Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

4 files changed, 1205 insertions, 0 deletions

diff --git a/third_party/rust/version_check/src/channel.rs b/third_party/rust/version_check/src/channel.rs
new file mode 100644
index 0000000000..f84c508d16
--- /dev/null
+++ b/third_party/rust/version_check/src/channel.rs
@@ -0,0 +1,193 @@
+use std::fmt;
+
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+enum Kind {
+    Dev,
+    Nightly,
+    Beta,
+    Stable,
+}
+
+/// Release channel: "dev", "nightly", "beta", or "stable".
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+pub struct Channel(Kind);
+
+impl Channel {
+    /// Reads the release channel of the running compiler. If it cannot be
+    /// determined (see the [top-level documentation](crate)), returns `None`.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Channel;
+    ///
+    /// match Channel::read() {
+    ///     Some(c) => format!("The channel is: {}", c),
+    ///     None => format!("Failed to read the release channel.")
+    /// };
+    /// ```
+    pub fn read() -> Option<Channel> {
+        ::get_version_and_date()
+            .and_then(|(version, _)| version)
+            .and_then(|version| Channel::parse(&version))
+    }
+
+    /// Parse a Rust release channel from a Rust release version string (of the
+    /// form `major[.minor[.patch[-channel]]]`). Returns `None` if `version` is
+    /// not a valid Rust version string.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Channel;
+    ///
+    /// let dev = Channel::parse("1.3.0-dev").unwrap();
+    /// assert!(dev.is_dev());
+    ///
+    /// let nightly = Channel::parse("1.42.2-nightly").unwrap();
+    /// assert!(nightly.is_nightly());
+    ///
+    /// let beta = Channel::parse("1.32.0-beta").unwrap();
+    /// assert!(beta.is_beta());
+    ///
+    /// let stable = Channel::parse("1.4.0").unwrap();
+    /// assert!(stable.is_stable());
+    /// ```
+    pub fn parse(version: &str) -> Option<Channel> {
+        let version = version.trim();
+        if version.contains("-dev") || version == "dev" {
+            Some(Channel(Kind::Dev))
+        } else if version.contains("-nightly") || version == "nightly" {
+            Some(Channel(Kind::Nightly))
+        } else if version.contains("-beta") || version == "beta" {
+            Some(Channel(Kind::Beta))
+        } else if !version.contains("-") {
+            Some(Channel(Kind::Stable))
+        } else {
+            None
+        }
+    }
+
+    /// Returns the name of the release channel.
+    fn as_str(&self) -> &'static str {
+        match self.0 {
+            Kind::Dev => "dev",
+            Kind::Beta => "beta",
+            Kind::Nightly => "nightly",
+            Kind::Stable => "stable",
+        }
+    }
+
+    /// Returns `true` if this channel supports feature flags. In other words,
+    /// returns `true` if the channel is either `dev` or `nightly`.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Channel;
+    ///
+    /// let dev = Channel::parse("1.3.0-dev").unwrap();
+    /// assert!(dev.supports_features());
+    ///
+    /// let nightly = Channel::parse("1.42.2-nightly").unwrap();
+    /// assert!(nightly.supports_features());
+    ///
+    /// let beta = Channel::parse("1.32.0-beta").unwrap();
+    /// assert!(!beta.supports_features());
+    ///
+    /// let stable = Channel::parse("1.4.0").unwrap();
+    /// assert!(!stable.supports_features());
+    /// ```
+    pub fn supports_features(&self) -> bool {
+        match self.0 {
+            Kind::Dev | Kind::Nightly => true,
+            Kind::Beta | Kind::Stable => false
+        }
+    }
+
+    /// Returns `true` if this channel is `dev` and `false` otherwise.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Channel;
+    ///
+    /// let dev = Channel::parse("1.3.0-dev").unwrap();
+    /// assert!(dev.is_dev());
+    ///
+    /// let stable = Channel::parse("1.0.0").unwrap();
+    /// assert!(!stable.is_dev());
+    /// ```
+    pub fn is_dev(&self) -> bool {
+        match self.0 {
+            Kind::Dev => true,
+            _ => false
+        }
+    }
+
+    /// Returns `true` if this channel is `nightly` and `false` otherwise.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Channel;
+    ///
+    /// let nightly = Channel::parse("1.3.0-nightly").unwrap();
+    /// assert!(nightly.is_nightly());
+    ///
+    /// let stable = Channel::parse("1.0.0").unwrap();
+    /// assert!(!stable.is_nightly());
+    /// ```
+    pub fn is_nightly(&self) -> bool {
+        match self.0 {
+            Kind::Nightly => true,
+            _ => false
+        }
+    }
+
+    /// Returns `true` if this channel is `beta` and `false` otherwise.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Channel;
+    ///
+    /// let beta = Channel::parse("1.3.0-beta").unwrap();
+    /// assert!(beta.is_beta());
+    ///
+    /// let stable = Channel::parse("1.0.0").unwrap();
+    /// assert!(!stable.is_beta());
+    /// ```
+    pub fn is_beta(&self) -> bool {
+        match self.0 {
+            Kind::Beta => true,
+            _ => false
+        }
+    }
+
+    /// Returns `true` if this channel is `stable` and `false` otherwise.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Channel;
+    ///
+    /// let stable = Channel::parse("1.0.0").unwrap();
+    /// assert!(stable.is_stable());
+    ///
+    /// let beta = Channel::parse("1.3.0-beta").unwrap();
+    /// assert!(!beta.is_stable());
+    /// ```
+    pub fn is_stable(&self) -> bool {
+        match self.0 {
+            Kind::Stable => true,
+            _ => false
+        }
+    }
+}
+
+impl fmt::Display for Channel {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.as_str())
+    }
+}
diff --git a/third_party/rust/version_check/src/date.rs b/third_party/rust/version_check/src/date.rs
new file mode 100644
index 0000000000..de0b2d05d7
--- /dev/null
+++ b/third_party/rust/version_check/src/date.rs
@@ -0,0 +1,203 @@
+use std::fmt;
+
+/// Release date including year, month, and day.
