Add experimental support for Emscripten JSPI

...which I've seen fundamentally working when building with recent emsdk against
recent Qt6 trunk (and including <https://github.com/qt/qtbase/pull/108> "Update
the check for WebAssembly JSPI support") and running on recent Chrome (with JSPI
enabled under <chrome://flags/>)

Change-Id: I98c11c5ee7e95b135ddc33c95c95752055ecd4c5
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/176031
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <stephan.bergmann@allotropia.de>

config_host.mk.in

@@ -176,6 +176,7 @@ export ENABLE_DEBUG=@ENABLE_DEBUG@
 ENABLE_DOTNET=@ENABLE_DOTNET@
 SYSTEM_DRAGONBOX=@SYSTEM_DRAGONBOX@
 SYSTEM_FROZEN=@SYSTEM_FROZEN@
+export ENABLE_EMSCRIPTEN_JSPI=@ENABLE_EMSCRIPTEN_JSPI@
 export ENABLE_EMSCRIPTEN_PROXY_POSIX_SOCKETS=@ENABLE_EMSCRIPTEN_PROXY_POSIX_SOCKETS@
 export ENABLE_EMSCRIPTEN_PROXY_TO_PTHREAD=@ENABLE_EMSCRIPTEN_PROXY_TO_PTHREAD@
 export ENABLE_EPOXY=@ENABLE_EPOXY@

config_host/config_emscripten.h.in

@@ -9,6 +9,8 @@
 
 #pragma once
 
+#define HAVE_EMSCRIPTEN_JSPI 0
+
 #define HAVE_EMSCRIPTEN_PROXY_POSIX_SOCKETS 0
 
 #define HAVE_EMSCRIPTEN_PROXY_TO_PTHREAD 0

configure.ac

@@ -2180,6 +2180,14 @@ AC_ARG_WITH(main-module,
         Default value is 'writer'.]),
 ,)
 
+if test "$_os" = Emscripten; then
+    AC_ARG_ENABLE(emscripten-jspi,
+        AS_HELP_STRING([--enable-emscripten-jspi],
+            [Experimentally enable use of the Emscripten -sJSPI feature.]))
+else
+    enable_emscripten_jspi=
+fi
+
 if test "$_os" = Emscripten; then
     AC_ARG_ENABLE(emscripten-proxy-to-pthread,
         AS_HELP_STRING([--disable-emscripten-proxy-to-pthread],
@@ -4199,6 +4207,14 @@ AC_SUBST(ENABLE_WASM_STRIP)
 AC_SUBST(ENABLE_WASM_STRIP_WRITER)
 AC_SUBST(ENABLE_WASM_STRIP_CALC)
 
+if test "$enable_emscripten_jspi" = yes; then
+    ENABLE_EMSCRIPTEN_JSPI=TRUE
+    AC_DEFINE(HAVE_EMSCRIPTEN_JSPI)
+else
+    ENABLE_EMSCRIPTEN_JSPI=
+fi
+AC_SUBST(ENABLE_EMSCRIPTEN_JSPI)
+
 if test "$enable_emscripten_proxy_to_pthread" = yes; then
     ENABLE_EMSCRIPTEN_PROXY_TO_PTHREAD=TRUE
     AC_DEFINE(HAVE_EMSCRIPTEN_PROXY_TO_PTHREAD)

solenv/gbuild/platform/EMSCRIPTEN_INTEL_GCC.mk

@@ -30,6 +30,10 @@ gb_EMSCRIPTEN_LDFLAGS += -sSTACK_SIZE=131072 -sDEFAULT_PTHREAD_STACK_SIZE=65536
 gb_EMSCRIPTEN_LDFLAGS += --bind -s FORCE_FILESYSTEM=1 -s WASM_BIGINT=1 -s ERROR_ON_UNDEFINED_SYMBOLS=1 -s FETCH=1 -s ASSERTIONS=1 -s EXIT_RUNTIME=0 -s EXPORTED_RUNTIME_METHODS=["UTF16ToString","stringToUTF16","UTF8ToString","ccall","cwrap","addOnPreMain","addOnPostRun","registerType","throwBindingError"$(if $(ENABLE_QT6),$(COMMA)"FS"$(COMMA)"callMain"$(COMMA)"specialHTMLTargets")]
 gb_EMSCRIPTEN_QTDEFS := -DQT_NO_LINKED_LIST -DQT_NO_JAVA_STYLE_ITERATORS -DQT_NO_EXCEPTIONS -DQT_NO_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB
 
+ifeq ($(ENABLE_EMSCRIPTEN_JSPI),TRUE)
+gb_EMSCRIPTEN_LDFLAGS += -sJSPI
+endif
+
 ifeq ($(ENABLE_EMSCRIPTEN_PROXY_POSIX_SOCKETS),TRUE)
 gb_EMSCRIPTEN_LDFLAGS += -sPROXY_POSIX_SOCKETS -lwebsocket.js
 endif

vcl/qt5/QtInstance.cxx

@@ -53,6 +53,7 @@
 #include <vclpluginapi.h>
 #include <tools/debug.hxx>
 #include <comphelper/flagguard.hxx>
+#include <config_emscripten.h>
 #include <config_vclplug.h>
 #include <dndhelper.hxx>
 #include <vcl/qt/QtUtils.hxx>
@@ -298,7 +299,7 @@ QtInstance::QtInstance(std::unique_ptr<QApplication>& pQApp)
 
 #ifndef EMSCRIPTEN
     m_bSupportsOpenGL = true;
-#else
+#elif !HAVE_EMSCRIPTEN_JSPI
     ImplGetSVData()->maAppData.m_bUseSystemLoop = true;
 #endif
 }