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Native build configuration

Allocator

MOONBIT_ALLOCATOR selects the allocator used by native runtime builds:

  • mimalloc compiles the runtime for mimalloc and links the shipped libmoonbitrun.o support object.
  • system compiles the runtime for the system allocator and does not link libmoonbitrun.o.

The selected value is defined both when compiling the shipped runtime sources and when compiling the C emitted by moonc link-core, so the program inlines the same allocator as the runtime it links against.

When the variable is unset, Moon preserves the platform and toolchain default. Selecting mimalloc fails when its support object is unavailable, including on Windows and with TCC.

Reference cycle collection

Set MOON_COLLECT_REF_CYCLE=1 to enable experimental reference cycle collection:

MOON_COLLECT_REF_CYCLE=1 moon run main --target native
MOON_COLLECT_REF_CYCLE=1 moon test --target wasm

It is off by default. Unset the variable or set it to 0 to disable it; only the value 1 enables it.

The setting applies to build, run, test, and bench, including standalone files, in both debug and release builds. Native builds support both generated C and the machine backend (direct object output), with either native allocator. Enabling collection preserves the usual backend selection, including MOONBIT_NEW_NATIVE. Machine builds require a compiler with trial-deletion support; Wasm builds require one supporting -enable-trial-deletion. The setting has no effect on WasmGC, JavaScript, or LLVM.