ci: build OCCT shared on Linux so plug-ins share one OCCT instance

`geom.tree().select()` silently returns zero results (or raises SWIG's
"An unknown error occurred") in the Linux release packages, while the same
commit built from source returns correct answers. `select_box()` agrees
between both, and geometry conversion is bit-identical -- only operations
that touch a stored TopoDS_Shape diverge.

Cause is linkage, not code. 8bdaa8c7c narrowed the Rocky builds from
`--shared` to `--ifcopenshell-shared`, which shares IfcOpenShell's own
libraries but leaves every dependency static. OCCT is then compiled
privately into each plug-in that uses it -- 15 of them, verified by their
own copies of the BRepClass3d/BRepExtrema/Standard_Failure strings.

That contradicts what the binaries already declare. tree.h:1748 casts a
`conversion_result_shape*` to `open_cascade_shape*`, moves the
TopoDS_Shape out of it and frees it; `open_cascade_shape` is defined once
in ifcopenshell_geometry_kernel_opencascade.so and left undefined in
ifcopenshell_geometry_tree_opencascade_brep.so for the loader to resolve.
So the two plug-ins are designed to share one OCCT-based type system, yet
static linking gives each its own Standard_Type registry and allocator.
Shapes get read and released by a different OCCT instance than made them.

Add `--opencascade-shared`, mirroring the existing `--ifcopenshell-shared`
precedent, and use it on both Rocky workflows. It cannot be spelled
`--occt-shared`: build-all.py parses any `occt-*` flag as a version
override.

BUILD_STATIC drives three things at once -- dependency link type,
-fvisibility=hidden, and BUILD_SHARED_LIBS -- so making one dependency
shared means overriding all three for it. Visibility is the subtle one:
OCCT's Standard_EXPORT expands to nothing on Unix, so it relies on default
visibility to export its API. Built shared under -fvisibility=hidden it
exports almost nothing and its own libraries cannot resolve against each
other (libTKMath.so fails to find
NCollection_BaseAllocator::CommonBaseAllocator in libTKernel.so). Static
archives are immune, which is why this surfaces only once OCCT goes
shared. Compile OCCT with the pre-visibility flag set instead.

Link the OCCT set with --as-needed. FindOpenCASCADE.cmake's config branch
uses OCCT's *complete* module list, Visualization included, which against a
static OCCT costs nothing -- an unreferenced module contributes no objects.
Against a shared OCCT all 47 become hard DT_NEEDED entries, and libTKV3d
pulls libGL.so.1 + libEGL.so.1, so `import ifcopenshell` fails on any
headless machine with "libEGL.so.1: cannot open shared object file" even
though nothing ever opens a window. Measured through the real find_package
path with the LINK_GROUP workaround composed: 67 DT_NEEDED without the
flag, 3 with it, TKV3d and TKOpenGl gone.

The flag is deliberately left open rather than closed with
-Wl,--no-as-needed. CMake emits the imported targets'
INTERFACE_LINK_LIBRARIES -- where OCCT lists libGL/libEGL -- after that
item, so closing the bracket switches the flag off immediately before the
libraries it exists to exclude. Verified against the shipped artifact:
closed, the kernel plug-in fell from 47 DT_NEEDED libTK entries to 14 and
lost TKV3d, yet still carried a direct libEGL.so.1 and still failed to
import on a headless server; open, the same 14 remain and libGL/libEGL are
gone. None of the 14 retained modules depends on GL.

Put the shared OCCT on LD_LIBRARY_PATH for the build itself. Nothing else
points at it -- IfcOpenShell's libraries get INSTALL_RPATH=$ORIGIN and OCCT
sits in its own dependency prefix -- so the post-build `import ifcopenshell`
check fails the same way. This is build-time only; the shipped packages get
libTK*.so* staged beside the payload with an $ORIGIN RUNPATH instead.

Suffix OCCT's install directory with `-shared` when it applies. Static and
shared installs are not interchangeable, but `build_dependency` skips any
dependency whose install dir already exists and cache_dependencies.py keys
its tarballs purely on that directory name -- so the static
`cache-occt-7.8.1.tar.gz` restored from the build-outputs repo silently
satisfied the build and BUILD_LIBRARY_TYPE was never applied. This is the
same cache stickiness 8bdaa8c7c described, pointing the other way. The
suffix makes the key configuration-aware, so it self-invalidates and the
static tarball stays valid for builds that still want static.

