Compiler & testing

Use the compiler both to produce executables and to check your source. Tests are ordinary Valk declarations that become the program's entry point in a test build.

Common build commands#

Run these from the project root:

valk build src -o app
valk build src --run
valk build src --lint
valk build src -o app --release

The first command writes an executable. --run builds and starts the program. --lint checks every source in the package without requiring a main or producing an executable. --release requests an optimized build.

Use --watch --run for a development loop that rebuilds and runs as files change. Format input source files in place with valk build src --fmt. valk build --help lists the available options.

Write a test#

Put the function and test below in a .valk file:

fn line_total(price: int, quantity: int) int {
    return price * quantity
}

test "Line total uses the requested quantity" {
    assert(line_total(12, 3) == 36)
    assert(line_total(12, 0) == 0)
}

Build and execute tests with:

valk build src --test --run

The generated test entry point runs tests instead of main. Test declarations are omitted from normal builds. Add a separate tests directory to the command if you keep tests outside src:

valk build src tests --test --run

Isolate tests that change shared state#

Regular test declarations run concurrently. Use synctest when a test changes process-wide state or needs isolation:

global counter: int (0)

synctest "Reset shared test state" {
    counter = 0
    counter++
    assert(counter == 1)
}

All regular tests finish before synctests start. Synctests then run sequentially in declaration order. A test can still create its own coroutines to verify concurrent behavior.

Filter by part of a test's name when investigating a failure:

valk build src tests --test --filter "Line total" --run

Select platform-specific code#

Compile-time conditions choose which code is included:

fn main() {
    #if OS == "linux"
    println("Running the Linux build")
    #elif OS == "macos"
    println("Running the macOS build")
    #else
    println("Running another platform build")
    #end
}

Built-in definitions include OS, ARCH, and TEST; --def supplies additional definitions. Source location values such as __FILE__ and __LINE__ are also available for diagnostics.

Choose a compilation target#

--target selects a target such as linux-x64 or macos-arm64. A target executable must be run on a compatible system, and native dependencies must be available for that target. Use native library build options when producing a library instead of an application.