Add docs for json feature, make frontend error pub

- Build all features on docs.rs
- Add a `docsrs` cfg attr and add to items that are public but only when
  the json feature is enabled
- Make the `JsonFrontendError` type nameable, this type is referred to in
  a public variant of `Error` but was not accessible outside the crate.

Signed-off-by: Ross MacArthur <[email protected]>

Author: rossmacarthur

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Upcoming Release
 
+- [[#91]](https://github.com/rust-vmm/seccompiler/pull/91): Actually make
+  `JsonFrontendError` type publicly accessible, this type is referred to in a
+  public variant of `Error` but was not accessible outside the crate.
+
 # v0.5.0
 
 ## Added

Cargo.toml

@@ -9,6 +9,10 @@ keywords = ["seccomp", "jail", "sandbox"]
 license = "Apache-2.0 OR BSD-3-Clause"
 edition = "2021"
 
+[package.metadata.docs.rs]
+all-features = true
+rustdoc-args = ["--cfg", "docsrs"]
+
 [features]
 json = ["serde", "serde_json"]
 

src/frontend/json.rs

@@ -31,6 +31,7 @@ use serde::{Deserialize, Deserializer};
 type Result<T> = result::Result<T, Error>;
 
 /// Error compiling JSON into IR.
+#[cfg_attr(docsrs, doc(cfg(feature = "json")))]
 #[derive(Debug)]
 pub enum Error {
     /// Backend error creating the `SeccompFilter` IR.

src/lib.rs

@@ -185,6 +185,8 @@
 //! [`SeccompRule`]: struct.SeccompRule.html
 //! [`SeccompAction`]: enum.SeccompAction.html
 
+#![cfg_attr(docsrs, feature(doc_cfg))]
+
 mod backend;
 #[cfg(feature = "json")]
 mod frontend;
@@ -200,8 +202,11 @@ use std::collections::HashMap;
 use std::fmt::{Display, Formatter};
 use std::io;
 
+#[cfg_attr(docsrs, doc(cfg(feature = "json")))]
+#[cfg(feature = "json")]
+pub use frontend::json::Error as JsonFrontendError;
 #[cfg(feature = "json")]
-use frontend::json::{Error as JsonFrontendError, JsonCompiler};
+use frontend::json::JsonCompiler;
 
 // Re-export the IR public types.
 pub use backend::{
@@ -238,6 +243,7 @@ pub enum Error {
     /// of the thread that caused the failure.
     ThreadSync(libc::c_long),
     /// Json Frontend Error.
+    #[cfg_attr(docsrs, doc(cfg(feature = "json")))]
     #[cfg(feature = "json")]
     JsonFrontend(JsonFrontendError),
 }
@@ -295,6 +301,7 @@ impl From<BackendError> for Error {
         Self::Backend(value)
     }
 }
+#[cfg_attr(docsrs, doc(cfg(feature = "json")))]
 #[cfg(feature = "json")]
 impl From<JsonFrontendError> for Error {
     fn from(value: JsonFrontendError) -> Self {