+// Internal storage is: y[31..9] | m[8..5] | d[5...0].
+#[derive(Debug, PartialEq, Eq, Copy, Clone, PartialOrd, Ord)]
+pub struct Date(u32);
+
+impl Date {
+    /// Reads the release date of the running compiler. If it cannot be
+    /// determined (see the [top-level documentation](crate)), returns `None`.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Date;
+    ///
+    /// match Date::read() {
+    ///     Some(d) => format!("The release date is: {}", d),
+    ///     None => format!("Failed to read the release date.")
+    /// };
+    /// ```
+    pub fn read() -> Option<Date> {
+        ::get_version_and_date()
+            .and_then(|(_, date)| date)
+            .and_then(|date| Date::parse(&date))
+    }
+
+    /// Parse a release date of the form `%Y-%m-%d`. Returns `None` if `date` is
+    /// not in `%Y-%m-%d` format.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Date;
+    ///
+    /// let date = Date::parse("2016-04-20").unwrap();
+    ///
+    /// assert!(date.at_least("2016-01-10"));
+    /// assert!(date.at_most("2016-04-20"));
+    /// assert!(date.exactly("2016-04-20"));
+    ///
+    /// assert!(Date::parse("2021-12-31").unwrap().exactly("2021-12-31"));
+    ///
+    /// assert!(Date::parse("March 13, 2018").is_none());
+    /// assert!(Date::parse("1-2-3-4-5").is_none());
+    /// assert!(Date::parse("2020-300-23120").is_none());
+    /// assert!(Date::parse("2020-12-12 1").is_none());
+    /// assert!(Date::parse("2020-10").is_none());
+    /// assert!(Date::parse("2020").is_none());
+    /// ```
+    pub fn parse(date: &str) -> Option<Date> {
+        let mut ymd = [0u16; 3];
+        for (i, split) in date.split('-').map(|s| s.parse::<u16>()).enumerate() {
+            ymd[i] = match (i, split) {
+                (3, _) | (_, Err(_)) => return None,
+                (_, Ok(v)) => v,
+            };
+        }
+
+        let (year, month, day) = (ymd[0], ymd[1], ymd[2]);
+        if year == 0 || month == 0 || month > 12 || day == 0 || day > 31 {
+            return None;
+        }
+
+        Some(Date::from_ymd(year, month as u8, day as u8))
+    }
+
+    /// Creates a `Date` from `(year, month, day)` date components.
+    ///
+    /// Does not check the validity of `year`, `month`, or `day`, but `year` is
+    /// truncated to 23 bits (% 8,388,608), `month` to 4 bits (% 16), and `day`
+    /// to 5 bits (% 32).
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Date;
+    ///
+    /// assert!(Date::from_ymd(2021, 7, 30).exactly("2021-07-30"));
+    /// assert!(Date::from_ymd(2010, 3, 23).exactly("2010-03-23"));
+    /// assert!(Date::from_ymd(2090, 1, 31).exactly("2090-01-31"));
+    ///
+    /// // Truncation: 33 % 32 == 0x21 & 0x1F == 1.
+    /// assert!(Date::from_ymd(2090, 1, 33).exactly("2090-01-01"));
+    /// ```
+    pub fn from_ymd(year: u16, month: u8, day: u8) -> Date {
+        let year = (year as u32) << 9;
+        let month = ((month as u32) & 0xF) << 5;
+        let day = (day as u32) & 0x1F;
+        Date(year | month | day)
+    }
+
+    /// Return the original (YYYY, MM, DD).
+    fn to_ymd(&self) -> (u16, u8, u8) {
+        let y = self.0 >> 9;
+        let m = (self.0 >> 5) & 0xF;
+        let d = self.0 & 0x1F;
+        (y as u16, m as u8, d as u8)
+    }
+
+    /// Returns `true` if `self` occurs on or after `date`.
+    ///
+    /// If `date` occurs before `self`, or if `date` is not in `%Y-%m-%d`
+    /// format, returns `false`.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Date;
+    ///
+    /// let date = Date::parse("2020-01-01").unwrap();
+    ///
+    /// assert!(date.at_least("2019-12-31"));
+    /// assert!(date.at_least("2020-01-01"));
+    /// assert!(date.at_least("2014-04-31"));
+    ///
+    /// assert!(!date.at_least("2020-01-02"));
+    /// assert!(!date.at_least("2024-08-18"));
+    /// ```
+    pub fn at_least(&self, date: &str) -> bool {
+        Date::parse(date)
+            .map(|date| self >= &date)
+            .unwrap_or(false)
+    }
+
+    /// Returns `true` if `self` occurs on or before `date`.
+    ///
+    /// If `date` occurs after `self`, or if `date` is not in `%Y-%m-%d`
+    /// format, returns `false`.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Date;
+    ///
+    /// let date = Date::parse("2020-01-01").unwrap();
+    ///
+    /// assert!(date.at_most("2020-01-01"));
+    /// assert!(date.at_most("2020-01-02"));
+    /// assert!(date.at_most("2024-08-18"));
+    ///
+    /// assert!(!date.at_most("2019-12-31"));
+    /// assert!(!date.at_most("2014-04-31"));
+    /// ```
+    pub fn at_most(&self, date: &str) -> bool {
+        Date::parse(date)
+            .map(|date| self <= &date)
+            .unwrap_or(false)
+    }
+
+    /// Returns `true` if `self` occurs exactly on `date`.
