CMake build: generate pkgconfig for public modules

After the update to the CMake based build system the ability to
generate pkgconfig files, like it was with QMake, was lost.

This patch adds pkgconfig generation again via a new internal command
named qt_internal_export_pkg_config_file.

The functionality of this command consists in checking if the target
is internal. Then gets the compile definitions. It performs a search
for dependencies that is somewhat similar to
qt_get_direct_module_dependencies, although it won't recurse down for
more deps. Each dependency is then again, checked if it's internal or
has a public interface. Later these deps get deduplicated and lastly
a pkgconfig file is filled.

The resulting pkgconfig files of many of the Qt6 packages were
validated via invocations of `pkg-config --validate` and
`pkg-config --simulate` commands and later used to build local
projects plus tests that use the pkg-config provided details at
compilation time.

Although it has some limitations, with qt_internal_add_qml_module if
it specifies non-public deps these won't be listed and with non-Qt
requirements, notably in static builds, not being appended to the
PkgConfig file.

Task-number: QTBUG-86080
Change-Id: I0690bb3ca729eec328500f227261db9b7e7628f6
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

8 files changed, 223 insertions, 18 deletions

diff --git a/cmake/PkgConfigLibrary.pc.in b/cmake/PkgConfigLibrary.pc.in
new file mode 100644
index 0000000000..609346cb39
--- /dev/null
+++ b/cmake/PkgConfigLibrary.pc.in
@@ -0,0 +1,13 @@
+prefix=@CMAKE_INSTALL_PREFIX@
+exec_prefix=${prefix}
+bindir=${prefix}/@INSTALL_BINDIR@
+libdir=${prefix}/@INSTALL_LIBDIR@
+includedir=${prefix}/@INSTALL_INCLUDEDIR@
+$<$<BOOL:@contains_mkspecs@>:mkspecsdir=${prefix}/@INSTALL_MKSPECSDIR@>
+$<1: >
+Name: @pkgconfig_name@
+Description: @pkgconfig_description@
+Version: @PROJECT_VERSION@
+Libs: $<$<NOT:@is_interface_library@>:-L${libdir} -l@pkgconfig_file@> @link_options@
+Cflags: @include_dirs@ @compile_defs@
+Requires: $<JOIN:$<REMOVE_DUPLICATES:@target_requires@>, >
diff --git a/cmake/QtBaseGlobalTargets.cmake b/cmake/QtBaseGlobalTargets.cmake
index 3696ddd958..0b1cc3a6f0 100644
--- a/cmake/QtBaseGlobalTargets.cmake
+++ b/cmake/QtBaseGlobalTargets.cmake
@@ -205,6 +205,7 @@ qt_install(FILES
 # They can only be used while building Qt itself.
 qt_copy_or_install(FILES
                    cmake/ModuleDescription.json.in
+                   cmake/PkgConfigLibrary.pc.in
                    cmake/Qt3rdPartyLibraryConfig.cmake.in
                    cmake/Qt3rdPartyLibraryHelpers.cmake
                    cmake/QtAndroidHelpers.cmake
@@ -227,6 +228,7 @@ qt_copy_or_install(FILES
                    cmake/QtFindPackageHelpers.cmake
                    cmake/QtFindWrapConfigExtra.cmake.in
