Temporarily revert unconstrained type parameter strictness in TS 4.7 (#48923)

* Revert a change around allowing unconstrained type parameters to '{}'.

* Accepted baselines.

Author: DanielRosenwasser

src/compiler/checker.ts

@@ -18772,9 +18772,6 @@ namespace ts {
                     return;
                 }
                 reportRelationError(headMessage, source, target);
-                if (strictNullChecks && source.flags & TypeFlags.TypeVariable && source.symbol?.declarations?.[0] && !getConstraintOfType(source as TypeVariable) && isRelatedTo(emptyObjectType, extractTypesOfKind(target, ~TypeFlags.NonPrimitive))) {
-                    associateRelatedInfo(createDiagnosticForNode(source.symbol.declarations[0], Diagnostics.This_type_parameter_probably_needs_an_extends_object_constraint));
-                }
             }
 
             function traceUnionsOrIntersectionsTooLarge(source: Type, target: Type): void {
@@ -19565,20 +19562,20 @@ namespace ts {
                     // IndexedAccess comparisons are handled above in the `targetFlags & TypeFlage.IndexedAccess` branch
                     if (!(sourceFlags & TypeFlags.IndexedAccess && targetFlags & TypeFlags.IndexedAccess)) {
                         const constraint = getConstraintOfType(source as TypeVariable);
-                        if (!strictNullChecks && (!constraint || (sourceFlags & TypeFlags.TypeParameter && constraint.flags & TypeFlags.Any))) {
+                        if (!constraint || (sourceFlags & TypeFlags.TypeParameter && constraint.flags & TypeFlags.Any)) {
                             // A type variable with no constraint is not related to the non-primitive object type.
                             if (result = isRelatedTo(emptyObjectType, extractTypesOfKind(target, ~TypeFlags.NonPrimitive), RecursionFlags.Both)) {
                                 resetErrorInfo(saveErrorInfo);
                                 return result;
                             }
                         }
                         // hi-speed no-this-instantiation check (less accurate, but avoids costly `this`-instantiation when the constraint will suffice), see #28231 for report on why this is needed
-                        else if (constraint && (result = isRelatedTo(constraint, target, RecursionFlags.Source, /*reportErrors*/ false, /*headMessage*/ undefined, intersectionState))) {
+                        else if (result = isRelatedTo(constraint, target, RecursionFlags.Source, /*reportErrors*/ false, /*headMessage*/ undefined, intersectionState)) {
                             resetErrorInfo(saveErrorInfo);
                             return result;
                         }
                         // slower, fuller, this-instantiated check (necessary when comparing raw `this` types from base classes), see `subclassWithPolymorphicThisIsAssignable.ts` test for example
-                        else if (constraint && (result = isRelatedTo(getTypeWithThisArgument(constraint, source), target, RecursionFlags.Source, reportErrors && !(targetFlags & sourceFlags & TypeFlags.TypeParameter), /*headMessage*/ undefined, intersectionState))) {
+                        else if (result = isRelatedTo(getTypeWithThisArgument(constraint, source), target, RecursionFlags.Source, reportErrors && !(targetFlags & sourceFlags & TypeFlags.TypeParameter), /*headMessage*/ undefined, intersectionState)) {
                             resetErrorInfo(saveErrorInfo);
                             return result;
                         }

src/compiler/diagnosticMessages.json

@@ -1506,10 +1506,6 @@
         "category": "Error",
         "code": 2207
     },
-    "This type parameter probably needs an `extends object` constraint.": {
-        "category": "Error",
-        "code": 2208
-    },
 
     "Duplicate identifier '{0}'.": {
         "category": "Error",

tests/baselines/reference/genericUnboundedTypeParamAssignability.errors.txt

@@ -1,10 +1,8 @@
 tests/cases/compiler/genericUnboundedTypeParamAssignability.ts(2,5): error TS2339: Property 'toString' does not exist on type 'T'.
-tests/cases/compiler/genericUnboundedTypeParamAssignability.ts(15,6): error TS2345: Argument of type 'T' is not assignable to parameter of type '{}'.
-tests/cases/compiler/genericUnboundedTypeParamAssignability.ts(16,6): error TS2345: Argument of type 'T' is not assignable to parameter of type 'Record<string, any>'.
 tests/cases/compiler/genericUnboundedTypeParamAssignability.ts(17,5): error TS2339: Property 'toString' does not exist on type 'T'.
 
 
-==== tests/cases/compiler/genericUnboundedTypeParamAssignability.ts (4 errors) ====
+==== tests/cases/compiler/genericUnboundedTypeParamAssignability.ts (2 errors) ====
     function f1<T>(o: T) {
       o.toString(); // error
         ~~~~~~~~
@@ -22,13 +20,7 @@ tests/cases/compiler/genericUnboundedTypeParamAssignability.ts(17,5): error TS23
     function user<T>(t: T) {
       f1(t);
       f2(t); // error in strict, unbounded T doesn't satisfy the constraint
-         ~
-!!! error TS2345: Argument of type 'T' is not assignable to parameter of type '{}'.
-!!! related TS2208 tests/cases/compiler/genericUnboundedTypeParamAssignability.ts:13:15: This type parameter probably needs an `extends object` constraint.
       f3(t); // error in strict, unbounded T doesn't satisfy the constraint
-         ~
-!!! error TS2345: Argument of type 'T' is not assignable to parameter of type 'Record<string, any>'.
-!!! related TS2208 tests/cases/compiler/genericUnboundedTypeParamAssignability.ts:13:15: This type parameter probably needs an `extends object` constraint.
       t.toString();  // error, for the same reason as f1()
         ~~~~~~~~
 !!! error TS2339: Property 'toString' does not exist on type 'T'.