+    ///
+    /// If `date` is not exactly `self`, or if `date` is not in `%Y-%m-%d`
+    /// format, returns `false`.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Date;
+    ///
+    /// let date = Date::parse("2020-01-01").unwrap();
+    ///
+    /// assert!(date.exactly("2020-01-01"));
+    ///
+    /// assert!(!date.exactly("2019-12-31"));
+    /// assert!(!date.exactly("2014-04-31"));
+    /// assert!(!date.exactly("2020-01-02"));
+    /// assert!(!date.exactly("2024-08-18"));
+    /// ```
+    pub fn exactly(&self, date: &str) -> bool {
+        Date::parse(date)
+            .map(|date| self == &date)
+            .unwrap_or(false)
+    }
+}
+
+impl fmt::Display for Date {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let (y, m, d) = self.to_ymd();
+        write!(f, "{}-{:02}-{:02}", y, m, d)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Date;
+
+    macro_rules! reflexive_display {
+        ($string:expr) => (
+            assert_eq!(Date::parse($string).unwrap().to_string(), $string);
+        )
+    }
+
+    #[test]
+    fn display() {
+        reflexive_display!("2019-05-08");
+        reflexive_display!("2000-01-01");
+        reflexive_display!("2000-12-31");
+        reflexive_display!("2090-12-31");
+        reflexive_display!("1999-02-19");
+        reflexive_display!("9999-12-31");
+    }
+}
diff --git a/third_party/rust/version_check/src/lib.rs b/third_party/rust/version_check/src/lib.rs
new file mode 100644
index 0000000000..6c16074822
--- /dev/null
+++ b/third_party/rust/version_check/src/lib.rs
@@ -0,0 +1,493 @@
+//! This tiny crate checks that the running or installed `rustc` meets some
+//! version requirements. The version is queried by calling the Rust compiler
+//! with `--version`. The path to the compiler is determined first via the
+//! `RUSTC` environment variable. If it is not set, then `rustc` is used. If
+//! that fails, no determination is made, and calls return `None`.
+//!
+//! # Examples
+//!
+//! * Set a `cfg` flag in `build.rs` if the running compiler was determined to
+//!   be at least version `1.13.0`:
+//!
+//!   ```rust
+//!   extern crate version_check as rustc;
+//!
+//!   if rustc::is_min_version("1.13.0").unwrap_or(false) {
+//!       println!("cargo:rustc-cfg=question_mark_operator");
+//!   }
+//!   ```
+//!
+//!   See [`is_max_version`] or [`is_exact_version`] to check if the compiler
+//!   is _at most_ or _exactly_ a certain version.
+//!
+//! * Check that the running compiler was released on or after `2018-12-18`:
+//!
+//!   ```rust
+//!   extern crate version_check as rustc;
+//!
+//!   match rustc::is_min_date("2018-12-18") {
+//!       Some(true) => "Yep! It's recent!",
+//!       Some(false) => "No, it's older.",
+//!       None => "Couldn't determine the rustc version."
+//!   };
+//!   ```
+//!
+//!   See [`is_max_date`] or [`is_exact_date`] to check if the compiler was
+//!   released _prior to_ or _exactly on_ a certain date.
+//!
+//! * Check that the running compiler supports feature flags:
+//!
+//!   ```rust
+//!   extern crate version_check as rustc;
+//!
+//!   match rustc::is_feature_flaggable() {
+//!       Some(true) => "Yes! It's a dev or nightly release!",
+//!       Some(false) => "No, it's stable or beta.",
+//!       None => "Couldn't determine the rustc version."
+//!   };
+//!   ```
+//!
+//! * Check that the running compiler supports a specific feature:
+//!
+//!   ```rust
+//!   extern crate version_check as rustc;
+//!
+//!   if let Some(true) = rustc::supports_feature("doc_cfg") {
+//!      println!("cargo:rustc-cfg=has_doc_cfg");
+//!   }
+//!   ```
+//!
+//! * Check that the running compiler is on the stable channel:
+//!
+//!   ```rust
+//!   extern crate version_check as rustc;
+//!
+//!   match rustc::Channel::read() {
+//!       Some(c) if c.is_stable() => format!("Yes! It's stable."),
+//!       Some(c) => format!("No, the channel {} is not stable.", c),
+//!       None => format!("Couldn't determine the rustc version.")
+//!   };
+//!   ```
+//!
+//! To interact with the version, release date, and release channel as structs,
+//! use [`Version`], [`Date`], and [`Channel`], respectively. The [`triple()`]
+//! function returns all three values efficiently.
+//!
+//! # Alternatives
+//!
+//! This crate is dead simple with no dependencies. If you need something more
+//! and don't care about panicking if the version cannot be obtained, or if you
+//! don't mind adding dependencies, see
+//! [rustc_version](https://crates.io/crates/rustc_version).
+
+#![allow(deprecated)]
+
+mod version;
+mod channel;
+mod date;
+
+use std::env;
+use std::process::Command;
+
+#[doc(inline)] pub use version::*;
+#[doc(inline)] pub use channel::*;
+#[doc(inline)] pub use date::*;
+
+/// Parses (version, date) as available from rustc version string.
+fn version_and_date_from_rustc_version(s: &str) -> (Option<String>, Option<String>) {
+    let last_line = s.lines().last().unwrap_or(s);
+    let mut components = last_line.trim().split(" ");
+    let version = components.nth(1);
+    let date = components.filter(|c| c.ends_with(')')).next()
+        .map(|s| s.trim_right().trim_right_matches(")").trim_left().trim_left_matches('('));
+    (version.map(|s| s.to_string()), date.map(|s| s.to_string()))
+}
+
+/// Parses (version, date) as available from rustc verbose version output.
