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>

9 files changed, 35 insertions, 6 deletions

diff --git a/cmake/QtAutoDetect.cmake b/cmake/QtAutoDetect.cmake
index 60aa532d23..6c46f3b470 100644
--- a/cmake/QtAutoDetect.cmake
+++ b/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)
 
diff --git a/cmake/QtFlagHandlingHelpers.cmake b/cmake/QtFlagHandlingHelpers.cmake
index 08bc9177d2..25a0e0e290 100644
--- a/cmake/QtFlagHandlingHelpers.cmake
+++ b/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)
diff --git a/cmake/QtTargetHelpers.cmake b/cmake/QtTargetHelpers.cmake
index fefb614a72..7e1f7cdc2d 100644
--- a/cmake/QtTargetHelpers.cmake
+++ b/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()
diff --git a/cmake/QtWasmHelpers.cmake b/cmake/QtWasmHelpers.cmake
index 7a0830abc0..198ebbff23 100644
--- a/cmake/QtWasmHelpers.cmake
+++ b/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)
diff --git a/configure.cmake b/configure.cmake
index f188b99201..570a260715 100644
--- a/configure.cmake
+++ b/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)")
diff --git a/src/corelib/Qt6CoreConfigExtras.cmake.in b/src/corelib/Qt6CoreConfigExtras.cmake.in
index 8b4d3164cf..a2a27fe016 100644
--- a/src/corelib/Qt6CoreConfigExtras.cmake.in
+++ b/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()
 
diff --git a/src/gui/CMakeLists.txt b/src/gui/CMakeLists.txt
index f08a7ea950..9bf98d9ac6 100644
--- a/src/gui/CMakeLists.txt
+++ b/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
diff --git a/src/plugins/platforms/wasm/qwasmcompositor.h b/src/plugins/platforms/wasm/qwasmcompositor.h
index 3609f44c5e..b2bb51fc52 100644
--- a/src/plugins/platforms/wasm/qwasmcompositor.h
+++ b/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>
diff --git a/src/plugins/platforms/wasm/qwasmtheme.cpp b/src/plugins/platforms/wasm/qwasmtheme.cpp
index 51399159c4..b188dcb4b6 100644
--- a/src/plugins/platforms/wasm/qwasmtheme.cpp
+++ b/src/plugins/platforms/wasm/qwasmtheme.cpp
@@ -4,6 +4,7 @@
 #include "qwasmtheme.h"
 #include <QtCore/qvariant.h>
 #include <QFontDatabase>
+#include <QList>
 
 QT_BEGIN_NAMESPACE