pkg/search: fix dir search with logical not constraints

As demonstrated by the test case added in this commit, a
search panics if the DirConstraint contains a LogicalConstraint
with Op set to "not". This is because the isFileOrDirConstraint
function doesn't account for unset "B".

Change-Id: I111ace62486160254ba22ab1498de78cde2a5e9b

pkg/search/query.go

@@ -2063,6 +2063,9 @@ func (c *DirConstraint) checkValid() error {
 
 func (c *Constraint) isFileOrDirConstraint() bool {
 	if l := c.Logical; l != nil {
+		if l.Op == "not" {
+			return l.A.isFileOrDirConstraint() // l.B is nil
+		}
 		return l.A.isFileOrDirConstraint() && l.B.isFileOrDirConstraint()
 	}
 	return c.File != nil || c.Dir != nil

pkg/search/query_test.go

@@ -789,6 +789,48 @@ func TestQueryDirWithFileConstraint(t *testing.T) {
 	})
 }
 
+// find a dir that doesn't contain any text files
+func TestQueryDirWithLogicalNotConstraint(t *testing.T) {
+	testQuery(t, func(qt *queryTest) {
+		id := qt.id
+		fileRef1, _ := id.UploadFile("some-stuff.txt", "hello", time.Unix(123, 0))
+		qt.t.Logf("fileRef1 = %q", fileRef1)
+		fileRef2, _ := id.UploadFile("more-stuff.txt", "world", time.Unix(456, 0))
+		qt.t.Logf("fileRef2 = %q", fileRef2)
+		dirRef1 := id.UploadDir("somedir", []blob.Ref{fileRef1, fileRef2}, time.Unix(789, 0))
+		qt.t.Logf("dirRef1 = %q", dirRef1)
+		p1 := id.NewPlannedPermanode("1")
+		id.SetAttribute(p1, "camliContent", dirRef1.String())
+
+		fileRef3, _ := id.UploadFile("other-file", "hellooooo", time.Unix(101112, 0))
+		qt.t.Logf("fileRef3 = %q", fileRef3)
+		dirRef2 := id.UploadDir("anotherdir", []blob.Ref{fileRef3}, time.Unix(181112, 0))
+		qt.t.Logf("dirRef2 = %q", dirRef2)
+		p2 := id.NewPlannedPermanode("2")
+		id.SetAttribute(p2, "camliContent", dirRef2.String())
+
+		sq := &SearchQuery{
+			Constraint: &Constraint{
+				Dir: &DirConstraint{
+					Contains: &Constraint{
+						Logical: &LogicalConstraint{
+							A: &Constraint{
+								File: &FileConstraint{
+									FileName: &StringConstraint{
+										HasSuffix: ".txt",
+									},
+								},
+							},
+							Op: "not",
+						},
+					},
+				},
+			},
+		}
+		qt.wantRes(sq, dirRef2)
+	})
+}
+
 // find permanode with a dir that contains a certain file or dir
 func TestQueryDirWithFileOrDirConstraint(t *testing.T) {
 	testQuery(t, func(qt *queryTest) {