From 71a884571c94fc32c8e20379172334d58b35b557 Mon Sep 17 00:00:00 2001
From: Ivan Grokhotkov <ivan@espressif.com>
Date: Wed, 1 Dec 2021 23:09:12 +0100
Subject: [PATCH] cmake: add idf_component_optional_requires utility function

It can be used in component CMakeLists.txt files when adding "weak"
dependencies between component. A "weak" dependency from A to B is
similar to target_link_libraries(A PRIVATE B), but it gets added only
if B is included in the build.
Use it instead of specifying B as part of PRIV_REQUIRES when the
component can be built (even if with reduced functionality) without
component B being available.
---
 tools/cmake/component.cmake | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/tools/cmake/component.cmake b/tools/cmake/component.cmake
index 5e3053dba5..e28a52f4ca 100644
--- a/tools/cmake/component.cmake
+++ b/tools/cmake/component.cmake
@@ -576,6 +576,28 @@ function(idf_component_mock)
       )
 endfunction()
 
+# idf_component_optional_requires
+#
+# @brief Add a dependency on a given component only if it is included in the build.
+#
+# Calling idf_component_optional_requires(PRIVATE dependency_name) has the similar effect to
+# target_link_libraries(${COMPONENT_LIB} PRIVATE idf::dependency_name), only if 'dependency_name'
+# component is part of the build. Otherwise, no dependency gets added. Multiple names may be given.
+#
+# @param[in]  type of the dependency, one of: PRIVATE, PUBLIC, INTERFACE
+# @param[in, multivalue] list of component names which should be added as dependencies
+#
+function(idf_component_optional_requires req_type)
+    set(optional_reqs ${ARGN})
+    idf_build_get_property(build_components BUILD_COMPONENTS)
+    foreach(req ${optional_reqs})
+        if(req IN_LIST build_components)
+            idf_component_get_property(req_lib ${req} COMPONENT_LIB)
+            target_link_libraries(${COMPONENT_LIB} ${req_type} ${req_lib})
+        endif()
+    endforeach()
+endfunction()
+
 #
 # Deprecated functions
 #