add std.heap.AutoAllocator

[gooncreeper]

Provides a convenient abstraction for this relatively complex logic.

Additionally, utilizes it in src/main.zig.

[alexrp]

This will probably need an init() method accepting a struct of options that gets passed to the underlying allocator.

[alexrp]

Test failures happening because build_options.debug_gpa is no longer respected in the compiler.

[tensorush]

If I can throw my two cents in here, could we bring the GeneralPurposeAllocator name back for this?

Auto and Allocator side-by-side might be misinterpreted as "an allocator that auto-manages it's allocations", instead of "an allocator that auto-initializes an allocator instance for the general case".

Also, gpa is a pretty nice and already established convention for naming such general-purpose allocator instances.

Basically, I'd love to have this code working as is again:

var gpa_state: std.heap.GeneralPurposeAllocator(.{}) = .init;
const gpa = gpa_state.allocator();
defer if (gpa_state.deinit() == .leak) {
    @panic("Memory leak has occurred!");
};

[alexrp]

FWIW, the name that was suggested on Zulip was DefaultAllocator.

[gooncreeper]

I think both can work. I changed it to AutoAllocator since it is similar to AutoHashMap in the sense it automatically chooses the implementation, and it also leads to a bit more friction over choosing an allocator yourself. Though, I can change it back if you think DefaultAllocator makes more sense.

[gooncreeper]

@alexrp The CI timeout is due to the compiler now defaulting to the DebugAllocator for debug builds. Based on empirical testing, it seems that it is 70% slower for x86_64-linux-debug (this was also the case before the patch if you passed -Ddebug-allocator), meaning it would take a bit over 8.5 hours to complete (on aarch-linux-debug it took a 30% hit and aarch-macos-debug a 20% hit.) I can change it back to using a faster allocator unless you think it makes sense to bump the CI time.

[alexrp]

I can change it back to using a faster allocator

That would probably be best.