Update to C++20

[hoshinolina]

Description

Current CEF requires compiling as C++20.

Motivation and Context

Fails to build with CEF 145.

How Has This Been Tested?

Tested as local build, testing in Fedora shortly.

Types of changes

• Code cleanup (non-breaking change which makes code smaller or more readable)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[RytoEX]

Fix the merge conflict caused by #518.

[RytoEX]

Super nit, but looks fine otherwise.

[PatTheMav]

I'm on board with increasing the language level to C++20, however that change should affect all targets (and not just the Linux ones).

obs-browser is not a "standalone module" (I removed CMake code to that end IIRC) and thus should always inherit what the main project sets up as (via CMAKE_CXX_STANDARD).

And moving the project to C++20 is indeed in the works already, so the issue will be solved automatically through that.

[hoshinolina]

FWIW this patch is needed to build OBS with current CEF today. I'm not a CMake nor C++ expert, but building just the browser bits as C++20 (which is what this PR does) seems to work fine (and this patch is what Fedora is shipping).

[WizardCM]

I can confirm updating obs-browser (or parent) is required for CEF 145+ compatibility, and that this PR on its own works correctly on Linux and Windows.

Approving with the understanding that this change could either be merged via this PR, or via a PR to the obs-studio repository itself (per Pat's comment)

[out]

This patch is also needed on macOS, but it misses the macOS helper targets.

I hit this building #523 against CEF 147 on macOS arm64. Bumping obs-browser alone isn't enough there: cmake/os-macos.cmake creates four separate helper executables (browser-helper, browser-helper_gpu, browser-helper_plugin, browser-helper_renderer) in a loop, and they compile browser-app.cpp / obs-browser-page-main.cpp — so they pull in the CEF headers too. They set no standard of their own, so they inherit obs-studio's global set(CMAKE_CXX_STANDARD 17) and fail:

In file included from cef/include/cef_base.h:42:
In file included from cef/include/internal/cef_ptr.h:37:
In file included from cef/include/base/cef_ref_counted.h:54:
cef/include/base/cef_scoped_refptr.h:101:16: error: no member named 'same_as' in namespace 'std'
  101 |   return !std::same_as<std::decay_t<decltype(GetRefCountPreference<T>())>,
      |                ^~~~~~~
cef/include/base/cef_scoped_refptr.h:127:22: error: no member named 'derived_from' in namespace 'std'
cef/include/base/cef_scoped_refptr.h:296:19: error: no template named 'convertible_to' in namespace 'std'

The equivalent of the os-linux.cmake change, inside the foreach(helper IN LISTS helper_suffixes) loop:

--- a/cmake/os-macos.cmake
+++ b/cmake/os-macos.cmake
   target_compile_definitions(${target_name} PRIVATE ENABLE_BROWSER_SHARED_TEXTURE)
+
+  target_compile_features(${target_name} PRIVATE cxx_std_20)

With that plus this PR's existing changes, obs-browser builds and runs on macOS against CEF 147 — browser sources render and Chrome Runtime initialises correctly.

For context on why the helpers need explicit opt-in: obs-studio's C++20 groundwork has already landed (obsproject/obs-studio#12630 and obsproject/obs-studio#13320), but cmake/common/compiler_common.cmake still sets CMAKE_CXX_STANDARD 17 globally — so per-target target_compile_features is currently the only thing raising the standard, and any target that doesn't ask for it silently stays on C++17.

One question I can't answer from here: cmake/os-windows.cmake defines obs-browser-helper as its own executable and likewise sets no standard, so it looks like it would need the same line. I have no Windows machine to verify that on, so I may be missing something that covers it there.

Environment

OS	macOS 26.5.2, arm64
Toolchain	Xcode 26.6 (17F113), Apple clang 21.0.0, CMake 4.1.2
CEF	147.0.14+g76d2442+chromium-147.0.7727.138 (macosarm64)
obs-studio	0218aa658