[dart2js] Remove checks to support migration with mixed null safety

`_potentiallyAssertNotNull` would insert null checks to catch issues
from mixing libraries sound and unsound null safety. The null checks
are now always optimized away so we might as well never insert them.

Bug: #60327
Change-Id: I092a4fb336e46bf33b9b3cd9867dd7b6d8f9c65e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/427569
Reviewed-by: Mayank Patke <[email protected]>
Commit-Queue: Stephen Adams <[email protected]>
Reviewed-by: Jake Macdonald <[email protected]>

Author: rakudrama

pkg/compiler/lib/src/ssa/builder.dart

@@ -670,7 +670,6 @@ class KernelSsaGraphBuilder extends ir.VisitorDefault<void>
     // TODO(sra): The source information should indicate the field and
     // possibly its type but not the initializer.
     value.sourceInformation ??= _sourceInformationBuilder.buildSet(node);
-    value = _potentiallyAssertNotNull(field, node, value, type);
     if (!_fieldAnalysis.getFieldData(field).isElided) {
       add(HFieldSet(field, thisInstruction, value));
     }
@@ -1999,13 +1998,6 @@ class KernelSsaGraphBuilder extends ir.VisitorDefault<void>
           type,
         );
       }
-      // TODO(sra): Hoist out of loop.
-      newParameter = _potentiallyAssertNotNull(
-        member,
-        variable,
-        newParameter,
-        type,
-      );
       localsHandler.updateLocal(local, newParameter);
     }
 
@@ -2036,49 +2028,6 @@ class KernelSsaGraphBuilder extends ir.VisitorDefault<void>
     }
   }
 
-  /// In mixed mode, inserts an assertion of the form `assert(x != null)` for
-  /// parameters in opt-in libraries that have a static type that cannot be
-  /// nullable under a strong interpretation.
-  HInstruction _potentiallyAssertNotNull(
-    MemberEntity member,
-    ir.TreeNode context,
-    HInstruction value,
-    DartType type,
-  ) {
-    if (!dartTypes.isNonNullable(type)) return value;
-
-    // `operator==` is usually augmented to handle a `null`-argument before this
-    // test would be inserted.  There are a few exceptions (Object,
-    // Interceptor), where the body of the `==` method is designed to handle a
-    // `null` argument. In the usual case the null assertion is unnecessary and
-    // will be optimized away. In the exception cases a null assertion would be
-    // incorrect. Either way we should not do a null-assertion on the parameter
-    // of any `operator==` method.
-    if (member.name == '==') return value;
-
-    if (options.enableUserAssertions) {
-      pushCheckNull(value);
-      push(HNot(pop(), _abstractValueDomain.boolType));
-      var sourceInformation = _sourceInformationBuilder.buildAssert(context);
-      _pushStaticInvocation(
-        _commonElements.assertHelper,
-        [pop()],
-        _typeInferenceMap.getReturnTypeOf(_commonElements.assertHelper),
-        const <DartType>[],
-        sourceInformation: sourceInformation,
-      );
-      pop();
-      return value;
-    } else {
-      HInstruction nullCheck = HNullCheck(
-        value,
-        _abstractValueDomain.excludeNull(value.instructionType),
-      )..sourceInformation = value.sourceInformation;
-      add(nullCheck);
-      return nullCheck;
-    }
-  }
-
   /// Builds an SSA graph for FunctionNodes of external methods.
   void _buildExternalFunctionNode(
     FunctionEntity function,
@@ -8595,12 +8544,6 @@ class KernelSsaGraphBuilder extends ir.VisitorDefault<void>
           type,
         );
       }
-      checkedOrTrusted = _potentiallyAssertNotNull(
-        function,
-        variable,
-        checkedOrTrusted,
-        type,
-      );
       localsHandler.updateLocal(parameter, checkedOrTrusted);
     });
   }

tests/language/function_subtype/regress41680_strong_test.dart

@@ -5,6 +5,7 @@
 // Requirements=nnbd-strong
 
 import "package:expect/expect.dart";
+import 'package:expect/variations.dart' as v;
 
 typedef dynamicToDynamic = dynamic Function(dynamic);
 
@@ -22,5 +23,8 @@ main() {
   Expect.throwsTypeError(() => dynamicNull as dynamicToDynamic);
   Expect.throwsTypeError(() => cast<dynamic Function(dynamic)>(dynamicNull));
   Expect.throwsTypeError(() => dynamicNull as voidToT);
-  Expect.throwsTypeError(() => allowsArgument(dynamicNull));
+  Expect.throwsTypeErrorWhen(
+    v.checkedParameters,
+    () => allowsArgument(dynamicNull),
+  );
 }