+fn version_and_date_from_rustc_verbose_version(s: &str) -> (Option<String>, Option<String>) {
+    let (mut version, mut date) = (None, None);
+    for line in s.lines() {
+        let split = |s: &str| s.splitn(2, ":").nth(1).map(|s| s.trim().to_string());
+        match line.trim().split(" ").nth(0) {
+            Some("rustc") => {
+                let (v, d) = version_and_date_from_rustc_version(line);
+                version = version.or(v);
+                date = date.or(d);
+            },
+            Some("release:") => version = split(line),
+            Some("commit-date:") if line.ends_with("unknown") => date = None,
+            Some("commit-date:") => date = split(line),
+            _ => continue
+        }
+    }
+
+    (version, date)
+}
+
+/// Returns (version, date) as available from `rustc --version`.
+fn get_version_and_date() -> Option<(Option<String>, Option<String>)> {
+    let rustc = env::var("RUSTC").unwrap_or_else(|_| "rustc".to_string());
+    Command::new(rustc).arg("--verbose").arg("--version").output().ok()
+        .and_then(|output| String::from_utf8(output.stdout).ok())
+        .map(|s| version_and_date_from_rustc_verbose_version(&s))
+}
+
+/// Reads the triple of [`Version`], [`Channel`], and [`Date`] of the installed
+/// or running `rustc`.
+///
+/// If any attribute cannot be determined (see the [top-level
+/// documentation](crate)), returns `None`.
+///
+/// To obtain only one of three attributes, use [`Version::read()`],
+/// [`Channel::read()`], or [`Date::read()`].
+pub fn triple() -> Option<(Version, Channel, Date)> {
+    let (version_str, date_str) = match get_version_and_date() {
+        Some((Some(version), Some(date))) => (version, date),
+        _ => return None
+    };
+
+    // Can't use `?` or `try!` for `Option` in 1.0.0.
+    match Version::parse(&version_str) {
+        Some(version) => match Channel::parse(&version_str) {
+            Some(channel) => match Date::parse(&date_str) {
+                Some(date) => Some((version, channel, date)),
+                _ => None,
+            },
+            _ => None,
+        },
+        _ => None
+    }
+}
+
+/// Checks that the running or installed `rustc` was released **on or after**
+/// some date.
+///
+/// The format of `min_date` must be YYYY-MM-DD. For instance: `2016-12-20` or
+/// `2017-01-09`.
+///
+/// If the date cannot be retrieved or parsed, or if `min_date` could not be
+/// parsed, returns `None`. Otherwise returns `true` if the installed `rustc`
+/// was release on or after `min_date` and `false` otherwise.
+pub fn is_min_date(min_date: &str) -> Option<bool> {
+    match (Date::read(), Date::parse(min_date)) {
+        (Some(rustc_date), Some(min_date)) => Some(rustc_date >= min_date),
+        _ => None
+    }
+}
+
+/// Checks that the running or installed `rustc` was released **on or before**
+/// some date.
+///
+/// The format of `max_date` must be YYYY-MM-DD. For instance: `2016-12-20` or
+/// `2017-01-09`.
+///
+/// If the date cannot be retrieved or parsed, or if `max_date` could not be
+/// parsed, returns `None`. Otherwise returns `true` if the installed `rustc`
+/// was release on or before `max_date` and `false` otherwise.
+pub fn is_max_date(max_date: &str) -> Option<bool> {
+    match (Date::read(), Date::parse(max_date)) {
+        (Some(rustc_date), Some(max_date)) => Some(rustc_date <= max_date),
+        _ => None
+    }
+}
+
+/// Checks that the running or installed `rustc` was released **exactly** on
+/// some date.
+///
+/// The format of `date` must be YYYY-MM-DD. For instance: `2016-12-20` or
+/// `2017-01-09`.
+///
+/// If the date cannot be retrieved or parsed, or if `date` could not be parsed,
+/// returns `None`. Otherwise returns `true` if the installed `rustc` was
+/// release on `date` and `false` otherwise.
+pub fn is_exact_date(date: &str) -> Option<bool> {
+    match (Date::read(), Date::parse(date)) {
+        (Some(rustc_date), Some(date)) => Some(rustc_date == date),
+        _ => None
+    }
+}
+
+/// Checks that the running or installed `rustc` is **at least** some minimum
+/// version.
+///
+/// The format of `min_version` is a semantic version: `1.3.0`, `1.15.0-beta`,
+/// `1.14.0`, `1.16.0-nightly`, etc.
+///
+/// If the version cannot be retrieved or parsed, or if `min_version` could not
+/// be parsed, returns `None`. Otherwise returns `true` if the installed `rustc`
+/// is at least `min_version` and `false` otherwise.
+pub fn is_min_version(min_version: &str) -> Option<bool> {
+    match (Version::read(), Version::parse(min_version)) {
+        (Some(rustc_ver), Some(min_ver)) => Some(rustc_ver >= min_ver),
+        _ => None
+    }
+}
+
+/// Checks that the running or installed `rustc` is **at most** some maximum
+/// version.
+///
+/// The format of `max_version` is a semantic version: `1.3.0`, `1.15.0-beta`,
+/// `1.14.0`, `1.16.0-nightly`, etc.
+///
+/// If the version cannot be retrieved or parsed, or if `max_version` could not
+/// be parsed, returns `None`. Otherwise returns `true` if the installed `rustc`
+/// is at most `max_version` and `false` otherwise.
+pub fn is_max_version(max_version: &str) -> Option<bool> {
+    match (Version::read(), Version::parse(max_version)) {
+        (Some(rustc_ver), Some(max_ver)) => Some(rustc_ver <= max_ver),
+        _ => None
+    }
+}
+
+/// Checks that the running or installed `rustc` is **exactly** some version.
+///
+/// The format of `version` is a semantic version: `1.3.0`, `1.15.0-beta`,
+/// `1.14.0`, `1.16.0-nightly`, etc.
+///
+/// If the version cannot be retrieved or parsed, or if `version` could not be
+/// parsed, returns `None`. Otherwise returns `true` if the installed `rustc` is
+/// exactly `version` and `false` otherwise.
