From 1b60519efea58c668c61ff42171ee7babca8e46f Mon Sep 17 00:00:00 2001
From: Arno Moonen <arno.moonen@airios.eu>
Date: Wed, 24 Aug 2022 14:34:28 +0200
Subject: [PATCH] Add support for conditional dependencies via INCLUDE_IF
 keyword.

See cpm-cmake/CPM.cmake#391 for more details.
---
 README.md       |  1 +
 cmake/CPM.cmake | 76 ++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 76 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 2fd49a64..1b213cdb 100644
--- a/README.md
+++ b/README.md
@@ -33,6 +33,7 @@ CPMAddPackage(
   VERSION       # The minimum version of the dependency (optional, defaults to 0)
   OPTIONS       # Configuration options passed to the dependency (optional)
   DOWNLOAD_ONLY # If set, the project is downloaded, but not configured (optional)
+  INCLUDE_IF    # If set, the value has to evaluate to true for the dependency to be added (optional)
   [...]         # Origin parameters forwarded to FetchContent_Declare, see below
 )
 ```
diff --git a/cmake/CPM.cmake b/cmake/CPM.cmake
index 7aa8b665..d845fcdf 100644
--- a/cmake/CPM.cmake
+++ b/cmake/CPM.cmake
@@ -262,7 +262,7 @@ endfunction()
 
 # Find a package locally or fallback to CPMAddPackage
 function(CPMFindPackage)
-  set(oneValueArgs NAME VERSION GIT_TAG FIND_PACKAGE_ARGUMENTS)
+  set(oneValueArgs NAME VERSION GIT_TAG FIND_PACKAGE_ARGUMENTS INCLUDE_IF)
 
   cmake_parse_arguments(CPM_ARGS "" "${oneValueArgs}" "" ${ARGN})
 
@@ -272,6 +272,33 @@ function(CPMFindPackage)
     endif()
   endif()
 
+  if(DEFINED CPM_ARGS_INCLUDE_IF)
+
+    # Filter out INCLUDE_IF from arguments
+    cpm_remove_one_value_arg(INCLUDE_IF ARGN ${ARGN})
+
+    # If INCLUDE_IF evaluates to false, do not add the package, but do add it to the package lock
+    # and register it.
+    if(NOT CPM_ARGS_INCLUDE_IF)
+      CPMRegisterPackage("${CPM_ARGS_NAME}" "${CPM_ARGS_VERSION}")
+      if(CPM_PACKAGE_LOCK_ENABLED)
+        if((CPM_ARGS_VERSION AND NOT CPM_ARGS_SOURCE_DIR) OR CPM_INCLUDE_ALL_IN_PACKAGE_LOCK)
+          cpm_add_to_package_lock(${CPM_ARGS_NAME} "${ARGN}")
+        elseif(CPM_ARGS_SOURCE_DIR)
+          cpm_add_comment_to_package_lock(${CPM_ARGS_NAME} "local directory")
+        else()
+          cpm_add_comment_to_package_lock(${CPM_ARGS_NAME} "${ARGN}")
+        endif()
+      endif()
+
+      message(
+        STATUS
+          "${CPM_INDENT} skipping package ${CPM_ARGS_NAME}@${CPM_ARGS_VERSION} (INCLUDE_IF: ${CPM_ARGS_INCLUDE_IF})"
+      )
+      return()
+    endif()
+  endif()
+
   set(downloadPackage ${CPM_DOWNLOAD_ALL})
   if(DEFINED CPM_DOWNLOAD_${CPM_ARGS_NAME})
     set(downloadPackage ${CPM_DOWNLOAD_${CPM_ARGS_NAME}})
@@ -495,6 +522,25 @@ function(cpm_override_fetchcontent contentName)
   set_property(GLOBAL PROPERTY ${propertyName} TRUE)
 endfunction()
 
+# filter out a one value keyword and its value from a list of arguments
+function(cpm_remove_one_value_arg KEYWORD OUTPUT_VAR)
+  # Always start with a copy of the data
+  set(RESULT ${ARGN})
+
+  # Find the keyword location
+  list(FIND RESULT ${KEYWORD} KEYWORD_INDEX)
+  if(KEYWORD_INDEX GREATER_EQUAL 0)
+    # Keyword found; remove data at the same index twice to get rid of the keyword and its value
+    list(REMOVE_AT RESULT ${KEYWORD_INDEX})
+    list(REMOVE_AT RESULT ${KEYWORD_INDEX})
+  endif()
+
+  set(${OUTPUT_VAR}
+      ${RESULT}
+      PARENT_SCOPE
+  )
+endfunction()
+
 # Download and add a package from source
 function(CPMAddPackage)
   cpm_set_policies()
@@ -524,6 +570,7 @@ function(CPMAddPackage)
       GIT_SHALLOW
       EXCLUDE_FROM_ALL
       SOURCE_SUBDIR
+      INCLUDE_IF
   )
 
   set(multiValueArgs URL OPTIONS)
@@ -538,6 +585,33 @@ function(CPMAddPackage)
     endif()
   endif()
 
+  if(DEFINED CPM_ARGS_INCLUDE_IF)
+
+    # Filter out INCLUDE_IF from arguments
+    cpm_remove_one_value_arg(INCLUDE_IF ARGN ${ARGN})
+
+    # If INCLUDE_IF evaluates to false, do not add the package, but do add it to the package lock
+    # and register it.
+    if(NOT CPM_ARGS_INCLUDE_IF)
+      CPMRegisterPackage("${CPM_ARGS_NAME}" "${CPM_ARGS_VERSION}")
+      if(CPM_PACKAGE_LOCK_ENABLED)
+        if((CPM_ARGS_VERSION AND NOT CPM_ARGS_SOURCE_DIR) OR CPM_INCLUDE_ALL_IN_PACKAGE_LOCK)
+          cpm_add_to_package_lock(${CPM_ARGS_NAME} "${ARGN}")
+        elseif(CPM_ARGS_SOURCE_DIR)
+          cpm_add_comment_to_package_lock(${CPM_ARGS_NAME} "local directory")
+        else()
+          cpm_add_comment_to_package_lock(${CPM_ARGS_NAME} "${ARGN}")
+        endif()
+      endif()
+
+      message(
+        STATUS
+          "${CPM_INDENT} skipping package ${CPM_ARGS_NAME}@${CPM_ARGS_VERSION} (INCLUDE_IF: ${CPM_ARGS_INCLUDE_IF})"
+      )
+      return()
+    endif()
+  endif()
+
   if(CPM_ARGS_DOWNLOAD_ONLY)
     set(DOWNLOAD_ONLY ${CPM_ARGS_DOWNLOAD_ONLY})
   else()