Packaging is the other half, and is why 8bdaa8c7c backed the flag out --
`stage_runtime_payload` only copies from install/ifcopenshell, so OCCT in
install/occt-* was never staged and `--shared` "worked by accident" off
cached static outputs. Stage libTK*.so* alongside, then give every staged
library an $ORIGIN RUNPATH: the core libs currently carry dead
build-machine RPATHs and the plug-ins carry none, resolving only because
the Python wrapper pulls them in by SONAME first. Shared OCCT has no such
first loader, since it is reached through the dlopen'd plug-ins.

The packages shrink: the python zip goes from 109.4 MB to 85.6 MB, because
the duplicated OCCT was 113 MB of the 287 MB unpacked payload (the eight
geometry_writer_ifc* plug-ins alone were 4.6 MB each) against ~67 MB for
one shared copy. Same argument as a91b1da28 ("Reduce Rocky package size")
and 402591e71.

macOS and Windows are affected too but are not fixed here. Their
packaging resolves via @loader_path install names and would need
install_name_tool rewriting, which cannot be verified from Linux; adding
the flag without that would ship a package that fails to load.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.github/workflows/build_rocky.yml

@@ -80,7 +80,7 @@ jobs:
           set -o pipefail
           CXXFLAGS="-O3" CFLAGS="-O3" ADD_COMMIT_SHA=1 BUILD_CFG=Release BUILD_BONSAIVIEWER=ON \
             uv run --with aqtinstall ./nix/build-all.py \
-            -v --diskcleanup --ifcopenshell-shared 2>&1 \
+            -v --diskcleanup --ifcopenshell-shared --opencascade-shared 2>&1 \
             | tee build.log
 
       - name: Upload Build Logs
@@ -147,6 +147,22 @@ jobs:
               done
           }
 
+          # Copy the shared OCCT from the dependency prefix to the provided `$1`.
+          # OCCT is built shared (`--opencascade-shared`) so that the opencascade kernel
+          # and tree plug-ins share a single OCCT instance: `open_cascade_shape` objects
+          # are created by the kernel plug-in and then have their `TopoDS_Shape` moved out
+          # and freed by a tree plug-in. A private static OCCT per plug-in gives each its
+          # own Standard_Type registry and allocator, which silently corrupts those shapes.
+          # These libs live under `install/occt-*` rather than `install/ifcopenshell`,
+          # so `stage_runtime_payload` does not pick them up on its own.
+          stage_occt_runtime_payload() {
+              dest="$1"
+              for occt_lib_dir in "$(dirname "$install_root")"/occt-*/lib "$(dirname "$install_root")"/occt-*/lib64; do
+                  [ -d "$occt_lib_dir" ] || continue
+                  find "$occt_lib_dir" -maxdepth 1 \( -type f -o -type l \) -name "libTK*.so*" -exec cp -P {} "$dest/" \;
+              done
+          }
+
           # Copy all libs from `install/ifcopenshell` to the provided `$1`.
           # Set `$2` to `0` to skip including geometry writers.
           stage_runtime_payload() {
@@ -163,7 +179,14 @@ jobs:
                       find "$runtime_dir" \( -type f -o -type l \) \( -name "*.so" -o -name "*.so.*" -o -name "*.dylib" -o -name "*.dll" \)
                   done
               )
+              stage_occt_runtime_payload "$dest"
               ensure_soname_links "$dest"
+              # The core libs ship with dead build-machine RPATHs and the plug-ins have
+              # none; today they resolve only because the Python wrapper ($ORIGIN) pulls
+              # them in by SONAME before any plug-in is dlopen'd. Shared OCCT has no such
+              # first loader -- it is reached through the plug-ins -- so give every staged
+              # library an $ORIGIN of its own.
+              find "$dest" -maxdepth 1 -type f -name "*.so*" -exec patchelf --set-rpath '$ORIGIN' {} \;
           }
 
