
-declare function negative(t: Something): boolean;
+declare function negative(t: Something): t is Rock;

testdata/baselines/reference/submodule/compiler/inferTypePredicates.js.diff

@@ -58,10 +58,4 @@
 +}) => fb is {
      type: "foo";
      foo: number;
- };
-@@= skipped -15, +21 lines =@@
- type Something = Animal | Rock;
- declare function isAnimal(something: Something): something is Animal;
- declare function positive(t: Something): t is Animal;
--declare function negative(t: Something): t is Rock;
-+declare function negative(t: Something): boolean;
+ };

testdata/baselines/reference/submodule/compiler/inferTypePredicates.types

@@ -1092,7 +1092,7 @@ function positive(t: Something) {
 }
 
 function negative(t: Something) { 
->negative : (t: Something) => boolean
+>negative : (t: Something) => t is Rock
 >t : Something
 
   return !isAnimal(t)

testdata/baselines/reference/submodule/compiler/inferTypePredicates.types.diff

@@ -141,13 +141,4 @@
 +>foobarPred : (fb: { type: "foo"; foo: number; } | { type: "bar"; bar: string; }) => fb is { type: "foo"; foo: number; }
  >foobar : { type: "foo"; foo: number; } | { type: "bar"; bar: string; }
 
-   foobar.foo;
-@@= skipped -88, +88 lines =@@
- }
-
- function negative(t: Something) { 
-->negative : (t: Something) => t is Rock
-+>negative : (t: Something) => boolean
- >t : Something
-
-   return !isAnimal(t)
+   foobar.foo;