Vendor things

third-party/vendor/cfg_aliases/README.md

@@ -0,0 +1,110 @@
+# CFG Aliases
+
+CFG Aliases is a tiny utility to help save you a lot of effort with long winded `#[cfg()]` checks. This crate provides a single [`cfg_aliases!`] macro that doesn't have any dependencies and specifically avoids pulling in `syn` or `quote` so that the impact on your comile times should be negligible.
+
+You use the the [`cfg_aliases!`] macro in your `build.rs` script to define aliases such as `x11` that could then be used in the `cfg` attribute or macro for conditional compilation: `#[cfg(x11)]`.
+
+## Example
+
+**Cargo.toml:**
+
+```toml
+[build-dependencies]
+cfg_aliases = "0.1.0"
+```
+
+**build.rs:**
+
+```rust
+use cfg_aliases::cfg_aliases;
+
+fn main() {
+    // Setup cfg aliases
+    cfg_aliases! {
+        // Platforms
+        wasm: { target_arch = "wasm32" },
+        android: { target_os = "android" },
+        macos: { target_os = "macos" },
+        linux: { target_os = "linux" },
+        // Backends
+        surfman: { all(unix, feature = "surfman", not(wasm)) },
+        glutin: { all(feature = "glutin", not(wasm)) },
+        wgl: { all(windows, feature = "wgl", not(wasm)) },
+        dummy: { not(any(wasm, glutin, wgl, surfman)) },
+    }
+}
+```
+
+Now that we have our aliases setup we can use them just like you would expect:
+
+```rust
+#[cfg(wasm)]
+println!("This is running in WASM");
+
+#[cfg(surfman)]
+{
+    // Do stuff related to surfman
+}
+
+#[cfg(dummy)]
+println!("We're in dummy mode, specify another feature if you want a smarter app!");
+```
+
+This greatly improves what would otherwise look like this without the aliases:
+
+```rust
+#[cfg(target_arch = "wasm32")]
+println!("We're running in WASM");
+
+#[cfg(all(unix, feature = "surfman", not(target_arch = "wasm32")))]
+{
+    // Do stuff related to surfman
+}
+
+#[cfg(not(any(
+    target_arch = "wasm32",
+    all(unix, feature = "surfman", not(target_arch = "wasm32")),
+    all(windows, feature = "wgl", not(target_arch = "wasm32")),
+    all(feature = "glutin", not(target_arch = "wasm32")),
+)))]
+println!("We're in dummy mode, specify another feature if you want a smarter app!");
+```
+
+You can also use the `cfg!` macro or combine your aliases with other checks using `all()`, `not()`, and `any()`. Your aliases are genuine `cfg` flags now!
+
+```rust
+if cfg!(glutin) {
+    // use glutin
+} else {
+    // Do something else
+}
+
+#[cfg(all(glutin, surfman))]
+compile_error!("You cannot specify both `glutin` and `surfman` features");
+```
+
+## Syntax and Error Messages
+
+The aliase names are restricted to the same rules as rust identifiers which, for one, means that they cannot have dashes ( `-` ) in them. Additionally, if you get certain syntax elements wrong, such as the alias name, the macro will error saying that the recursion limit was reached instead of giving a clear indication of what actually went wrong. This is due to a nuance with the macro parser and it might be fixed in a later release of this crate. It is also possible that aliases with dashes in the name might be supported in a later release. Open an issue if that is something that you would like implemented.
+
+Finally, you can also induce an infinite recursion by having rules that both reference each-other, but this isn't a real limitation because that doesn't make logical sense anyway:
+
+```rust,ignore
+// This causes an error!
+cfg_aliases! {
+    test1: { not(test2) },
+    test2: { not(test1) },
+}
+```
+
+## Attribution and Thanks
+
+- Thanks to my God and Father who led me through figuring this out and to whome I owe everything.
+- Thanks to @Yandros on the Rust forum for [showing me][sm] some crazy macro hacks!
+- Thanks to @sfackler for [pointing out][po] the way to make cargo add the cfg flags.
+- Thanks to the authors of the [`tectonic_cfg_support::target_cfg`] macro from which most of the cfg attribute parsing logic is taken from. Also thanks to @ratmice for [bringing it up][bip] on the Rust forum.
+
+[`tectonic_cfg_support::target_cfg`]: https://docs.rs/tectonic_cfg_support/0.0.1/src/tectonic_cfg_support/lib.rs.html#166-298
+[po]: https://users.rust-lang.org/t/any-such-thing-as-cfg-aliases/40100/2
+[bip]: https://users.rust-lang.org/t/any-such-thing-as-cfg-aliases/40100/13
+[sm]: https://users.rust-lang.org/t/any-such-thing-as-cfg-aliases/40100/3