           # Copy all libs from `QT_DIR` to the provided `$2`.

.github/workflows/build_rocky_arm.yml

@@ -92,7 +92,7 @@ jobs:
           set -o pipefail
           CXXFLAGS="-O3" CFLAGS="-O3" ADD_COMMIT_SHA=1 BUILD_CFG=Release BUILD_BONSAIVIEWER=ON \
             uv run --with aqtinstall ./nix/build-all.py \
-            -v --diskcleanup --ifcopenshell-shared 2>&1 \
+            -v --diskcleanup --ifcopenshell-shared --opencascade-shared 2>&1 \
             | tee build.log
 
       - name: Upload Build Logs
@@ -156,6 +156,22 @@ jobs:
               done
           }
 
+          # Copy the shared OCCT from the dependency prefix to the provided `$1`.
+          # OCCT is built shared (`--opencascade-shared`) so that the opencascade kernel
+          # and tree plug-ins share a single OCCT instance: `open_cascade_shape` objects
+          # are created by the kernel plug-in and then have their `TopoDS_Shape` moved out
+          # and freed by a tree plug-in. A private static OCCT per plug-in gives each its
+          # own Standard_Type registry and allocator, which silently corrupts those shapes.
+          # These libs live under `install/occt-*` rather than `install/ifcopenshell`,
+          # so `stage_runtime_payload` does not pick them up on its own.
+          stage_occt_runtime_payload() {
+              dest="$1"
+              for occt_lib_dir in "$(dirname "$install_root")"/occt-*/lib "$(dirname "$install_root")"/occt-*/lib64; do
+                  [ -d "$occt_lib_dir" ] || continue
+                  find "$occt_lib_dir" -maxdepth 1 \( -type f -o -type l \) -name "libTK*.so*" -exec cp -P {} "$dest/" \;
+              done
+          }
+
           stage_runtime_payload() {
               dest="$1"
               include_geometry_writers="${2:-1}"
@@ -170,7 +186,14 @@ jobs:
                       find "$runtime_dir" \( -type f -o -type l \) \( -name "*.so" -o -name "*.so.*" -o -name "*.dylib" -o -name "*.dll" \)
                   done
               )
+              stage_occt_runtime_payload "$dest"
               ensure_soname_links "$dest"
+              # The core libs ship with dead build-machine RPATHs and the plug-ins have
+              # none; today they resolve only because the Python wrapper ($ORIGIN) pulls
+              # them in by SONAME before any plug-in is dlopen'd. Shared OCCT has no such
+              # first loader -- it is reached through the plug-ins -- so give every staged
+              # library an $ORIGIN of its own.
+              find "$dest" -maxdepth 1 -type f -name "*.so*" -exec patchelf --set-rpath '$ORIGIN' {} \;
           }
 
           stage_qt_runtime_payload() {

cmake/FindOpenCASCADE.cmake

@@ -54,6 +54,41 @@ if(NOT OCC_INCLUDE_DIR AND NOT OCC_LIBRARY_DIR)
         set(OpenCASCADE_LIBRARIES "$<LINK_GROUP:RESCAN,${OpenCASCADE_LIBRARIES}>")
     endif()
 
