Allow emscripten to be used as non cross compiler

[Cloudef]

Emscripten can produce binaries that you can actually run. Flat out refusing to compile kinda sucks. Similarly I hope cross-compilation is also not forced on non native toolchains, since it's possible to run non-native binaries by using binfmt and qemu-static for example.

[nirbheek]

How do you run binaries produced by emscripten? Is there an exe_wrapper or something? If so, what's wrong with cross-compiling with an exe_wrapper?

[Cloudef]

Emscripten produces node scripts that has the node hashbang on them. In practice they work as any normal binary.

[nirbheek]

Well, then you'll have to paste more information about what fails and how it fails. From the information you've given right now it should already work, or at least it seems like it should be easy to fix :)

I noticed that we also do not have any CI with this, so once this is fixed, ideally we'd want that to make sure that it keeps working and doesn't break.

[Cloudef]

meson/mesonbuild/compilers/c.py

Line 140 in 1682058

raise MesonException('Emscripten compiler can only be used for cross compilation.')

what currently happens is this. Even if you remove these checks it will later fail at linker stuff. Removing the "emscripten detection" all together makes it work though.

[nirbheek]

Sounds like you're well-placed to make a pull request? :)

[Cloudef]

It looks like @jpakkane is the original author of the emscripten support. So before I do any PRs, I'd want to ask what would be the best approach to go here, as in to not break other people's build envs.

[Cloudef]

@jpakkane
I created a cross file with contents:

[properties]
needs_exe_wrapper=false

But trying to build pixman gives:

Build started at 2020-03-04T04:03:23.998316
Main binary: /usr/bin/python
Build Options: -Db_lto=true -Db_pie=true -Dloongson-mmi=disabled -Dvmx=disabled -Darm-simd=disabled -Dneon=disabled -Diwmmxt=disabled -Dmips-dspr2=disabled -Dgtk=disabled -Dprefix=/usr -Dlibexecdir=lib -Dsbindir=bin -Dauto_features=disabled -Dbuildtype=plain -Ddefault_library=static -Dwrap_mode=nodownload '--cross-file /etc/emscripten.toolchain.meson'
Python system: Linux
The Meson build system
Version: 0.53.2
Source dir: /home/jari/dev/personal/pacbox/easyrpg-player/pixman/src/pixman-0.38.4
Build dir: /home/jari/dev/personal/pacbox/easyrpg-player/pixman/src/build
Build type: cross build
Project name: pixman
Project version: 0.38.4
Appending CFLAGS from environment: '-pipe -fno-plt -flto -s ALLOW_MEMORY_GROWTH=1 -s NODERAWFS=1 -s WASM_MEM_MAX=512MB '
Appending LDFLAGS from environment: ['-L/usr/lib', '-flto', '--llvm-lto', '1']
Appending CPPFLAGS from environment: '-D_FORTIFY_SOURCE=2 -isystem /usr/include '

meson.build:21:0: ERROR: Emscripten compiler can only be used for cross compilation.