mozilla-central/third_party/rust/cfg_aliases/src/lib.rs

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//! # 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 = "22")))]
//! {
//! // 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.
//!
#![allow(clippy::needless_doctest_main)]
// In the `cfg_aliases!` macro below, all of the rules that start with @parser were derived from
// the `target_cfg!` macro here:
//
//
// The `target_cfg!` macro is excellently commented while the one below is not very well commented
// yet, so if you need some help understanding it you might benefit by reading that implementation.
// Also check out this forum topic for more history on the macro development:
//
/// Create `cfg` aliases
///
/// **build.rs:**
///
/// ```rust
/// # use cfg_aliases::cfg_aliases;
/// // 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)) },
/// }
/// ```
///
/// After you put this in your build script you can then check for those conditions like so:
///
/// ```rust
/// #[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(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!");
/// ```
#[macro_export]
macro_rules! cfg_aliases {
// Helper that just checks whether the CFG environment variable is set
(@cfg_is_set $cfgname:ident) => {
std::env::var(
format!(
"CARGO_CFG_{}",
&stringify!($cfgname).to_uppercase().replace("-", "_")
)
).is_ok()
};
// Helper to check for the presense of a feature
(@cfg_has_feature $feature:expr) => {
{
std::env::var(
format!(
"CARGO_FEATURE_{}",
&stringify!($feature).to_uppercase().replace("-", "_").replace('"', "")
)
).map(|x| x == "1").unwrap_or(false)
}
};
// Helper that checks whether a CFG environment contains the given value
(@cfg_contains $cfgname:ident = $cfgvalue:expr) => {
std::env::var(
format!(
"CARGO_CFG_{}",
&stringify!($cfgname).to_uppercase().replace("-", "_")
)
).unwrap_or("".to_string()).split(",").find(|x| x == &$cfgvalue).is_some()
};
// Emitting `any(clause1,clause2,...)`: convert to `$crate::cfg_aliases!(clause1) && $crate::cfg_aliases!(clause2) && ...`
(
@parser_emit
all
$({$($grouped:tt)+})+
) => {
($(
($crate::cfg_aliases!(@parser $($grouped)+))
)&&+)
};
// Likewise for `all(clause1,clause2,...)`.
(
@parser_emit
any
$({$($grouped:tt)+})+
) => {
($(
($crate::cfg_aliases!(@parser $($grouped)+))
)||+)
};
// "@clause" rules are used to parse the comma-separated lists. They munch
// their inputs token-by-token and finally invoke an "@emit" rule when the
// list is all grouped. The general pattern for recording the parser state
// is:
//
// ```
// $crate::cfg_aliases!(
// @clause $operation
// [{grouped-clause-1} {grouped-clause-2...}]
// [not-yet-parsed-tokens...]
// current-clause-tokens...
// )
// ```
// This rule must come first in this section. It fires when the next token
// to parse is a comma. When this happens, we take the tokens in the
// current clause and add them to the list of grouped clauses, adding
// delimeters so that the grouping can be easily extracted again in the
// emission stage.
(
@parser_clause
$op:ident
[$({$($grouped:tt)+})*]
[, $($rest:tt)*]
$($current:tt)+
) => {
$crate::cfg_aliases!(@parser_clause $op [
$(
{$($grouped)+}
)*
{$($current)+}
] [
$($rest)*
]);
};
// This rule comes next. It fires when the next un-parsed token is *not* a
// comma. In this case, we add that token to the list of tokens in the
// current clause, then move on to the next one.
(
@parser_clause
$op:ident
[$({$($grouped:tt)+})*]
[$tok:tt $($rest:tt)*]
$($current:tt)*
) => {
$crate::cfg_aliases!(@parser_clause $op [
$(
{$($grouped)+}
)*
] [
$($rest)*
] $($current)* $tok);
};
// This rule fires when there are no more tokens to parse in this list. We
// finish off the "current" token group, then delegate to the emission
// rule.
(
@parser_clause
$op:ident
[$({$($grouped:tt)+})*]
[]
$($current:tt)+
) => {
$crate::cfg_aliases!(@parser_emit $op
$(
{$($grouped)+}
)*
{$($current)+}
);
};
// `all(clause1, clause2...)` : we must parse this comma-separated list and
// partner with `@emit all` to output a bunch of && terms.
(
@parser
all($($tokens:tt)+)
) => {
$crate::cfg_aliases!(@parser_clause all [] [$($tokens)+])
};
// Likewise for `any(clause1, clause2...)`
(
@parser
any($($tokens:tt)+)
) => {
$crate::cfg_aliases!(@parser_clause any [] [$($tokens)+])
};
// `not(clause)`: compute the inner clause, then just negate it.
(
@parser
not($($tokens:tt)+)
) => {
!($crate::cfg_aliases!(@parser $($tokens)+))
};
// `feature = value`: test for a feature.
(@parser feature = $value:expr) => {
$crate::cfg_aliases!(@cfg_has_feature $value)
};
// `param = value`: test for equality.
(@parser $key:ident = $value:expr) => {
$crate::cfg_aliases!(@cfg_contains $key = $value)
};
// Parse a lone identifier that might be an alias
(@parser $e:ident) => {
__cfg_aliases_matcher__!($e)
};
// Entrypoint that defines the matcher
(
@with_dollar[$dol:tt]
$( $alias:ident : { $($config:tt)* } ),* $(,)?
) => {
// Create a macro that expands other aliases and outputs any non
// alias by checking whether that CFG value is set
macro_rules! __cfg_aliases_matcher__ {
// Parse config expression for the alias
$(
( $alias ) => {
$crate::cfg_aliases!(@parser $($config)*)
};
)*
// Anything that doesn't match evaluate the item
( $dol e:ident ) => {
$crate::cfg_aliases!(@cfg_is_set $dol e)
};
}
$(
if $crate::cfg_aliases!(@parser $($config)*) {
println!("cargo:rustc-cfg={}", stringify!($alias));
}
)*
};
// Catch all that starts the macro
($($tokens:tt)*) => {
$crate::cfg_aliases!(@with_dollar[$] $($tokens)*)
}
}