Fix handling of panics in GetOrCreate

One could argue that the func passed in should never panic, but before this commit this could easily lead to deadlocks.

Author: bep

lazycache.go

@@ -1,6 +1,7 @@
 package lazycache
 
 import (
+	"fmt"
 	"sync"
 
 	"github.com/hashicorp/golang-lru/v2/simplelru"
@@ -121,19 +122,28 @@ func (c *Cache[K, V]) GetOrCreate(key K, create func(key K) (V, error)) (V, bool
 	c.lru.Add(key, w)
 	c.mu.Unlock()
 
-	// Create the  value with the lock released.
-	v, err := create(key)
-	w.err = err
-	w.value = v
-	w.found = err == nil
+	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
+			close(w.ready)
+
+			if err != nil {
+				v = c.zerov
+				c.Delete(key)
+			}
+		}()
+		// Create the  value with the lock released.
+		v, err = create(key)
 
-	close(w.ready)
+		return
+	}()
 
-	if err != nil {
-		c.Delete(key)
-		return c.zerov, false, err
-	}
-	return v, false, nil
+	return v, false, err
 }
 
 // Resize changes the cache size and returns the number of entries evicted.

lazycache_test.go

@@ -57,6 +57,24 @@ func TestCache(t *testing.T) {
 	c.Assert(func() { New[int, any](Options[int, any]{MaxEntries: -1}) }, qt.PanicMatches, "must provide a positive size")
 }
 
+func TestPanic(t *testing.T) {
+	c := qt.New(t)
+
+	cache := New(Options[int, any]{MaxEntries: 1000})
+	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")
+		})
+		c.Assert(err, qt.IsNotNil)
+		c.Assert(err, qt.ErrorMatches, "panic: failed2")
+	}
+}
+
 func TestDeleteFunc(t *testing.T) {
 	c := qt.New(t)