From b5da1bf062222e9533660a8bfa00e54fefb933b1 Mon Sep 17 00:00:00 2001
From: Andrea Pappacoda <tachi@debian.org>
Date: Tue, 19 Aug 2025 17:03:29 +0200
Subject: [PATCH] build: simplify headers handling with file sets

CMake 3.23 introduced a nice way of handling C and C++ header files
together with libraries, File Sets:
<https://cmake.org/cmake/help/latest/command/target_sources.html#file-sets>

Compared to using the PUBLIC_HEADER property, which were originally just
thought for Apple Frameworks anyway, they properly handle adding the
correct directories to the include paths during builds and in installed
exported targets, mark headers as HEADER_FILE_ONLY, and other goodies
documented in the docs.
---
 CMakeLists.txt | 61 ++++++++++++--------------------------------------
 1 file changed, 14 insertions(+), 47 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index cd0c3f2a..925221ca 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -15,7 +15,7 @@
 
 #]===================================================================]
 
-cmake_minimum_required( VERSION 3.7 )
+cmake_minimum_required( VERSION 3.23 )
 
 project( date VERSION 3.0.4 )
 set(ABI_VERSION 3) # used as SOVERSION, increment when ABI changes
@@ -69,16 +69,13 @@ print_option( DISABLE_STRING_VIEW )
 #]===================================================================]
 add_library( date INTERFACE )
 add_library( date::date ALIAS date )
-target_include_directories( date INTERFACE
-    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
-    $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}> )
-# adding header sources just helps IDEs
-target_sources( date INTERFACE
-    $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>/date/date.h
-    $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>/date/solar_hijri.h
-    $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>/date/islamic.h
-    $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>/date/iso_week.h
-    $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>/date/julian.h
+target_sources(date
+    PUBLIC FILE_SET HEADERS BASE_DIRS "include" FILES
+    "include/date/date.h"
+    "include/date/solar_hijri.h"
+    "include/date/islamic.h"
+    "include/date/iso_week.h"
+    "include/date/julian.h"
 )
 
 set( APPLE_MOBILE_PLATFORM FALSE )
@@ -91,19 +88,6 @@ if ( IOS
     set( APPLE_MOBILE_PLATFORM TRUE )
 endif()
 
-set(TARGET_HEADERS
-    include/date/date.h
-    include/date/solar_hijri.h
-    include/date/islamic.h
-    include/date/iso_week.h
-    include/date/julian.h
-)
-
-if (CMAKE_VERSION VERSION_GREATER_EQUAL 3.15)
-    # public headers will get installed:
-    set_target_properties( date PROPERTIES PUBLIC_HEADER "${TARGET_HEADERS}" )
-endif ()
-
 # These used to be set with generator expressions,
 #
 #   ONLY_C_LOCALE=$<IF:$<BOOL:${COMPILE_WITH_C_LOCALE}>,1,0>
@@ -132,23 +116,20 @@ if( BUILD_TZ_LIB )
     add_library( date-tz )
     target_compile_definitions( date-tz PRIVATE BUILD_TZ_LIB=1 )
     target_sources( date-tz
-      PUBLIC
-        $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>/date/tz.h
+      PUBLIC FILE_SET HEADERS BASE_DIRS "include" FILES
+        include/date/tz.h
       PRIVATE
         include/date/tz_private.h
         src/tz.cpp )
     if ( APPLE_MOBILE_PLATFORM )
       target_sources( date-tz
-        PUBLIC
-          $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>/date/ios.h
+        PUBLIC FILE_SET HEADERS BASE_DIRS "include" FILES
+          include/date/ios.h
         PRIVATE
           src/ios.mm )
     endif()
     add_library( date::date-tz ALIAS date-tz )
     target_link_libraries( date-tz PUBLIC date )
-    target_include_directories( date-tz PUBLIC
-        $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
-        $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}> )
 
     if ( USE_SYSTEM_TZ_DB OR MANUAL_TZ_DB )
       target_compile_definitions( date-tz PRIVATE AUTO_DOWNLOAD=0 HAS_REMOTE_API=0 )
@@ -166,14 +147,8 @@ if( BUILD_TZ_LIB )
       target_compile_definitions( date-tz PUBLIC DATE_BUILD_DLL=1 )
     endif()
 
-    set(TZ_HEADERS include/date/tz.h)
-
-    if( APPLE_MOBILE_PLATFORM )
-        list(APPEND TZ_HEADERS include/date/ios.h)
-    endif( )
     set_target_properties( date-tz PROPERTIES
         POSITION_INDEPENDENT_CODE ON
-        PUBLIC_HEADER "${TZ_HEADERS}"
         VERSION "${PROJECT_VERSION}"
         SOVERSION "${ABI_VERSION}" )
     if( NOT MSVC )
@@ -199,21 +174,13 @@ if( ENABLE_DATE_INSTALL )
 
   install( TARGETS date
       EXPORT dateConfig
-      PUBLIC_HEADER DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/date )
+      FILE_SET HEADERS)
   export( TARGETS date NAMESPACE date:: FILE dateTargets.cmake )
-  if (CMAKE_VERSION VERSION_LESS 3.15)
-      install(
-          FILES ${TARGET_HEADERS}
-          DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/date )
-  endif ()
 
   if( BUILD_TZ_LIB )
       install( TARGETS date-tz
           EXPORT dateConfig
-          PUBLIC_HEADER DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/date
-          ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
-          LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
-          RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR} )  # This is for Windows
+          FILE_SET HEADERS)
       export( TARGETS date-tz NAMESPACE date:: APPEND FILE dateTargets.cmake )
   endif( )