testing/quick: probabilistically generate nil pointers

The documentation for quick.Value says that it "returns an arbitrary
value of the given type." In spite of this, nil values for pointers were
never generated, which seems more like an oversight than an intentional
choice.

The lack of nil values meant that testing recursive type like

  type Node struct {
  	Next *Node
  }

with testing/quick would lead to a stack overflow since the data
structure would never terminate.

This change may break tests that don't check for nil with pointers
returned from quick.Value. Two such instances were found in the standard
library, one of which was in the testing/quick package itself.

Fixes #8818.

Change-Id: Id390dcce649d12fbbaa801ce6f58f5defed77e60
Reviewed-on: https://go-review.googlesource.com/10821
Reviewed-by: Adam Langley <agl@golang.org>
Run-TryBot: Adam Langley <agl@golang.org>

diff --git a/src/encoding/pem/pem_test.go b/src/encoding/pem/pem_test.go
index 1913f44c1fb74a731267532e4c5df68aa1752c9a..ab656c6261c4012a112b7a9e426d5e6589c41ae4 100644 (file)
--- a/src/encoding/pem/pem_test.go
+++ b/src/encoding/pem/pem_test.go
@@ -146,7 +146,7 @@ func TestLineBreaker(t *testing.T) {
 }
 
 func TestFuzz(t *testing.T) {
-       testRoundtrip := func(block *Block) bool {
+       testRoundtrip := func(block Block) bool {
                for key := range block.Headers {
                        if strings.Contains(key, ":") {
                                // Keys with colons cannot be encoded.
@@ -155,14 +155,14 @@ func TestFuzz(t *testing.T) {
                }
 
                var buf bytes.Buffer
-               err := Encode(&buf, block)
+               err := Encode(&buf, &block)
                decoded, rest := Decode(buf.Bytes())
 
                switch {
                case err != nil:
-                       t.Errorf("Encode of %#v resulted in error: %s", block, err)
-               case !reflect.DeepEqual(block, decoded):
-                       t.Errorf("Encode of %#v decoded as %#v", block, decoded)
+                       t.Errorf("Encode of %#v resulted in error: %s", &block, err)
+               case !reflect.DeepEqual(&block, decoded):
+                       t.Errorf("Encode of %#v decoded as %#v", &block, decoded)
                case len(rest) != 0:
                        t.Errorf("Encode of %#v decoded correctly, but with %x left over", block, rest)
                default:
@@ -172,7 +172,7 @@ func TestFuzz(t *testing.T) {
        }
 
        // Explicitly test the empty block.
-       if !testRoundtrip(&Block{
+       if !testRoundtrip(Block{
                Type:    "EMPTY",
                Headers: make(map[string]string),
                Bytes:   []byte{},

diff --git a/src/testing/quick/quick.go b/src/testing/quick/quick.go
index 35b7b636b4ea71a9eca5a42e533e1c365fc2a28c..0e36810eb62cc9762a844a43bf1f351ef1f689e8 100644 (file)
--- a/src/testing/quick/quick.go
+++ b/src/testing/quick/quick.go
@@ -102,12 +102,16 @@ func Value(t reflect.Type, rand *rand.Rand) (value reflect.Value, ok bool) {
                        v.SetMapIndex(key, value)
                }
        case reflect.Ptr:
-               elem, ok := Value(concrete.Elem(), rand)
-               if !ok {
-                       return reflect.Value{}, false
+               if rand.Intn(complexSize) == 0 {
+                       v.Set(reflect.Zero(concrete)) // Generate nil pointer.
+               } else {
+                       elem, ok := Value(concrete.Elem(), rand)
+                       if !ok {
+                               return reflect.Value{}, false
+                       }
+                       v.Set(reflect.New(concrete.Elem()))
+                       v.Elem().Set(elem)
                }
-               v.Set(reflect.New(concrete.Elem()))
-               v.Elem().Set(elem)
        case reflect.Slice:
                numElems := rand.Intn(complexSize)
                v.Set(reflect.MakeSlice(concrete, numElems, numElems))

diff --git a/src/testing/quick/quick_test.go b/src/testing/quick/quick_test.go
index 1b973027d5277dbb952b53b82eb457e5fb88584e..c79f30ea1dbee049ef71398d47ea4349526142c6 100644 (file)
--- a/src/testing/quick/quick_test.go
+++ b/src/testing/quick/quick_test.go
@@ -83,6 +83,9 @@ type TestMapAlias map[int]int
 func fMapAlias(a TestMapAlias) TestMapAlias { return a }
 
 func fPtr(a *int) *int {
+       if a == nil {
+               return nil
+       }
        b := *a
        return &b
 }
@@ -255,3 +258,17 @@ func TestFailure(t *testing.T) {
                t.Errorf("#3 Error was not a SetupError: %s", err)
        }
 }
+
+// The following test didn't terminate because nil pointers were not
+// generated.
+// Issue 8818.
+func TestNilPointers(t *testing.T) {
+       type Recursive struct {
+               Next *Recursive
+       }
+
+       f := func(rec Recursive) bool {
+               return true
+       }
+       Check(f, nil)
+}