feat: in-manifest and in-lib documentation of feature toggles (#329)

Author: Byron

Diff for: Cargo.lock

@@ -62,53 +62,7 @@ Documented in [its documentation](https://docs.rs/git-actor).
 
 ### git-features
 
-A crate to help controlling which capabilities are available from the top-level crate that uses `gitoxide-core` or any other
-`gitoxide` crate that uses `git-features`.
-All feature toggles are additive.
-
-* **progress**
-    * Provide traits and utilities for providing progress information. These can then be rendered using facilities provided by
-      the `prodash` crate.
-* **parallel**
-    * Use scoped threads and channels to parallelize common workloads on multiple objects. If enabled, it is used everywhere
-      where it makes sense.
-    * As caches are likely to be used and instantiated per thread, more memory will be used on top of the costs for threads.
-    * The `threading` module will contain thread-safe primitives for shared ownership and mutation, otherwise these will be their single threaded counterparts.
-        * This way, single-threaded applications don't have to pay for threaded primitives.
-* **crc32**
-    * provide a proven and fast `crc32` implementation.
-* **io-pipe**
-    * an in-memory unidirectional pipe using `bytes` as efficient transfer mechanism
-* **zlib**
-    * Enable the usage of zlib related utilities to compress or decompress data.
-    * By default it uses a pure rust implementation which is slower than the **zlib-ng-compat** version, but might be relevant if you prefer a pure-rust build
-      and reduced performance is acceptable. Note that a competitive Zlib implementation is critical to `gitoxide's` performance.
-    * Additional backends are supported, each of which overriding the default Rust backend.
-      * _mutually-exclusive_
-       * **zlib-ng-compat**
-         * Use a C-based backend which can compress and decompress significantly faster.
-      * **cloudflare-zlib**
-         * Another incarnation of a faster-than-normal zlib backend.
-      * **_zlib-rust-backend_**
-         * available for completeness even though it's the default - it may be chosen for more maintainable feature flags.
-    
-* **walkdir**
-    * Makes facilities of the `walkdir` crate partially available.
-    * In conjunction with the **parallel** feature, directory walking will be parallel instead behind a compatible interface.
-* _mutually-exclusive_
-    * **fast-sha1**
-        * a multi-crate implementation that can use hardware acceleration, thus bearing the potential for up to 2Gb/s throughput on
-          CPUs that support it, like AMD Ryzen or Intel Core i3, as well as Apple Silicon like M1.
-        * Takes precedence over `rustsha1` if both are specified.
-        * A fast SHA1 implementation is critical to `gitoxide's` performance
-    * **rustsha1**
-        * A standard and well performing pure Rust implementation of Sha1. Will significantly slow down various git operations.
-
-* **cache-efficiency-debug**
-    * Caches implement this by default, which costs nothing unless this feature is enabled
-    * Count cache hits and misses and print that debug information on drop
-* **time**
-    * Make the `time` module available with access to the local time as configured by the system.
+Documented in [its documentation](https://docs.rs/git-features).
 
 ### git-packetline
 

Diff for: cargo-features.md

@@ -12,16 +12,55 @@ doctest = false
 test = false
 
 [features]
+
 default = []
+## Provide traits and utilities for providing progress information. These can then be rendered
+## using facilities of the `prodash` crate.
 progress = ["prodash"]
+
+## Use scoped threads and channels to parallelize common workloads on multiple objects. If enabled, it is used everywhere
+## where it makes sense.
+## As caches are likely to be used and instantiated per thread, more memory will be used on top of the costs for threads.
+## The `threading` module will contain thread-safe primitives for shared ownership and mutation, otherwise these will be their single threaded counterparts.
+## This way, single-threaded applications don't have to pay for threaded primitives.
 parallel = ["crossbeam-utils", "crossbeam-channel", "num_cpus", "jwalk", "parking_lot"]
-fast-sha1 = ["sha-1"]
-rustsha1 = ["sha1_smol"]
+#* an in-memory unidirectional pipe using `bytes` as efficient transfer mechanism.
 io-pipe = ["bytes"]
+## provide a proven and fast `crc32` implementation.
 crc32 = ["crc32fast"]
+
+#! ### Mutually Exclusive ZLIB
+
+## Enable the usage of zlib related utilities to compress or decompress data.
+## By default it uses a pure rust implementation which is slower than the **zlib-ng-compat** version, but might be relevant if you prefer a pure-rust build
+## and reduced performance is acceptable. Note that a competitive Zlib implementation is critical to `gitoxide's` object database performance.
+## Additional backends are supported, each of which overriding the default Rust backend.
 zlib = ["flate2", "flate2/rust_backend", "quick-error"]
+## Use a C-based backend which can compress and decompress significantly faster.
 zlib-ng-compat = ["flate2/zlib-ng-compat"]
+## available for completeness even though it's the default - it may be chosen for more specific feature flag names, instead of a bare `zlib`.
 zlib-rust-backend = ["flate2/rust_backend"]
+
+#! ### Mutually Exclusive SHA1
+## A fast SHA1 implementation is critical to `gitoxide's` object database performance
+## A multi-crate implementation that can use hardware acceleration, thus bearing the potential for up to 2Gb/s throughput on
+## CPUs that support it, like AMD Ryzen or Intel Core i3, as well as Apple Silicon like M1.
+## Takes precedence over `rustsha1` if both are specified.
+fast-sha1 = ["sha-1"]
+## A standard and well performing pure Rust implementation of Sha1. Will significantly slow down various git operations.
+rustsha1 = ["sha1_smol"]
+
+#! ### Optional Dependencies
+#!
+#! - **`time`** - make the `time` module available with access to the local time as configured by the system.
+#! - **`walkdir`**
+#!     - Makes facilities of the `walkdir` crate partially available.
+#!     - In conjunction with the **parallel** feature, directory walking will be parallel instead behind a compatible interface.
+
+#! ### Other
+
+## Count cache hits and misses and print that debug information on drop.
+## Caches implement this by default, which costs nothing unless this feature is enabled
 cache-efficiency-debug = []
 
 [[test]]
@@ -78,10 +117,13 @@ bytes = { version = "1.0.0", optional = true }
 flate2 = { version = "1.0.17", optional = true, default-features = false }
 quick-error = { version = "2.0.0", optional = true }
 
-# time module
+# time
 time = { version = "0.3.2", optional = true, default-features = false, features = ["local-offset"] }
 
+document-features = { version = "0.1.0", optional = true }
+
 [package.metadata.docs.rs]
+features = ["document-features"]
 all-features = true
 
 # Assembly doesn't yet compile on MSVC on windows, but does on GNU, see https://github.com/RustCrypto/asm-hashes/issues/17

Diff for: git-features/Cargo.toml

@@ -8,6 +8,11 @@
 //!
 //! Thus all features provided here commonly have a 'cheap' base implementation, with the option to pull in
 //! counterparts with higher performance.
+//! ## Feature Flags
+#![cfg_attr(
+    feature = "document-features",
+    cfg_attr(doc, doc = ::document_features::document_features!())
+)]
 
 ///
 pub mod cache;