refactor(rust): Refactor Schema to use generic struct from new `pol…

…ars-schema` crate (#18539)

Cargo.toml

@@ -53,7 +53,7 @@ flate2 = { version = "1", default-features = false }
 futures = "0.3.25"
 hashbrown = { version = "0.14", features = ["rayon", "ahash", "serde"] }
 hex = "0.4.3"
-indexmap = { version = "2", features = ["std"] }
+indexmap = { version = "2", features = ["std", "serde"] }
 itoa = "1.0.6"
 itoap = { version = "1", features = ["simd"] }
 libc = "0.2"
@@ -112,6 +112,7 @@ polars-pipe = { version = "0.42.0", path = "crates/polars-pipe", default-feature
 polars-plan = { version = "0.42.0", path = "crates/polars-plan", default-features = false }
 polars-python = { version = "0.42.0", path = "crates/polars-python", default-features = false }
 polars-row = { version = "0.42.0", path = "crates/polars-row", default-features = false }
+polars-schema = { version = "0.42.0", path = "crates/polars-schema", default-features = false }
 polars-sql = { version = "0.42.0", path = "crates/polars-sql", default-features = false }
 polars-stream = { version = "0.42.0", path = "crates/polars-stream", default-features = false }
 polars-time = { version = "0.42.0", path = "crates/polars-time", default-features = false }

crates/polars-core/Cargo.toml

@@ -12,6 +12,7 @@ description = "Core of the Polars DataFrame library"
 polars-compute = { workspace = true }
 polars-error = { workspace = true }
 polars-row = { workspace = true }
+polars-schema = { workspace = true }
 polars-utils = { workspace = true }
 
 ahash = { workspace = true }
@@ -116,7 +117,7 @@ dtype-struct = []
 bigidx = ["arrow/bigidx", "polars-utils/bigidx"]
 python = []
 
-serde = ["dep:serde", "bitflags/serde"]
+serde = ["dep:serde", "bitflags/serde", "polars-schema/serde"]
 serde-lazy = ["serde", "arrow/serde", "indexmap/serde", "chrono/serde"]
 
 docs-selection = [

crates/polars-core/src/datatypes/field.rs

@@ -13,6 +13,12 @@ pub struct Field {
     pub dtype: DataType,
 }
 
+impl From<Field> for (PlSmallStr, DataType) {
+    fn from(value: Field) -> Self {
+        (value.name, value.dtype)
+    }
+}
+
 pub type FieldRef = Arc<Field>;
 
 impl Field {

crates/polars-core/src/frame/mod.rs

@@ -539,7 +539,10 @@ impl DataFrame {
     /// # Ok::<(), PolarsError>(())
     /// ```
     pub fn schema(&self) -> Schema {
-        self.columns.as_slice().into()
+        self.columns
+            .iter()
+            .map(|x| (x.name().clone(), x.dtype().clone()))
+            .collect()
     }
 
     /// Get a reference to the [`DataFrame`] columns.