Support building phobos against a system copy of zlib

This is achieved by linking the dynamic variant of phobos against zlib
and having the compiler add -lz when linking an application that
embeds the static variant of phobos.

Signed-off-by: Andrei Horodniceanu <a.horodniceanu@proton.me>

CMakeLists.txt

@@ -149,6 +149,9 @@ set(LDC_ENABLE_ASSERTIONS "${LLVM_ENABLE_ASSERTIONS}" CACHE BOOL "Enable LDC ass
 # Allow user to specify mimalloc.o location, to be linked with `ldc2` only
 set(ALTERNATIVE_MALLOC_O   ""     CACHE STRING "If specified, adds ALTERNATIVE_MALLOC_O object file to LDC link, to override the CRT malloc.")
 
+# Most linux distributions have a policy of not bundling dependencies like zlib
+set(PHOBOS_SYSTEM_ZLIB OFF CACHE BOOL "Use system zlib instead of Phobos' vendored version")
+
 if(D_VERSION EQUAL 1)
     message(FATAL_ERROR "D version 1 is no longer supported.
 Please consider using D version 2 or checkout the 'd1' git branch for the last version supporting D version 1.")
@@ -290,6 +293,9 @@ if(SANITIZE)
     endif()
 endif()
 append("${SANITIZE_CXXFLAGS}" LDC_CXXFLAGS)
+if(PHOBOS_SYSTEM_ZLIB)
+    append("-DPHOBOS_SYSTEM_ZLIB" LDC_CXXFLAGS)
+endif()
 # LLVM_CXXFLAGS may contain -Werror which causes compile errors with dmd source
 string(REPLACE "-Werror " "" LLVM_CXXFLAGS ${LLVM_CXXFLAGS})
 if (UNIX AND NOT "${LLVM_LDFLAGS}" STREQUAL "")

driver/linker-gcc.cpp

@@ -583,6 +583,10 @@ void ArgsBuilder::build(llvm::StringRef outputPath,
   for (const auto &name : defaultLibNames) {
     args.push_back("-l" + name);
   }
+#ifdef PHOBOS_SYSTEM_ZLIB
+  if (!defaultLibNames.empty() && !linkAgainstSharedDefaultLibs())
+      args.push_back("-lz");
+#endif
 
   // libs added via pragma(lib, libname)
   for (auto ls : global.params.linkswitches) {

runtime/CMakeLists.txt

@@ -61,6 +61,10 @@ if (RT_SUPPORT_SANITIZERS)
     list(APPEND D_FLAGS -d-version=SupportSanitizers)
 endif()
 
+if(PHOBOS_SYSTEM_ZLIB)
+    message(STATUS "-- Building PHOBOS against system zlib")
+endif()
+
 # Auto-detect TARGET_SYSTEM from host
 if("${TARGET_SYSTEM}" STREQUAL "AUTO")
     set(TARGET_SYSTEM ${CMAKE_SYSTEM_NAME})
@@ -243,14 +247,22 @@ if(PHOBOS2_DIR)
         list(REMOVE_ITEM PHOBOS2_D ${PHOBOS2_D_WINDOWS})
     endif()
 
-    # Phobos C parts
+    if(PHOBOS_SYSTEM_ZLIB)
-    file(GLOB_RECURSE PHOBOS2_C ${PHOBOS2_DIR}/etc/*.c)
+	find_package(ZLIB REQUIRED)
-    # remove zlib test modules
+    else()
-    list(REMOVE_ITEM PHOBOS2_C
+	# Phobos C parts
-        ${PHOBOS2_DIR}/etc/c/zlib/test/example.c
+	file(GLOB_RECURSE PHOBOS2_C ${PHOBOS2_DIR}/etc/*.c)
-        ${PHOBOS2_DIR}/etc/c/zlib/test/infcover.c
+	# remove zlib test modules
-        ${PHOBOS2_DIR}/etc/c/zlib/test/minigzip.c
+	list(REMOVE_ITEM PHOBOS2_C
-    )
+            ${PHOBOS2_DIR}/etc/c/zlib/test/example.c
+            ${PHOBOS2_DIR}/etc/c/zlib/test/infcover.c
+            ${PHOBOS2_DIR}/etc/c/zlib/test/minigzip.c
+	)
+	CHECK_INCLUDE_FILE(unistd.h HAVE_UNISTD_H)
+	if (HAVE_UNISTD_H)
+	    append("-DHAVE_UNISTD_H" CMAKE_C_FLAGS)
+	endif()
+    endif()
 endif()
 
