add WillIterateCycle event

src/event.rs

@@ -59,6 +59,13 @@ pub enum EventKind {
         database_key: DatabaseKeyIndex,
     },
 
+    WillIterateCycle {
+        /// The database-key for the cycle head. Implements `Debug`.
+        database_key: DatabaseKeyIndex,
+        iteration_count: u32,
+        fell_back: bool,
+    },
+
     /// Indicates that `unwind_if_cancelled` was called and salsa will check if
     /// the current revision has been cancelled.
     WillCheckCancellation,

src/function/execute.rs

@@ -123,6 +123,13 @@ where
                     if iteration_count > MAX_ITERATIONS {
                         panic!("{database_key_index:?}: execute: too many cycle iterations");
                     }
+                    db.salsa_event(&|| {
+                        Event::new(EventKind::WillIterateCycle {
+                            database_key: database_key_index,
+                            iteration_count,
+                            fell_back,
+                        })
+                    });
                     revisions
                         .cycle_heads
                         .update_iteration_count(database_key_index, iteration_count);

tests/common/mod.rs

@@ -128,6 +128,7 @@ impl Database for ExecuteValidateLoggerDatabase {
         let event = event();
         match event.kind {
             salsa::EventKind::WillExecute { .. }
+            | salsa::EventKind::WillIterateCycle { .. }
             | salsa::EventKind::DidValidateMemoizedValue { .. } => {
                 self.push_log(format!("salsa_event({:?})", event.kind));
             }

tests/cycle.rs

@@ -871,7 +871,7 @@ fn cycle_unchanged() {
     a.assert_value(&db, 59);
     b.assert_value(&db, 60);
 
-    db.assert_logs_len(4);
+    db.assert_logs_len(5);
 
     // next revision, we change only A, which is not part of the cycle and the cycle does not
     // depend on.
@@ -917,7 +917,7 @@ fn cycle_unchanged_nested() {
     a.assert_value(&db, 59);
     b.assert_value(&db, 60);
 
-    db.assert_logs_len(10);
+    db.assert_logs_len(13);
 
     // next revision, we change only A, which is not part of the cycle and the cycle does not
     // depend on.
@@ -984,7 +984,7 @@ fn cycle_unchanged_nested_intertwined() {
             e.assert_value(&db, 60);
         }
 
-        db.assert_logs_len(12 + i);
+        db.assert_logs_len(15 + i);
 
         // next revision, we change only A, which is not part of the cycle and the cycle does not
         // depend on.
@@ -1031,6 +1031,7 @@ fn repeat_provisional_query() {
             "salsa_event(WillExecute { database_key: min_iterate(Id(0)) })",
             "salsa_event(WillExecute { database_key: min_panic(Id(1)) })",
             "salsa_event(WillExecute { database_key: min_panic(Id(2)) })",
+            "salsa_event(WillIterateCycle { database_key: min_iterate(Id(0)), iteration_count: 1, fell_back: false })",
             "salsa_event(WillExecute { database_key: min_panic(Id(1)) })",
             "salsa_event(WillExecute { database_key: min_panic(Id(2)) })",
         ]"#]]);

tests/cycle_tracked.rs

@@ -163,6 +163,7 @@ fn main() {
             "WillExecute { database_key: cost_to_start(Id(401)) }",
             "WillCheckCancellation",
             "WillCheckCancellation",
+            "WillIterateCycle { database_key: cost_to_start(Id(403)), iteration_count: 1, fell_back: false }",
             "WillCheckCancellation",
             "WillCheckCancellation",
             "WillCheckCancellation",