[analyzer/ffi] Fix Unwrap typed data error messages

Fixes issues reported by:

TEST=pkg/analyzer/test/verify_diagnostics_test.dart

* Fixes error messages on asFunction.
* Fixes validation by introducing Uint8List to mock sdk.
* Removes unused typed_data import in example snippet.
* Fixes error locations in example snippets

Bug: https://github.com/dart-lang/sdk/issues/44589
Change-Id: I82261eea5e55cbafa686865a92131a449a7642f5
Cq-Include-Trybots: luci.dart.try:pkg-linux-debug-try,pkg-linux-release-try,pkg-mac-release-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/340921
Commit-Queue: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>

pkg/analyzer/lib/src/generated/ffi_verifier.dart

@@ -910,7 +910,7 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
       }
       _validateFfiTypedDataUnwrapping(
         F,
-        T,
+        TPrime,
         errorNode,
         isLeaf: isLeaf,
         isCall: true,
@@ -1086,6 +1086,11 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
       int i = 0;
       final nativeParamTypes = nativeType.normalParameterTypes.flattenVarArgs();
       for (final dartParam in dartType.normalParameterTypes) {
+        if (i >= nativeParamTypes.length) {
+          // Cascading error as not the same amount of arguments.
+          // Already results in an error earlier.
+          return;
+        }
         final nativeParam = nativeParamTypes[i];
         i++;
         if (dartParam.isTypedData && nativeParam.isPointer) {

pkg/analyzer/lib/src/test_utilities/mock_sdk.dart

@@ -1378,6 +1378,10 @@ final MockSdkLibrary _LIB_TYPED_DATA = MockSdkLibrary(
       '''
 library dart.typed_data;
 
+abstract final class Uint8List {
+  external factory Uint8List(int length);
+}
+
 abstract final class Int8List {
   external factory Int8List(int length);
 }

pkg/analyzer/messages.yaml

@@ -19859,7 +19859,7 @@ FfiCode:
       import 'dart:typed_data';
 
       void f(Pointer<NativeFunction<Void Function(Pointer<Uint8>)>> p) {
-        [!p.asFunction<void Function(Uint8List)>()!];
+        p.asFunction<[!void Function(Uint8List)!]>();
       }
       ```
 
@@ -19905,7 +19905,7 @@ FfiCode:
       import 'dart:typed_data';
 
       void f(Pointer<NativeFunction<Pointer<Uint8> Function()>> p) {
-        [!p.asFunction<Uint8List Function()>()!];
+        p.asFunction<[!Uint8List Function()!]>();
       }
       ```
 
@@ -19915,7 +19915,6 @@ FfiCode:
 
       ```dart
       import 'dart:ffi';
-      import 'dart:typed_data';
 
       void f(Pointer<NativeFunction<Pointer<Uint8> Function()>> p) {
         p.asFunction<Pointer<Uint8> Function()>();
@@ -19949,7 +19948,7 @@ FfiCode:
       void f(Uint8List i) {}
 
       void g() {
-        Pointer.fromFunction<Void Function(Pointer<Uint8>)>(f);
+        Pointer.fromFunction<Void Function(Pointer<Uint8>)>([!f!]);
       }
       ```
 
@@ -19959,7 +19958,6 @@ FfiCode:
 
       ```dart
       import 'dart:ffi';
-      import 'dart:typed_data';
 
       void f(Pointer<Uint8> i) {}
 

pkg/analyzer/tool/diagnostics/diagnostics.md

@@ -1918,6 +1918,90 @@ extension [!mixin!] on int {}
 
 Choose a different name for the declaration.
 
