Revert "Put AVIF_NODISCARD after AVIF_API" again

[wantehchang]

This reverts commit da268fb.

I tested this with Visual Studio 2022 Version 17.10.3. It does not work. I must have made a mistake when I tested this with Visual Studio last time.

I found two webpages that support my test results:
https://stackoverflow.com/questions/67502217/warning-c5240-nodiscard-attribute-is-ignored-in-this-syntactic-position microsoft/STL#1702

I think this issue is settled.

[wantehchang]

Here is my latest test of a standalone file.

The compiler version:

C:\src>cl
Microsoft (R) C/C++ Optimizing Compiler Version 19.40.33811 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

usage: cl [ option... ] filename... [ /link linkoption... ]

The bad code:

C:\src>type bad.c
__declspec(dllimport) [[nodiscard]] int Add(int x, int y);

__declspec(dllexport) [[nodiscard]] int Double(int x) {
  return Add(x, x);
}
C:\src>cl /std:clatest /W4 /c bad.c
Microsoft (R) C/C++ Optimizing Compiler Version 19.40.33811 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

bad.c
bad.c(1): error C2059: syntax error: 'type'
bad.c(3): error C2059: syntax error: 'type'

The good code:

C:\src>type good.c
[[nodiscard]] __declspec(dllimport) int Add(int x, int y);

[[nodiscard]] __declspec(dllexport) int Double(int x) {
  return Add(x, x);
}
C:\src>cl /std:clatest /W4 /c good.c
Microsoft (R) C/C++ Optimizing Compiler Version 19.40.33811 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

good.c

[wantehchang]

I forgot to request code review. PTAL. Thanks!

[vrabaud]

How come the CI does not catch it?

[wantehchang]

To catch the compilation error (either MSVC or clang-cl), we need a shared library build (-DBUILD_SHARED_LIBS=ON).

There are some two build errors in our shared library build. One is easy to fix (two gtest-based tests need to link with theavif_internal library). The other is a strange linker unresolved symbol error that I cannot reproduce locally. I haven't figured out what caused it, but one of my experiments worked, so at least we have a workaround. (I call it a workaround rarher than a fix because I cannot explain why it works.)

Finally, we cannot run the tests in a shared library build on Windows because the tests and avif.dll are in different directories, so the tests cannot find avif.dll. We should be able to fix this by setting the Path envirnonment variable before running the tests, or by copying avif.dll to the tests directory.

[jzern]

lgtm