added postgres trim_array function

diesel/src/pg/expression/functions.rs

@@ -996,3 +996,45 @@ define_sql_function! {
     ///
     fn cardinality<Arr:ArrayOrNullableArray + SingleValue>(a: Arr) -> Nullable<Integer>;
 }
+
+#[cfg(feature = "postgres_backend")]
+define_sql_function! {
+    /// Trims an array by removing the last n elements. If the array is multidimensional, only the first dimension is trimmed.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// # include!("../../doctest_setup.rs");
+    /// #
+    /// # fn main(){
+    /// #    run_test().unwrap();
+    /// # }
+    /// # fn run_test()->QueryResult<()>{
+    /// #   use diesel::dsl::trim_array;
+    /// #   use diesel::sql_types::{Nullable,Array,Integer};
+    /// #   let connection = &mut establish_connection();
+    ///
+    /// let trimmed_array = diesel::select(trim_array::<Array<Integer>, _, _>(vec![1, 2, 3, 4], 3))
+    ///     .get_result::<Vec<i32>>(connection)?;
+    /// assert_eq!(vec![1], trimmed_array);
+    ///
+    /// let trimmed_array = diesel::select(trim_array::<Array<Nullable<Integer>>, _, _>(vec![Some(1), Some(2), Some(3)], 1))
+    ///     .get_result::<Vec<Option<i32>>>(connection)?;
+    /// assert_eq!(vec![Some(1), Some(2)], trimmed_array);
+    ///
+    /// let trimmed_array = diesel::select(trim_array::<Array<Integer>, _, _>(Vec::<i32>::new(), 0))
+    ///     .get_result::<Vec<i32>>(connection)?;
+    /// assert_eq!(Vec::<i32>::new(), trimmed_array);
+    ///
+    /// let trimmed_array = diesel::select(trim_array::<Nullable<Array<Integer>>, _, _>(None::<Vec<i32>>, 0))
+    ///     .get_result::<Option<Vec<i32>>>(connection)?;
+    /// assert_eq!(None, trimmed_array);
+    /// 
+    /// let trimmed_array = diesel::select(trim_array::<Nullable<Array<Integer>>, _, _>(None::<Vec<i32>>, 1))
+    ///     .get_result::<Option<Vec<i32>>>(connection)?;
+    /// assert_eq!(None, trimmed_array);
+    /// # Ok(())
+    /// # }
+    ///
+    fn trim_array<Arr:ArrayOrNullableArray + SingleValue>(a: Arr, n: Integer) -> Arr;
+}

diesel/src/pg/expression/helper_types.rs

@@ -403,3 +403,8 @@ pub type array_remove<A, E> = super::functions::array_remove<SqlTypeOf<A>, SqlTy
 #[allow(non_camel_case_types)]
 #[cfg(feature = "postgres_backend")]
 pub type cardinality<A> = super::functions::cardinality<SqlTypeOf<A>, A>;
+
+/// Return type of [`trim_array(array)`](super::functions::trim_array())
+#[allow(non_camel_case_types)]
+#[cfg(feature = "postgres_backend")]
+pub type trim_array<A, N> = super::functions::trim_array<SqlTypeOf<A>, A, N>;

diesel_derives/tests/auto_type.rs

@@ -421,6 +421,7 @@ fn postgres_functions() -> _ {
         array_to_string(pg_extras::array, pg_extras::name),
         array_to_string_with_null_string(pg_extras::array, pg_extras::name, pg_extras::name),
         cardinality(pg_extras::array),
+        trim_array(pg_extras::array, pg_extras::id),
     )
 }