+    if(UNIX AND NOT APPLE)
+        # Record only the OCCT modules whose symbols are actually referenced.
+        #
+        # OpenCASCADE_LIBRARIES is OCCT's *complete* module list, Visualization
+        # included -- TKV3d, TKOpenGl, TKService. Against a static OCCT that
+        # costs nothing, because an unreferenced module contributes no objects.
+        # Against a shared OCCT every entry becomes a hard DT_NEEDED, and
+        # libTKV3d pulls libGL.so.1 + libEGL.so.1, so `import ifcopenshell`
+        # dies on any headless machine with
+        #     ImportError: libEGL.so.1: cannot open shared object file
+        # even though IfcOpenShell never opens a window. Measured on a full
+        # 67-module link: 67 DT_NEEDED entries without the flag, 3 with it,
+        # and TKV3d/TKOpenGl gone in the second case.
+        #
+        # Goes before the LINK_GROUP above rather than inside it, and is a
+        # no-op for a static OCCT (--as-needed only governs shared libraries),
+        # so this is safe for both link types.
+        #
+        # Deliberately NOT closed with -Wl,--no-as-needed. CMake emits the
+        # imported targets' INTERFACE_LINK_LIBRARIES -- which is where OCCT
+        # lists libGL/libEGL -- *after* this item, so a closing bracket
+        # switches the flag back off just before the libraries it was added to
+        # exclude. Measured: with the bracket closed the plug-ins dropped from
+        # 47 DT_NEEDED libTK entries to 14 and lost TKV3d, yet still carried a
+        # direct libEGL.so.1 and failed to import on a headless server; with it
+        # left open the same 14 remain and libGL/libEGL are gone.
+        #
+        # The cost is that --as-needed stays in effect for whatever follows on
+        # the link line. That is the default on Debian/Ubuntu so it is
+        # well-trodden, but it does mean a library needed only for
+        # static-initialiser side effects could be dropped -- the thing to
+        # suspect first if a serialiser stops registering itself.
+        set(OpenCASCADE_LIBRARIES "-Wl,--as-needed" "${OpenCASCADE_LIBRARIES}")
+    endif()
+
     if(OpenCASCADE_VERSION VERSION_LESS "7.9.0" AND WIN32)
         # Bug in OCCT cmake configs < 7.9.0 - missing linked library.
         list(APPEND OpenCASCADE_LIBRARIES WSOCK32.lib)

nix/build-all.py

@@ -42,6 +42,13 @@ Available arguments:
     ``-shared`` - build shared libraries. By default will build static.
     ``-ifcopenshell-shared`` - build only IfcOpenShell's own libraries as shared
         (dependencies stay static). Redundant if ``-shared`` is also passed.
+    ``-opencascade-shared`` - build OCCT as shared libraries (other dependencies stay
+        static). Redundant if ``-shared`` is also passed. Required whenever more than one
+        plug-in uses OCCT: `open_cascade_shape` instances are created by the opencascade
+        kernel plug-in and consumed by the opencascade tree plug-ins, which move a
+        `TopoDS_Shape` out of them and free them. A private static OCCT per plug-in gives
+        each one its own `Standard_Type` registry and allocator, so those shapes are read
+        and released by a different OCCT instance than the one that made them.
     ``-diskcleanup`` - clean up build directories after finishing building dependencies
     ``-build-examples`` - build IfcOpenShell examples
     ``-lto`` - enable link-time optimization (adds ``-flto`` to compiler flags)
@@ -410,6 +417,8 @@ BUILD_STATIC = "shared" not in flags
 """Whether dependencies are built static."""
 IFCOPENSHELL_STATIC = BUILD_STATIC and "ifcopenshell-shared" not in flags
 """Whether IfcOpenShell's own libraries are built static."""
+OCCT_STATIC = BUILD_STATIC and "opencascade-shared" not in flags
+"""Whether OCCT is built static. See ``-opencascade-shared``."""
 ENABLE_FLAG = "--enable-static" if BUILD_STATIC else "--enable-shared"
 DISABLE_FLAG = "--disable-shared" if BUILD_STATIC else "--disable-static"
 LINK_TYPE = "static" if BUILD_STATIC else "shared"
@@ -423,6 +432,32 @@ if any(f.startswith("py-") for f in flags):
 if any(f.startswith("occt-") for f in flags):
     OCCT_VERSION = next(f.split("-", 1)[1] for f in flags if f.startswith("occt-"))
 
