added ability to limit the max number of disjunction clauses

set DisjunctionMaxClauseCount to a non-zero value to enforce
the limit

search/searchers/search_disjunction.go

@@ -10,6 +10,7 @@
 package searchers
 
 import (
+	"fmt"
 	"math"
 	"sort"
 
@@ -18,6 +19,11 @@ import (
 	"github.com/blevesearch/bleve/search/scorers"
 )
 
+// DisjunctionMaxClauseCount is a compile time setting that applications can
+// adjust to non-zero value to cause the DisjunctionSearcher to return an
+// error instead of exeucting searches when the size exceeds this value.
+var DisjunctionMaxClauseCount = 0
+
 type DisjunctionSearcher struct {
 	initialized bool
 	indexReader index.IndexReader
@@ -30,6 +36,9 @@ type DisjunctionSearcher struct {
 }
 
 func NewDisjunctionSearcher(indexReader index.IndexReader, qsearchers []search.Searcher, min float64, explain bool) (*DisjunctionSearcher, error) {
+	if DisjunctionMaxClauseCount != 0 && len(qsearchers) > DisjunctionMaxClauseCount {
+		return nil, fmt.Errorf("TooManyClauses[maxClauseCount is set to %d]", DisjunctionMaxClauseCount)
+	}
 	// build the downstream searchers
 	searchers := make(OrderedSearcherList, len(qsearchers))
 	for i, searcher := range qsearchers {

search/searchers/search_disjunction_test.go

@@ -166,3 +166,41 @@ func TestDisjunctionAdvance(t *testing.T) {
 		t.Errorf("expected 3, got nil")
 	}
 }
+
+func TestDisjunctionSearchTooMany(t *testing.T) {
+
+	// set to max to a low non-zero value
+	DisjunctionMaxClauseCount = 2
+	defer func() {
+		// reset it after the test
+		DisjunctionMaxClauseCount = 0
+	}()
+
+	twoDocIndexReader, err := twoDocIndex.Reader()
+	if err != nil {
+		t.Error(err)
+	}
+	defer func() {
+		err := twoDocIndexReader.Close()
+		if err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	martyTermSearcher, err := NewTermSearcher(twoDocIndexReader, "marty", "name", 1.0, true)
+	if err != nil {
+		t.Fatal(err)
+	}
+	dustinTermSearcher, err := NewTermSearcher(twoDocIndexReader, "dustin", "name", 1.0, true)
+	if err != nil {
+		t.Fatal(err)
+	}
+	steveTermSearcher, err := NewTermSearcher(twoDocIndexReader, "steve", "name", 1.0, true)
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, err = NewDisjunctionSearcher(twoDocIndexReader, []search.Searcher{martyTermSearcher, dustinTermSearcher, steveTermSearcher}, 0, true)
+	if err == nil {
+		t.Fatal(err)
+	}
+}