+pub fn is_exact_version(version: &str) -> Option<bool> {
+    match (Version::read(), Version::parse(version)) {
+        (Some(rustc_ver), Some(version)) => Some(rustc_ver == version),
+        _ => None
+    }
+}
+
+/// Checks whether the running or installed `rustc` supports feature flags.
+///
+/// In other words, if the channel is either "nightly" or "dev".
+///
+/// Note that support for specific `rustc` features can be enabled or disabled
+/// via the `allow-features` compiler flag, which this function _does not_
+/// check. That is, this function _does not_ check whether a _specific_ feature
+/// is supported, but instead whether features are supported at all. To check
+/// for support for a specific feature, use [`supports_feature()`].
+///
+/// If the version could not be determined, returns `None`. Otherwise returns
+/// `true` if the running version supports feature flags and `false` otherwise.
+pub fn is_feature_flaggable() -> Option<bool> {
+    Channel::read().map(|c| c.supports_features())
+}
+
+/// Checks whether the running or installed `rustc` supports `feature`.
+///
+/// Returns _true_ _iff_ [`is_feature_flaggable()`] returns `true` _and_ the
+/// feature is not disabled via exclusion in `allow-features` via `RUSTFLAGS` or
+/// `CARGO_ENCODED_RUSTFLAGS`. If the version could not be determined, returns
+/// `None`.
+///
+/// # Example
+///
+/// ```rust
+/// use version_check as rustc;
+///
+/// if let Some(true) = rustc::supports_feature("doc_cfg") {
+///    println!("cargo:rustc-cfg=has_doc_cfg");
+/// }
+/// ```
+pub fn supports_feature(feature: &str) -> Option<bool> {
+    match is_feature_flaggable() {
+        Some(true) => { /* continue */ }
+        Some(false) => return Some(false),
+        None => return None,
+    }
+
+    let env_flags = env::var_os("CARGO_ENCODED_RUSTFLAGS")
+        .map(|flags| (flags, '\x1f'))
+        .or_else(|| env::var_os("RUSTFLAGS").map(|flags| (flags, ' ')));
+
+    if let Some((flags, delim)) = env_flags {
+        const ALLOW_FEATURES: &'static str = "allow-features=";
+
+        let rustflags = flags.to_string_lossy();
+        let allow_features = rustflags.split(delim)
+            .map(|flag| flag.trim_left_matches("-Z").trim())
+            .filter(|flag| flag.starts_with(ALLOW_FEATURES))
+            .map(|flag| &flag[ALLOW_FEATURES.len()..]);
+
+        if let Some(allow_features) = allow_features.last() {
+            return Some(allow_features.split(',').any(|f| f.trim() == feature));
+        }
+    }
+
+    // If there are no `RUSTFLAGS` or `CARGO_ENCODED_RUSTFLAGS` or they don't
+    // contain an `allow-features` flag, assume compiler allows all features.
+    Some(true)
+}
+
+#[cfg(test)]
+mod tests {
+    use std::{env, fs};
+
+    use super::version_and_date_from_rustc_version;
+    use super::version_and_date_from_rustc_verbose_version;
+
+    macro_rules! check_parse {
+        (@ $f:expr, $s:expr => $v:expr, $d:expr) => ({
+            if let (Some(v), d) = $f(&$s) {
+                let e_d: Option<&str> = $d.into();
+                assert_eq!((v, d), ($v.to_string(), e_d.map(|s| s.into())));
+            } else {
+                panic!("{:?} didn't parse for version testing.", $s);
+            }
+        });
+        ($f:expr, $s:expr => $v:expr, $d:expr) => ({
+            let warn = "warning: invalid logging spec 'warning', ignoring it";
+            let warn2 = "warning: sorry, something went wrong :(sad)";
+            check_parse!(@ $f, $s => $v, $d);
+            check_parse!(@ $f, &format!("{}\n{}", warn, $s) => $v, $d);
+            check_parse!(@ $f, &format!("{}\n{}", warn2, $s) => $v, $d);
+            check_parse!(@ $f, &format!("{}\n{}\n{}", warn, warn2, $s) => $v, $d);
+            check_parse!(@ $f, &format!("{}\n{}\n{}", warn2, warn, $s) => $v, $d);
+        })
+    }
+
+    macro_rules! check_terse_parse {
+        ($($s:expr => $v:expr, $d:expr,)+) => {$(
+            check_parse!(version_and_date_from_rustc_version, $s => $v, $d);
+        )+}
+    }
+
+    macro_rules! check_verbose_parse {
+        ($($s:expr => $v:expr, $d:expr,)+) => {$(
+            check_parse!(version_and_date_from_rustc_verbose_version, $s => $v, $d);
+        )+}
+    }
+
+    #[test]
+    fn test_version_parse() {
+        check_terse_parse! {
+            "rustc 1.18.0" => "1.18.0", None,
+            "rustc 1.8.0" => "1.8.0", None,
+            "rustc 1.20.0-nightly" => "1.20.0-nightly", None,
+            "rustc 1.20" => "1.20", None,
+            "rustc 1.3" => "1.3", None,
+            "rustc 1" => "1", None,
+            "rustc 1.5.1-beta" => "1.5.1-beta", None,
+            "rustc 1.20.0 (2017-07-09)" => "1.20.0", Some("2017-07-09"),
+            "rustc 1.20.0-dev (2017-07-09)" => "1.20.0-dev", Some("2017-07-09"),
+            "rustc 1.20.0-nightly (d84693b93 2017-07-09)" => "1.20.0-nightly", Some("2017-07-09"),
+            "rustc 1.20.0 (d84693b93 2017-07-09)" => "1.20.0", Some("2017-07-09"),
+            "rustc 1.30.0-nightly (3bc2ca7e4 2018-09-20)" => "1.30.0-nightly", Some("2018-09-20"),
+        };
+    }
+
+    #[test]
+    fn test_verbose_version_parse() {
+        check_verbose_parse! {
