Allow customization of the --build flag

README.md

@@ -65,6 +65,12 @@ If you need to customize the profile, you can do so by modifying the value of `C
 * `-DCONAN_BUILD_PROFILE=/path/to/profile`: alternatively, provide a path to a profile file that may be anywhere in the filesystem.
 * `-DCONAN_HOST_PROFILE=default;custom`: semi-colon separated list of profiles. A compound profile will be used (see [docs](https://docs.conan.io/2.0/reference/commands/install.html#profiles-settings-options-conf)) - compunded from left to right, where right has the highest priority.
 
+### Customizing Conan install --build flag
+By default, the CMake-Conan dependency provider will pass the `--build=missing` flag to  `conan install` to build any packages that don't have a compatible binary. If you would like to override this setting, you can pass one or more `--build` options in a `CONAN_BUILD` CMake cache variable. Some examples:
+
+* `-DCONAN_BUILD=never`: use binary packages or fail if a binary package is not found
+* `-DCONAN_BUILD=fmt;zlib`: build the `fmt` and `zlib` packages from source
+
 ## Development, contributors
 
 There are some tests, you can run in python, with pytest, for example:

conan_provider.cmake

@@ -484,6 +484,17 @@ macro(construct_profile_argument argument_variable profile_list)
 endmacro()
 
 
+macro(construct_build_flag_argument argument_variable build_flag_list)
+    set(${argument_variable} "")
+    set(_arg_flag "--build=")
+    set(_build_flag_list "${${build_flag_list}}")
+    list(TRANSFORM _build_flag_list PREPEND ${_arg_flag})
+    set(${argument_variable} ${_build_flag_list})
+    unset(_arg_flag)
+    unset(_build_flag_list)
+endmacro()
+
+
 macro(conan_provide_dependency method package_name)
     set_property(GLOBAL PROPERTY CONAN_PROVIDE_DEPENDENCY_INVOKED TRUE)
     get_property(_conan_install_success GLOBAL PROPERTY CONAN_INSTALL_SUCCESS)
@@ -500,6 +511,7 @@ macro(conan_provide_dependency method package_name)
         endif()
         construct_profile_argument(_host_profile_flags CONAN_HOST_PROFILE)
         construct_profile_argument(_build_profile_flags CONAN_BUILD_PROFILE)
+        construct_build_flag_argument(_build_flags CONAN_BUILD)
         if(EXISTS "${CMAKE_SOURCE_DIR}/conanfile.py")
             file(READ "${CMAKE_SOURCE_DIR}/conanfile.py" outfile)
             if(NOT "${outfile}" MATCHES ".*CMakeDeps.*")
@@ -517,11 +529,11 @@ macro(conan_provide_dependency method package_name)
         get_property(_multiconfig_generator GLOBAL PROPERTY GENERATOR_IS_MULTI_CONFIG)
         if(NOT _multiconfig_generator)
             message(STATUS "CMake-Conan: Installing single configuration ${CMAKE_BUILD_TYPE}")
-            conan_install(${_host_profile_flags} ${_build_profile_flags} --build=missing ${generator})
+            conan_install(${_host_profile_flags} ${_build_profile_flags} ${_build_flags} ${generator})
         else()
             message(STATUS "CMake-Conan: Installing both Debug and Release")
-            conan_install(${_host_profile_flags} ${_build_profile_flags} -s build_type=Release --build=missing ${generator})
-            conan_install(${_host_profile_flags} ${_build_profile_flags} -s build_type=Debug --build=missing ${generator})
+            conan_install(${_host_profile_flags} ${_build_profile_flags} -s build_type=Release ${_build_flags} ${generator})
+            conan_install(${_host_profile_flags} ${_build_profile_flags} -s build_type=Debug ${_build_flags} ${generator})
         endif()
         unset(_host_profile_flags)
         unset(_build_profile_flags)
@@ -594,3 +606,4 @@ cmake_language(DEFER DIRECTORY "${CMAKE_SOURCE_DIR}" CALL conan_provide_dependen
 # Configurable variables for Conan profiles
 set(CONAN_HOST_PROFILE "default;auto-cmake" CACHE STRING "Conan host profile")
 set(CONAN_BUILD_PROFILE "default" CACHE STRING "Conan build profile")
+set(CONAN_BUILD "missing" CACHE STRING "List of values for 'conan install' --build flag")

tests/test_smoke.py

@@ -376,6 +376,23 @@ def test_profile_pass_path(self, capfd, basic_cmake_project):
         assert "ERROR: Invalid setting 'JuliusOS' is not a valid 'settings.os' value." in err
 
 
+class TestBuildFlagCustomization:
+    def test_build_flag_default(self, capfd, basic_cmake_project):
+        """Test the default --build flag"""
+        source_dir, binary_dir = basic_cmake_project
+        run(f"cmake -S {source_dir} -B {binary_dir} -DCMAKE_PROJECT_TOP_LEVEL_INCLUDES={conan_provider} -DCMAKE_BUILD_TYPE=Release", check=True)
+        out, _ = capfd.readouterr()
+        assert "--build=missing" in out
+
+    def test_build_flag_list(self, capfd, basic_cmake_project):
+        """Test passing a list of --build flags"""
+        source_dir, binary_dir = basic_cmake_project
+        run(f'cmake -S {source_dir} -B {binary_dir} -DCMAKE_PROJECT_TOP_LEVEL_INCLUDES={conan_provider} -DCMAKE_BUILD_TYPE=Release -DCONAN_BUILD="fmt;zlib"', check=True)
+        out, _ = capfd.readouterr()
+        assert "--build=fmt" in out
+        assert "--build=zlib" in out
+
+
 class TestSubdir:
     @pytest.fixture(scope="class", autouse=True)
     def subdir_setup(self, tmp_path_factory):