feature: Add new crate gix-macros

Cargo.toml

@@ -244,6 +244,7 @@ members = [
     "gix-packetline",
     "gix-packetline-blocking",
     "gix-mailmap",
+    "gix-macros",
     "gix-note",
     "gix-negotiate",
     "gix-fetchhead",

gix-macros/Cargo.toml

@@ -0,0 +1,25 @@
+[package]
+name = "gix-macros"
+version = "0.0.0"
+edition = "2021"
+description = "Proc-macro utilities for gix"
+authors = [
+    "Jiahao XU <Jiahao_XU@outlook.com>",
+    "Andre Bogus <bogusandre@gmail.com>",
+    "Sebastian Thiel <sebastian.thiel@icloud.com>",
+]
+repository = "https://github.com/Byron/gitoxide"
+license = "MIT OR Apache-2.0"
+include = ["src/**/*", "LICENSE-*", "CHANGELOG.md"]
+rust-version = "1.65"
+
+[lib]
+proc_macro = true
+
+[dependencies]
+syn = { version = "2.0", features = ["full", "fold"] }
+quote = "1.0"
+proc-macro2 = "1.0"
+
+[dev-dependencies]
+trybuild = "1.0"

gix-macros/LICENSE-APACHE

@@ -0,0 +1 @@
+../LICENSE-APACHE

gix-macros/LICENSE-MIT

@@ -0,0 +1 @@
+../LICENSE-MIT

gix-macros/src/lib.rs

@@ -0,0 +1,25 @@
+//! A crate of useful macros used in `gix` primarily.
+//!
+//! Note that within `gix-*` crates, monomorphization should never be used for convenience, but only for performance
+//! reasons. And in the latter case, manual denomophization should be considered if the trait in questions isn't called
+//! often enough or measurements indicate that `&dyn Trait` is increasing the runtime. Thus, `gix-*` crates should probably
+//! by default prefer using `&dyn` unless measurements indicate otherwise.
+use proc_macro::TokenStream;
+
+/// When applied to functions or methods, it will turn it into a wrapper that will immediately call
+/// a de-monomorphized implementation (i.e. one that uses `&dyn Trait`).
+///
+/// That way, the landing-pads for convenience will be as small as possible which then delegate to a single
+/// function or method for implementation.
+///
+/// The parameters using the following traits can be de-monomorphized:
+///
+/// * `Into`
+/// * `AsRef`
+/// * `AsMut`
+#[proc_macro_attribute]
+pub fn momo(_attrs: TokenStream, input: TokenStream) -> TokenStream {
+    momo::inner(input.into()).into()
+}
+
+mod momo;