                    cmake/QtFindWrapHelper.cmake
+                   cmake/QtFinishPkgConfigFile.cmake
                    cmake/QtFinishPrlFile.cmake
                    cmake/QtFlagHandlingHelpers.cmake
                    cmake/QtFrameworkHelpers.cmake
@@ -245,6 +247,7 @@ qt_copy_or_install(FILES
                    cmake/QtModuleToolsDependencies.cmake.in
                    cmake/QtModuleToolsVersionlessTargets.cmake.in
                    cmake/QtNoLinkTargetHelpers.cmake
+                   cmake/QtPkgConfigHelpers.cmake
                    cmake/QtPlatformAndroid.cmake
                    cmake/QtPlatformSupport.cmake
                    cmake/QtPluginConfig.cmake.in
diff --git a/cmake/QtBuild.cmake b/cmake/QtBuild.cmake
index 2cd06c435d..d293c0d083 100644
--- a/cmake/QtBuild.cmake
+++ b/cmake/QtBuild.cmake
@@ -524,6 +524,7 @@ include(QtModuleHelpers)
 include(QtNoLinkTargetHelpers)
 include(QtPluginHelpers)
 include(QtPrecompiledHeadersHelpers)
+include(QtPkgConfigHelpers)
 include(QtPriHelpers)
 include(QtPrlHelpers)
 include(QtQmakeHelpers)
diff --git a/cmake/QtFinishPkgConfigFile.cmake b/cmake/QtFinishPkgConfigFile.cmake
new file mode 100644
index 0000000000..63545df139
--- /dev/null
+++ b/cmake/QtFinishPkgConfigFile.cmake
@@ -0,0 +1,28 @@
+# Finish a preliminary .pc file.
+#
+# - Appends to each requirement the proper configuration postfix.
+# - Strips empty PkgConfig fields.
+#
+# This file is to be used in CMake script mode with the following variables set:
+# IN_FILE: path to the step 2 preliminary .pc file.
+# OUT_FILE: path to the .pc file that is going to be created.
+# POSTFIX: postfix for each requirement (optional).
+
+cmake_policy(SET CMP0057 NEW)
+file(STRINGS "${IN_FILE}" lines)
+set(content "")
+set(emptied "Libs:" "Cflags:" "Requires:")
+foreach(line ${lines})
+    if(POSTFIX)
+        if(line MATCHES "^Libs:")
+            string(REGEX REPLACE "( -lQt[^ ]+)" "\\1${POSTFIX}" line "${line}")
+        elseif(line MATCHES "^Requires:")
+            string(REGEX REPLACE "( Qt[^ ]+)" "\\1${POSTFIX}" line "${line}")
+        endif()
+    endif()
+    string(REGEX REPLACE " +$" "" line "${line}")
+    if(NOT line IN_LIST emptied)
+        string(APPEND content "${line}\n")
+    endif()
+endforeach()
+file(WRITE "${OUT_FILE}" "${content}")
diff --git a/cmake/QtModuleHelpers.cmake b/cmake/QtModuleHelpers.cmake
index 11f8eca3bd..eedf05b4fa 100644
--- a/cmake/QtModuleHelpers.cmake
+++ b/cmake/QtModuleHelpers.cmake
@@ -821,6 +821,7 @@ function(qt_finalize_module target)
     qt_finalize_framework_headers_copy(${target})
     qt_generate_prl_file(${target} "${INSTALL_LIBDIR}")
     qt_generate_module_pri_file("${target}" ${ARGN})
+    qt_internal_generate_pkg_config_file(${target})
 endfunction()
 