+### callback_must_not_use_typed_data
+
+_FFI callbacks can't take typed data arguments or return value._
+
+#### Description
+
+The analyzer produces this diagnostic when an invocation of
+`Pointer.fromFunction`, one of`NativeCallable`'s constructors has a
+typed data argument or return value."
+
+Typed data unwrapping is only supported on arguments for leaf FFI calls.
+
+For more information about FFI, see [C interop using dart:ffi][ffi].
+
+#### Example
+
+The following code produces this diagnostic because the parameter type
+of `g` is a typed data.
+
+{% prettify dart tag=pre+code %}
+import 'dart:ffi';
+import 'dart:typed_data';
+
+void f(Uint8List i) {}
+
+void g() {
+  Pointer.fromFunction<Void Function(Pointer<Uint8>)>([!f!]);
+}
+{% endprettify %}
+
+#### Common fixes
+
+Use the `Pointer` type instead:
+
+{% prettify dart tag=pre+code %}
+import 'dart:ffi';
+
+void f(Pointer<Uint8> i) {}
+
+void g() {
+  Pointer.fromFunction<Void Function(Pointer<Uint8>)>(f);
+}
+{% endprettify %}
+
+### call_must_not_return_typed_data
+
+_FFI calls can't return typed data._
+
+#### Description
+
+The analyzer produces this diagnostic when the return type of
+`Pointer.asFunction`, `DynamicLibrary.lookupFunction`, or
+`@Native` is a typed data.
+
+Typed data unwrapping is only supported on arguments for leaf FFI calls.
+
+For more information about FFI, see [C interop using dart:ffi][ffi].
+
+#### Example
+
+The following code produces this diagnostic because the dart function
+signature contains a typed data, but the `isLeaf` argument is `false`:
+
+{% prettify dart tag=pre+code %}
+import 'dart:ffi';
+import 'dart:typed_data';
+
+void f(Pointer<NativeFunction<Pointer<Uint8> Function()>> p) {
+  p.asFunction<[!Uint8List Function()!]>();
+}
+{% endprettify %}
+
+#### Common fixes
+
+Use the `Pointer` type instead:
+
+{% prettify dart tag=pre+code %}
+import 'dart:ffi';
+
+void f(Pointer<NativeFunction<Pointer<Uint8> Function()>> p) {
+  p.asFunction<Pointer<Uint8> Function()>();
+}
+{% endprettify %}
+
 ### case_block_not_terminated
 
 _The last statement of the 'case' should be 'break', 'continue', 'rethrow',
@@ -15167,6 +15251,52 @@ class A {
 class B implements A {}
 {% endprettify %}
 
+### non_leaf_call_must_not_take_typed_data
+
+_FFI non-leaf calls can't take typed data arguments._
+
+#### Description
+
+The analyzer produces this diagnostic when the value of the `isLeaf`
+argument of `Pointer.asFunction`, `DynamicLibrary.lookupFunction`, or
+`@Native` is `false` and the Dart function signature contains a typed
+data parameter.
+
+Typed data unwrapping is only supported on arguments for leaf FFI calls.
+
+For more information about FFI, see [C interop using dart:ffi][ffi].
+
+#### Example
+
+The following code produces this diagnostic because the dart function
+signature contains a typed data, but the `isLeaf` argument is `false`:
+
+{% prettify dart tag=pre+code %}
+import 'dart:ffi';
+import 'dart:typed_data';
+
+void f(Pointer<NativeFunction<Void Function(Pointer<Uint8>)>> p) {
+  p.asFunction<[!void Function(Uint8List)!]>();
+}
+{% endprettify %}
+
+#### Common fixes
+
+If the function has at least one typed data parameter, then add
+the `isLeaf` argument:
+
+{% prettify dart tag=pre+code %}
+import 'dart:ffi';
+import 'dart:typed_data';
+
+void f(Pointer<NativeFunction<Void Function(Pointer<Uint8>)>> p) {
+  p.asFunction<void Function(Uint8List)>(isLeaf: true);
+}
+{% endprettify %}
+
+If the function also uses `Handle`s, then it must be non-leaf. In That
+case use `Pointer`s instead of typed data.
+
 ### non_native_function_type_argument_to_pointer
 
 _Can't invoke 'asFunction' because the function signature '{0}' for the pointer

tests/ffi/vmspecific_static_checks_typeddata_test.dart

@@ -90,4 +90,12 @@ void g2() {
   // [analyzer] COMPILE_TIME_ERROR.CALLBACK_MUST_NOT_USE_TYPED_DATA
 }
 
+void foo1(Pointer<NativeFunction<Pointer<Uint8> Function()>> p) {
+  p.asFunction<Uint8List Function()>(isLeaf: true);
+  //^
+  // [cfe] FFI calls can't return typed data.
+  //           ^^^^^^^^^^^^^^^^^^^^
+  // [analyzer] COMPILE_TIME_ERROR.CALL_MUST_NOT_RETURN_TYPED_DATA
+}
+
 // TODO(https://dartbug.com/54181): Write negative tests for @Natives.