[env]

[env]
required = ["DATABASE_URL", "API_KEY"]

Key	Type	Default	Description
required	list of strings	[]	Environment variables that must resolve at build time. Any comptime env() lookup on a missing required variable fails the build.

How it works

comptime let bindings call env(name, default?) inside the sandboxed interpreter at build time. If a name appears in [env] required but is not set in the build environment, the lookup fails the build with tyc::comptime:

comptime let DB_URL: str = env("DATABASE_URL")

[env]
required = ["DATABASE_URL"]

Build without DATABASE_URL set:

error[tyc::comptime]: required environment variable `DATABASE_URL` is not set
 ┌─ src/main.ty:1:33
 │
1 │ comptime let DB_URL: str = env("DATABASE_URL")
 │                             ^^^^^^^^^^^^^^^^^^^^

Build with it set:

DATABASE_URL=postgres://localhost/myapp tyc build
# success; DB_URL inlined as the literal "postgres://localhost/myapp"

Why declare requirements?

You could rely on env("X") failing the build implicitly — a missing key raises a sandbox error. Listing them in [env] required does two extra things:

1. Documents the contract. Anyone reading the manifest sees what the build needs.
2. Fail-fast at the start of the build. The compiler can check the environment before doing any work — missing required vars surface immediately, not after partial compilation.

Optional env vars

Use env("NAME", "default") for optional values. No need to list in [env] required — the default kicks in if unset:

comptime let PORT: int = int(env("PORT", "8080"))

What env vars are not

• Not Python’s os.environ. That’s a runtime concern. comptime env() reads the build-time environment only.
• Not secrets-management. Treat values inlined into the build as visible in the emitted Python. For secret-rotation, read at runtime instead.

CI integration

- name: Build
  env:
    DATABASE_URL: ${{ secrets.DATABASE_URL }}
    API_KEY: ${{ secrets.API_KEY }}
  run: tyc build

Make sure CI has the required vars before running tyc build, the same way you’d ensure they’re set in production.

Where next

• comptime — the sandboxed evaluator.
• Build-Time Env Validation (recipe) — worked patterns.