Added support for SQLite's IS and IS NOT

CHANGELOG.md

@@ -58,6 +58,8 @@ for Rust libraries in [RFC #1105](https://github.com/rust-lang/rfcs/blob/master/
 
 * Added ability to create custom collation functions in SQLite.
 
+* Added support for SQLite's `IS` and `IS NOT`.
+
 ### Removed
 
 * All previously deprecated items have been removed.

diesel/src/expression/helper_types.rs

@@ -119,3 +119,7 @@ pub use super::functions::helper_types::*;
 #[doc(inline)]
 #[cfg(feature = "postgres")]
 pub use crate::pg::expression::helper_types::*;
+
+#[doc(inline)]
+#[cfg(feature = "sqlite")]
+pub use crate::sqlite::expression::helper_types::*;

diesel/src/expression_methods/mod.rs

@@ -24,3 +24,7 @@ pub use self::text_expression_methods::TextExpressionMethods;
 #[cfg(feature = "postgres")]
 #[doc(inline)]
 pub use crate::pg::expression::expression_methods::*;
+
+#[cfg(feature = "sqlite")]
+#[doc(inline)]
+pub use crate::sqlite::expression::expression_methods::*;

diesel/src/sqlite/expression/expression_methods.rs

@@ -0,0 +1,72 @@
+//! Sqlite specific expression methods.
+
+use super::operators::*;
+use crate::dsl;
+use crate::expression::grouped::Grouped;
+use crate::expression::{AsExpression, Expression};
+use crate::sql_types::SqlType;
+
+/// Sqlite specific methods which are present on all expressions.
+pub trait SqliteExpressionMethods: Expression + Sized {
+    /// Creates a Sqlite `IS` expression.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// # include!("../../doctest_setup.rs");
+    /// #
+    /// # fn main() {
+    /// #     run_test().unwrap();
+    /// # }
+    /// #
+    /// # fn run_test() -> QueryResult<()> {
+    /// #     use schema::animals::dsl::*;
+    /// #     let connection = establish_connection();
+    /// let jack_is_a_dog = animals
+    ///     .select(name)
+    ///     .filter(species.is("dog"))
+    ///     .get_results::<Option<String>>(&connection)?;
+    /// assert_eq!(vec![Some("Jack".to_string())], jack_is_a_dog);
+    /// #     Ok(())
+    /// # }
+    /// ```
+    fn is<T>(self, other: T) -> dsl::Is<Self, T>
+    where
+        Self::SqlType: SqlType,
+        T: AsExpression<Self::SqlType>,
+    {
+        Grouped(Is::new(self, other.as_expression()))
+    }
+
+    /// Creates a Sqlite `IS NOT` expression.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// # include!("../../doctest_setup.rs");
+    /// #
+    /// # fn main() {
+    /// #     run_test().unwrap();
+    /// # }
+    /// #
+    /// # fn run_test() -> QueryResult<()> {
+    /// #     use schema::animals::dsl::*;
+    /// #     let connection = establish_connection();
+    /// let jack_is_not_a_spider = animals
+    ///     .select(name)
+    ///     .filter(species.is_not("spider"))
+    ///     .get_results::<Option<String>>(&connection)?;
+    /// assert_eq!(vec![Some("Jack".to_string())], jack_is_not_a_spider);
+    /// #     Ok(())
+    /// # }
+    /// ```
+    fn is_not<T>(self, other: T) -> dsl::IsNot<Self, T>
+    where
+        Self::SqlType: SqlType,
+        T: AsExpression<Self::SqlType>,
+    {
+        Grouped(IsNot::new(self, other.as_expression()))
+    }
+}
+
+impl<T: Expression> SqliteExpressionMethods for T {}

diesel/src/sqlite/expression/helper_types.rs

@@ -0,0 +1,8 @@
+use crate::dsl::AsExpr;
+use crate::expression::grouped::Grouped;
+
+/// The return type of `lhs.is(rhs)`.
+pub type Is<Lhs, Rhs> = Grouped<super::operators::Is<Lhs, AsExpr<Rhs, Lhs>>>;
+
+/// The return type of `lhs.is_not(rhs)`.
+pub type IsNot<Lhs, Rhs> = Grouped<super::operators::IsNot<Lhs, AsExpr<Rhs, Lhs>>>;

diesel/src/sqlite/expression/mod.rs

@@ -0,0 +1,11 @@
+//! Sqlite related query builder extensions.
+//!
+//! Everything in this module is re-exported from database agnostic locations.
+//! You should rely on the re-exports rather than this module directly. It is
+//! kept separate purely for documentation purposes.
+
+pub(crate) mod expression_methods;
+#[doc(hidden)]
+pub mod helper_types;
+#[doc(hidden)]
+pub mod operators;

diesel/src/sqlite/expression/operators.rs

@@ -0,0 +1,5 @@
+use crate::sql_types::Bool;
+use crate::sqlite::Sqlite;
+
+__diesel_infix_operator!(Is, " IS ", ConstantNullability Bool, backend: Sqlite);
+__diesel_infix_operator!(IsNot, " IS NOT ", ConstantNullability Bool, backend: Sqlite);

diesel/src/sqlite/mod.rs

@@ -6,6 +6,7 @@
 
 mod backend;
 mod connection;
+pub(crate) mod expression;
 mod types;
 
 pub mod query_builder;