docker build from readme thows error

[AntonMerkulov]

I've cloned online-main and tried to build a docker image.
And I got error:
.....
650.3 checking whether g++ supports C++20... yes (-std=c++20)
651.5 checking whether the compiler is clang... no
651.6 checking for CollaboraOffice path... given
651.6 checking whether to run tests against a CollaboraOffice... no
651.6 configure: error: /build/builddir/poco-engine/config_host.mk not found; build the engine first so its standard-library ABI can be matched
651.6 configure: using POCO built in the engine: /build/builddir/poco-engine/workdir/LinkTarget/StaticLibrary

Dockerfile:41

39 | COPY / $BUILDDIR/
40 |
41 | >>> RUN bash build.sh
42 |
43 | # Build the final image

Dockerfile I used: online-main/docker/from-source-gh-action/Dockerfile
What am I doing wrong?

[tt-a1i]

This is a regression in the current main build path, not a missing package on your side.

The Docker build still passes --with-lo-builddir=/build/builddir/poco-engine, but the newer configure check expects the engine build directory to contain config_host.mk. The poco-engine directory is only a POCO shim, which is why configure stops at exactly that check.

There is already an open fix in #16085. It changes --with-lo-builddir to /build/builddir/online/engine and adjusts the paths stored in the prebuilt engine assets. Until that lands, applying that PR (or building its branch) is the cleanest workaround.

One separate detail: the Dockerfile expects docker/from-source-gh-action to be the build context. From the repository root, the equivalent command is:

docker build -t code \
  -f docker/from-source-gh-action/Dockerfile \
  docker/from-source-gh-action

Using the repository root as the final build context would copy the wrong build.sh into the image.