CMake: Use default location for installing metatypes json files

Previously configuring a standalone example that had no explicit
INSTALL_DIR option for qt6_generate_meta_types_json_file would fail.

When no explicit location is specified to
qt6_generate_meta_types_json_file via INSTALL_DIR option, default
to installing into a lib/metatypes location relative to the install
prefix.

This is required for supporting calling
qt6_generate_meta_types_json_file when building standalone applications
or libraries (not part of the Qt build).

Make sure not to install the metatypes.json file for executables.
Install it only for libraries (aka modules).

Task-number: QTBUG-84403
Change-Id: Ie0dd75fca0cde71ccb4eb48030871e72d31d1725
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

1 files changed, 66 insertions, 47 deletions

diff --git a/src/corelib/Qt6CoreMacros.cmake b/src/corelib/Qt6CoreMacros.cmake
index 88cdd3ce96..557bb6b140 100644
--- a/src/corelib/Qt6CoreMacros.cmake
+++ b/src/corelib/Qt6CoreMacros.cmake
@@ -567,9 +567,11 @@ endif()
 # MANUAL_MOC_JSON_FILES parameter. The latter can be obtained by running moc with
 # the --output-json parameter.
 # Params:
-#   INSTALL_DIR: Location where to install the metatypes file (Optional)
-#   COPY_OVER_INSTALL: When present will install the file via a post build step
-#   copy rather than using install
+#   INSTALL_DIR: Location where to install the metatypes file. For public consumption,
+#                defaults to a ${CMAKE_INSTALL_PREFIX}/lib/metatypes directory.
+#                Executable metatypes files are never installed.
+#   COPY_OVER_INSTALL: (Qt Internal) When present will install the file via a post build step
+#   copy rather than using install.
 function(qt6_generate_meta_types_json_file target)
 
     get_target_property(existing_meta_types_file ${target} INTERFACE_QT_META_TYPES_BUILD_FILE)
@@ -579,22 +581,6 @@ function(qt6_generate_meta_types_json_file target)
 
     cmake_parse_arguments(arg "COPY_OVER_INSTALL" "INSTALL_DIR" "MANUAL_MOC_JSON_FILES" ${ARGN})
 
-    if (NOT QT_BUILDING_QT)
-        if (NOT arg_INSTALL_DIR)
-            message(FATAL_ERROR "Please specify an install directory using INSTALL_DIR")
-        endif()
-    else()
-        # Automatically fill install args when building qt
-        set(metatypes_install_dir ${INSTALL_LIBDIR}/metatypes)
-        set(args)
-        if (NOT QT_WILL_INSTALL)
-            set(arg_COPY_OVER_INSTALL TRUE)
-        endif()
-        if (NOT arg_INSTALL_DIR)
-            set(arg_INSTALL_DIR "${metatypes_install_dir}")
-        endif()
-    endif()
-
     get_target_property(target_type ${target} TYPE)
     if (target_type STREQUAL "INTERFACE_LIBRARY")
         message(FATAL_ERROR "Meta types generation does not work on interface libraries")
@@ -606,6 +592,19 @@ function(qt6_generate_meta_types_json_file target)
         return()
     endif()
 
+    # Whether the generated json file needs to be installed for prefix-builds, or copied for
+    # non-prefix builds. Regardless of the type of build, executable metatypes.json files should
+    # not be installed. Only library .json files should be installed.
+    set(should_install "TRUE")
+    if (target_type STREQUAL "EXECUTABLE")
+        set(should_install "FALSE")
+    endif()
+
+    # Automatically fill default install args when not specified.
+    if (NOT arg_INSTALL_DIR)
+        set(arg_INSTALL_DIR "lib/metatypes")
+    endif()
+
     get_target_property(target_binary_dir ${target} BINARY_DIR)
     set(type_list_file "${target_binary_dir}/meta_types/${target}_json_file_list.txt")
     set(type_list_file_manual "${target_binary_dir}/meta_types/${target}_json_file_list_manual.txt")
@@ -613,7 +612,7 @@ function(qt6_generate_meta_types_json_file target)
     get_target_property(uses_automoc ${target} AUTOMOC)
     set(automoc_args)
     set(automoc_dependencies)
-    #Handle automoc generated data
+    # Handle automoc generated data
     if (uses_automoc)
         # Tell automoc to output json files)
         set_property(TARGET "${target}" APPEND PROPERTY
@@ -729,7 +728,8 @@ function(qt6_generate_meta_types_json_file target)
         set(arg_INSTALL_DIR "${CMAKE_INSTALL_PREFIX}/${arg_INSTALL_DIR}")
     endif()
 
