fix: bound column name ref leak (#3646)

`duckdb_vx_expr_get_bound_column_ref_get_name` returns a heap allocated
string that needs to freed with `duckdb_free`.

---------

Signed-off-by: Alexander Droste <[email protected]>

Author: 0ax1

vortex-duckdb/src/duckdb/expr.rs

@@ -4,7 +4,7 @@ use std::ptr;
 
 use crate::cpp::duckdb_vx_expr_class;
 use crate::duckdb::{ScalarFunction, Value};
-use crate::{cpp, wrapper};
+use crate::{cpp, duckdb, wrapper};
 
 wrapper!(Expression, cpp::duckdb_vx_expr, cpp::duckdb_vx_destroy_expr);
 
@@ -30,8 +30,9 @@ impl Expression {
                 cpp::DUCKDB_VX_EXPR_CLASS::DUCKDB_VX_EXPR_CLASS_BOUND_COLUMN_REF => {
                     let ptr =
                         unsafe { cpp::duckdb_vx_expr_get_bound_column_ref_get_name(self.as_ptr()) };
+
                     ExpressionClass::BoundColumnRef(BoundColumnRef {
-                        name: unsafe { CStr::from_ptr(ptr) },
+                        name: duckdb::string::String::from_ptr(ptr),
                     })
                 }
                 cpp::DUCKDB_VX_EXPR_CLASS::DUCKDB_VX_EXPR_CLASS_BOUND_CONSTANT => {
@@ -133,7 +134,7 @@ impl Expression {
 }
 
 pub enum ExpressionClass<'a> {
-    BoundColumnRef(BoundColumnRef<'a>),
+    BoundColumnRef(BoundColumnRef),
     BoundConstant(BoundConstant),
     BoundComparison(BoundComparison),
     BoundConjunction(BoundConjunction<'a>),
@@ -142,8 +143,8 @@ pub enum ExpressionClass<'a> {
     BoundFunction(BoundFunction<'a>),
 }
 
-pub struct BoundColumnRef<'a> {
-    pub name: &'a CStr,
+pub struct BoundColumnRef {
+    pub name: duckdb::string::String,
 }
 
 pub struct BoundConstant {

vortex-duckdb/src/duckdb/mod.rs

@@ -7,6 +7,7 @@ mod logical_type;
 mod query_result;
 mod scalar_function;
 mod selection_vector;
+mod string;
 mod table_filter;
 mod table_function;
 mod value;
@@ -24,6 +25,7 @@ pub use logical_type::*;
 pub use query_result::*;
 pub use scalar_function::*;
 pub use selection_vector::*;
+pub use string::*;
 pub use table_filter::*;
 pub use table_function::*;
 pub use value::*;

vortex-duckdb/src/duckdb/string.rs

@@ -0,0 +1,42 @@
+use std::ffi::{CStr, c_char};
+use std::fmt::{Debug, Display, Formatter};
+use std::str::Utf8Error;
+
+use crate::cpp;
+
+/// Wraps a heap allocated DuckDB string.
+pub struct String {
+    ptr: *const c_char,
+}
+
+impl String {
+    pub fn from_ptr(ptr: *const c_char) -> Self {
+        String { ptr }
+    }
+
+    pub fn as_cstr(&self) -> &CStr {
+        unsafe { CStr::from_ptr(self.ptr) }
+    }
+
+    pub fn to_str(&self) -> Result<&str, Utf8Error> {
+        self.as_cstr().to_str()
+    }
+}
+
+impl Debug for String {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{:?}", self.as_cstr())
+    }
+}
+
+impl Display for String {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.as_cstr().to_string_lossy())
+    }
+}
+
+impl Drop for String {
+    fn drop(&mut self) {
+        unsafe { cpp::duckdb_free(self.ptr.cast_mut().cast()) };
+    }
+}