Nullable errors on unconstrained generic types in strictNullChecks mode

Author: ahejlsberg

src/compiler/checker.ts

@@ -1226,8 +1226,11 @@ export const enum TypeFacts {
     Falsy = 1 << 23,              // !x
     IsUndefined = 1 << 24,        // Contains undefined or intersection with undefined
     IsNull = 1 << 25,             // Contains null or intersection with null
+    IsPossiblyUndefined = 1 << 26, // Possibly undefined
+    IsPossiblyNull = 1 << 27,     // Possibly null
     IsUndefinedOrNull = IsUndefined | IsNull,
-    All = (1 << 27) - 1,
+    IsPossiblyUndefinedOrNull = IsPossiblyUndefined | IsPossiblyNull,
+    All = (1 << 29) - 1,
     // The following members encode facts about particular kinds of types for use in the getTypeFacts function.
     // The presence of a particular fact means that the given test is true for some (and possibly all) values
     // of that kind of type.
@@ -1270,11 +1273,12 @@ export const enum TypeFacts {
     FunctionStrictFacts = TypeofEQFunction | TypeofEQHostObject | TypeofNEString | TypeofNENumber | TypeofNEBigInt | TypeofNEBoolean | TypeofNESymbol | TypeofNEObject | NEUndefined | NENull | NEUndefinedOrNull | Truthy,
     FunctionFacts = FunctionStrictFacts | EQUndefined | EQNull | EQUndefinedOrNull | Falsy,
     VoidFacts = TypeofNEString | TypeofNENumber | TypeofNEBigInt | TypeofNEBoolean | TypeofNESymbol | TypeofNEObject | TypeofNEFunction | TypeofNEHostObject | EQUndefined | EQUndefinedOrNull | NENull | Falsy,
-    UndefinedFacts = TypeofNEString | TypeofNENumber | TypeofNEBigInt | TypeofNEBoolean | TypeofNESymbol | TypeofNEObject | TypeofNEFunction | TypeofNEHostObject | EQUndefined | EQUndefinedOrNull | NENull | Falsy | IsUndefined,
-    NullFacts = TypeofEQObject | TypeofNEString | TypeofNENumber | TypeofNEBigInt | TypeofNEBoolean | TypeofNESymbol | TypeofNEFunction | TypeofNEHostObject | EQNull | EQUndefinedOrNull | NEUndefined | Falsy | IsNull,
-    EmptyObjectStrictFacts = All & ~(EQUndefined | EQNull | EQUndefinedOrNull | IsUndefinedOrNull),
-    EmptyObjectFacts = All & ~IsUndefinedOrNull,
-    UnknownFacts = All & ~IsUndefinedOrNull,
+    UndefinedFacts = TypeofNEString | TypeofNENumber | TypeofNEBigInt | TypeofNEBoolean | TypeofNESymbol | TypeofNEObject | TypeofNEFunction | TypeofNEHostObject | EQUndefined | EQUndefinedOrNull | NENull | Falsy | IsUndefined | IsPossiblyUndefined,
+    NullFacts = TypeofEQObject | TypeofNEString | TypeofNENumber | TypeofNEBigInt | TypeofNEBoolean | TypeofNESymbol | TypeofNEFunction | TypeofNEHostObject | EQNull | EQUndefinedOrNull | NEUndefined | Falsy | IsNull | IsPossiblyNull,
+    EmptyObjectStrictFacts = All & ~(EQUndefined | EQNull | EQUndefinedOrNull | IsUndefinedOrNull | IsPossiblyUndefinedOrNull),
+    EmptyObjectFacts = All & ~(IsUndefinedOrNull | IsPossiblyUndefinedOrNull),
+    UnknownStrictFacts = All & ~IsUndefinedOrNull,
+    UnknownFacts = All & ~(IsUndefinedOrNull | IsPossiblyUndefinedOrNull),
     AllTypeofNE = TypeofNEString | TypeofNENumber | TypeofNEBigInt | TypeofNEBoolean | TypeofNESymbol | TypeofNEObject | TypeofNEFunction | NEUndefined,
     // Masks
     OrFactsMask = TypeofEQFunction | TypeofNEObject,
@@ -27477,7 +27481,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         if (flags & TypeFlags.Intersection) {
             return getIntersectionTypeFacts(type as IntersectionType, callerOnlyNeeds);
         }
-        return TypeFacts.UnknownFacts;
+        return strictNullChecks && flags & TypeFlags.Unknown ? TypeFacts.UnknownStrictFacts : TypeFacts.UnknownFacts;
     }
 
     function getIntersectionTypeFacts(type: IntersectionType, callerOnlyNeeds: TypeFacts): TypeFacts {
@@ -33699,7 +33703,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             }
             error(
                 node,
-                facts & TypeFacts.IsUndefined ? facts & TypeFacts.IsNull ?
+                facts & TypeFacts.IsPossiblyUndefined ? facts & TypeFacts.IsPossiblyNull ?
                     Diagnostics._0_is_possibly_null_or_undefined :
                     Diagnostics._0_is_possibly_undefined :
                     Diagnostics._0_is_possibly_null,
@@ -33709,7 +33713,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         else {
             error(
                 node,
-                facts & TypeFacts.IsUndefined ? facts & TypeFacts.IsNull ?
+                facts & TypeFacts.IsPossiblyUndefined ? facts & TypeFacts.IsPossiblyNull ?
                     Diagnostics.Object_is_possibly_null_or_undefined :
                     Diagnostics.Object_is_possibly_undefined :
                     Diagnostics.Object_is_possibly_null,
@@ -33720,7 +33724,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     function reportCannotInvokePossiblyNullOrUndefinedError(node: Node, facts: TypeFacts) {
         error(
             node,
-            facts & TypeFacts.IsUndefined ? facts & TypeFacts.IsNull ?
+            facts & TypeFacts.IsPossiblyUndefined ? facts & TypeFacts.IsPossiblyNull ?
                 Diagnostics.Cannot_invoke_an_object_which_is_possibly_null_or_undefined :
                 Diagnostics.Cannot_invoke_an_object_which_is_possibly_undefined :
                 Diagnostics.Cannot_invoke_an_object_which_is_possibly_null,
@@ -33743,8 +33747,8 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             error(node, Diagnostics.Object_is_of_type_unknown);
             return errorType;
         }
-        const facts = getTypeFacts(type, TypeFacts.IsUndefinedOrNull);
-        if (facts & TypeFacts.IsUndefinedOrNull) {
+        const facts = getTypeFacts(type, TypeFacts.IsPossiblyUndefinedOrNull);
+        if (facts & TypeFacts.IsPossiblyUndefinedOrNull) {
             reportError(node, facts);
             const t = getNonNullableType(type);
             return t.flags & (TypeFlags.Nullable | TypeFlags.Never) ? errorType : t;