Implement ZeroMapKV for Pattern<SinglePlaceholder, str> (#5030)

Author: younies

utils/pattern/Cargo.toml

@@ -29,6 +29,7 @@ litemap = { workspace = true, default-features = false, optional = true }
 serde = { workspace = true, features = ["derive", "alloc"], optional = true }
 yoke = { workspace = true, features = ["derive"], optional = true }
 zerofrom = { workspace = true, features = ["derive"], optional = true }
+zerovec = { workspace = true, default-features = false, optional = true }
 
 [dev-dependencies]
 zerofrom = { workspace = true, features = ["alloc"] }
@@ -45,3 +46,4 @@ litemap = ["dep:litemap"]
 serde = ["alloc", "dep:serde"]
 yoke = ["dep:yoke"]
 zerofrom = ["dep:zerofrom"]
+zerovec = ["dep:zerovec"]

utils/pattern/src/implementations.rs

@@ -0,0 +1,45 @@
+// This file is part of ICU4X. For terms of use, please see the file
+// called LICENSE at the top level of the ICU4X source tree
+// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
+
+use crate::{Pattern, SinglePlaceholder, SinglePlaceholderPattern};
+
+use alloc::boxed::Box;
+use zerovec::{maps::ZeroMapKV, ule::VarULE, VarZeroSlice, VarZeroVec, ZeroVecError};
+
+impl<'a> ZeroMapKV<'a> for Pattern<SinglePlaceholder, str> {
+    type Container = VarZeroVec<'a, Pattern<SinglePlaceholder, str>>;
+    type Slice = VarZeroSlice<Pattern<SinglePlaceholder, str>>;
+    type GetType = Pattern<SinglePlaceholder, str>;
+    type OwnedType = Box<Pattern<SinglePlaceholder, str>>;
+}
+
+/// # Safety
+///
+/// Safety checklist for `ULE`:
+///
+/// 1. `str` does not include any uninitialized or padding bytes.
+/// 2. `str` is aligned to 1 byte.
+/// 3. The implementation of `validate_byte_slice()` returns an error
+///    if any byte is not valid.
+/// 4. The implementation of `validate_byte_slice()` returns an error
+///    if the slice cannot be used to build a `Pattern<SinglePlaceholder, str>`
+///    in its entirety.
+/// 5. The implementation of `from_byte_slice_unchecked()` returns a reference to the same data.
+/// 6. `parse_byte_slice()` is equivalent to `validate_byte_slice()` followed by `from_byte_slice_unchecked()`.
+/// 7. `str` byte equality is semantic equality.
+unsafe impl VarULE for Pattern<SinglePlaceholder, str> {
+    fn validate_byte_slice(bytes: &[u8]) -> Result<(), ZeroVecError> {
+        SinglePlaceholderPattern::try_from_utf8_store(bytes)
+            .map_err(|_| ZeroVecError::VarZeroVecFormatError)?;
+        Ok(())
+    }
+
+    unsafe fn from_byte_slice_unchecked(bytes: &[u8]) -> &Self {
+        // SAFETY: As `validate_byte_slice` succeeded, `try_from_utf8_store` succeeded, which implies valid UTF-8
+        let store = core::str::from_utf8_unchecked(bytes);
+
+        // SAFETY: As `validate_byte_slice` succeeded, `try_from_utf8_store` also succeeded
+        SinglePlaceholderPattern::from_borrowed_store_unchecked(store)
+    }
+}

utils/pattern/src/lib.rs

@@ -55,6 +55,8 @@ mod common;
 mod double;
 mod error;
 mod frontend;
+#[cfg(all(feature = "zerovec", feature = "alloc"))]
+mod implementations;
 mod multi_named;
 #[cfg(feature = "alloc")]
 mod parser;