implement array_dims

diesel/src/pg/expression/functions.rs

@@ -748,3 +748,34 @@ define_sql_function! {
     /// ```
     fn array_append<Arr: ArrayOrNullableArray<Inner=T> + SingleValue, T: SingleValue>(a: Arr, e: T) -> Array<T>;
 }
+
+#[cfg(feature = "postgres_backend")]
+define_sql_function! {
+    /// Returns a text representation of the array's dimensions
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// # include!("../../doctest_setup.rs");
+    /// #
+    /// # fn main(){
+    /// #    run_test().unwrap();
+    /// # }
+    /// # fn run_test()->QueryResult<()>{
+    /// #   use diesel::dsl::array_dims;
+    /// #   use diesel::sql_types::{Nullable,Array,Integer};
+    /// #   let connection = &mut establish_connection();
+    ///
+    /// let dims = diesel::select(array_dims::<Array<_>,_,_>(vec![1,2]))
+    ///     .get_result::<String>(connection).unwrap();
+    /// assert!(String::from("[1:2]").eq(&dims));
+    ///
+    /// let dims = diesel::select(array_dims::<Array<_>,_,_>(vec![vec![1,2,3],vec![4,5,6]]))
+    /// .get_result::<String>(connection).unwrap();
+    /// assert!(String::from("[1:2][1:3]").eq(&dims));
+    ///
+    /// # Ok(())
+    /// # }
+    ///
+    fn array_dims<Arr:ArrayOrNullableArray<Inner=T> + SingleValue,T:SingleValue>(arr:Arr) -> Text;
+}

diesel/src/pg/expression/helper_types.rs

@@ -352,3 +352,8 @@ pub type range_merge<R1, R2> = super::functions::range_merge<SqlTypeOf<R1>, SqlT
 #[allow(non_camel_case_types)]
 #[cfg(feature = "postgres_backend")]
 pub type array_append<A, E> = super::functions::array_append<SqlTypeOf<A>, SqlTypeOf<E>, A, E>;
+
+/// Return type of [`array_dims(array)`](super::functions::array_append())
+#[allow(non_camel_case_types)]
+#[cfg(feature = "postgres_backend")]
+pub type array_dims<A,T> = super::functions::array_dims<SqlTypeOf<A>,SqlTypeOf<T>, A>;

diesel_derives/tests/auto_type.rs

@@ -411,6 +411,7 @@ fn postgres_functions() -> _ {
             bound,
         ),
         array_append(pg_extras::array, pg_extras::id),
+        array_dims(pg_extras::array)
     )
 }