+# Static and shared OCCT installs are not interchangeable, so they must not share
+# a directory: `build_dependency` skips a dependency whose install dir already
+# exists, and cache_dependencies.py keys its tarballs purely on that directory
+# name. Without the suffix a cached static OCCT silently satisfies a shared build
+# (and vice versa) and the requested link type is never applied.
+OCCT_DIR_NAME = f"occt-{OCCT_VERSION}" + ("" if OCCT_STATIC else "-shared")
+
+if not OCCT_STATIC:
+    # A shared OCCT has to be resolvable at run time by everything this script
+    # executes out of the install tree -- most visibly the post-build
+    # `import ifcopenshell` sanity check, which otherwise dies with
+    # "libTKernel.so.7.8: cannot open shared object file". Nothing points there:
+    # IfcOpenShell's libraries get INSTALL_RPATH=$ORIGIN (see SET_INSTALL_SELF_RPATH
+    # in cmake/utilities.cmake) and OCCT lives in its own dependency prefix.
+    #
+    # This is a build-time concern only. The shipped packages do not rely on it:
+    # the workflows stage libTK*.so* next to the payload and patchelf an $ORIGIN
+    # RUNPATH onto every staged library.
+    _occt_lib_dirs = [
+        os.path.join(DEPS_DIR, "install", OCCT_DIR_NAME, libdir)
+        for libdir in ("lib", "lib64")
+    ]
+    os.environ["LD_LIBRARY_PATH"] = os.pathsep.join(
+        [*_occt_lib_dirs, os.environ.get("LD_LIBRARY_PATH", "")]
+    ).rstrip(os.pathsep)
+
 if explicit_targets:
     targets = {dep for target in explicit_targets for dep in gather_dependencies(target)}
 else:
@@ -1045,12 +1080,34 @@ if USE_OCCT and "occ" in targets:
     if WASM:
         patches.append("./patches/occt/no_em_js.patch")
 
+    if not OCCT_STATIC:
+        # BUILD_STATIC drives three things at once: the dependency link type,
+        # -fvisibility=hidden, and BUILD_SHARED_LIBS. Building only OCCT shared
+        # means overriding all three for it, not just the link type.
+        #
+        # Visibility matters most. OCCT's Standard_EXPORT expands to nothing on
+        # Unix (Standard_Macro.hxx), so it relies on default visibility to export
+        # its API. Built shared under -fvisibility=hidden it exports almost
+        # nothing and its libraries fail to resolve against each other -- e.g.
+        # libTKMath.so cannot find NCollection_BaseAllocator::CommonBaseAllocator
+        # in libTKernel.so. Static archives are immune, which is why this only
+        # appears once OCCT goes shared. CXXFLAGS_MINIMAL is the pre-visibility
+        # flag set, so this restores default visibility without dropping -O3/-fPIC.
+        #
+        # These come after the generic flags in the cmake command line, and the
+        # last -D for a given variable wins.
+        occt_args.append(f"-DCMAKE_CXX_FLAGS={CXXFLAGS_MINIMAL}")
+        occt_args.append(f"-DCMAKE_C_FLAGS={CFLAGS_MINIMAL}")
+        # Suppresses the generic -DBUILD_SHARED_LIBS=OFF that BUILD_STATIC would
+        # otherwise add, which contradicts BUILD_LIBRARY_TYPE=Shared.
+        occt_args.append("-DBUILD_SHARED_LIBS=ON")
+
     build_dependency(
-        name=f"occt-{OCCT_VERSION}",
+        name=OCCT_DIR_NAME,
         mode="cmake",
         build_tool_args=[
-            f"-DINSTALL_DIR={DEPS_DIR}/install/occt-{OCCT_VERSION}",
-            f"-DBUILD_LIBRARY_TYPE={LINK_TYPE_UCFIRST}",
+            f"-DINSTALL_DIR={DEPS_DIR}/install/{OCCT_DIR_NAME}",
+            f"-DBUILD_LIBRARY_TYPE={'Static' if OCCT_STATIC else 'Shared'}",
             f"-DBUILD_MODULE_Draw=0",
             f"-DBUILD_RELEASE_DISABLE_EXCEPTIONS=Off",
             # Disable xlib explicitly, as it tries to use it on Desktop Ubuntu, adding unnecessary dependency.
@@ -1487,7 +1544,7 @@ if "cgal" in targets:
     cmake_args.append(f"-DCGAL_WITH_GMPXX=Off")
 
 if "occ" in targets and USE_OCCT:
-    cmake_args_prefix_path.append(f"{DEPS_DIR}/install/occt-{OCCT_VERSION}")
+    cmake_args_prefix_path.append(f"{DEPS_DIR}/install/{OCCT_DIR_NAME}")
 
 elif "occ" in targets:
     # We don't support find_package for OCE.