[vm/ffi] Use Pointer<Null> as the type of nullptr.

Also clean up test/benchmark/sample code using nullptr and fix pubspec.yaml in the SQLite sample.

Fixes https://github.com/dart-lang/sdk/issues/37362

Change-Id: I6fa0522374af28020ef8f096ac22b23712aedb5a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/121122
Commit-Queue: Samir Jindel <sjindel@google.com>
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>

benchmarks/FfiBoringssl/dart/FfiBoringssl.dart

@@ -49,7 +49,7 @@ String hash(Pointer<Data> data, int length, Pointer<EVP_MD> hashAlgorithm) {
   EVP_DigestUpdate(context, data, length);
   final int resultSize = EVP_MD_CTX_size(context);
   final Pointer<Bytes> result = allocate<Uint8>(count: resultSize).cast();
-  EVP_DigestFinal(context, result, nullptr.cast());
+  EVP_DigestFinal(context, result, nullptr);
   EVP_MD_CTX_free(context);
   final String hash = base64Encode(toUint8List(result.ref, resultSize));
   free(result);

samples/ffi/sqlite/docs/sqlite-tutorial.md

@@ -106,7 +106,7 @@ Now we have all ingredients to call `sqlite3_prepare_v2`.
 Pointer<StatementPointer> statementOut = allocate();
 CString queryC = CString.allocate(query);
 int resultCode = sqlite3_prepare_v2(
-    _database, queryC, -1, statementOut, fromAddress(0));
+    _database, queryC, -1, statementOut, nullptr);
 ```
 
 With `dart:ffi` we are responsible for freeing C memory that we allocate.

samples/ffi/sqlite/lib/src/database.dart

@@ -30,7 +30,7 @@ class Database {
     Pointer<Pointer<types.Database>> dbOut = allocate();
     final pathC = Utf8.toUtf8(path);
     final int resultCode =
-        bindings.sqlite3_open_v2(pathC, dbOut, flags, Pointer.fromAddress(0));
+        bindings.sqlite3_open_v2(pathC, dbOut, flags, nullptr);
     _database = dbOut.value;
     free(dbOut);
     free(pathC);
@@ -66,7 +66,7 @@ class Database {
     Pointer<Pointer<Statement>> statementOut = allocate();
     Pointer<Utf8> queryC = Utf8.toUtf8(query);
     int resultCode = bindings.sqlite3_prepare_v2(
-        _database, queryC, -1, statementOut, Pointer.fromAddress(0));
+        _database, queryC, -1, statementOut, nullptr);
     Pointer<Statement> statement = statementOut.value;
     free(statementOut);
     free(queryC);
@@ -85,7 +85,7 @@ class Database {
     Pointer<Pointer<Statement>> statementOut = allocate();
     Pointer<Utf8> queryC = Utf8.toUtf8(query);
     int resultCode = bindings.sqlite3_prepare_v2(
-        _database, queryC, -1, statementOut, Pointer.fromAddress(0));
+        _database, queryC, -1, statementOut, nullptr);
     Pointer<Statement> statement = statementOut.value;
     free(statementOut);
     free(queryC);

samples/ffi/sqlite/pubspec.yaml

@@ -5,5 +5,8 @@ description: >-
 author: Daco Harkes <dacoharkes@google.com>, Samir Jindel <sjindel@google.com>
 environment:
   sdk: '>=2.1.0 <3.0.0'
+dependencies:
+  ffi:
+    path: ../../../third_party/pkg/ffi
 dev_dependencies:
   test: ^1.5.3

sdk/lib/ffi/ffi.dart

@@ -26,8 +26,9 @@ part "struct.dart";
 /// Includes padding and alignment of structs.
 external int sizeOf<T extends NativeType>();
 
-/// Represents a pointer into the native C memory.
-final Pointer<Void> nullptr = Pointer.fromAddress(0);
+/// Represents a pointer into the native C memory corresponding to "NULL", e.g.
+/// a pointer with address 0.
+final Pointer<Null> nullptr = Pointer.fromAddress(0);
 
 /// Represents a pointer into the native C memory. Cannot be extended.
 @pragma("vm:entry-point")

sdk_nnbd/lib/ffi/ffi.dart

@@ -28,8 +28,9 @@ part "struct.dart";
 /// Includes padding and alignment of structs.
 external int sizeOf<T extends NativeType>();
 
-/// Represents a pointer into the native C memory.
-final Pointer<Void> nullptr = Pointer.fromAddress(0);
+/// Represents a pointer into the native C memory corresponding to "NULL", e.g.
+/// a pointer with address 0.
+final Pointer<Null> nullptr = Pointer.fromAddress(0);
 
 /// Represents a pointer into the native C memory. Cannot be extended.
 @pragma("vm:entry-point")

tests/ffi/data_test.dart

@@ -55,6 +55,7 @@ void main() {
   testSizeOfNativeType();
   testDynamicInvocation();
   testMemoryAddressTruncation();
+  testNullptrCast();
 }
 
 void testPointerBasic() {
@@ -328,7 +329,7 @@ void testPointerPointer() {
 
