Vendor things

third-party/vendor/proc-macro-crate/README.md

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+# proc-macro-crate
+
+
+[![](https://docs.rs/proc-macro-crate/badge.svg)](https://docs.rs/proc-macro-crate/) [![](https://img.shields.io/crates/v/proc-macro-crate.svg)](https://crates.io/crates/proc-macro-crate) [![](https://img.shields.io/crates/d/proc-macro-crate.png)](https://crates.io/crates/proc-macro-crate) [![Build Status](https://travis-ci.org/bkchr/proc-macro-crate.png?branch=master)](https://travis-ci.org/bkchr/proc-macro-crate)
+
+Providing support for `$crate` in procedural macros.
+
+* [Introduction](#introduction)
+* [Example](#example)
+* [License](#license)
+
+### Introduction
+
+In `macro_rules!` `$crate` is used to get the path of the crate where a macro is declared in. In
+procedural macros there is currently no easy way to get this path. A common hack is to import the
+desired crate with a know name and use this. However, with rust edition 2018 and dropping
+`extern crate` declarations from `lib.rs`, people start to rename crates in `Cargo.toml` directly.
+However, this breaks importing the crate, as the proc-macro developer does not know the renamed
+name of the crate that should be imported.
+
+This crate provides a way to get the name of a crate, even if it renamed in `Cargo.toml`. For this
+purpose a single function `crate_name` is provided. This function needs to be called in the context
+of a proc-macro with the name of the desired crate. `CARGO_MANIFEST_DIR` will be used to find the
+current active `Cargo.toml` and this `Cargo.toml` is searched for the desired crate.
+
+### Example
+
+```rust
+use quote::quote;
+use syn::Ident;
+use proc_macro2::Span;
+use proc_macro_crate::{crate_name, FoundCrate};
+
+fn import_my_crate() {
+    let found_crate = crate_name("my-crate").expect("my-crate is present in `Cargo.toml`");
+
+    match found_crate {
+        FoundCrate::Itself => quote!( crate::Something ),
+        FoundCrate::Name(name) => {
+            let ident = Ident::new(&name, Span::call_site());
+            quote!( #ident::Something )
+        }
+    };
+}
+
+```
+
+### Edge cases
+
+There are multiple edge cases when it comes to determining the correct crate. If you for example
+import a crate as its own dependency, like this:
+
+```toml
+[package]
+name = "my_crate"
+
+[dev-dependencies]
+my_crate = { version = "0.1", features = [ "test-feature" ] }
+```
+
+The crate will return `FoundCrate::Itself` and you will not be able to find the other instance
+of your crate in `dev-dependencies`. Other similar cases are when one crate is imported multiple
+times:
+
+```toml
+[package]
+name = "my_crate"
+
+[dependencies]
+some-crate = { version = "0.5" }
+some-crate-old = { package = "some-crate", version = "0.1" }
+```
+
+When searching for `some-crate` in this `Cargo.toml` it will return `FoundCrate::Name("some_old_crate")`,
+aka the last definition of the crate in the `Cargo.toml`.
+
+### License
+
+Licensed under either of
+
+ * [Apache License, Version 2.0](https://www.apache.org/licenses/LICENSE-2.0)
+
+ * [MIT license](https://opensource.org/licenses/MIT)
+
+at your option.
+
+License: MIT OR Apache-2.0