+            "rustc 1.0.0 (a59de37e9 2015-05-13) (built 2015-05-14)\n\
+                binary: rustc\n\
+                commit-hash: a59de37e99060162a2674e3ff45409ac73595c0e\n\
+                commit-date: 2015-05-13\n\
+                build-date: 2015-05-14\n\
+                host: x86_64-unknown-linux-gnu\n\
+                release: 1.0.0" => "1.0.0", Some("2015-05-13"),
+
+            "rustc 1.0.0 (a59de37e9 2015-05-13) (built 2015-05-14)\n\
+                commit-hash: a59de37e99060162a2674e3ff45409ac73595c0e\n\
+                commit-date: 2015-05-13\n\
+                build-date: 2015-05-14\n\
+                host: x86_64-unknown-linux-gnu\n\
+                release: 1.0.0" => "1.0.0", Some("2015-05-13"),
+
+            "rustc 1.50.0 (cb75ad5db 2021-02-10)\n\
+                binary: rustc\n\
+                commit-hash: cb75ad5db02783e8b0222fee363c5f63f7e2cf5b\n\
+                commit-date: 2021-02-10\n\
+                host: x86_64-unknown-linux-gnu\n\
+                release: 1.50.0" => "1.50.0", Some("2021-02-10"),
+
+            "rustc 1.52.0-nightly (234781afe 2021-03-07)\n\
+                binary: rustc\n\
+                commit-hash: 234781afe33d3f339b002f85f948046d8476cfc9\n\
+                commit-date: 2021-03-07\n\
+                host: x86_64-unknown-linux-gnu\n\
+                release: 1.52.0-nightly\n\
+                LLVM version: 12.0.0" => "1.52.0-nightly", Some("2021-03-07"),
+
+            "rustc 1.41.1\n\
+                binary: rustc\n\
+                commit-hash: unknown\n\
+                commit-date: unknown\n\
+                host: x86_64-unknown-linux-gnu\n\
+                release: 1.41.1\n\
+                LLVM version: 7.0" => "1.41.1", None,
+
+            "rustc 1.49.0\n\
+                binary: rustc\n\
+                commit-hash: unknown\n\
+                commit-date: unknown\n\
+                host: x86_64-unknown-linux-gnu\n\
+                release: 1.49.0" => "1.49.0", None,
+
+            "rustc 1.50.0 (Fedora 1.50.0-1.fc33)\n\
+                binary: rustc\n\
+                commit-hash: unknown\n\
+                commit-date: unknown\n\
+                host: x86_64-unknown-linux-gnu\n\
+                release: 1.50.0" => "1.50.0", None,
+        };
+    }
+
+    fn read_static(verbose: bool, channel: &str, minor: usize) -> String {
+        use std::fs::File;
+        use std::path::Path;
+        use std::io::{BufReader, Read};
+
+        let subdir = if verbose { "verbose" } else { "terse" };
+        let path = Path::new(STATIC_PATH)
+            .join(channel)
+            .join(subdir)
+            .join(format!("rustc-1.{}.0", minor));
+
+        let file = File::open(path).unwrap();
+        let mut buf_reader = BufReader::new(file);
+        let mut contents = String::new();
+        buf_reader.read_to_string(&mut contents).unwrap();
+        contents
+    }
+
+    static STATIC_PATH: &'static str = concat!(env!("CARGO_MANIFEST_DIR"), "/static");
+
+    static DATES: [&'static str; 51] = [
+        "2015-05-13", "2015-06-19", "2015-08-03", "2015-09-15", "2015-10-27",
+        "2015-12-04", "2016-01-19", "2016-02-29", "2016-04-11", "2016-05-18",
+        "2016-07-03", "2016-08-15", "2016-09-23", "2016-11-07", "2016-12-16",
+        "2017-01-19", "2017-03-10", "2017-04-24", "2017-06-06", "2017-07-17",
+        "2017-08-27", "2017-10-09", "2017-11-20", "2018-01-01", "2018-02-12",
+        "2018-03-25", "2018-05-07", "2018-06-19", "2018-07-30", "2018-09-11",
+        "2018-10-24", "2018-12-04", "2019-01-16", "2019-02-28", "2019-04-10",
+        "2019-05-20", "2019-07-03", "2019-08-13", "2019-09-23", "2019-11-04",
+        "2019-12-16", "2020-01-27", "2020-03-09", "2020-04-20", "2020-06-01",
+        "2020-07-13", "2020-08-24", "2020-10-07", "2020-11-16", "2020-12-29",
+        "2021-02-10",
+    ];
+
+    #[test]
+    fn test_stable_compatibility() {
+        if env::var_os("FORCE_STATIC").is_none() && fs::metadata(STATIC_PATH).is_err() {
+            // We exclude `/static` when we package `version_check`, so don't
+            // run if static files aren't present unless we know they should be.
+            return;
+        }
+
+        // Ensure we can parse all output from all Linux stable releases.
+        for v in 0..DATES.len() {
+            let (version, date) = (&format!("1.{}.0", v), Some(DATES[v]));
+            check_terse_parse!(read_static(false, "stable", v) => version, date,);
+            check_verbose_parse!(read_static(true, "stable", v) => version, date,);
+        }
+    }
+
+    #[test]
+    fn test_parse_current() {
+        let (version, channel) = (::Version::read(), ::Channel::read());
+        assert!(version.is_some());
+        assert!(channel.is_some());
+
+        if let Ok(known_channel) = env::var("KNOWN_CHANNEL") {
+            assert_eq!(channel, ::Channel::parse(&known_channel));
+        }
+    }
+}
diff --git a/third_party/rust/version_check/src/version.rs b/third_party/rust/version_check/src/version.rs
new file mode 100644
index 0000000000..2bc18aae2b
--- /dev/null
+++ b/third_party/rust/version_check/src/version.rs
@@ -0,0 +1,316 @@
+use std::fmt;
+
+/// Version number: `major.minor.patch`, ignoring release channel.
