Vendor dependencies

Let's see how I like this workflow.

vendor/iana-time-zone/src/tz_macos.rs

@@ -0,0 +1,144 @@
+pub(crate) fn get_timezone_inner() -> Result<String, crate::GetTimezoneError> {
+    get_timezone().ok_or(crate::GetTimezoneError::OsError)
+}
+
+#[inline]
+fn get_timezone() -> Option<String> {
+    // The longest name in the IANA time zone database is 25 ASCII characters long.
+    const MAX_LEN: usize = 32;
+    let mut buf = [0; MAX_LEN];
+
+    // Get system time zone, and borrow its name.
+    let tz = system_time_zone::SystemTimeZone::new()?;
+    let name = tz.name()?;
+
+    // If the name is encoded in UTF-8, copy it directly.
+    let name = if let Some(name) = name.as_utf8() {
+        name
+    } else {
+        // Otherwise convert the name to UTF-8.
+        name.to_utf8(&mut buf)?
+    };
+
+    if name.is_empty() || name.len() >= MAX_LEN {
+        // The name should not be empty, or excessively long.
+        None
+    } else {
+        Some(name.to_owned())
+    }
+}
+
+mod system_time_zone {
+    //! create a safe wrapper around `CFTimeZoneRef`
+
+    use core_foundation_sys::base::{CFRelease, CFTypeRef};
+    use core_foundation_sys::timezone::{CFTimeZoneCopySystem, CFTimeZoneGetName, CFTimeZoneRef};
+
+    pub(crate) struct SystemTimeZone(CFTimeZoneRef);
+
+    impl Drop for SystemTimeZone {
+        fn drop(&mut self) {
+            // SAFETY: `SystemTimeZone` is only ever created with a valid `CFTimeZoneRef`.
+            unsafe { CFRelease(self.0 as CFTypeRef) };
+        }
+    }
+
+    impl SystemTimeZone {
+        pub(crate) fn new() -> Option<Self> {
+            // SAFETY: No invariants to uphold. We'll release the pointer when we don't need it anymore.
+            let v: CFTimeZoneRef = unsafe { CFTimeZoneCopySystem() };
+            if v.is_null() {
+                None
+            } else {
+                Some(SystemTimeZone(v))
+            }
+        }
+
+        /// Get the time zone name as a [super::string_ref::StringRef].
+        ///
+        /// The lifetime of the `StringRef` is bound to our lifetime. Mutable
+        /// access is also prevented by taking a reference to `self`.
+        pub(crate) fn name(&self) -> Option<super::string_ref::StringRef<'_, Self>> {
+            // SAFETY: `SystemTimeZone` is only ever created with a valid `CFTimeZoneRef`.
+            let string = unsafe { CFTimeZoneGetName(self.0) };
+            if string.is_null() {
+                None
+            } else {
+                // SAFETY: here we ensure that `string` is a valid pointer.
+                Some(unsafe { super::string_ref::StringRef::new(string, self) })
+            }
+        }
+    }
+}
+
+mod string_ref {
+    //! create safe wrapper around `CFStringRef`
+
+    use std::convert::TryInto;
+
+    use core_foundation_sys::base::{Boolean, CFRange};
+    use core_foundation_sys::string::{
+        kCFStringEncodingUTF8, CFStringGetBytes, CFStringGetCStringPtr, CFStringGetLength,
+        CFStringRef,
+    };
+
+    pub(crate) struct StringRef<'a, T> {
+        string: CFStringRef,
+        // We exclude mutable access to the parent by taking a reference to the
+        // parent (rather than, for example, just using a marker to enforce the
+        // parent's lifetime).
+        _parent: &'a T,
+    }
+
+    impl<'a, T> StringRef<'a, T> {
+        // SAFETY: `StringRef` must be valid pointer
+        pub(crate) unsafe fn new(string: CFStringRef, _parent: &'a T) -> Self {
+            Self { string, _parent }
+        }
+
+        pub(crate) fn as_utf8(&self) -> Option<&'a str> {
+            // SAFETY: `StringRef` is only ever created with a valid `CFStringRef`.
+            let v = unsafe { CFStringGetCStringPtr(self.string, kCFStringEncodingUTF8) };
+            if !v.is_null() {
+                // SAFETY: `CFStringGetCStringPtr()` returns NUL-terminated strings.
+                let v = unsafe { std::ffi::CStr::from_ptr(v) };
+                if let Ok(v) = v.to_str() {
+                    return Some(v);
+                }
+            }
+            None
+        }
+
+        pub(crate) fn to_utf8<'b>(&self, buf: &'b mut [u8]) -> Option<&'b str> {
+            // SAFETY: `StringRef` is only ever created with a valid `CFStringRef`.
+            let length = unsafe { CFStringGetLength(self.string) };
+
+            let mut buf_bytes = 0;
+            let range = CFRange {
+                location: 0,
+                length,
+            };
+
+            let converted_bytes = unsafe {
+                // SAFETY: `StringRef` is only ever created with a valid `CFStringRef`.
+                CFStringGetBytes(
+                    self.string,
+                    range,
+                    kCFStringEncodingUTF8,
+                    b'\0',
+                    false as Boolean,
+                    buf.as_mut_ptr(),
+                    buf.len() as isize,
+                    &mut buf_bytes,
+                )
+            };
+            if converted_bytes != length {
+                return None;
+            }
+
+            let len = buf_bytes.try_into().ok()?;
+            let s = buf.get(..len)?;
+            std::str::from_utf8(s).ok()
+        }
+    }
+}