Arena allocation example

[dullbananas]

[folkertdev]

we have a test that checks that all examples are part of a cli_run test (to prevent the examples going stale). Could you add such a test?

[dullbananas]

i tried to add a test, but it fails

output of cargo test arena_allocator in cli_run directory:

running 1 test
test cli_run::arena_allocator ... FAILED

failures:

---- cli_run::arena_allocator stdout ----
thread 'cli_run::arena_allocator' panicked at '`valgrind` exited with exit code 127. valgrind stdout was: ""

valgrind stderr was: "/workspaces/roc/examples/arena-allocator/arena-alloc: symbol lookup error: /workspaces/roc/examples/arena-allocator/arena-alloc: undefined symbol: roc__mainForHost_size
==7068==  If you believe this happened as a result of a stack
==7068==  overflow in your program's main thread (unlikely but
==7068==  possible), you can try to increase the size of the
==7068==  main thread stack using the --main-stacksize= flag.
==7068==  The main thread stack size used in this run was 8388608.
"', cli/tests/cli_run.rs:117:17

[folkertdev]

@bhansconnect the test/program fails when using the surgical linker. Not sure if that is easy to fix or if we should find a workaround for now

[bhansconnect]

I can't currently test, but hopefully will be able to check into it in the next couple of days.

[bhansconnect]

I am not fully sure the issue, but the root cause is this:

usingnamespace struct {
    extern fn roc__mainForHost_1_exposed(output: [*]u8) void;
    pub const roc_main = roc__mainForHost_1_exposed;

    extern fn roc__mainForHost_size() i64;
    pub const roc_main_size = roc__mainForHost_size;

    extern fn roc__mainForHost_1_Fx_caller(flags: *const u8, closure_data: [*]u8, output: [*]u8) void;
    pub const call_fx = roc__mainForHost_1_Fx_caller;

    extern fn roc__mainForHost_1_Fx_size() i64;
    pub const fx_size = roc__mainForHost_1_Fx_size;

    extern fn roc__mainForHost_1_Fx_result_size() i64;
    pub const fx_result_size = roc__mainForHost_1_Fx_result_size;
};

If each function is used directly in global scope, it works as expected. I will need to look into what the exact structure generated here is in order to make the surgical linker deal with it.

Honestly a bit surprised this breaks at all.

[kili-ilo]

@dullbananas @folkertdev @bhansconnect Do you still want this? An arena allocator example sounds like a great thing to have, do any of our other examples today happen to use such a system?

[dullbananas]

None of the other example platforms have arena allocation or anything else that doesn't just call malloc, so this example should still be added

[kili-ilo]

Any known issues with this PR? Maybe just rebasing would heal some of the testing issues?

[bhansconnect]

I think it is mostly a matter of updating to latest roc and maybe modifying the platform slightly.