http: fail loudly when wxUSE_WEBREQUEST is not set - #481

Summary

Closes the diagnostic gap surfaced by #479.

CHTTPDownloadThread is built directly on top of wxWebRequest / wxWebSession / wxWebRequestEvent, all of which are gated on wxUSE_WEBREQUEST in wx/webrequest.h. wxUSE_WEBREQUEST is itself gated on a backend being present at wx-build time:

When wx is compiled without that backend — wxGTK on Gentoo with USE="-curl", a hand-rolled wx source build that didn't pick up libcurl, etc. — wxUSE_WEBREQUEST collapses to 0 and none of the classes we depend on are defined. The compile then fails with a wall of "wxWebRequest does not name a type", "wxWebSession has not been declared", "wxEVT_WEBREQUEST_STATE was not declared" diagnostics. The "did you mean wxWebRequestEvent?" hint that follows is misleading — that name is only visible because of our forward declaration further down the same header (HTTPDownload.h:36), not because wx provides it.

What changes

A check_cxx_source_compiles probe added to cmake/wx.cmake after find_package(wxWidgets ...), gated on wx_NEED_NET (the same flag that pulls in the net component for HTTPDownload). The probe includes <wx/webrequest.h> against the wx include dirs and definitions reported by FindwxWidgets, and fails the configure step with a clear FATAL_ERROR if wxUSE_WEBREQUEST is 0.

Two small details worth noting in the cmake change:

• wxWidgets_DEFINITIONS is reported by FindwxWidgets as bare names (WXUSINGDLL, __WXGTK__, _FILE_OFFSET_BITS=64); we re-prefix each with -D before assigning to CMAKE_REQUIRED_DEFINITIONS. Without that, wx/defs.h trips its own "No Target! You should use wx-config program for compilation flags!" #error and the probe fails for the wrong reason.
• CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY keeps the probe compile-only — we are inspecting a preprocessor symbol from wx/setup.h, not exercising any wx symbols, so we don't need CMAKE_REQUIRED_LIBRARIES wired up.

Why CI didn't see this

Distro CI (Ubuntu, Debian, Fedora) ships wxgtk with libcurl, so wxUSE_WEBREQUEST=1 is the default and the project's GitHub Actions runners never hit this path. Gentoo is unusual because users compile wx themselves with explicit USE flags.

Test plan

Verified both directions on the same Linux ARM64 box, by switching only the wx that find_package(wxWidgets) resolves:

• Positive — Ubuntu distro wxgtk-3.2.8 (wxUSE_WEBREQUEST=1, wxUSE_WEBREQUEST_CURL=1):

  -- Performing Test amule_HAVE_WXWEBREQUEST
  -- Performing Test amule_HAVE_WXWEBREQUEST - Success
  -- Configuring done (4.4s)
  

• Negative — hand-built wx-3.3.2 configured without libcurl (wxUSE_WEBREQUEST=0, wxUSE_WEBREQUEST_CURL=0, mirroring the Gentoo USE="-curl" shape):

  -- Performing Test amule_HAVE_WXWEBREQUEST
  -- Performing Test amule_HAVE_WXWEBREQUEST - Failed
  CMake Error at cmake/wx.cmake:122 (message):
    wxWidgets was found but wxUSE_WEBREQUEST is 0 in this build.
  
    aMule's HTTP download path requires wxWebRequest, which needs a backend
    at wx-build time:
  
      - Linux / *BSD: libcurl   (rebuild wx with --with-libcurl,
                                or on Gentoo emerge net-libs/wxGTK
                                with USE="curl")
      - Windows     : WinHTTP   (always present on supported releases)
      - macOS       : NSURLSession (always present)
  
    Then re-run cmake.
  -- Configuring incomplete, errors occurred!
  

• macOS Cocoa GUI build (Homebrew wxwidgets-3.3.2, wxUSE_WEBREQUEST=1) — clean.