-    if (arg_COPY_OVER_INSTALL AND NOT EXISTS ${arg_INSTALL_DIR}/${metatypes_file_name})
+    if (should_install AND arg_COPY_OVER_INSTALL
+          AND NOT EXISTS ${arg_INSTALL_DIR}/${metatypes_file_name})
         file(MAKE_DIRECTORY "${arg_INSTALL_DIR}")
         file(TOUCH "${arg_INSTALL_DIR}/${metatypes_file_name}")
     endif()
@@ -751,50 +751,69 @@ function(qt6_generate_meta_types_json_file target)
     set(metatypes_file_genex_build)
     set(metatypes_file_genex_install)
     if (arg_COPY_OVER_INSTALL)
-        set(metatypes_file_genex_build
-            "$<BUILD_INTERFACE:$<$<BOOL:$<TARGET_PROPERTY:QT_CONSUMES_METATYPES>>:${arg_INSTALL_DIR}/${metatypes_file_name}>>"
-        )
+        if(should_install)
+            set(metatypes_file_genex_build
+                "$<BUILD_INTERFACE:$<$<BOOL:$<TARGET_PROPERTY:QT_CONSUMES_METATYPES>>:${arg_INSTALL_DIR}/${metatypes_file_name}>>"
+            )
+        endif()
     else()
         set(metatypes_file_genex_build
             "$<BUILD_INTERFACE:$<$<BOOL:$<TARGET_PROPERTY:QT_CONSUMES_METATYPES>>:${metatypes_file}>>"
         )
-        set(metatypes_file_genex_install
-            "$<INSTALL_INTERFACE:$<$<BOOL:$<TARGET_PROPERTY:QT_CONSUMES_METATYPES>>:$<INSTALL_PREFIX>/${arg_INSTALL_DIR}/${metatypes_file_name}>>"
-        )
+        if(should_install)
+            set(metatypes_file_genex_install
+                "$<INSTALL_INTERFACE:$<$<BOOL:$<TARGET_PROPERTY:QT_CONSUMES_METATYPES>>:$<INSTALL_PREFIX>/${arg_INSTALL_DIR}/${metatypes_file_name}>>"
+            )
+        endif()
     endif()
     set_source_files_properties(${metatypes_file} PROPERTIES HEADER_FILE_ONLY TRUE)
 
     set_target_properties(${target} PROPERTIES
         INTERFACE_QT_MODULE_HAS_META_TYPES YES
         INTERFACE_QT_MODULE_META_TYPES_FROM_BUILD YES
-        INTERFACE_QT_META_TYPES_BUILD_FILE ${metatypes_file}
+        INTERFACE_QT_META_TYPES_BUILD_FILE "${metatypes_file}"
         QT_MODULE_META_TYPES_FILE_GENEX_BUILD "${metatypes_file_genex_build}"
         QT_MODULE_META_TYPES_FILE_GENEX_INSTALL "${metatypes_file_genex_install}"
     )
     target_sources(${target} INTERFACE ${metatypes_file_genex_build} ${metatypes_file_genex_install})
 
-    if (arg_COPY_OVER_INSTALL)
-        get_target_property(target_type ${target} TYPE)
-        set(command_args
-            COMMAND ${CMAKE_COMMAND} -E copy_if_different
-                "${metatypes_file}"
-                "${arg_INSTALL_DIR}/${metatypes_file_name}"
-        )
-        if (target_type STREQUAL "OBJECT_LIBRARY")
-            add_custom_target(${target}_metatypes_copy
-                DEPENDS "${metatypes_file}"
-                ${command_args}
+    # Installation is complicated, because there are multiple combinations.
+    # In non-prefix builds (signaled by arg_COPY_OVER_INSTALL == TRUE), Qt modules are /copied/
+    # into the qt_prefix/lib/metatypes.
+    # In prefix builds (signaled by arg_COPY_OVER_INSTALL == FALSE), Qt modules are /installed/
+    # into the qt_prefix/lib/metatypes.
+    # Currently only the internal qt_add_module sets arg_COPY_OVER_INSTALL.
+    #
+    # Tests and examples are executables, and thus will not have their meta types installed, but
+    # they will have them generated (if this function is called).
+    #
+    # Regular libraries and plugins (which are not part of the Qt build), will be /installed/
+    # into a lib/metatypes directory relative to their prefix, rather than the Qt prefix (only
+    # outside of a Qt build).
+    # We don't support non-prefix builds for libraries or plugins which are not part of the official
+    # Qt build. Aka everything non-prefix / COPY_OVER_INSTALL related are implementation details
+    # that users shouldn't use.
+    if(should_install)
+        if (arg_COPY_OVER_INSTALL)
+            set(command_args
+                COMMAND ${CMAKE_COMMAND} -E copy_if_different
+                    "${metatypes_file}"
+                    "${arg_INSTALL_DIR}/${metatypes_file_name}"
             )
-            add_dependencies(${target} ${target}_metatypes_copy)
+            if (target_type STREQUAL "OBJECT_LIBRARY")
+                add_custom_target(${target}_metatypes_copy
+                    DEPENDS "${metatypes_file}"
+                    ${command_args}
+                )
+                add_dependencies(${target} ${target}_metatypes_copy)
+            else()
+                add_custom_command(TARGET ${target} POST_BUILD
+                    ${command_args}
+                )
+            endif()
         else()
-            add_custom_command(TARGET ${target} POST_BUILD
-                ${command_args}
-            )
+            install(FILES "${metatypes_file}" DESTINATION "${arg_INSTALL_DIR}")
         endif()
-    else()
-        install(FILES "${metatypes_file}"
-            DESTINATION "${arg_INSTALL_DIR}"
-        )
     endif()
 endfunction()