Coming from mocalpha

Which moc flags map to moxzi, and which deliberately differ?

moxzi aims to be a drop-in replacement for moc on the common path: compile a Motoko entry file into a deployable canister module, with the same diagnostics and the same package flag. The constraint is that it is a different compiler implementation of the same language, so the surface it exposes is narrower on purpose — there is no interpreter, no REPL, and no warning-control machinery.

The flags below were checked against moxzi build --help from the CLI's clap definitions (moxzi/src/main.rs) and against moc --help from moc 1.14.1, the version the compiler is ported to — the string a moxzi-built canister carries in its motoko:compiler metadata is 1.14.1, and it earns that claim by measurement: zero unported upstream language tests, a 384-of-384 module sweep over the top 40 mops packages, and a byte-identical self-compile.

The command itself#

moc -c --idl -o main.wasm --package base .mops/base@0.16.0/src src/Main.mo
moxzi build src/Main.mo -o main.wasm --package base .mops/base@0.16.0/src

The differences visible in that one line: the entry file is a positional argument to a build subcommand rather than a trailing operand, -c is implied, and --idl is implied (moxzi always writes the .did unless told not to).

Direct equivalents#

Deliberate differences#

Verified behavioural difference: --debug#

moc's --debug is the default and keeps debug { … } expressions; --release strips them. In moxzi, --debug currently makes no observable difference:

moxzi build dbg.mo -o dbg-rel.wasm
moxzi build dbg.mo -o dbg-dbg.wasm --debug
cmp dbg-rel.wasm dbg-dbg.wasm     # identical

For the same source, moc's --release output contains no trace of the debug string while its --debug output does; both moxzi outputs contain it. In other words moxzi behaves like moc's default, and there is no --release equivalent that strips debug expressions. If you rely on --release stripping, do not assume it here.

Flags with no moxzi equivalent#

moxzi flags moc has no analogue for#

The environment variables moxzi reads are MOXZI_COMPILER, MOXZI_LINKER, MOXZI_MOPS, MOXZI_IDENTITY, MOXZI_WASM_STACK, MOXZI_NATIVE_STACK, MOXZI_MEM_RESERVE, MOXZI_FUEL and MOXZI_PARSE_WINDOW.

Unverified / to confirm#

These could not be checked against a running binary in this repo and should be treated as open questions rather than documented behaviour:

• Whether moxzi's --stable-regions, --max-stable-pages, --stabilization-instruction-limit, --measure-rts-stack and --trap-on-call-error produce byte-identical results to moc's. The flags exist on both sides and moxzi documents them as passthroughs; no differential test for them was found here.
• -v. Both compilers have it and they are not the same thing: moc's is general verbose output, moxzi's forwards the compiler canister's debug output and prints the resolved closure. Treat the outputs as unrelated.
• --debug's intended semantics. The option is wired through to the compiler's release-mode environment, so the observed no-op may be an unimplemented stripping pass rather than a design choice.

Next#

• Reading diagnostics — the codes are moc's; this is how to read them and report a mismatch.
• Compiling and linking — how moxzi build maps onto moc -c plus a separate link step.
• Projects and packages — --package and the mops path in detail.