[ddc] Support warnings/errors in weak mode

In the new runtime type system when running with weak null safety,
perform type tests multiple times to produce optional warnings or
errors when a test passes but would fail in sound null safety.
This is the same technique DDC uses with the current type system.

Issue: #48585
Change-Id: Ic1514987a6f4ffeb127a0d2be5ec15b606016212
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/266543
Reviewed-by: Mark Zhou <[email protected]>
Reviewed-by: Anna Gringauze <[email protected]>
Commit-Queue: Nicholas Shahan <[email protected]>

Author: nshahan

pkg/dev_compiler/lib/src/kernel/compiler.dart

@@ -5935,7 +5935,13 @@ class ProgramCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
             case 'PRINT_LEGACY_STARS':
               return js.boolean(_options.printLegacyStars);
             case 'LEGACY':
-              return js.boolean(!_options.soundNullSafety);
+              return _options.soundNullSafety
+                  ? js.boolean(false)
+                  // When running the new runtime type system with weak null
+                  // safety this flag gets toggled when performing `is` and `as`
+                  // checks. This allows DDC to produce optional warnings or
+                  // errors when tests pass but would fail in sound null safety.
+                  : runtimeCall('legacyTypeChecks');
             case 'MINIFIED':
               return js.boolean(false);
             case 'NEW_RUNTIME_TYPES':
@@ -6563,16 +6569,24 @@ class ProgramCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
         type.nullability == Nullability.nonNullable &&
         type != _types.coreTypes.intNonNullableRawType) {
       return js.call('typeof # == #', [lhs, js.string(typeofName, "'")]);
-    } else {
-      return _options.newRuntimeTypes
+    }
+
+    if (_options.newRuntimeTypes) {
+      // When using the new runtime type system with sound null safety we can
+      // call to the library directly. In weak mode we call a DDC only method
+      // that can optionally produce warnings or errors when the check passes
+      // but would fail with sound null safety.
+      return _options.soundNullSafety
           ? js.call('#.#(#)', [
               _emitType(type),
               _emitMemberName(js_ast.FixedNames.rtiIsField,
                   memberClass: rtiClass),
               lhs
             ])
-          : js.call('#.is(#)', [_emitType(type), lhs]);
+          : runtimeCall('is(#, #)', [lhs, _emitType(type)]);
     }
+
+    return js.call('#.is(#)', [_emitType(type), lhs]);
   }
 
   @override
@@ -6649,15 +6663,21 @@ class ProgramCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
 
   js_ast.Expression _emitCast(js_ast.Expression expr, DartType type) {
     if (_types.isTop(type)) return expr;
-
-    return _options.newRuntimeTypes
-        ? js.call('#.#(#)', [
-            _emitType(type),
-            _emitMemberName(js_ast.FixedNames.rtiAsField,
-                memberClass: rtiClass),
-            expr
-          ])
-        : js.call('#.as(#)', [_emitType(type), expr]);
+    if (_options.newRuntimeTypes) {
+      // When using the new runtime type system with sound null safety we can
+      // call to the library directly. In weak mode we call a DDC only method
+      // that can optionally produce warnings or errors when the cast passes but
+      // would fail with sound null safety.
+      return _options.soundNullSafety
+          ? js.call('#.#(#)', [
+              _emitType(type),
+              _emitMemberName(js_ast.FixedNames.rtiAsField,
+                  memberClass: rtiClass),
+              expr
+            ])
+          : runtimeCall('as(#, #)', [expr, _emitType(type)]);
+    }
+    return js.call('#.as(#)', [_emitType(type), expr]);
   }
 
