fix completions protected members in recursive generic types (#19192) (#19242)

Author: Kingwl

src/compiler/checker.ts

@@ -15162,12 +15162,11 @@ namespace ts {
             if (flags & ModifierFlags.Static) {
                 return true;
             }
-            // An instance property must be accessed through an instance of the enclosing class
-            if (type.flags & TypeFlags.TypeParameter && (type as TypeParameter).isThisType) {
+             if (type.flags & TypeFlags.TypeParameter) {
                 // get the original type -- represented as the type constraint of the 'this' type
-                type = getConstraintOfTypeParameter(<TypeParameter>type);
+                type = (type as TypeParameter).isThisType ? getConstraintOfTypeParameter(<TypeParameter>type) : getBaseConstraintOfType(<TypeParameter>type);
             }
-            if (!(getObjectFlags(getTargetType(type)) & ObjectFlags.ClassOrInterface && hasBaseType(type, enclosingClass))) {
+            if (!type || !hasBaseType(type, enclosingClass)) {
                 error(errorNode, Diagnostics.Property_0_is_protected_and_only_accessible_through_an_instance_of_class_1, symbolToString(prop), typeToString(enclosingClass));
                 return false;
             }

tests/cases/fourslash/completionsForRecursiveGenericTypesMember.ts

@@ -0,0 +1,18 @@
+/// <reference path="fourslash.ts" />
+
+//// export class TestBase<T extends TestBase<T>>
+//// {   
+////     public publicMethod(p: any): void {}
+////     private privateMethod(p: any): void {}
+////     protected protectedMethod(p: any): void {}
+////     public test(t: T): void
+////     {
+////         t./**/
+////     }
+//// }
+
+goTo.marker();
+
+verify.completionListContains('publicMethod');
+verify.completionListContains('privateMethod');
+verify.completionListContains('protectedMethod');