Reset member resolution after base type resolution

internal/checker/checker.go

@@ -18332,6 +18332,11 @@ func (c *Checker) getBaseTypes(t *Type) []*Type {
 				}
 			}
 		}
+		// In general, base type resolution always precedes member resolution. However, it is possible
+		// for resolution of type parameter defaults to cause circularity errors, possibly leaving
+		// members partially resolved. Here we ensure any such partial resolution is reset.
+		// See https://github.com/microsoft/TypeScript/issues/16861 for an example.
+		t.objectFlags &^= ObjectFlagsMembersResolved
 		data.baseTypesResolved = true
 	}
 	return data.resolvedBaseTypes
@@ -18395,14 +18400,6 @@ func (c *Checker) resolveBaseTypesOfClass(t *Type) {
 		c.error(t.symbol.ValueDeclaration, diagnostics.Type_0_recursively_references_itself_as_a_base_type, c.TypeToString(t))
 		return
 	}
-	// !!! This logic is suspicious. We really shouldn't be un-resolving members after they've been resolved.
-	// if t.resolvedBaseTypes == resolvingEmptyArray {
-	// 	// Circular reference, likely through instantiation of default parameters
-	// 	// (otherwise there'd be an error from hasBaseType) - this is fine, but `.members` should be reset
-	// 	// as `getIndexedAccessType` via `instantiateType` via `getTypeFromClassOrInterfaceReference` forces a
-	// 	// partial instantiation of the members without the base types fully resolved
-	// 	t.members = nil
-	// }
 	t.AsInterfaceType().resolvedBaseTypes = []*Type{reducedBaseType}
 }
 

testdata/baselines/reference/submodule/compiler/circularConstraintYieldsAppropriateError.errors.txt

@@ -1,8 +1,7 @@
 circularConstraintYieldsAppropriateError.ts(10,7): error TS2310: Type 'Foo' recursively references itself as a base type.
-circularConstraintYieldsAppropriateError.ts(17,5): error TS2339: Property 'bar' does not exist on type 'Foo'.
 
 
-==== circularConstraintYieldsAppropriateError.ts (2 errors) ====
+==== circularConstraintYieldsAppropriateError.ts (1 errors) ====
     // https://github.com/Microsoft/TypeScript/issues/16861
     class BaseType<T> {
         bar: T
@@ -21,6 +20,4 @@ circularConstraintYieldsAppropriateError.ts(17,5): error TS2339: Property 'bar'
     }
 
     const foo = new Foo();
-    foo.bar.test
-        ~~~
-!!! error TS2339: Property 'bar' does not exist on type 'Foo'.
+    foo.bar.test

testdata/baselines/reference/submodule/compiler/circularConstraintYieldsAppropriateError.symbols

@@ -42,5 +42,9 @@ const foo = new Foo();
 >Foo : Symbol(Foo, Decl(circularConstraintYieldsAppropriateError.ts, 7, 1))
 
 foo.bar.test
+>foo.bar.test : Symbol(test, Decl(circularConstraintYieldsAppropriateError.ts, 10, 15))
+>foo.bar : Symbol(BaseType.bar, Decl(circularConstraintYieldsAppropriateError.ts, 1, 19))
 >foo : Symbol(foo, Decl(circularConstraintYieldsAppropriateError.ts, 15, 5))
+>bar : Symbol(BaseType.bar, Decl(circularConstraintYieldsAppropriateError.ts, 1, 19))
+>test : Symbol(test, Decl(circularConstraintYieldsAppropriateError.ts, 10, 15))
 

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

@@ -37,9 +37,9 @@ const foo = new Foo();
 >Foo : typeof Foo
 
 foo.bar.test
->foo.bar.test : any
->foo.bar : any
+>foo.bar.test : true
+>foo.bar : { test: true; }
 >foo : Foo
->bar : any
->test : any
+>bar : { test: true; }
+>test : true