+#[derive(PartialEq, Eq, Copy, Clone, PartialOrd, Ord)]
+pub struct Version(u64);
+
+impl Version {
+    /// Reads the version of the running compiler. If it cannot be determined
+    /// (see the [top-level documentation](crate)), returns `None`.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Version;
+    ///
+    /// match Version::read() {
+    ///     Some(d) => format!("Version is: {}", d),
+    ///     None => format!("Failed to read the version.")
+    /// };
+    /// ```
+    pub fn read() -> Option<Version> {
+        ::get_version_and_date()
+            .and_then(|(version, _)| version)
+            .and_then(|version| Version::parse(&version))
+    }
+
+
+    /// Parse a Rust release version (of the form
+    /// `major[.minor[.patch[-channel]]]`), ignoring the release channel, if
+    /// any. Returns `None` if `version` is not a valid Rust version string.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Version;
+    ///
+    /// let version = Version::parse("1.18.0").unwrap();
+    /// assert!(version.exactly("1.18.0"));
+    ///
+    /// let version = Version::parse("1.20.0-nightly").unwrap();
+    /// assert!(version.exactly("1.20.0"));
+    /// assert!(version.exactly("1.20.0-beta"));
+    ///
+    /// let version = Version::parse("1.3").unwrap();
+    /// assert!(version.exactly("1.3.0"));
+    ///
+    /// let version = Version::parse("1").unwrap();
+    /// assert!(version.exactly("1.0.0"));
+    ///
+    /// assert!(Version::parse("one.two.three").is_none());
+    /// assert!(Version::parse("1.65536.2").is_none());
+    /// assert!(Version::parse("1. 2").is_none());
+    /// assert!(Version::parse("").is_none());
+    /// assert!(Version::parse("1.").is_none());
+    /// assert!(Version::parse("1.2.3.4").is_none());
+    /// ```
+    pub fn parse(version: &str) -> Option<Version> {
+        let splits = version.split('-')
+            .nth(0)
+            .unwrap_or("")
+            .split('.')
+            .map(|s| s.parse::<u16>());
+
+        let mut mmp = [0u16; 3];
+        for (i, split) in splits.enumerate() {
+            mmp[i] = match (i, split) {
+                (3, _) | (_, Err(_)) => return None,
+                (_, Ok(v)) => v,
+            };
+        }
+
+        let (maj, min, patch) = (mmp[0], mmp[1], mmp[2]);
+        Some(Version::from_mmp(maj, min, patch))
+    }
+
+    /// Creates a `Version` from `(major, minor, patch)` version components.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Version;
+    ///
+    /// assert!(Version::from_mmp(1, 35, 0).exactly("1.35.0"));
+    /// assert!(Version::from_mmp(1, 33, 0).exactly("1.33.0"));
+    /// assert!(Version::from_mmp(1, 35, 1).exactly("1.35.1"));
+    /// assert!(Version::from_mmp(1, 13, 2).exactly("1.13.2"));
+    /// ```
+    pub fn from_mmp(major: u16, minor: u16, patch: u16) -> Version {
+        Version(((major as u64) << 32) | ((minor as u64) << 16) | patch as u64)
+    }
+
+    /// Returns the `(major, minor, patch)` version components of `self`.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Version;
+    ///
+    /// assert_eq!(Version::parse("1.35.0").unwrap().to_mmp(), (1, 35, 0));
+    /// assert_eq!(Version::parse("1.33.0").unwrap().to_mmp(), (1, 33, 0));
+    /// assert_eq!(Version::parse("1.35.1").unwrap().to_mmp(), (1, 35, 1));
+    /// assert_eq!(Version::parse("1.13.2").unwrap().to_mmp(), (1, 13, 2));
+    /// ```
+    pub fn to_mmp(&self) -> (u16, u16, u16) {
+        let major = self.0 >> 32;
+        let minor = self.0 >> 16;
+        let patch = self.0;
+        (major as u16, minor as u16, patch as u16)
+    }
+
+    /// Returns `true` if `self` is greater than or equal to `version`.
+    ///
+    /// If `version` is greater than `self`, or if `version` is not a valid Rust
+    /// version string, returns `false`.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Version;
+    ///
+    /// let version = Version::parse("1.35.0").unwrap();
+    ///
+    /// assert!(version.at_least("1.33.0"));
+    /// assert!(version.at_least("1.35.0"));
+    /// assert!(version.at_least("1.13.2"));
+    ///
+    /// assert!(!version.at_least("1.35.1"));
+    /// assert!(!version.at_least("1.55.0"));
+    ///
+    /// let version = Version::parse("1.12.5").unwrap();
+    ///
+    /// assert!(version.at_least("1.12.0"));
+    /// assert!(!version.at_least("1.35.0"));
+    /// ```
+    pub fn at_least(&self, version: &str) -> bool {
+        Version::parse(version)
+            .map(|version| self >= &version)
+            .unwrap_or(false)
+    }
+
+    /// Returns `true` if `self` is less than or equal to `version`.
+    ///
+    /// If `version` is less than `self`, or if `version` is not a valid Rust
+    /// version string, returns `false`.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Version;
+    ///
+    /// let version = Version::parse("1.35.0").unwrap();
+    ///
+    /// assert!(version.at_most("1.35.1"));
+    /// assert!(version.at_most("1.55.0"));
+    /// assert!(version.at_most("1.35.0"));
+    ///
+    /// assert!(!version.at_most("1.33.0"));
+    /// assert!(!version.at_most("1.13.2"));
+    /// ```
+    pub fn at_most(&self, version: &str) -> bool {
+        Version::parse(version)
+            .map(|version| self <= &version)
+            .unwrap_or(false)
+    }
+
+    /// Returns `true` if `self` is exactly equal to `version`.
