1# Chapter 21: cargo-gen/src, two verbs
2
3One file with two verbs:
4
5```text
6cargo-gen generate <out-dir> <version> <edition> <majors> <third-party/Cargo.toml> <meta.json>...
7cargo-gen write <generated-dir>
8```
9
10`generate` runs inside the buck build (`:manifests`). It reads every
11target's JSON, groups targets into packages, and writes the tree of
12manifests the BUCK files imply: the root workspace with its members and
13`[workspace.dependencies]` (crates.io versions from `third-party/Cargo.toml`,
14pgrx at `=0.19.2` with its major feature stripped, so the per-crate `pgNN`
15features choose it), and one `Cargo.toml` per package, a package's unit-test
16target adding its dev-dependencies. `write` runs outside it (`:update`) and
17copies that tree into the checkout that holds the current directory.
18
19> **Try it.** Read the header of [main.rs](main.rs), then compare the root
20> [Cargo.toml](../../../Cargo.toml): its first four lines are the warning the
21> tool writes at the top of every file it owns.
22
23## For the people who maintain it
24
25| File | What |
26| --- | --- |
27| [main.rs](main.rs) | `generate` and `write`. Errors go to stderr as `cargo-gen: …` with exit code 1. |
28
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