wasm: add support for building Qt as shared libraries

This implements the build system bits required to build Qt
as as separate wasm modules a.k.a Emscripten side modules.

Enable by configuring with the "-shared" flag.

This is the first step towards shared library support and gets
us as far as being able to load QtCore and instantiate a
QCoreApplication.

Task-number: QTBUG-63925
Change-Id: Ib8f07f80fb5b13c8dbba65c7db735dc557b70d0e
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

cmake/QtAutoDetect.cmake

@@ -35,6 +35,10 @@ function(qt_auto_detect_wasm)
             __qt_internal_query_emsdk_version("${EMROOT_PATH}" TRUE CMAKE_EMSDK_REGEX_VERSION)
             set(EMCC_VERSION "${CMAKE_EMSDK_REGEX_VERSION}" CACHE STRING INTERNAL FORCE)
 
+            if(NOT DEFINED BUILD_SHARED_LIBS)
+                qt_internal_ensure_static_qt_config()
+            endif()
+
             # Find toolchain file
             if(NOT DEFINED CMAKE_TOOLCHAIN_FILE)
                 __qt_internal_get_emscripten_cmake_toolchain_file_path_from_emsdk_env(
@@ -49,8 +53,6 @@ function(qt_auto_detect_wasm)
                 __qt_internal_show_error_no_emscripten_toolchain_file_found_when_building_qt()
             endif()
 
-            qt_internal_ensure_static_qt_config()
-
             __qt_internal_get_emcc_recommended_version(recommended_version)
             set(QT_EMCC_RECOMMENDED_VERSION "${recommended_version}" CACHE STRING INTERNAL FORCE)
 

cmake/QtFlagHandlingHelpers.cmake

@@ -9,6 +9,10 @@
 #    PRIVATE_CONTENT_FILE specifies the pre-cooked content of Qt_<version>_PRIVATE_API section.
 #       Requires the content file available at build time.
 function(qt_internal_add_linker_version_script target)
+    if(WASM)
+        return()
+    endif()
+
     qt_parse_all_arguments(arg "qt_internal_add_linker_version_script"
         ""
         "PRIVATE_CONTENT_FILE"
@@ -94,7 +98,7 @@ function(qt_internal_add_linker_version_script target)
 endfunction()
 
 function(qt_internal_add_link_flags_no_undefined target)
-    if (NOT QT_BUILD_SHARED_LIBS)
+    if (NOT QT_BUILD_SHARED_LIBS OR WASM)
         return()
     endif()
     if ((GCC OR CLANG) AND NOT MSVC)

cmake/QtTargetHelpers.cmake

@@ -530,6 +530,8 @@ endif()\n\n")
         if(target_type STREQUAL "SHARED_LIBRARY")
             if(WIN32)
                 set(write_implib TRUE)
+            elseif(WASM)
+                # Keep write_soname at FALSE
             else()
                 set(write_soname TRUE)
             endif()

cmake/QtWasmHelpers.cmake

@@ -6,7 +6,6 @@
 function (qt_internal_setup_wasm_target_properties wasmTarget)
 
     target_link_options("${wasmTarget}" INTERFACE
-    "SHELL:-s ERROR_ON_UNDEFINED_SYMBOLS=1"
     "SHELL:-s MAX_WEBGL_VERSION=2"
     "SHELL:-s FETCH=1"
     "SHELL:-s WASM_BIGINT=1")
@@ -82,6 +81,25 @@ function (qt_internal_setup_wasm_target_properties wasmTarget)
     #  Set ASYNCIFY_IMPORTS unconditionally in order to support enabling asyncify at link time.
     target_link_options("${wasmTarget}" INTERFACE "SHELL:-sASYNCIFY_IMPORTS=qt_asyncify_suspend_js,qt_asyncify_resume_js")
 
+    if(QT_FEATURE_shared)
+
+        set_property(GLOBAL PROPERTY TARGET_SUPPORTS_SHARED_LIBS TRUE)
+
+        # plugins are SIDE_MODULE
+        target_compile_options("${wasmTarget}" INTERFACE
+        "$<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,MODULE_LIBRARY>:" -s SIDE_MODULE=1>)
+        target_link_options("${wasmTarget}" INTERFACE
+        "$<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,MODULE_LIBRARY>:" -s SIDE_MODULE=1>)
+
+        # shared libs are SIDE_MODULE
+        target_compile_options("${wasmTarget}" INTERFACE
+        "$<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,SHARED_LIBRARY>:" -s SIDE_MODULE=1>)
+        target_link_options("${wasmTarget}" INTERFACE
+        "$<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,SHARED_LIBRARY>:" -s SIDE_MODULE=1>)
+
+    else()
+        target_link_options("${wasmTarget}" INTERFACE "SHELL:-s ERROR_ON_UNDEFINED_SYMBOLS=1")
+    endif()
 endfunction()
 
 function(qt_internal_wasm_add_finalizers target)

configure.cmake

@@ -390,7 +390,7 @@ qt_feature("android-style-assets" PRIVATE
 )
 qt_feature("shared" PUBLIC
     LABEL "Building shared libraries"
-    AUTODETECT NOT UIKIT AND NOT WASM
+    AUTODETECT NOT UIKIT
     CONDITION BUILD_SHARED_LIBS
 )
 qt_feature_definition("shared" "QT_STATIC" NEGATE PREREQUISITE "!defined(QT_SHARED) && !defined(QT_STATIC)")

src/corelib/Qt6CoreConfigExtras.cmake.in

@@ -65,6 +65,7 @@ if(ANDROID_PLATFORM)
 endif()
 
 if(EMSCRIPTEN)
+    set_property(GLOBAL PROPERTY TARGET_SUPPORTS_SHARED_LIBS TRUE)
     include("${CMAKE_CURRENT_LIST_DIR}/@QT_CMAKE_EXPORT_NAMESPACE@WasmMacros.cmake")
 endif()
 

src/gui/CMakeLists.txt

@@ -851,7 +851,7 @@ qt_internal_extend_target(Gui CONDITION QT_FEATURE_opengles2
         opengl/qopengles2ext.h
 )
 
-qt_internal_extend_target(Gui CONDITION QT_FEATURE_egl AND QT_FEATURE_opengl
+qt_internal_extend_target(Gui CONDITION QT_FEATURE_egl AND QT_FEATURE_opengl AND NOT WASM
     SOURCES
         opengl/platform/egl/qeglpbuffer.cpp opengl/platform/egl/qeglpbuffer_p.h
         opengl/platform/egl/qeglplatformcontext.cpp opengl/platform/egl/qeglplatformcontext_p.h

src/plugins/platforms/wasm/qwasmcompositor.h

@@ -8,6 +8,7 @@
 
 #include <QtGui/qregion.h>
 #include <qpa/qplatformwindow.h>
+#include <QMap>
 
 #include <QtOpenGL/qopengltextureblitter.h>
 #include <QtGui/qpalette.h>

src/plugins/platforms/wasm/qwasmtheme.cpp

@@ -4,6 +4,7 @@
 #include "qwasmtheme.h"
 #include <QtCore/qvariant.h>
 #include <QFontDatabase>
+#include <QList>
 
 QT_BEGIN_NAMESPACE