Add "model" macro to simplify model definitions

This removes a lot of repetitive attributes and type modifiers through the use
of an attribute-style procedural macro applied to our model structs.

workspaces/deny.toml

@@ -39,6 +39,7 @@ skip = [
     { name = "laika", licenses = [] },
     { name = "migration-helpers", licenses = [] },
     { name = "migrator", licenses = [] },
+    { name = "model-derive", licenses = [] },
     { name = "models", licenses = [] },
     { name = "moondog", licenses = [] },
     { name = "netdog", licenses = [] },

workspaces/models/Cargo.toml

@@ -9,6 +9,7 @@ build = "build.rs"
 [dependencies]
 base64 = "0.11"
 lazy_static = "1.2"
+model-derive = { path = "model-derive" }
 regex = "1.1"
 serde = { version = "1.0", features = ["derive"] }
 snafu = "0.6"

workspaces/models/README.md

@@ -16,6 +16,8 @@ This `Settings` essentially becomes the schema for the variant's data store.
 
 At the field level, standard Rust types can be used, or ["modeled types"](src/modeled_types) that add input validation.
 
+The `#[model]` attribute on Settings and its sub-structs reduces duplication and adds some required metadata; see [its docs](model-derive/) for details.
+
 ### aws-k8s: Kubernetes
 
 * [Model](src/aws-k8s/mod.rs)

workspaces/models/model-derive/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "model-derive"
+version = "0.1.0"
+authors = ["Tom Kirchner <tjk@amazon.com>"]
+edition = "2018"
+publish = false
+build = "build.rs"
+
+[lib]
+path = "src/lib.rs"
+proc-macro = true
+
+[dependencies]
+darling = "0.10"
+proc-macro2 = "1.0"
+quote = "1.0"
+syn = { version = "1.0", default-features = false, features = ["full", "parsing", "printing", "proc-macro", "visit-mut"] }
+
+[build-dependencies]
+cargo-readme = "3.1"

workspaces/models/model-derive/README.md

@@ -0,0 +1,44 @@
+# model-derive
+
+Current version: 0.1.0
+
+## Overview
+
+This module provides a attribute-style procedural macro, `model`, that makes sure a struct is
+ready to be used as an API model.
+
+The goal is to reduce cognitive overhead when reading models.
+We do this by automatically specifying required attributes on structs and fields.
+
+Several arguments are available to override default behavior; see below.
+
+## Changes it makes
+
+### Visibility
+
+All types must be public, so `pub` is added.
+Override this (at a per-struct or per-field level) by specifying your own visibility.
+
+### Derives
+
+All structs must serde-`Serializable` and -`Deserializable`, and comparable via `PartialEq`.
+`Debug` is added for convenience.
+`Default` can also be added by specifying the argument `impl_default = true`.
+
+### Serde
+
+Structs have a `#[serde(...)]` attribute added to deny unknown fields and rename fields to kebab-case.
+The struct can be renamed (for ser/de purposes) by specifying the argument `rename = "bla"`.
+
+Fields have a `#[serde(...)]` attribute added to skip `Option` fields that are `None`.
+This is because we accept updates in the API that are structured the same way as the model, but we don't want to require users to specify fields they aren't changing.
+This can be disabled by specifying the argument `add_option = false`.
+
+### Option
+
+Fields are all wrapped in `Option<...>`.
+Similar to the `serde` attribute added to fields, this is because we don't want users to have to specify fields they aren't changing, and can be disabled the same way, by specifying `add_option = false`.
+
+## Colophon
+
+This text was generated from `README.tpl` using [cargo-readme](https://crates.io/crates/cargo-readme), and includes the rustdoc from `src/lib.rs`.

workspaces/models/model-derive/README.tpl

@@ -0,0 +1,9 @@
+# {{crate}}
+
+Current version: {{version}}
+
+{{readme}}
+
+## Colophon
+
+This text was generated from `README.tpl` using [cargo-readme](https://crates.io/crates/cargo-readme), and includes the rustdoc from `src/lib.rs`.

workspaces/models/model-derive/build.rs

@@ -0,0 +1,32 @@
+// Automatically generate README.md from rustdoc.
+
+use std::env;
+use std::fs::File;
+use std::io::Write;
+use std::path::PathBuf;
+
+fn main() {
+    // Check for environment variable "SKIP_README". If it is set,
+    // skip README generation
+    if env::var_os("SKIP_README").is_some() {
+        return;
+    }
+
+    let mut lib = File::open("src/lib.rs").unwrap();
+    let mut template = File::open("README.tpl").unwrap();
+
+    let content = cargo_readme::generate_readme(
+        &PathBuf::from("."), // root
+        &mut lib,            // source
+        Some(&mut template), // template
+        // The "add x" arguments don't apply when using a template.
+        true,  // add title
+        false, // add badges
+        false, // add license
+        true,  // indent headings
+    )
+    .unwrap();
+
+    let mut readme = File::create("README.md").unwrap();
+    readme.write_all(content.as_bytes()).unwrap();
+}