build(ariadne): vendor serde crates

third_party/crates/memchr-2.8.3/src/cow.rs

@@ -0,0 +1,109 @@
+use core::ops;
+
+/// A specialized copy-on-write byte string.
+///
+/// The purpose of this type is to permit usage of a "borrowed or owned
+/// byte string" in a way that keeps std/no-std compatibility. That is, in
+/// no-std/alloc mode, this type devolves into a simple &[u8] with no owned
+/// variant available. We can't just use a plain Cow because Cow is not in
+/// core.
+#[derive(Clone, Debug)]
+pub struct CowBytes<'a>(Imp<'a>);
+
+// N.B. We don't use alloc::borrow::Cow here since we can get away with a
+// Box<[u8]> for our use case, which is 1/3 smaller than the Vec<u8> that
+// a Cow<[u8]> would use.
+#[cfg(feature = "alloc")]
+#[derive(Clone, Debug)]
+enum Imp<'a> {
+    Borrowed(&'a [u8]),
+    Owned(alloc::boxed::Box<[u8]>),
+}
+
+#[cfg(not(feature = "alloc"))]
+#[derive(Clone, Debug)]
+struct Imp<'a>(&'a [u8]);
+
+impl<'a> ops::Deref for CowBytes<'a> {
+    type Target = [u8];
+
+    #[inline(always)]
+    fn deref(&self) -> &[u8] {
+        self.as_slice()
+    }
+}
+
+impl<'a> CowBytes<'a> {
+    /// Create a new borrowed CowBytes.
+    #[inline(always)]
+    pub(crate) fn new<B: ?Sized + AsRef<[u8]>>(bytes: &'a B) -> CowBytes<'a> {
+        CowBytes(Imp::new(bytes.as_ref()))
+    }
+
+    /// Create a new owned CowBytes.
+    #[cfg(feature = "alloc")]
+    #[inline(always)]
+    pub(crate) fn new_owned(
+        bytes: alloc::boxed::Box<[u8]>,
+    ) -> CowBytes<'static> {
+        CowBytes(Imp::Owned(bytes))
+    }
+
+    /// Return a borrowed byte string, regardless of whether this is an owned
+    /// or borrowed byte string internally.
+    #[inline(always)]
+    pub(crate) fn as_slice(&self) -> &[u8] {
+        self.0.as_slice()
+    }
+
+    /// Return an owned version of this copy-on-write byte string.
+    ///
+    /// If this is already an owned byte string internally, then this is a
+    /// no-op. Otherwise, the internal byte string is copied.
+    #[cfg(feature = "alloc")]
+    #[inline(always)]
+    pub(crate) fn into_owned(self) -> CowBytes<'static> {
+        match self.0 {
+            Imp::Borrowed(b) => {
+                CowBytes::new_owned(alloc::boxed::Box::from(b))
+            }
+            Imp::Owned(b) => CowBytes::new_owned(b),
+        }
+    }
+}
+
+impl<'a> Imp<'a> {
+    #[inline(always)]
+    pub fn new(bytes: &'a [u8]) -> Imp<'a> {
+        #[cfg(feature = "alloc")]
+        {
+            Imp::Borrowed(bytes)
+        }
+        #[cfg(not(feature = "alloc"))]
+        {
+            Imp(bytes)
+        }
+    }
+
+    #[cfg(feature = "alloc")]
+    #[inline(always)]
+    pub fn as_slice(&self) -> &[u8] {
+        #[cfg(feature = "alloc")]
+        {
+            match self {
+                Imp::Owned(ref x) => x,
+                Imp::Borrowed(x) => x,
+            }
+        }
+        #[cfg(not(feature = "alloc"))]
+        {
+            self.0
+        }
+    }
+
+    #[cfg(not(feature = "alloc"))]
+    #[inline(always)]
+    pub fn as_slice(&self) -> &[u8] {
+        self.0
+    }
+}