 #
@@ -397,11 +409,6 @@ if("${TARGET_SYSTEM}" MATCHES "MSVC")
     # warning C4996: zlib uses 'deprecated' POSIX names
     append("/wd4100 /wd4127 /wd4131 /wd4206 /wd4244 /wd4245 /wd4267 /wd4996" CMAKE_C_FLAGS_RELEASE)
 endif()
-CHECK_INCLUDE_FILE(unistd.h HAVE_UNISTD_H)
-if (HAVE_UNISTD_H)
-    # Needed for zlib
-    append("-DHAVE_UNISTD_H" CMAKE_C_FLAGS)
-endif()
 # 2) Set all other CMAKE_C_FLAGS variants to CMAKE_C_FLAGS_RELEASE
 set(variables
     CMAKE_C_FLAGS_DEBUG
@@ -412,6 +419,16 @@ foreach(variable ${variables})
     set(${variable} "${CMAKE_C_FLAGS_RELEASE}")
 endforeach()
 
+function(link_zlib phobos_target library_type)
+    if(PHOBOS_SYSTEM_ZLIB)
+	if(${library_type} STREQUAL "SHARED")
+	    target_link_libraries(${phobos_target} ZLIB::ZLIB)
+	endif()
+    else()
+	target_sources(${phobos_target} PRIVATE ${PHOBOS2_C})
+    endif()
+endfunction()
+
 # Compiles the given D modules to object files, and if enabled, bitcode files.
 # The paths of the output files are appended to outlist_o and outlist_bc, respectively.
 macro(dc src_files src_basedir d_flags output_basedir emit_bc all_at_once single_obj_name outlist_o outlist_bc)
@@ -638,8 +655,8 @@ macro(build_runtime_libs druntime_o druntime_bc phobos2_o phobos2_bc c_flags ld_
     list(APPEND ${outlist_targets} druntime-ldc${target_suffix})
 
     if(PHOBOS2_DIR)
-        add_library(phobos2-ldc${target_suffix} ${library_type}
+        add_library(phobos2-ldc${target_suffix} ${library_type} ${phobos2_o})
-            ${phobos2_o} ${PHOBOS2_C})
+	link_zlib(phobos2-ldc${target_suffix} ${library_type})
         set_common_library_properties(phobos2-ldc${target_suffix}
             phobos2-ldc${lib_suffix} ${output_path}
             "${c_flags}" "${ld_flags}" ${is_shared}
@@ -669,8 +686,8 @@ macro(build_runtime_libs druntime_o druntime_bc phobos2_o phobos2_bc c_flags ld_
             "${c_flags}" "${ld_flags}" OFF
         )
 
-        add_library(phobos2-ldc-lto${target_suffix} STATIC
+        add_library(phobos2-ldc-lto${target_suffix} STATIC ${phobos2_bc})
-            ${phobos2_bc} ${PHOBOS2_C})
+	link_zlib(phobos2-ldc-lto${target_suffix} STATIC)
         set_common_library_properties(phobos2-ldc-lto${target_suffix}
             phobos2-ldc-lto${lib_suffix} ${output_path}
             "${c_flags}" "${ld_flags}" OFF
@@ -1004,6 +1021,9 @@ function(build_test_runners name_suffix path_suffix d_flags linkflags is_shared)
             LINK_FLAGS      ${linkflags}
             LINK_DEPENDS    ${tested_lib_path}
         )
+	if(PHOBOS_SYSTEM_ZLIB AND "${is_shared}" STREQUAL "OFF")
+	    target_link_libraries(${phobos_name} ZLIB::ZLIB)
+	endif()
         add_test(build-${phobos_name} "${CMAKE_COMMAND}" --build ${CMAKE_BINARY_DIR} --target ${phobos_name})
         set(_GLOBAL_TESTRUNNERS "${_GLOBAL_TESTRUNNERS};${phobos_name}" CACHE INTERNAL "")
     endif()