refactor(rust): Migrate to hashbrown 0.15

Cargo.toml

@@ -51,7 +51,9 @@ fallible-streaming-iterator = "0.1.9"
 fast-float = { version = "0.2" }
 flate2 = { version = "1", default-features = false }
 futures = "0.3.25"
-hashbrown = { version = "=0.14.5", features = ["rayon", "ahash", "serde"] }
+hashbrown = { version = "0.15.0", features = ["rayon", "serde"] }
+# https://github.com/rust-lang/hashbrown/issues/564
+hashbrown_old_nightly_hack = { package = "hashbrown", version = "0.14.5", features = ["rayon", "serde"] }
 hex = "0.4.3"
 indexmap = { version = "2", features = ["std", "serde"] }
 itoa = "1.0.6"

crates/polars-core/Cargo.toml

@@ -25,6 +25,7 @@ chrono-tz = { workspace = true, optional = true }
 comfy-table = { version = "7.1.1", default-features = false, optional = true }
 either = { workspace = true }
 hashbrown = { workspace = true }
+hashbrown_old_nightly_hack = { workspace = true }
 indexmap = { workspace = true }
 ndarray = { workspace = true, optional = true }
 num-traits = { workspace = true }
@@ -48,7 +49,7 @@ version_check = { workspace = true }
 
 [features]
 simd = ["arrow/simd", "polars-compute/simd"]
-nightly = ["simd", "hashbrown/nightly", "polars-utils/nightly", "arrow/nightly"]
+nightly = ["simd", "hashbrown/nightly", "hashbrown_old_nightly_hack/nightly", "polars-utils/nightly", "arrow/nightly"]
 avx512 = []
 docs = []
 temporal = ["regex", "chrono", "polars-error/regex"]

crates/polars-core/src/chunked_array/builder/list/categorical.rs

@@ -1,3 +1,6 @@
+use hashbrown::hash_table::Entry;
+use hashbrown::HashTable;
+
 use super::*;
 
 pub fn create_categorical_chunked_listbuilder(
@@ -75,15 +78,12 @@ impl ListBuilderTrait for ListEnumCategoricalChunkedBuilder {
 
 struct ListLocalCategoricalChunkedBuilder {
     inner: ListPrimitiveChunkedBuilder<UInt32Type>,
-    idx_lookup: PlHashMap<KeyWrapper, ()>,
+    idx_lookup: HashTable<u32>,
     ordering: CategoricalOrdering,
     categories: MutablePlString,
     categories_hash: u128,
 }
 
-// Wrap u32 key to avoid incorrect usage of hashmap with custom lookup
-struct KeyWrapper(u32);
-
 impl ListLocalCategoricalChunkedBuilder {
     #[inline]
     pub fn get_hash_builder() -> PlRandomState {
@@ -104,10 +104,7 @@ impl ListLocalCategoricalChunkedBuilder {
                 values_capacity,
                 DataType::UInt32,
             ),
-            idx_lookup: PlHashMap::with_capacity_and_hasher(
-                capacity,
-                ListLocalCategoricalChunkedBuilder::get_hash_builder(),
-            ),
+            idx_lookup: HashTable::with_capacity(capacity),
             ordering,
             categories: MutablePlString::with_capacity(capacity),
             categories_hash: hash,
@@ -141,33 +138,24 @@ impl ListBuilderTrait for ListLocalCategoricalChunkedBuilder {
 
             // Custom hashing / equality functions for comparing the &str to the idx
             // SAFETY: index in hashmap are within bounds of categories
-            let r = unsafe {
-                self.idx_lookup.raw_table_mut().find_or_find_insert_slot(
+            unsafe {
+                let r = self.idx_lookup.entry(
                     hash_cat,
-                    |(k, _)| self.categories.value_unchecked(k.0 as usize) == cat,
-                    |(k, _): &(KeyWrapper, ())| {
-                        hash_builder.hash_one(self.categories.value_unchecked(k.0 as usize))
+                    |k| self.categories.value_unchecked(*k as usize) == cat,
+                    |k| hash_builder.hash_one(self.categories.value_unchecked(*k as usize)),
+                );
+
+                match r {
+                    Entry::Occupied(v) => {
+                        // SAFETY: bucket is initialized.
+                        idx_mapping.insert_unique_unchecked(idx as u32, *v.get());
+                    },
+                    Entry::Vacant(slot) => {
+                        idx_mapping.insert_unique_unchecked(idx as u32, len as u32);
+                        self.categories.push(Some(cat));
+                        slot.insert(len as u32);
                     },
-                )
-            };
-
-            match r {
-                Ok(v) => {
-                    // SAFETY: Bucket is initialized
-                    idx_mapping.insert_unique_unchecked(idx as u32, unsafe { v.as_ref().0 .0 });
-                },
-                Err(e) => {
-                    idx_mapping.insert_unique_unchecked(idx as u32, len as u32);
-                    self.categories.push(Some(cat));
-                    // SAFETY: No mutations in hashmap since find_or_find_insert_slot call
-                    unsafe {
-                        self.idx_lookup.raw_table_mut().insert_in_slot(
-                            hash_cat,
-                            e,
-                            (KeyWrapper(len as u32), ()),
-                        )
-                    };
-                },
+                }
             }
         }