Add some more documentation about some function calls

diesel_derives/src/lib.rs

@@ -1631,7 +1631,7 @@ pub fn table_proc(input: TokenStream) -> TokenStream {
 ///
 /// Support for additional types can be added by providing manual implementations of
 /// `HasSqlType`, `FromSql` and `ToSql` for the corresponding type, all databases included
-/// in your enum, and the backend generated by this derive called MultiBackend.
+/// in your enum, and the backend generated by this derive called `MultiBackend`.
 /// For example to support `diesel::sql_types::TimestamptzSqlite` with the `time` crate:
 /// ```
 /// # #[cfg(all(feature = "sqlite", feature = "time"))]
@@ -1646,20 +1646,26 @@ pub fn table_proc(input: TokenStream) -> TokenStream {
 ///     Sqlite(diesel::SqliteConnection),
 /// }
 ///
+/// // The `MultiBackend` type is generated by `#[derive(diesel::MultiConnection)]`
 /// impl HasSqlType<diesel::sql_types::TimestamptzSqlite> for MultiBackend {
 ///    fn metadata(lookup: &mut Self::MetadataLookup) -> Self::TypeMetadata {
+///        // The `lookup_sql_type` function is exposed by the `MultiBackend` type
 ///        MultiBackend::lookup_sql_type::<diesel::sql_types::TimestamptzSqlite>(lookup)
 ///    }
 /// }
 ///
 /// impl FromSql<diesel::sql_types::TimestamptzSqlite, MultiBackend> for time::OffsetDateTime {
 ///    fn from_sql(bytes: <MultiBackend as Backend>::RawValue<'_>) -> deserialize::Result<Self> {
+///        // The `from_sql` function is exposed by the `RawValue` type of the
+///        // `MultiBackend` type
 ///        bytes.from_sql::<time::OffsetDateTime, diesel::sql_types::TimestamptzSqlite>()
 ///    }
 /// }
 ///
 /// impl ToSql<diesel::sql_types::TimestamptzSqlite, MultiBackend> for time::OffsetDateTime {
 ///    fn to_sql<'b>(&'b self, out: &mut serialize::Output<'b, '_, MultiBackend>) -> serialize::Result {
+///        /// `set_value` expects a tuple consisting of the target SQL type
+///        /// and self for `MultiBackend`
 ///        out.set_value((diesel::sql_types::TimestamptzSqlite, self));
 ///        Ok(IsNull::No)
 ///    }