feature: add 'std' feature, deprecated 'use_std'

We'll remove 'use_std' in regex 2, but keep it around for backward
compatibility.

Fixes #474

CHANGELOG.md

@@ -1,3 +1,14 @@
+UNRELEASED
+==========
+
+New features:
+
+* [FEATURE #474](https://github.com/rust-lang/regex/issues/474):
+  The `use_std` feature has been deprecated in favor of the `std` feature.
+  The `use_std` feature will be removed in regex 2. Until then, `use_std` will
+  remain as an alias for the `std` feature.
+
+
 1.2.1 (2019-08-03)
 ==================
 This release does a bit of house cleaning. Namely:

Cargo.toml

@@ -45,17 +45,22 @@ rand = "0.6.5"
 doc-comment = "0.3"
 
 [features]
-default = ["use_std"]
-# The 'use_std' feature permits the regex crate to use the standard library.
-# This is intended to support future use cases where the regex crate may be
-# able to compile without std, and instead just rely on 'core' and 'alloc'
-# (for example). Currently, this isn't supported, and removing the 'use_std'
-# feature will prevent regex from compiling.
-use_std = []
+default = ["std"]
+# The 'std' feature permits the regex crate to use the standard library. This
+# is intended to support future use cases where the regex crate may be able
+# to compile without std, and instead just rely on 'core' and 'alloc' (for
+# example). Currently, this isn't supported, and removing the 'std' feature
+# will prevent regex from compiling.
+std = []
+# The 'use_std' feature is DEPRECATED. It will be removed in regex 2. Until
+# then, it is alias for the 'std' feature.
+use_std = ["std"]
+
 # A blanket feature that governs whether unstable features are enabled or not.
 # Unstable features are disabled by default, and typically rely on unstable
 # features in rustc itself.
 unstable = ["pattern"]
+
 # Enable to use the unstable pattern traits defined in std. This is enabled
 # by default if the unstable feature is enabled.
 pattern = []

src/lib.rs

@@ -22,7 +22,7 @@ used by adding `regex` to your dependencies in your project's `Cargo.toml`.
 regex = "1"
 ```
 
-and this to your crate root:
+If you're using Rust 2015, then you'll also need to add it to your crate root:
 
 ```rust
 extern crate regex;
@@ -511,8 +511,8 @@ another matching engine with fixed memory requirements.
 #![cfg_attr(test, deny(warnings))]
 #![cfg_attr(feature = "pattern", feature(pattern))]
 
-#[cfg(not(feature = "use_std"))]
-compile_error!("`use_std` feature is currently required to build this crate");
+#[cfg(not(feature = "std"))]
+compile_error!("`std` feature is currently required to build this crate");
 
 extern crate aho_corasick;
 extern crate memchr;
@@ -527,16 +527,16 @@ extern crate regex_syntax as syntax;
 #[cfg(test)]
 doc_comment::doctest!("../README.md");
 
-#[cfg(feature = "use_std")]
+#[cfg(feature = "std")]
 pub use error::Error;
-#[cfg(feature = "use_std")]
+#[cfg(feature = "std")]
 pub use re_builder::set_unicode::*;
-#[cfg(feature = "use_std")]
+#[cfg(feature = "std")]
 pub use re_builder::unicode::*;
-#[cfg(feature = "use_std")]
+#[cfg(feature = "std")]
 pub use re_set::unicode::*;
-#[cfg(feature = "use_std")]
-#[cfg(feature = "use_std")]
+#[cfg(feature = "std")]
+#[cfg(feature = "std")]
 pub use re_unicode::{
     escape, CaptureLocations, CaptureMatches, CaptureNames, Captures,
     Locations, Match, Matches, NoExpand, Regex, Replacer, ReplacerRef, Split,
@@ -630,7 +630,7 @@ When the `s` flag is enabled, `.` matches any byte.
 In general, one should expect performance on `&[u8]` to be roughly similar to
 performance on `&str`.
 */
-#[cfg(feature = "use_std")]
+#[cfg(feature = "std")]
 pub mod bytes {
     pub use re_builder::bytes::*;
     pub use re_builder::set_bytes::*;
@@ -663,7 +663,7 @@ mod utf8;
 /// testing different matching engines and supporting the `regex-debug` CLI
 /// utility.
 #[doc(hidden)]
-#[cfg(feature = "use_std")]
+#[cfg(feature = "std")]
 pub mod internal {
     pub use compile::Compiler;
     pub use exec::{Exec, ExecBuilder};