Properly account for 'this' parameter in type predicate checks

ahejlsberg · ahejlsberg · commit e3b4c9097006 · 2017-04-22T17:08:52.000-07:00
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -11565,7 +11565,7 @@ namespace ts {
                 }
 
                 if (isIdentifierTypePredicate(predicate)) {
-                    const predicateArgument = callExpression.arguments[predicate.parameterIndex];
+                    const predicateArgument = callExpression.arguments[predicate.parameterIndex - (signature.thisParameter ? 1 : 0)];
                     if (predicateArgument) {
                         if (isMatchingReference(reference, predicateArgument)) {
                             return getNarrowedType(type, predicate.type, assumeTrue, isTypeSubtypeOf);

Original file line number	Diff line number	Diff line change
`@@ -11565,7 +11565,7 @@ namespace ts {`
`11565`	`11565`	`}`
`11566`	`11566`
`11567`	`11567`	`if (isIdentifierTypePredicate(predicate)) {`
`11568`		`- const predicateArgument = callExpression.arguments[predicate.parameterIndex];`
	`11568`	`+ const predicateArgument = callExpression.arguments[predicate.parameterIndex - (signature.thisParameter ? 1 : 0)];`
`11569`	`11569`	`if (predicateArgument) {`
`11570`	`11570`	`if (isMatchingReference(reference, predicateArgument)) {`
`11571`	`11571`	`return getNarrowedType(type, predicate.type, assumeTrue, isTypeSubtypeOf);`