 # Get a set of Qt module related values based on the target.
diff --git a/cmake/QtPkgConfigHelpers.cmake b/cmake/QtPkgConfigHelpers.cmake
new file mode 100644
index 0000000000..d88be5fe78
--- /dev/null
+++ b/cmake/QtPkgConfigHelpers.cmake
@@ -0,0 +1,142 @@
+function(qt_internal_collect_direct_target_dependencies target targets_out_var)
+    __qt_internal_walk_libs("${target}" "${targets_out_var}" _rcc_objects
+                            "qt_direct_targets_dict" "direct_targets")
+    set("${targets_out_var}" "${${targets_out_var}}" PARENT_SCOPE)
+endfunction()
+
+macro(qt_internal_set_pkg_config_cpp_flags var options flag)
+    set(tmpopts "${options}")
+    list(FILTER tmpopts EXCLUDE REGEX "\\$<BUILD_INTERFACE:[^,>]+>")
+    list(FILTER tmpopts EXCLUDE REGEX "\\$<TARGET_PROPERTY:[^,>]+>")
+    list(TRANSFORM tmpopts REPLACE "\\$<INSTALL_INTERFACE:([^,>]+)>" "\\1")
+    list(TRANSFORM tmpopts REPLACE ">" "$<ANGLE-R>")
+    list(TRANSFORM tmpopts REPLACE "," "$<COMMA>")
+    set(${var} "$<$<BOOL:${tmpopts}>:${flag}$<JOIN:$<REMOVE_DUPLICATES:${tmpopts}>, ${flag}>>")
+    unset(tmpopts)
+endmacro()
+
+# Create a Qt6*.pc file intended for pkg-config consumption.
+function(qt_internal_generate_pkg_config_file module)
+    # TODO: PkgConfig is supported under MSVC with pkgconf (github.com/pkgconf/pkgconf)
+    if((NOT UNIX OR QT_FEATURE_framework) AND NOT MINGW OR CMAKE_VERSION VERSION_LESS "3.20")
+        return()
+    endif()
+    if(NOT BUILD_SHARED_LIBS)
+        return()
+    endif()
+
+    set(pkgconfig_file "${QT_CMAKE_EXPORT_NAMESPACE}${module}")
+    set(pkgconfig_name "${QT_CMAKE_EXPORT_NAMESPACE} ${module}")
+    set(pkgconfig_description "Qt ${module} module")
+    set(target "${QT_CMAKE_EXPORT_NAMESPACE}::${module}")
+    set(is_interface_library "$<STREQUAL:$<TARGET_PROPERTY:${target},TYPE>,INTERFACE_LIBRARY>")
+    # The flags macro expanded this variables so it's better to set them at
+    # their corresponding PkgConfig string.
+    set(includedir "\${includedir}")
+    set(mkspecsdir "\${mkspecsdir}")
+
+    get_target_property(is_internal_module ${target} _qt_is_internal_module)
+    if(is_internal_module)
+        return()
+    endif()
+
+    get_target_property(loose_link_options ${target} INTERFACE_LINK_OPTIONS)
+    get_target_property(loose_compile_defs ${target} INTERFACE_COMPILE_DEFINITIONS)
+    get_target_property(loose_include_dirs ${target} INTERFACE_INCLUDE_DIRECTORIES)
+    list(TRANSFORM loose_include_dirs REPLACE "${INSTALL_INCLUDEDIR}" "\${includedir}")
+    list(TRANSFORM loose_include_dirs REPLACE "${INSTALL_MKSPECSDIR}" "\${mkspecsdir}")
+
+    qt_internal_set_pkg_config_cpp_flags(link_options "${loose_link_options}" "")
+    qt_internal_set_pkg_config_cpp_flags(compile_defs "${loose_compile_defs}" -D)
+    qt_internal_set_pkg_config_cpp_flags(include_dirs "${loose_include_dirs}" -I)
+    if("${include_dirs}" MATCHES "\\${mkspecsdir}")
+        set(contains_mkspecs TRUE)
+    endif()
+
+    # TODO: Handle macOS framework builds
+    qt_internal_collect_direct_target_dependencies(${target} loose_target_requires)
+    foreach(dep IN LISTS loose_target_requires)
+        if(dep MATCHES "^Qt::")
+            string(REGEX REPLACE "Qt" "${QT_CMAKE_EXPORT_NAMESPACE}" dep ${dep})
+        else()
+            # TODO: Figure out a way to get non-Qt requirements PkgConfig files.
+            continue()
+        endif()
