[ffi] Varargs should give an error on uint8, int8, uint16, int16 and float

[dcharkes]

Passing 8 bit or 16 bit ints in varargs is undefined behavior.

Clang will alert us:

Second argument to 'va_arg' is of promotable type 'uint16_t' (aka 'unsigned short'); this va_arg has undefined behavior because arguments will be promoted to 'int'clang(-Wvarargs)

But we allow this in dart:ffi, leading to undefined behavior.

We should consider adding an error message.

Discovered on:

• CI on windows is flaky native#1191

[vaishnavi-2901]

hey
can work on it, please assign this task to me

[dcharkes]

hey can work on it, please assign this task to me

Hi @vaishnavi-2901! That's great!

Please start with https://github.com/dart-lang/sdk/blob/main/CONTRIBUTING.md

A PR for this issue will involve adding error messages both to the CFE (the compiler used when doing dart ...) and analyzer (used in the IDE for giving error messages).

Some pointers to point you in the right direction:

• Analyzer
  • https://dart-review.googlesource.com/c/sdk/+/278343 analyzer implementation for varargs, not including any error messages.
  • https://dart-review.googlesource.com/c/sdk/+/336040 How error messages are defined.
  • You can see in the ffi_verifier.dart file in the first PR how to emit error messages from the analyzer.
• CFE
  • https://dart-review.googlesource.com/c/sdk/+/276921/49/pkg/vm/lib/transformations/ffi/common.dart -> This is where the error checking for the FFI is done.
• Tests
  • The tests should be in here. tests/ffi/static_checks/vmspecific_static_checks_varargs_test.dart Note that this test needs to be converted from //# 1: compile-time error to tests/ffi/static_checks/vmspecific_static_checks_test.dart style with // [cfe].

It's probably easiest to

1. First convert the test
2. Then make an analyzer PR
3. And then in a third PR try to tackle the CFE.

[trivedikavya]

hey sir can i work on it ..?

[dcharkes]

@vaishnavi-2901 are you still working on this?

[trivedikavya]

Dear respected sir let she work and let me also work on it. as I am beginning the open source contribution first you will check the request of both and then you will see what to do
I have one Question sir just tell me in which file I have to contribute .