Require CMake 3.13+ for Emscripten and WebGL 2.

And drop all nasty workarounds related to this.

doc/changelog.dox

@@ -45,6 +45,9 @@ See also:
     versions are not supported anymore and all workarounds for them were
     removed. This is a conservative change, as there are no known supported
     distributions which would have anything older than 3.5.
+-   Minimal supported CMake version for Emscripten WebGL 2 compilation is now
+    3.13, in order to be able to set linker options for enabling WebGL 2
+    without having to pollute the global `CMAKE_EXE_LINKER_FLAGS` variable.
 
 @subsection changelog-latest-new New features
 

doc/snippets/CMakeLists.txt

@@ -36,12 +36,6 @@ set_directory_properties(PROPERTIES
     CORRADE_CXX_STANDARD 11
     CORRADE_USE_PEDANTIC_FLAGS ON)
 
-# Emscripten needs special flag to use WebGL 2
-if(CORRADE_TARGET_EMSCRIPTEN AND NOT MAGNUM_TARGET_GLES2)
-    # TODO: give me INTERFACE_LINK_OPTIONS or something, please
-    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -s USE_WEBGL2=1")
-endif()
-
 set(snippets_Magnum_SRCS
     Magnum.cpp
     MagnumAnimation.cpp

modules/FindMagnum.cmake

@@ -894,6 +894,13 @@ foreach(_component ${Magnum_FIND_COMPONENTS})
                 find_package(OpenGLES3 REQUIRED)
                 set_property(TARGET Magnum::${_component} APPEND PROPERTY
                     INTERFACE_LINK_LIBRARIES OpenGLES3::OpenGLES3)
+                if(CORRADE_TARGET_EMSCRIPTEN)
+                    if(CMAKE_VERSION VERSION_LESS 3.13)
+                        message(FATAL_ERROR "CMake 3.13+ is required in order to specify Emscripten linker options")
+                    endif()
+                    set_property(TARGET Magnum::${_component} APPEND PROPERTY
+                        INTERFACE_LINK_OPTIONS "SHELL:-s USE_WEBGL2=1")
+                endif()
             endif()
 
         # MaterialTools library
@@ -1047,24 +1054,6 @@ if(CORRADE_TARGET_EMSCRIPTEN)
         MAGNUM_EMSCRIPTENAPPLICATION_JS
         MAGNUM_WINDOWLESSEMSCRIPTENAPPLICATION_JS
         MAGNUM_WEBAPPLICATION_CSS)
-
-    # If we are on CMake 3.13 and up, `-s USE_WEBGL2=1` linker option is
-    # propagated from FindOpenGLES3.cmake already. If not (and the GL library
-    # is used), we need to modify the global CMAKE_EXE_LINKER_FLAGS. Do it here
-    # instead of in FindOpenGLES3.cmake so it works also for CMake subprojects
-    # (in which case find_package(OpenGLES3) is called in (and so
-    # CMAKE_EXE_LINKER_FLAGS would be modified in) Magnum's root CMakeLists.txt
-    # and thus can't affect the variable in the outer project). CMake supports
-    # IN_LIST as an operator since 3.1 (Emscripten needs at least 3.7), but
-    # it's behind a policy, so enable that one as well.
-    cmake_policy(SET CMP0057 NEW)
-    # TODO since 1.39.19 it's possible to use `-sUSE_WEBGL2=1`, which can be
-    #   then passed via target_link_libraries() etc. without requiring CMake
-    #   3.13: https://github.com/emscripten-core/emscripten/blob/main/ChangeLog.md#13919-07072020
-    #   -- change to that once we drop support for older Emscripten versions
-    if(CMAKE_VERSION VERSION_LESS 3.13 AND GL IN_LIST Magnum_FIND_COMPONENTS AND NOT MAGNUM_TARGET_GLES2 AND NOT CMAKE_EXE_LINKER_FLAGS MATCHES "-s USE_WEBGL2=1")
-        set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -s USE_WEBGL2=1")
-    endif()
 endif()
 
 # For CMake 3.16+ with REASON_FAILURE_MESSAGE, provide additional potentially

src/CMakeLists.txt

@@ -29,18 +29,6 @@ if(CMAKE_CXX_COMPILER_ID STREQUAL "MSVC" OR CMAKE_CXX_SIMULATE_ID STREQUAL "MSVC
     string(REPLACE "/W3" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
 endif()
 
