# syncdoc
[](https://crates.io/crates/syncdoc)
[](https://docs.rs/syncdoc)
[](./LICENSE)
[](https://results.pre-commit.ci/latest/github/lmmx/syncdoc/master)
[](https://github.com/fasterthanlime/free-of-syn)
syncdoc is a procedural macro that automatically injects documentation from external files into your Rust code, eliminating the need to manually maintain inline doc comments.
Use syncdoc when you want to keep documentation separate from implementation.
Stick with inline docs when you prefer co-location of docs and code.
## Motivation
Extensive documentation is great for users, but inline docstrings make code hard to read:
```rust
/// This is a very long doc comment
/// that spans many lines and makes
/// the actual code hard to see...
/// [more lines]
mod A {
/// And another long doc comment
/// [many more lines]
fn b() { ... }
/// Yet another long doc comment
/// [many more lines]
fn c() { ... }
}
```
One solution is typically to add an `#[include_str!]` attribute pointing to a file,
but this creates line noise of its own (relative paths ascending to the doc files).
syncdoc solves this by automatically resolving documentation from external files like `include_str!`
according to each item's subpath.
One `#[omnidoc]` attribute call produces multiple such `#[doc = !include_str(...)]` annotations.
The example below is for a scenario where `docs-path` has been set in Cargo.toml. Syncdoc never assumes where
your docs live. When migrating, it stores them by default in `docs/` under the Cargo manifest dir
(the dir with Cargo.toml in) and writes the `docs-path` metadata in Cargo.toml for you.
```rust
use syncdoc::omnidoc;
#[omnidoc] // Docs from docs/A.md
mod A {
fn b() { ... } // Docs from docs/A/b.md
fn c() { ... } // Docs from docs/A/c.md
}
```
## Installation
Add syncdoc to your `Cargo.toml`:
```toml
[dependencies]
syncdoc = "0.1"
```
## Setup
### `docs-path` (recommended)
To avoid specifying `path` in every attribute, add a default to your `Cargo.toml`
(it must be set one way or the other or the build will error).
```toml
[package.metadata.syncdoc]
docs-path = "docs"
```
Now you can use `#[omnidoc]` without arguments - syncdoc calculates the correct relative path automatically
(thanks to [this](https://docs.rs/proc-macro2/latest/proc_macro2/struct.Span.html#method.local_file) little trick specifically).
### `cfg-attr` (optional)
To generate `#[cfg_attr(doc, doc = "...")]` instead of `#[doc = "..."]` (meaning your docstrings will be `#[cfg(doc)]`-gated
(so `cargo doc` will generate them but `cargo build`/`check`/`test` will not), set the `cfg-attr` key to "doc" in your `Cargo.toml`.
```toml
[package.metadata.syncdoc]
cfg-attr = "doc"
```
See the _Build Configuration_ section below for more details.
### Migration
The CLI automatically migrates code from doc comments to syncdoc `#[omnidoc]` attributes.
#### CLI Installation
- pre-built binary: `cargo binstall syncdoc` (requires [cargo-binstall][cargo-binstall]),
- build from source: `cargo install syncdoc --features cli`
[cargo-binstall]: https://github.com/cargo-bins/cargo-binstall
#### CLI Usage
Commit your code before running with `-c`/`--cut` or `-r`/`--rewrite` as they modify source files.
```help
Usage: syncdoc [OPTIONS] <SOURCE>
Migrate Rust documentation to external markdown files.
Arguments:
<SOURCE> Path to source directory to process (default: 'src')
Options:
-d, --docs <dir> Path to docs directory (default: 'docs' or from Cargo.toml if set)
-m, --migrate Swap doc comments for #[omnidoc] (cut + add + touch)
-c, --cut Cut out doc comments from source files
-a, --add Rewrite code with #[omnidoc] attributes
-t, --touch Touch empty markdown files for any that don't exist
--inline-paths Use inline path= parameters instead of Cargo.toml
-n, --dry-run Preview changes without writing files
-v, --verbose Show verbose output
-h, --help Show this help message
```
#### Examples
- 'Sync' the docs dir with the docstrings in src/
```sh
syncdoc
```
- Preview a full migration without running it
```sh
syncdoc --migrate --dry-run (or `-m -n` for short)
```
- Full migration: cut docs, add attributes, and touch missing files
```sh
syncdoc --migrate (or `-m` for short, equal to `--cut --add --touch`)
```
- Migrate with inline paths instead of Cargo.toml config
```sh
syncdoc --migrate --inline-paths
```
#### `syncdoc-migrate`
The migration CLI uses a standard diffing algorithm ([Myers][myers], as used git), and should be able to correctly
identify how to migrate your code to the omnidoc macro. Syncdoc relies on `rustfmt` and will not
work if `rustfmt` cannot process your code. The only effects from a "round trip" through syncdoc
migrate/restore should be to 'fix' docstrings (move them above attribute macros, trim
leading/trailing blank lines).
