Add DisplayWithDb

components/salsa-2022/src/display.rs

@@ -0,0 +1,27 @@
+use std::fmt::{self, Display, Formatter};
+
+pub trait DisplayWithDb<'db, DB: ?Sized + 'db> {
+    fn fmt_with(&self, db: &DB, f: &mut Formatter<'_>) -> fmt::Result;
+
+    fn display_with(&self, db: &DB) -> impl Display {
+        FormatterFn(|f| self.fmt_with(db, f))
+    }
+
+    fn to_string_with(&self, db: &DB) -> String {
+        self.display_with(db).to_string()
+    }
+}
+
+// TODO: replace with `[std::fmt::FormatterFn]` when it becomes stable
+struct FormatterFn<F>(pub F)
+where
+    F: Fn(&mut fmt::Formatter<'_>) -> fmt::Result;
+
+impl<F> Display for FormatterFn<F>
+where
+    F: Fn(&mut fmt::Formatter<'_>) -> fmt::Result,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (self.0)(f)
+    }
+}

components/salsa-2022/src/lib.rs

@@ -3,6 +3,7 @@ pub mod cancelled;
 pub mod cycle;
 pub mod database;
 pub mod debug;
+pub mod display;
 pub mod durability;
 pub mod event;
 pub mod function;
@@ -32,6 +33,7 @@ pub use self::database::ParallelDatabase;
 pub use self::database::Snapshot;
 pub use self::debug::DebugWith;
 pub use self::debug::DebugWithDb;
+pub use self::display::DisplayWithDb;
 pub use self::durability::Durability;
 pub use self::event::Event;
 pub use self::event::EventKind;

salsa-2022-tests/tests/display.rs

@@ -0,0 +1,76 @@
+//! Test that `DisplayWithDb` works correctly
+
+use std::fmt::Display;
+
+use expect_test::expect;
+use salsa::DisplayWithDb;
+
+#[salsa::jar(db = Db)]
+struct Jar(MyInput, ComplexStruct);
+
+trait Db: salsa::DbWithJar<Jar> {}
+
+#[salsa::input]
+struct MyInput {
+    field: u32,
+}
+
+impl<'db> DisplayWithDb<'db, dyn Db + 'db> for MyInput {
+    fn fmt_with(&self, db: &dyn Db, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "MyInput({})", self.field(db))
+    }
+}
+
+#[derive(Debug, Eq, PartialEq, Clone)]
+struct NotSalsa {
+    field: String,
+}
+
+impl Display for NotSalsa {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "NotSalsa({})", self.field)
+    }
+}
+
+#[salsa::input]
+struct ComplexStruct {
+    my_input: MyInput,
+    not_salsa: NotSalsa,
+}
+
+impl<'db> DisplayWithDb<'db, dyn Db + 'db> for ComplexStruct {
+    fn fmt_with(&self, db: &dyn Db, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(
+            f,
+            "ComplexStruct {{ {}, {} }}",
+            self.my_input(db).display_with(db),
+            self.not_salsa(db)
+        )
+    }
+}
+
+#[salsa::db(Jar)]
+#[derive(Default)]
+struct Database {
+    storage: salsa::Storage<Self>,
+}
+
+impl salsa::Database for Database {}
+
+impl Db for Database {}
+
+#[test]
+fn input() {
+    let db = Database::default();
+
+    let input = MyInput::new(&db, 22);
+    let not_salsa = NotSalsa {
+        field: "it's salsa time".to_string(),
+    };
+    let complex_struct = ComplexStruct::new(&db, input, not_salsa);
+
+    // all fields
+    let actual = format!("{}", complex_struct.display_with(&db));
+    let expected = expect!["ComplexStruct { MyInput(22), NotSalsa(it's salsa time) }"];
+    expected.assert_eq(&actual);
+}