Expose row columns for MySQL

This is my attempt to fix #181 .

I am not sure if you have the same implementation in mind so let me know if I am
on the right track.

I was not sure how to verify the column type in tests as I couldn't construct
`MySqlTypeInfo` due to `TypeId` being crate-private.

sqlx-core/src/mysql/row.rs

@@ -1,9 +1,10 @@
 use std::collections::HashMap;
 use std::sync::Arc;
+use std::vec::Vec;
 
 use crate::mysql::protocol;
 use crate::mysql::{MySql, MySqlValue};
-use crate::row::{ColumnIndex, Row};
+use crate::row::{Column, ColumnIndex, Row};
 
 pub struct MySqlRow<'c> {
     pub(super) row: protocol::Row<'c>,
@@ -35,6 +36,24 @@ impl<'c> Row<'c> for MySqlRow<'c> {
 
         Ok(value)
     }
+
+    fn columns(&self) -> Box<[Column<Self::Database>]> {
+        let mut columns = Vec::with_capacity(self.row.columns.len());
+        for (index, column_type) in self.row.columns.iter().enumerate() {
+            let name = self
+                .names
+                .iter()
+                .find(|(_name, name_index)| (**name_index as usize) == index)
+                .map(|(name, _)| name.as_ref());
+
+            columns.push(Column {
+                name,
+                type_info: Some(column_type),
+            });
+        }
+
+        columns.into_boxed_slice()
+    }
 }
 
 impl<'c> ColumnIndex<'c, MySqlRow<'c>> for usize {

sqlx-core/src/postgres/row.rs

@@ -5,7 +5,7 @@ use crate::postgres::protocol::{DataRow, TypeFormat};
 use crate::postgres::type_info::SharedStr;
 use crate::postgres::value::PgValue;
 use crate::postgres::{PgTypeInfo, Postgres};
-use crate::row::{ColumnIndex, Row};
+use crate::row::{self, ColumnIndex, Row};
 
 // A statement has 0 or more columns being returned from the database
 // For Postgres, each column has an OID and a format (binary or text)
@@ -68,6 +68,10 @@ impl<'c> Row<'c> for PgRow<'c> {
 
         Ok(value)
     }
+
+    fn columns(&self) -> Box<[row::Column<Self::Database>]> {
+        todo!()
+    }
 }
 
 impl<'c> ColumnIndex<'c, PgRow<'c>> for usize {

sqlx-core/src/row.rs

@@ -185,6 +185,9 @@ where
     ) -> crate::Result<<Self::Database as HasRawValue<'c>>::RawValue>
     where
         I: ColumnIndex<'c, Self>;
+
+    /// Get all columns.
+    fn columns(&self) -> Box<[Column<Self::Database>]>;
 }
 
 // Prevent users from implementing the `Row` trait.
@@ -235,6 +238,11 @@ where
     fn from_row(row: &R) -> crate::Result<Self>;
 }
 
+pub struct Column<'r, DB: Database> {
+    pub name: Option<&'r str>,
+    pub type_info: Option<&'r DB::TypeInfo>,
+}
+
 // Macros to help unify the internal implementations as a good chunk
 // is very similar
 

sqlx-core/src/sqlite/row.rs

@@ -1,4 +1,4 @@
-use crate::row::{ColumnIndex, Row};
+use crate::row::{Column, ColumnIndex, Row};
 use crate::sqlite::statement::Statement;
 use crate::sqlite::value::SqliteValue;
 use crate::sqlite::{Sqlite, SqliteConnection};
@@ -43,6 +43,10 @@ impl<'c> Row<'c> for SqliteRow<'c> {
             index: index.index(self)? as i32,
         })
     }
+
+    fn columns(&self) -> Box<[Column<Self::Database>]> {
+        todo!()
+    }
 }
 
 impl<'c> ColumnIndex<'c, SqliteRow<'c>> for usize {

tests/mysql.rs

@@ -1,5 +1,5 @@
 use futures::TryStreamExt;
-use sqlx::{mysql::MySqlQueryAs, Connection, Executor, MySql, MySqlPool};
+use sqlx::{mysql::MySqlQueryAs, Connection, Cursor, Executor, MySql, MySqlPool, Row};
 use sqlx_test::new;
 use std::time::Duration;
 
@@ -232,3 +232,37 @@ async fn test_fetch_one_and_ping() -> anyhow::Result<()> {
 
     Ok(())
 }
+
+#[cfg_attr(feature = "runtime-async-std", async_std::test)]
+#[cfg_attr(feature = "runtime-tokio", tokio::test)]
+async fn test_row_columns() -> anyhow::Result<()> {
+    let mut conn = new::<MySql>().await?;
+
+    let _ = conn
+        .execute(
+            r#"
+        CREATE TEMPORARY TABLE row_columns_test (
+            id int primary key auto_increment,
+            name text not null,
+            age int
+        );
+
+        INSERT INTO row_columns_test (name, age) VALUES ('James', 12);
+    "#,
+        )
+        .await?;
+
+    let mut cursor = conn.fetch("SELECT * FROM row_columns_test");
+    let row = cursor.next().await?.unwrap();
+    let columns = row.columns();
+
+    assert_eq!(columns.len(), 3);
+    assert_eq!(columns[0].name, Some("id"));
+    assert_eq!(columns[0].type_info.is_some(), true);
+    assert_eq!(columns[1].name, Some("name"));
+    assert_eq!(columns[1].type_info.is_some(), true);
+    assert_eq!(columns[2].name, Some("age"));
+    assert_eq!(columns[2].type_info.is_some(), true);
+
+    Ok(())
+}