[myers]: https://docs.rs/imara-diff/latest/imara_diff/
After running, you should inspect the git diff and `cargo check` the output to confirm the codegen builds.
If you run the `-m`/`--migrate` flag it should touch all the files it requires so the result still builds.
Please send feedback on anything it gets wrong, ideally with a minimal repro.
### Usage
Apply the `#[omnidoc]` attribute to any struct, function, enum, impl block, or inline module:
```rust
use syncdoc::omnidoc;
#[omnidoc]
mod my_functions {
fn foo(x: i32) -> i32 {
x * 2
}
fn bar(y: i32) -> i32 {
y + 1
}
}
```
This will look for documentation in:
- `docs/my_functions/foo.md`
- `docs/my_functions/bar.md`
> **Note**: you cannot use a proc macro on an external module,
> see [this](https://github.com/rust-lang/rust/issues/54727) tracking issue.
>
> A workaround to document an entire module is to inline the entire module (`mod mymodule { ... }`)
> then re-export it with `pub use mymodule::*;`. If you do, note that the name of the inner module is
> the name the macro will look for at the path.
>
> - See
> [examples/demo_submodule](https://github.com/lmmx/syncdoc/tree/master/examples/demo_submodule)
>
> If that isn't to your liking, then just use it on impl blocks etc. and use a regular
> `syncdoc::omnidoc` attribute for individual items.
### Documenting Impl Blocks
syncdoc also works on impl blocks:
```rust
use syncdoc::omnidoc;
struct Calculator;
#[omnidoc]
impl Calculator {
pub fn new() -> Self {
Self
}
pub fn add(&self, a: i32, b: i32) -> i32 {
a + b
}
}
```
Documentation files:
- `docs/Calculator/new.md`
- `docs/Calculator/add.md`
### Single Function Documentation
You can also document individual functions.
```rust
use syncdoc::omnidoc;
#[omnidoc]
fn func1() {
// -> docs/func1.md
// = omnidoc(path) to root docs dir + submodule + fn name + .md
}
```
### Documenting Structs and Enums
syncdoc automatically documents struct fields and enum variants:
```rust
use syncdoc::omnidoc;
#[omnidoc]
mod types {
struct Config {
port: u16,
host: String,
}
enum Status {
Active,
Inactive,
Error(String),
}
}
```
Documentation files:
- `docs/types/Config.md` - struct documentation
- `docs/types/Config/port.md` - field documentation
- `docs/types/Config/host.md` - field documentation
- `docs/types/Status.md` - enum documentation
- `docs/types/Status/Active.md` - variant documentation
- `docs/types/Status/Inactive.md` - variant documentation
- `docs/types/Status/Error.md` - variant documentation
## How It Works
syncdoc uses a procedural macro to inject `#[doc = include_str!("path")]` attributes before function definitions.
It uses `proc-macro2` (it's [free of `syn`](https://github.com/fasterthanlime/free-of-syn)!) to parse tokens rather than doing full AST creation.
### Implementation Details
The macro:
1. **Parses tokens** to find function definitions
2. **Constructs doc paths** based on module hierarchy and function names
3. **Injects doc attributes** using `include_str!` for compile-time validation
4. **Preserves existing attributes** and doesn't interfere with other macros
For examples of the generated output, see the [test snapshots](https://github.com/lmmx/syncdoc/tree/master/syncdoc-core/tests/snapshots) which show the exact documentation attributes injected for various code patterns.
### What Gets Documented
- Regular functions: `fn foo() { ... }`
- Generic functions: `fn foo<T>(x: T) { ... }`
- Methods in impl blocks: `impl MyStruct { fn method(&self) { ... } }`
- Trait default methods: `trait MyTrait { fn method() { ... } }`
- Struct fields: `struct Foo { field: i32 }`
- Enum variants: `enum Bar { Variant1, Variant2(i32) }`
- Type aliases: `type MyType = String;`
- Constants: `const X: i32 = 42;`
- Statics: `static Y: i32 = 42;`
## Build Configuration
For faster builds, you can configure syncdoc to only generate documentation during `cargo doc`:
| `demo_cfg_attr_call` | `#[cfg_attr(doc, syncdoc::omnidoc)]` | ❌ none | `#[doc = include_str!(...)]` |
| `demo_cfg_attr_toml` | `#[syncdoc::omnidoc]` | ✅ `cfg-attr = "doc"` | `#[cfg_attr(doc, doc = include_str!(...))]` |
**Option 1** gates the macro itself, at the call site. **Option 2** gates the generated attributes, configured in TOML (it can also be done at the call site,
but I'd recommended to do it in Cargo.toml to reduce the line noise in your code).
When using either approach, gate the `missing_docs` lint (if using it):
```rust
#![cfg_attr(doc, deny(missing_docs))]
```
## License
This project is licensed under either of:
- Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or <http://www.apache.org/licenses/LICENSE-2.0>)
- MIT license ([LICENSE-MIT](LICENSE-MIT) or <http://opensource.org/licenses/MIT>)
at your option.