Fix recursive anon_target promises

Summary: Before recursive promises wouldn't get traversed - so if you had a promise wrapping a promise, you wouldn't see the provider collection. Fix that.

Reviewed By: krallin

Differential Revision: D42076206

fbshipit-source-id: c517de06136b823090e6f8f0af4a72c1a986adf7

buck2_build_api/src/interpreter/rule_defs/provider/collection.rs

@@ -161,11 +161,7 @@ impl<'v, V: ValueLike<'v>> ProviderCollectionGen<V> {
         mut value: Value<'v>,
     ) -> anyhow::Result<SmallMap<Arc<ProviderId>, Value<'v>>> {
         // Sometimes we might have a resolved promise here, in which case see through that
-        if let Some(promise) = StarlarkPromise::from_value(value) {
-            if let Some(x) = promise.get() {
-                value = x;
-            }
-        }
+        value = StarlarkPromise::get_recursive(value);
 
         let list = match List::from_value(value) {
             Some(v) => v,

buck2_interpreter/src/starlark_promise.rs

@@ -108,6 +108,21 @@ impl<'v> StarlarkPromise<'v> {
         }
     }
 
+    /// A recursive version of [`StarlarkPromise::get`], which continues to see through
+    /// promises while they are resolved.
+    /// The returned value will either be an unresolved promise, or not a promise.
+    pub fn get_recursive(mut value: Value<'v>) -> Value<'v> {
+        while let Some(promise) = StarlarkPromise::from_value(value) {
+            if let Some(x) = promise.get() {
+                value = x;
+            } else {
+                // We have an unresolved promise, stop looping
+                break;
+            }
+        }
+        value
+    }
+
     fn apply(
         f: Value<'v>,
         x: Value<'v>,