Build Profiles

nano-ros builds both C/C++ and Rust code on your behalf. You choose the optimization level once, in your own build system, and nano-ros propagates it to every crate and library it builds for you.

There are two knobs, not one, because the two languages have different option vocabularies and collapsing them would mean inventing a lossy middle language:

You are building with	You set	nano-ros propagates it to
CMake	`CMAKE_BUILD_TYPE`	your C/C++ code, and (mapped) the Rust it builds
Cargo only	a cargo profile	every nano-ros crate, as a normal path dependency

From a CMake build type

Set CMAKE_BUILD_TYPE as you would in any CMake project. nano-ros derives the cargo profile from it:

`CMAKE_BUILD_TYPE`	cargo profile	what it means
`Debug`	`dev`	debuggable, minimal optimization
`RelWithDebInfo`	`nros-relwithdebinfo`	opt-level 2, debug info, no LTO — the default
`MinSizeRel`	`nros-minsizerel`	opt-level `"s"`, fat LTO — smallest images
`Release`	`release`	opt-level 3, fat LTO — fastest code
(unset)	`nros-relwithdebinfo`	the development default

cmake -B build -DCMAKE_BUILD_TYPE=MinSizeRel
cmake --build build

Your C/C++ sources get -Os from CMake as usual, and the Rust nano-ros builds for you gets --profile nros-minsizerel. You do not need to add anything to any Cargo.toml — nano-ros supplies the definition of its own nros-* profiles.

An unrecognized build type is an error rather than a guess, so a custom type never silently produces an optimization level you did not ask for.

Choosing the Rust profile separately

NROS_CARGO_PROFILE overrides the mapping when you want the two halves to differ — for example a small C/C++ image with debuggable Rust:

cmake -B build -DCMAKE_BUILD_TYPE=MinSizeRel -DNROS_CARGO_PROFILE=nros-relwithdebinfo

Using your own profile

Name any profile you like. When the name is not one of nano-ros’s nros-* profiles, you own the definition — nano-ros passes the name through and injects nothing, so your settings are authoritative:

# your-workspace/Cargo.toml
[profile.prod]
inherits = "release"
opt-level = 3
lto = "fat"

cmake -B build -DCMAKE_BUILD_TYPE=Release -DNROS_CARGO_PROFILE=prod

If the profile is not defined, cargo reports error: profile 'prod' is not defined and points at your manifest — which is the right file to fix.

A pure-Cargo workspace

Nothing to configure. nano-ros crates are ordinary path dependencies, so your workspace-root profile already governs them:

cargo build --profile prod

Which profile is active?

nros profile resolve --build-type MinSizeRel   # -> nros-minsizerel
nros profile dir     nros-minsizerel           # -> the target/ subdirectory

A CMake configure also prints it:

-- nano-ros: cargo profile `nros-minsizerel` (CMAKE_BUILD_TYPE=MinSizeRel) → target/nros-minsizerel

Notes for embedded targets

Images grow at the default. nros-relwithdebinfo trades size for build speed. For flashing to a constrained board, build MinSizeRel.
Two platforms pin their own profile regardless of what you choose, and will say so: NuttX Rust images (a codegen miscompile at lto = "off") and FreeRTOS QEMU images (the emulated Cortex-M3 misses zenoh-pico’s handshake window at low optimization).

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