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Dependencies

A dependency is an edge in the build graph: one target consuming another's outputs. Edges define both order and data flow — heph runs a target only once every dependency has produced its outputs, and it makes those outputs available to the dependent.

Declaring an edge​

A target references another by address, or by the value returned from target() (which is its address):

BUILD
lib = target(name = "lib", driver = "bash", run = "go build -o $OUT .", out = "lib")

target(
    name = "image",
    driver = "bash",
    deps = ["//assets:bundle", lib],
    run = "...",
    out = "image",
)

Independent targets run concurrently; only a real edge forces ordering. The finer you split targets, the more heph can cache and parallelize.

Outputs and groups​

A target's outputs are its product. A target may split them into named output groups, and a dependent can select a single group with the |group selector:

//app:compile|bin     # depend on just the "bin" group

This keeps edges narrow: a consumer that needs only the binary doesn't rebuild when an unrelated output group changes.

How outputs reach the dependent​

The build graph defines that an edge exists; how a dependency's files are surfaced to a target is up to the driver that runs it. The exec driver, for instance, exposes each dependency group through $SRC_<group> environment variables inside the sandbox. See the driver's page for its specific contract.

note

Every input must be declared. If a target reads a file it didn't list as a dependency, the sandbox won't contain it — the build fails fast rather than silently depending on something untracked.