BLD: Add CMake option to build Python bindings without rebuilding libz3 (redux) (#8088)

* Add CMake option to build only Python bindings without rebuilding libz3

Introduce Z3_BUILD_LIBZ3_CORE option (default ON) to control whether libz3 is built.
When set to OFF with Z3_BUILD_PYTHON_BINDINGS=ON, only Python bindings are built
using a pre-installed libz3 library. This is useful for package managers like
conda-forge to avoid rebuilding libz3 for each Python version.

Changes:
- Add Z3_BUILD_LIBZ3_CORE option in src/CMakeLists.txt
- When OFF, find and use pre-installed libz3 as imported target
- Update Python bindings CMakeLists.txt to handle both built and imported libz3
- Add documentation in README-CMake.md with usage examples

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

* Fix CMake export issues when building only Python bindings

Conditionally export Z3_EXPORTED_TARGETS only when Z3_BUILD_LIBZ3_CORE=ON
to avoid errors when building Python bindings without building libz3.

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

* Disable executable and test builds when not building libz3 core

When Z3_BUILD_LIBZ3_CORE=OFF, automatically disable Z3_BUILD_EXECUTABLE
and Z3_BUILD_TEST_EXECUTABLES to avoid build/install errors.

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

* only build src/ folder if Z3_BUILD_LIBZ3_CORE is TRUE

* move z3 python bindings to main CMake

* move more logic to main CMakeLists.txt

* move Z3_API_HEADER_FILES_TO_SCAN to main CMakeLists.txt

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

src/CMakeLists.txt

@@ -1,29 +1,3 @@
-################################################################################
-# API header files
-################################################################################
-# This lists the API header files that are scanned by
-# some of the build rules to generate some files needed
-# by the build
-set(Z3_API_HEADER_FILES_TO_SCAN
-  z3_api.h
-  z3_ast_containers.h
-  z3_algebraic.h
-  z3_polynomial.h
-  z3_rcf.h
-  z3_fixedpoint.h
-  z3_optimization.h
-  z3_fpa.h
-  z3_spacer.h
-)
-set(Z3_FULL_PATH_API_HEADER_FILES_TO_SCAN "")
-foreach (header_file ${Z3_API_HEADER_FILES_TO_SCAN})
-  set(full_path_api_header_file "${CMAKE_CURRENT_SOURCE_DIR}/api/${header_file}")
-  list(APPEND Z3_FULL_PATH_API_HEADER_FILES_TO_SCAN "${full_path_api_header_file}")
-  if (NOT EXISTS "${full_path_api_header_file}")
-    message(FATAL_ERROR "API header file \"${full_path_api_header_file}\" does not exist")
-  endif()
-endforeach()
-
 ################################################################################
 # Traverse directories each adding a Z3 component
 ################################################################################
@@ -305,7 +279,7 @@ endif()
 ################################################################################
 cmake_dependent_option(Z3_BUILD_EXECUTABLE
     "Build the z3 executable" ON
-    "CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR" OFF)
+    "CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR;Z3_BUILD_LIBZ3_CORE" OFF)
 
 if (Z3_BUILD_EXECUTABLE)
     add_subdirectory(shell)
@@ -317,26 +291,13 @@ endif()
 
 cmake_dependent_option(Z3_BUILD_TEST_EXECUTABLES
     "Build test executables" ON
-    "CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR" OFF)
+    "CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR;Z3_BUILD_LIBZ3_CORE" OFF)
 
 
 if (Z3_BUILD_TEST_EXECUTABLES)
     add_subdirectory(test)
 endif()
 
-
-################################################################################
-# Z3 API bindings
-################################################################################
-option(Z3_BUILD_PYTHON_BINDINGS "Build Python bindings for Z3" OFF)
-if (Z3_BUILD_PYTHON_BINDINGS)
-  if (NOT Z3_BUILD_LIBZ3_SHARED)
-    message(FATAL_ERROR "The python bindings will not work with a static libz3. "
-            "You either need to disable Z3_BUILD_PYTHON_BINDINGS or enable Z3_BUILD_LIBZ3_SHARED")
-  endif()
-  add_subdirectory(api/python)
-endif()
-
 ################################################################################
 # .NET bindings
 ################################################################################

src/api/python/CMakeLists.txt

@@ -70,13 +70,32 @@ else()
 endif()
 
 # Link libz3 into the python directory so bindings work out of the box
-add_custom_command(OUTPUT "${z3py_bindings_build_dest}/libz3${CMAKE_SHARED_MODULE_SUFFIX}"
-  COMMAND "${CMAKE_COMMAND}" "-E" "${LINK_COMMAND}"
-    "${PROJECT_BINARY_DIR}/libz3${CMAKE_SHARED_MODULE_SUFFIX}"
-    "${z3py_bindings_build_dest}/libz3${CMAKE_SHARED_MODULE_SUFFIX}"
-  DEPENDS libz3
-  COMMENT "Linking libz3 into python directory"
-)
+# Handle both built libz3 and pre-installed libz3
+if (TARGET libz3)
+  # Get the libz3 location - handle both regular and imported targets
+  get_target_property(LIBZ3_IS_IMPORTED libz3 IMPORTED)
+  if (LIBZ3_IS_IMPORTED)
+    # For imported targets, get the IMPORTED_LOCATION
+    get_target_property(LIBZ3_SOURCE_PATH libz3 IMPORTED_LOCATION)
+    # No dependency on libz3 target since it's pre-built
+    set(LIBZ3_DEPENDS "")
+  else()
+    # For regular targets, use the build output location
+    set(LIBZ3_SOURCE_PATH "${PROJECT_BINARY_DIR}/libz3${CMAKE_SHARED_MODULE_SUFFIX}")
+    set(LIBZ3_DEPENDS libz3)
+  endif()
+
+  add_custom_command(OUTPUT "${z3py_bindings_build_dest}/libz3${CMAKE_SHARED_MODULE_SUFFIX}"
+    COMMAND "${CMAKE_COMMAND}" "-E" "${LINK_COMMAND}"
+      "${LIBZ3_SOURCE_PATH}"
+      "${z3py_bindings_build_dest}/libz3${CMAKE_SHARED_MODULE_SUFFIX}"
+    DEPENDS ${LIBZ3_DEPENDS}
+    COMMENT "Linking libz3 into python directory"
+  )
+else()
+  message(FATAL_ERROR "libz3 target not found. Cannot build Python bindings.")
+endif()
+
 
 # Convenient top-level target
 add_custom_target(build_z3_python_bindings