+    ///
+    /// If `version` is not equal to `self`, or if `version` is not a valid Rust
+    /// version string, returns `false`.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use version_check::Version;
+    ///
+    /// let version = Version::parse("1.35.0").unwrap();
+    ///
+    /// assert!(version.exactly("1.35.0"));
+    ///
+    /// assert!(!version.exactly("1.33.0"));
+    /// assert!(!version.exactly("1.35.1"));
+    /// assert!(!version.exactly("1.13.2"));
+    /// ```
+    pub fn exactly(&self, version: &str) -> bool {
+        Version::parse(version)
+            .map(|version| self == &version)
+            .unwrap_or(false)
+    }
+}
+
+impl fmt::Display for Version {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let (major, minor, patch) = self.to_mmp();
+        write!(f, "{}.{}.{}", major, minor, patch)
+    }
+}
+
+impl fmt::Debug for Version {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // We don't use `debug_*` because it's not available in `1.0.0`.
+        write!(f, "Version({:?}, {:?})", self.0, self.to_mmp())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Version;
+
+    macro_rules! assert_to_mmp {
+        // We don't use `.into::<Option<_>>` because it's not available in 1.0.
+        // We don't use the message part of `assert!` for the same reason.
+        ($s:expr, None) => (
+            assert_eq!(Version::parse($s), None);
+        );
+        ($s:expr, $mmp:expr) => (
+            assert_eq!(Version::parse($s).map(|v| v.to_mmp()), Some($mmp));
+        )
+    }
+
+    macro_rules! assert_from_mmp {
+        (($x:expr, $y:expr, $z:expr) => $s:expr) => {
+            assert_eq!(Some(Version::from_mmp($x, $y, $z)), Version::parse($s));
+        };
+    }
+
+    #[test]
+    fn test_str_to_mmp() {
+        assert_to_mmp!("1", (1, 0, 0));
+        assert_to_mmp!("1.2", (1, 2, 0));
+        assert_to_mmp!("1.18.0", (1, 18, 0));
+        assert_to_mmp!("3.19.0", (3, 19, 0));
+        assert_to_mmp!("1.19.0-nightly", (1, 19, 0));
+        assert_to_mmp!("1.12.2349", (1, 12, 2349));
+        assert_to_mmp!("0.12", (0, 12, 0));
+        assert_to_mmp!("1.12.5", (1, 12, 5));
+        assert_to_mmp!("1.12", (1, 12, 0));
+        assert_to_mmp!("1", (1, 0, 0));
+        assert_to_mmp!("1.4.4-nightly (d84693b93 2017-07-09))", (1, 4, 4));
+        assert_to_mmp!("1.58879.4478-dev", (1, 58879, 4478));
+        assert_to_mmp!("1.58879.4478-dev (d84693b93 2017-07-09))", (1, 58879, 4478));
+    }
+
+    #[test]
+    fn test_malformed() {
+        assert_to_mmp!("1.65536.2", None);
+        assert_to_mmp!("-1.2.3", None);
+        assert_to_mmp!("1. 2", None);
+        assert_to_mmp!("", None);
+        assert_to_mmp!(" ", None);
+        assert_to_mmp!(".", None);
+        assert_to_mmp!("one", None);
+        assert_to_mmp!("1.", None);
+        assert_to_mmp!("1.2.3.4.5.6", None);
+    }
+
+    #[test]
+    fn test_from_mmp() {
+        assert_from_mmp!((1, 18, 0) => "1.18.0");
+        assert_from_mmp!((3, 19, 0) => "3.19.0");
+        assert_from_mmp!((1, 19, 0) => "1.19.0");
+        assert_from_mmp!((1, 12, 2349) => "1.12.2349");
+        assert_from_mmp!((0, 12, 0) => "0.12");
+        assert_from_mmp!((1, 12, 5) => "1.12.5");
+        assert_from_mmp!((1, 12, 0) => "1.12");
+        assert_from_mmp!((1, 0, 0) => "1");
+        assert_from_mmp!((1, 4, 4) => "1.4.4");
+        assert_from_mmp!((1, 58879, 4478) => "1.58879.4478");
+    }
+
+    #[test]
+    fn test_comparisons() {
+        let version = Version::parse("1.18.0").unwrap();
+        assert!(version.exactly("1.18.0"));
+        assert!(version.at_least("1.12.0"));
+        assert!(version.at_least("1.12"));
+        assert!(version.at_least("1"));
+        assert!(version.at_most("1.18.1"));
+        assert!(!version.exactly("1.19.0"));
+        assert!(!version.exactly("1.18.1"));
+
+        let version = Version::parse("1.20.0-nightly").unwrap();
+        assert!(version.exactly("1.20.0-beta"));
+        assert!(version.exactly("1.20.0-nightly"));
+        assert!(version.exactly("1.20.0"));
+        assert!(!version.exactly("1.19"));
+
+        let version = Version::parse("1.3").unwrap();
+        assert!(version.exactly("1.3.0"));
+        assert!(version.exactly("1.3.0-stable"));
+        assert!(version.exactly("1.3"));
+        assert!(!version.exactly("1.5.0-stable"));
+
+        let version = Version::parse("1").unwrap();
+        assert!(version.exactly("1.0.0"));
+        assert!(version.exactly("1.0"));
+        assert!(version.exactly("1"));
+
+        assert!(Version::parse("one.two.three").is_none());
+    }
+
+    macro_rules! reflexive_display {
+        ($s:expr) => (
+            assert_eq!(Version::parse($s).unwrap().to_string(), $s);
+        )
+    }
+
+    #[test]
+    fn display() {
+        reflexive_display!("1.0.0");
+        reflexive_display!("1.2.3");
+        reflexive_display!("1.12.1438");
+        reflexive_display!("1.44.0");
+        reflexive_display!("2.44.0");
+        reflexive_display!("23459.28923.3483");
+    }
+}