Merge remote-tracking branch 'upstream/master' into 503-hover-doc-links

1 files changed, 48 insertions, 0 deletions

diff --git a/crates/base_db/src/cancellation.rs b/crates/base_db/src/cancellation.rs
new file mode 100644
index 000000000..7420a1976
--- /dev/null
+++ b/crates/base_db/src/cancellation.rs
@@ -0,0 +1,48 @@
+//! Utility types to support cancellation.
+//!
+//! In a typical IDE use-case, requests and modification happen concurrently, as
+//! in the following scenario:
+//!
+//!   * user types a character,
+//!   * a syntax highlighting process is started
+//!   * user types next character, while syntax highlighting *is still in
+//!     progress*.
+//!
+//! In this situation, we want to react to modification as quickly as possible.
+//! At the same time, in-progress results are not very interesting, because they
+//! are invalidated by the edit anyway. So, we first cancel all in-flight
+//! requests, and then apply modification knowing that it won't interfere with
+//! any background processing (this bit is handled by salsa, see the
+//! `BaseDatabase::check_canceled` method).
+
+/// An "error" signifying that the operation was canceled.
+#[derive(Clone, PartialEq, Eq, Hash)]
+pub struct Canceled {
+    _private: (),
+}
+
+impl Canceled {
+    pub(crate) fn new() -> Canceled {
+        Canceled { _private: () }
+    }
+
+    pub fn throw() -> ! {
+        // We use resume and not panic here to avoid running the panic
+        // hook (that is, to avoid collecting and printing backtrace).
+        std::panic::resume_unwind(Box::new(Canceled::new()))
+    }
+}
+
+impl std::fmt::Display for Canceled {
+    fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        fmt.write_str("canceled")
+    }
+}
+
+impl std::fmt::Debug for Canceled {
+    fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(fmt, "Canceled")
+    }
+}
+
+impl std::error::Error for Canceled {}