 void testPointerPointerNull() {
   Pointer<Pointer<Int8>> pointerToPointer = allocate();
-  Pointer<Int8> value = nullptr.cast();
+  Pointer<Int8> value = nullptr;
   pointerToPointer.value = value;
   value = pointerToPointer.value;
   Expect.equals(value, nullptr);
@@ -337,7 +338,7 @@ void testPointerPointerNull() {
   value = pointerToPointer.value;
   Expect.isNotNull(value);
   free(value);
-  value = nullptr.cast();
+  value = nullptr;
   pointerToPointer.value = value;
   value = pointerToPointer.value;
   Expect.equals(value, nullptr);
@@ -510,6 +511,16 @@ void testDynamicInvocation() {
   free(p);
 }
 
+final nullableInt64ElementAt1 = ffiTestFunctions.lookupFunction<
+    Pointer<Int64> Function(Pointer<Int64>),
+    Pointer<Int64> Function(Pointer<Int64>)>("NullableInt64ElemAt1");
+
+void testNullptrCast() {
+  Pointer<Int64> ptr = nullptr;
+  ptr = nullableInt64ElementAt1(ptr);
+  Expect.equals(ptr, nullptr);
+}
+
 void testMemoryAddressTruncation() {
   const int kIgnoreBytesPositive = 0x1122334400000000;
   const int kIgnoreBytesNegative = 0xffddccbb00000000;

tests/ffi/external_typed_data_test.dart

@@ -282,7 +282,7 @@ void testArrayStore() {
 }
 
 void testNegativeArray() {
-  Pointer<Int32> ptr = nullptr.cast();
+  Pointer<Int32> ptr = nullptr;
   Expect.throws<ArgumentError>(() => ptr.asExternalTypedData(count: -1));
 }
 

tests/ffi/function_structs_test.dart

@@ -35,8 +35,7 @@ void testFunctionWithStruct() {
       ffiTestFunctions.lookup("TransposeCoordinate");
   NativeCoordinateOp f1 = p1.asFunction();
 
-  Pointer<Coordinate> c1 =
-      Coordinate.allocate(10.0, 20.0, nullptr.cast<Coordinate>()).addressOf;
+  Pointer<Coordinate> c1 = Coordinate.allocate(10.0, 20.0, nullptr).addressOf;
   Pointer<Coordinate> c2 = Coordinate.allocate(42.0, 84.0, c1).addressOf;
   c1.ref.next = c2;
 
@@ -107,9 +106,9 @@ void testFunctionWithVeryLargeStruct() {
   vls1.numChildren = 2;
   vls1.children = vls1.addressOf;
   vls2.parent = vls2.addressOf;
-  vls2.parent = nullptr.cast();
+  vls2.parent = nullptr;
   vls2.numChildren = 0;
-  vls2.children = nullptr.cast();
+  vls2.children = nullptr;
 
   int result = f(vls1.addressOf);
   Expect.equals(2051, result);

tests/ffi/function_test.dart

@@ -355,7 +355,7 @@ Int64PointerUnOp nullableInt64ElemAt1 = ffiTestFunctions
     .lookupFunction<Int64PointerUnOp, Int64PointerUnOp>("NullableInt64ElemAt1");
 
 void testNullPointers() {
-  Pointer<Int64> result = nullableInt64ElemAt1(nullptr.cast());
+  Pointer<Int64> result = nullableInt64ElemAt1(nullptr);
   Expect.equals(result, nullptr);
 
   Pointer<Int64> p2 = allocate(count: 2);

tests/ffi/static_checks_test.dart

@@ -98,7 +98,7 @@ void testGetNativeType() {
 
 void testGetTypeMismatch() {
   Pointer<Pointer<Int16>> p = allocate();
-  Pointer<Int16> typedNull = nullptr.cast();
+  Pointer<Int16> typedNull = nullptr;
   p.value = typedNull;
 
   // this fails to compile due to type mismatch

tests/ffi/structs_test.dart

@@ -30,8 +30,7 @@ void main() {
 
 /// allocates each coordinate separately in c memory
 void testStructAllocate() {
-  Pointer<Coordinate> c1 =
-      Coordinate.allocate(10.0, 10.0, nullptr.cast()).addressOf;
+  Pointer<Coordinate> c1 = Coordinate.allocate(10.0, 10.0, nullptr).addressOf;
   Pointer<Coordinate> c2 = Coordinate.allocate(20.0, 20.0, c1).addressOf;
   Pointer<Coordinate> c3 = Coordinate.allocate(30.0, 30.0, c2).addressOf;
   c1.ref.next = c3;
@@ -82,11 +81,11 @@ void testStructFromAddress() {
 
 void testStructWithNulls() {
   Pointer<Coordinate> coordinate =
-      Coordinate.allocate(10.0, 10.0, nullptr.cast<Coordinate>()).addressOf;
+      Coordinate.allocate(10.0, 10.0, nullptr).addressOf;
   Expect.equals(coordinate.ref.next, nullptr);
   coordinate.ref.next = coordinate;
   Expect.notEquals(coordinate.ref.next, nullptr);
-  coordinate.ref.next = nullptr.cast();
+  coordinate.ref.next = nullptr;
   Expect.equals(coordinate.ref.next, nullptr);
   free(coordinate);
 }
@@ -122,7 +121,7 @@ void testBareStruct() {
 }
 
 void testTypeTest() {
-  Coordinate c = Coordinate.allocate(10, 10, nullptr.cast<Coordinate>());
+  Coordinate c = Coordinate.allocate(10, 10, nullptr);
   Expect.isTrue(c is Struct);
   Expect.isTrue(c is Struct<Coordinate>);
   free(c.addressOf);