+        if(NOT TARGET ${dep})
+            continue()
+        endif()
+        get_target_property(is_internal_module ${dep} _qt_is_internal_module)
+        if(is_internal_module OR dep MATCHES ".*Platform.*Internal")
+            continue()
+        endif()
+        get_target_property(type ${dep} TYPE)
+        if(type STREQUAL "INTERFACE_LIBRARY")
+            if(dep MATCHES "(.*)Private")
+                set(dep "${CMAKE_MATCH_1}")
+            endif()
+            get_target_property(type ${dep} TYPE)
+        endif()
+        string(REGEX REPLACE "::" "" req ${dep})
+        if(type STREQUAL "STATIC_LIBRARY")
+            list(APPEND target_libs -l${req})
+        else()
+            list(APPEND target_requires ${req})
+        endif()
+    endforeach()
+    string(APPEND link_options " $<JOIN:$<REMOVE_DUPLICATES:${target_libs}>, >")
+
+    qt_path_join(path_suffix "${INSTALL_LIBDIR}" pkgconfig)
+    qt_path_join(build_dir "${QT_BUILD_DIR}" "${path_suffix}")
+    qt_path_join(install_dir "${QT_INSTALL_DIR}" "${path_suffix}")
+
+    set(step_prefix "preliminary_pc_for_${pkgconfig_file}")
+    qt_path_join(template_pc "${QT_CMAKE_DIR}" PkgConfigLibrary.pc.in)
+    qt_path_join(pc_step1_path "${build_dir}" ${step_prefix}_step1.pc)
+    qt_path_join(pc_step2_path "${build_dir}" ${step_prefix}_$<CONFIG>_step2.pc)
+
+    configure_file("${template_pc}" "${pc_step1_path}" @ONLY)
+
+    file(GENERATE OUTPUT "${pc_step2_path}" INPUT "${pc_step1_path}")
+
+    if(QT_GENERATOR_IS_MULTI_CONFIG)
+        set(configs ${CMAKE_CONFIGURATION_TYPES})
+        set(rels ${configs})
+        list(FILTER rels INCLUDE REGEX "(Release|RelWithDebInfo|MinSizeRel)")
+        if(rels)
+            list(GET rels 0 release)
+        endif()
+    else()
+        set(configs ${CMAKE_BUILD_TYPE})
+        set(release ${configs})
+    endif()
+
+    foreach(config ${configs})
+        if(config STREQUAL "Debug" AND CMAKE_DEBUG_POSTFIX)
+            set(postfix ${CMAKE_DEBUG_POSTFIX})
+        elseif(NOT config STREQUAL release)
+            string(TOLOWER "_${config}" postfix)
+        else()
+            set(postfix "")
+        endif()
+        qt_path_join(pc_step2_path "${build_dir}" ${step_prefix}_${config}_step2.pc)
+        qt_path_join(final_pc_path "${build_dir}" ${pkgconfig_file}${postfix}.pc)
+
+        add_custom_command(
+            OUTPUT  "${final_pc_path}"
+            DEPENDS "${pc_step2_path}"
+                    "${QT_CMAKE_DIR}/QtFinishPkgConfigFile.cmake"
+            COMMAND ${CMAKE_COMMAND}
+                    "-DIN_FILE=${pc_step2_path}"
+                    "-DOUT_FILE=${final_pc_path}"
+                    "$<$<BOOL:${postfix}>:-DPOSTFIX=${postfix}>"
+                    -P "${QT_CMAKE_DIR}/QtFinishPkgConfigFile.cmake"
+            VERBATIM
+            COMMENT "Generating pc file for target ${target}"
+            )
+
+        # This is inspired by https://gitlab.kitware.com/cmake/cmake/-/issues/20842
+        target_sources(${module} PRIVATE "${final_pc_path}")
+
+        qt_install(FILES "${final_pc_path}" DESTINATION "${install_dir}")
+    endforeach()
+endfunction()
diff --git a/cmake/QtPlatformTargetHelpers.cmake b/cmake/QtPlatformTargetHelpers.cmake
index 49bc558cec..36b661741b 100644
--- a/cmake/QtPlatformTargetHelpers.cmake
+++ b/cmake/QtPlatformTargetHelpers.cmake
@@ -42,6 +42,9 @@ function(qt_internal_setup_public_platform_target)
 
