[qtbase] Fix qt.toolchain.cmake corruption for Emscripten builds

[boardend]

The regex replacement for __qt_chainload_toolchain_file was malformed, causing a literal \n to be written instead of an actual newline. This broke toolchain chaining for Emscripten/WebAssembly builds where vcpkg chainloads Qt's toolchain.

Follow up on #46314

Observed with 2025.12.12, fixes the resulting corrupted line (tested on e70ab1d , Qt 6.10.0):

  set(__qt_chainload_toolchain_file "${VCPKG_CHAINLOAD_TOOLCHAIN_FILE}\n")

Checklist

• Changes comply with the maintainer guide.
• SHA512s are updated for each updated download.
• The "supports" clause reflects platforms that may be fixed by this new version.
• Any fixed CI baseline entries are removed from that file.
• Any patches that are no longer applied are deleted from the port's directory.
• The version database is fixed by rerunning ./vcpkg x-add-version --all and committing the result.
• Only one version is added to each modified port's versions file.

[boardend]

@m-kuhn and @dg0yt would be thankful if one of you could confirm this is an issue. At least it fixed the problem for me.

[m-kuhn]

I can't confirm this is an issue (I was able to build using emscripten recently, I'm not sure what I'd need to change to trigger this behavior), but the \n in the quotes of the original version looks very suspicious.

This is what we get iiuc, but it's unlikely to be what we want:

set(__qt_chainload_toolchain_file "${VCPKG_CHAINLOAD_TOOLCHAIN_FILE}
")

[dg0yt]

set(__qt_chainload_toolchain_file "${VCPKG_CHAINLOAD_TOOLCHAIN_FILE}
")

This is also what I see for x64-linux native. Ugly, but not broken. Emscripten should be no different.

[boardend]

Thanks for the feedback

@dg0yt just tested again with emsdk 4.0.22 / CMake 3.30.4:

Error: CMake Error at build/vcpkg/packages/qtbase_wasm32-emscripten-qt-threads/share/Qt6/qt.toolchain.cmake:36:
  Parse error.  Expected a newline, got identifier with text "endif".
Call Stack (most recent call first):
  CMakeLists.txt:51 (include)

So the fix is definitely needed...

But I can confirm that your suggestion works and will just accept it.

[dg0yt]

Ugly, but not broken. Emscripten should be no different.

🤦 Of course broken, with a line break in a real filepath, as soon as __qt_chainload_toolchain_file is actually used.

[dg0yt]

Reminder: Before commit/push, you need to increment port-version in ports/qtbase/vcpkg.json, and the run vcpkg x-add-version qtbase.

[boardend]

@microsoft-github-policy-service agree company="OPENGIS.ch"

[boardend]

Tested again with ffc071e

[JavierMatosD]

I'm seeing there are two PRs that are touching qtbase -> #49191. I'm asking the contributor if they would like to absorb this change.