Preserve panics in create

In 24e43a4 we fixed deadlocks when the passed create func panics, but we also converted any panic into a returned err.

Preserving the panic is in many situations useful.

Author: bep

lazycache.go

@@ -1,7 +1,6 @@
 package lazycache
 
 import (
-	"fmt"
 	"sync"
 
 	"github.com/hashicorp/golang-lru/v2/simplelru"
@@ -122,23 +121,24 @@ func (c *Cache[K, V]) GetOrCreate(key K, create func(key K) (V, error)) (V, bool
 	c.lru.Add(key, w)
 	c.mu.Unlock()
 
+	isPanic := true
+
 	v, err := func() (v V, err error) {
 		defer func() {
-			if r := recover(); r != nil {
-				err = fmt.Errorf("panic: %v", r)
-			}
 			w.err = err
 			w.value = v
-			w.found = err == nil
+			w.found = err == nil && !isPanic
 			close(w.ready)
 
-			if err != nil {
+			if err != nil || isPanic {
 				v = c.zerov
 				c.Delete(key)
 			}
 		}()
+
 		// Create the  value with the lock released.
 		v, err = create(key)
+		isPanic = false
 
 		return
 	}()

lazycache_test.go

@@ -61,17 +61,29 @@ func TestPanic(t *testing.T) {
 	c := qt.New(t)
 
 	cache := New(Options[int, any]{MaxEntries: 1000})
+	ep := &errorProducer{}
+
+	willPanic := func(i int) func() {
+		return func() {
+			cache.GetOrCreate(i, func(key int) (any, error) {
+				ep.Panic(i)
+				return nil, nil
+			})
+		}
+	}
+
 	for i := 0; i < 2; i++ {
-		_, _, err := cache.GetOrCreate(42, func(key int) (any, error) {
-			panic("failed1")
-		})
-		c.Assert(err, qt.IsNotNil)
-		c.Assert(err, qt.ErrorMatches, "panic: failed1")
-		_, _, err = cache.GetOrCreate(i, func(key int) (any, error) {
-			panic("failed2")
+		for j := 0; j < 2; j++ {
+			c.Assert(willPanic(i), qt.PanicMatches, fmt.Sprintf("failed-%d", i))
+		}
+	}
+
+	for i := 0; i < 2; i++ {
+		v, _, err := cache.GetOrCreate(i, func(key int) (any, error) {
+			return key + 2, nil
 		})
-		c.Assert(err, qt.IsNotNil)
-		c.Assert(err, qt.ErrorMatches, "panic: failed2")
+		c.Assert(err, qt.IsNil)
+		c.Assert(v, qt.Equals, i+2)
 	}
 }
 
@@ -461,3 +473,9 @@ func BenchmarkCacheParallel(b *testing.B) {
 		})
 	})
 }
+
+type errorProducer struct{}
+
+func (e *errorProducer) Panic(i int) {
+	panic(fmt.Sprintf("failed-%d", i))
+}