-# Emscripten needs special flag to use WebGL 2. If we are on CMake 3.13 and up,
-# `-s USE_WEBGL2=1` linker option is propagated from FindOpenGLES3.cmake
-# already. If not (and the GL library is used), we need to modify the global
-# CMAKE_EXE_LINKER_FLAGS.
-# TODO since 1.39.19 it's possible to use `-sUSE_WEBGL2=1`, which can be then
-#   passed via target_link_libraries() etc. without requiring CMake 3.13
-#   https://github.com/emscripten-core/emscripten/blob/main/ChangeLog.md#13919-07072020
-#   -- change to that once we drop support for older Emscripten versions
-if(CORRADE_TARGET_EMSCRIPTEN AND CMAKE_VERSION VERSION_LESS 3.13 AND MAGNUM_WITH_GL AND NOT MAGNUM_TARGET_GLES2)
-    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -s USE_WEBGL2=1")
-endif()
-
 # On Windows enable UNICODE/_UNICODE macros to avoid accidentally passing UTF-8
 # values to ANSI functions
 if(CORRADE_TARGET_WINDOWS)

src/Magnum/GL/CMakeLists.txt

@@ -233,6 +233,12 @@ elseif(MAGNUM_TARGET_GLES2)
     target_link_libraries(MagnumGL PUBLIC OpenGLES2::OpenGLES2)
 else()
     target_link_libraries(MagnumGL PUBLIC OpenGLES3::OpenGLES3)
+    if(CORRADE_TARGET_EMSCRIPTEN)
+        if(CMAKE_VERSION VERSION_LESS 3.13)
+            message(FATAL_ERROR "CMake 3.13+ is required in order to specify Emscripten linker options")
+        endif()
+        target_link_options(MagnumGL PUBLIC "SHELL:-s USE_WEBGL2=1")
+    endif()
 endif()
 
 install(TARGETS MagnumGL
@@ -316,6 +322,9 @@ if(MAGNUM_BUILD_TESTS)
         target_link_libraries(MagnumGLTestLib PUBLIC OpenGLES2::OpenGLES2)
     else()
         target_link_libraries(MagnumGLTestLib PUBLIC OpenGLES3::OpenGLES3)
+        if(CORRADE_TARGET_EMSCRIPTEN)
+            target_link_options(MagnumGLTestLib PUBLIC "SHELL:-s USE_WEBGL2=1")
+        endif()
     endif()
 
     if(MAGNUM_BUILD_GL_TESTS)

src/Magnum/Platform/Test/CMakeLists.txt

@@ -44,15 +44,19 @@ if(MAGNUM_WITH_ANDROIDAPPLICATION)
 endif()
 
 if(MAGNUM_WITH_EMSCRIPTENAPPLICATION)
+    if(CMAKE_VERSION VERSION_LESS 3.13)
+        message(FATAL_ERROR "CMake 3.13+ is required in order to specify Emscripten linker options")
+    endif()
     add_executable(PlatformEmscriptenApplicationTest EmscriptenApplicationTest.cpp)
     target_link_libraries(PlatformEmscriptenApplicationTest PRIVATE
-        MagnumEmscriptenApplication MagnumGL
+        MagnumEmscriptenApplication MagnumGL)
+    target_link_options(PlatformEmscriptenApplicationTest PRIVATE
         # Test that the canvas and keylistener can be found with both the old
         # and the new Emscripten target behaviors
-        # TODO: use target_link_options() once we can require CMake 3.13
-        "-s DISABLE_DEPRECATED_FIND_EVENT_TARGET_BEHAVIOR=0"
+        "SHELL:-s DISABLE_DEPRECATED_FIND_EVENT_TARGET_BEHAVIOR=0"
         # Enable memory runtime checks
-        "-s ASSERTIONS=2 -s SAFE_HEAP=1")
+        "SHELL:-s ASSERTIONS=2"
+        "SHELL:-s SAFE_HEAP=1")
     add_custom_command(TARGET PlatformEmscriptenApplicationTest POST_BUILD
         COMMAND ${CMAKE_COMMAND} -E copy_if_different
             "${CMAKE_CURRENT_SOURCE_DIR}/../WebApplication.css"
@@ -64,11 +68,14 @@ if(MAGNUM_WITH_EMSCRIPTENAPPLICATION)
 
     add_executable(PlatformMultipleEmscriptenApplicationTest EmscriptenApplicationTest.cpp)
     target_link_libraries(PlatformMultipleEmscriptenApplicationTest PRIVATE
-        MagnumEmscriptenApplication MagnumGL
-        # TODO: use target_link_options() once we can require CMake 3.13
-        "-s MODULARIZE -s EXPORT_NAME=createModule"
-        "-s DISABLE_DEPRECATED_FIND_EVENT_TARGET_BEHAVIOR=1"
-        "-s ASSERTIONS=2 -s SAFE_HEAP=1")
+        MagnumEmscriptenApplication MagnumGL)
+    target_link_options(PlatformMultipleEmscriptenApplicationTest PRIVATE
+        # Test that the canvas and keylistener can be found with both the old
+        # and the new Emscripten target behaviors
+        "SHELL:-s DISABLE_DEPRECATED_FIND_EVENT_TARGET_BEHAVIOR=1"
+        # Enable memory runtime checks
+        "SHELL:-s ASSERTIONS=2"
+        "SHELL:-s SAFE_HEAP=1")
     target_compile_definitions(PlatformMultipleEmscriptenApplicationTest PRIVATE CUSTOM_CLEAR_COLOR=0x3bd267_rgbf)
     add_custom_command(TARGET PlatformMultipleEmscriptenApplicationTest POST_BUILD
         COMMAND ${CMAKE_COMMAND} -E copy_if_different