   @override

sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/operations.dart

@@ -456,12 +456,36 @@ dsetindex(obj, index, value) =>
 @notNull
 @JSExportName('is')
 bool instanceOf(obj, type) {
-  if (obj == null) {
-    return _equalType(type, Null) ||
-        _isTop(type) ||
-        _jsInstanceOf(type, NullableType);
+  if (JS_GET_FLAG('NEW_RUNTIME_TYPES')) {
+    var testRti = JS<rti.Rti>('!', '#', type);
+    // When running without sound null safety is type tests are dispatched here
+    // to issue optional warnings/errors when the result is true but would be
+    // false with sound null safety.
+    var legacyErasedRecipe =
+        rti.Rti.getLegacyErasedRecipe(JS<rti.Rti>('!', '#', testRti));
+    var legacyErasedType = rti.findType(legacyErasedRecipe);
+    legacyTypeChecks = false;
+    var result = JS<bool>('bool', '#.#(#)', legacyErasedType,
+        JS_GET_NAME(JsGetName.RTI_FIELD_IS), obj);
+    legacyTypeChecks = true;
+    if (result) return true;
+    result =
+        JS('bool', '#.#(#)', testRti, JS_GET_NAME(JsGetName.RTI_FIELD_IS), obj);
+    if (result) {
+      // Type test passes put would fail with sound null safety.
+      var t1 = runtimeType(obj);
+      var t2 = rti.createRuntimeType(testRti);
+      _nullWarn('$t1 is not a subtype of $t2.');
+    }
+    return result;
+  } else {
+    if (obj == null) {
+      return _equalType(type, Null) ||
+          _isTop(type) ||
+          _jsInstanceOf(type, NullableType);
+    }
+    return isSubtypeOf(getReifiedType(obj), type);
   }
-  return isSubtypeOf(getReifiedType(obj), type);
 }
 
 /// General implementation of the Dart `as` operator.
@@ -477,12 +501,33 @@ cast(obj, type) {
     // Check the null comparison cache to avoid emitting repeated warnings.
     _nullWarnOnType(type);
     return obj;
+  }
+  if (JS_GET_FLAG('NEW_RUNTIME_TYPES')) {
+    // When running without sound null safety casts are dispatched here to issue
+    // optional warnings/errors when casts pass but would fail with sound null
+    // safety.
+    var testRti = JS<rti.Rti>('!', '#', type);
+    var objRti = JS<rti.Rti>('!', '#', getReifiedType(obj));
+    var legacyErasedRecipe = rti.Rti.getLegacyErasedRecipe(testRti);
+    var legacyErasedType = rti.findType(legacyErasedRecipe);
+    legacyTypeChecks = false;
+    // Call `isSubtype()` to avoid throwing an error if it fails.
+    var result = rti.isSubtype(
+        JS_EMBEDDED_GLOBAL('', RTI_UNIVERSE), objRti, legacyErasedType);
+    legacyTypeChecks = true;
+    if (result) return obj;
+    // Perform the actual cast and allow the error to be thrown if it fails.
+    JS('bool', '#.#(#)', testRti, JS_GET_NAME(JsGetName.RTI_FIELD_AS), obj);
+    // Subtype check passes put would fail with sound null safety.
+    var t1 = runtimeType(obj);
+    var t2 = rti.createRuntimeType(testRti);
+    _nullWarn('$t1 is not a subtype of $t2.');
+    return obj;
   } else {
     var actual = getReifiedType(obj);
     if (isSubtypeOf(actual, type)) return obj;
+    return castError(obj, type);
   }
-
-  return castError(obj, type);
 }
 
 bool test(bool? obj) {

sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/runtime.dart

@@ -10,7 +10,15 @@ import 'dart:collection';
 
 import 'dart:_debugger' show stackTraceMapper, trackCall;
 import 'dart:_foreign_helper'
-    show JS, JS_CLASS_REF, JS_GET_FLAG, JS_GET_NAME, JSExportName, rest, spread;
+    show
+        JS,
+        JS_CLASS_REF,
+        JS_EMBEDDED_GLOBAL,
+        JS_GET_FLAG,
+        JS_GET_NAME,
+        JSExportName,
+        rest,
+        spread;
 import 'dart:_interceptors'
     show
         JSArray,
@@ -37,9 +45,13 @@ import 'dart:_js_helper'
 import 'dart:_js_shared_embedded_names';
 import 'dart:_rti' as rti
     show
+        createRuntimeType,
         constructorRtiCachePropertyName,
+        findType,
         instanceType,
-        interfaceTypeRecipePropertyName;
+        interfaceTypeRecipePropertyName,
+        isSubtype,
+        Rti;
 
 export 'dart:_debugger' show getDynamicStats, clearDynamicStats, trackCall;
 

sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/types.dart

@@ -16,6 +16,15 @@ external bool compileTimeFlag(String flag);
 _throwInvalidFlagError(String message) =>
     throw UnsupportedError('Invalid flag combination.\n$message');
 
+/// When running the new runtime type system with weak null safety this flag
+/// gets toggled to change the behavior of the dart:_rti library when performing
+/// `is` and `as` checks.
+///
+/// This allows DDC to produce optional warnings or errors when tests pass but
+/// would fail in sound null safety.
+@notNull
+bool legacyTypeChecks = !compileTimeFlag("soundNullSafety");
+
 @notNull
 bool _weakNullSafetyWarnings = false;