     # By default enable unicode on WIN32 platforms for both Qt and Qt consumers. Can be opted out.
     qt_internal_enable_unicode_defines(Platform)
+
+    # Generate a pkgconfig for Qt::Platform.
+    qt_internal_generate_pkg_config_file(Platform)
 endfunction()
 
 function(qt_internal_get_platform_definition_include_dir install_interface build_interface)
diff --git a/cmake/QtPublicWalkLibsHelpers.cmake b/cmake/QtPublicWalkLibsHelpers.cmake
index 7267bc9677..85f09b7679 100644
--- a/cmake/QtPublicWalkLibsHelpers.cmake
+++ b/cmake/QtPublicWalkLibsHelpers.cmake
@@ -73,6 +73,8 @@ endfunction()
 #                           Used for prl file generation.
 #            'promote_global' promotes walked imported targets to global scope.
 #            'collect_targets' collects all target names (discards framework or link flags)
+#            'direct_targets' collects only the direct target names (discards framework or link
+#                             flags)
 #
 #
 function(__qt_internal_walk_libs
@@ -83,6 +85,12 @@ function(__qt_internal_walk_libs
     endif()
     list(APPEND collected ${target})
 
+    if(operation MATCHES "^direct")
+        set(direct TRUE)
+    else()
+        set(direct FALSE)
+    endif()
+
     if(target STREQUAL "${QT_CMAKE_EXPORT_NAMESPACE}::EntryPointPrivate")
         # We can't (and don't need to) process EntryPointPrivate because it brings in
         # $<TARGET_PROPERTY:prop> genexes which get replaced with
@@ -184,21 +192,25 @@ function(__qt_internal_walk_libs
                 endif()
                 get_target_property(lib_target_type ${lib_target} TYPE)
                 if(lib_target_type STREQUAL "INTERFACE_LIBRARY")
-                    __qt_internal_walk_libs(
-                        ${lib_target}
-                        lib_libs_${target}
-                        lib_rcc_objects_${target}
-                        "${dict_name}" "${operation}" ${collected})
-                    if(lib_libs_${target})
-                        __qt_internal_merge_libs(libs ${lib_libs_${target}})
-                        set(is_module 0)
-                    endif()
-                    if(lib_rcc_objects_${target})
-                        __qt_internal_merge_libs(rcc_objects ${lib_rcc_objects_${target}})
+                    if(NOT ${direct})
+                        __qt_internal_walk_libs(
+                            ${lib_target}
+                            lib_libs_${target}
+                            lib_rcc_objects_${target}
+                            "${dict_name}" "${operation}" ${collected})
+                        if(lib_libs_${target})
+                            __qt_internal_merge_libs(libs ${lib_libs_${target}})
+                            set(is_module 0)
+                        endif()
+                        if(lib_rcc_objects_${target})
+                            __qt_internal_merge_libs(rcc_objects ${lib_rcc_objects_${target}})
+                        endif()
+                    else()
+                        __qt_internal_merge_libs(libs ${lib})
                     endif()
                 elseif(NOT lib_target_type STREQUAL "OBJECT_LIBRARY")
 
-                    if(operation STREQUAL "collect_targets")
+                    if(operation MATCHES "^(collect|direct)_targets$")
                         __qt_internal_merge_libs(libs ${lib_target})
                     else()
                         __qt_internal_merge_libs(libs "$<TARGET_LINKER_FILE:${lib_target}>")
@@ -209,11 +221,13 @@ function(__qt_internal_walk_libs
                         __qt_internal_merge_libs(rcc_objects ${target_rcc_objects})
                     endif()
 
-                    __qt_internal_walk_libs(
-                        ${lib_target}
-                        lib_libs_${target}
-                        lib_rcc_objects_${target}
-                        "${dict_name}" "${operation}" ${collected})
+                    if(NOT ${direct})
+                        __qt_internal_walk_libs(
+                            ${lib_target}
+                            lib_libs_${target}
+                            lib_rcc_objects_${target}
+                            "${dict_name}" "${operation}" ${collected})
+                    endif()
                     if(lib_libs_${target})
                         __qt_internal_merge_libs(libs ${lib_libs_${target}})
                     endif()
@@ -242,7 +256,7 @@ function(__qt_internal_walk_libs
                 message(FATAL_ERROR "The ${CMAKE_MATCH_1} target is mentioned as a dependency for \
 ${target}, but not declared.")
             else()
-                if(NOT operation STREQUAL "collect_targets")
+                if(NOT operation MATCHES "^(collect|direct)_targets$")
                     set(final_lib_name_to_merge "${lib_target}")
                     if(lib_target MATCHES "/([^/]+).framework$")
                         set(final_lib_name_to_merge "-framework ${CMAKE_MATCH_1}")