Fix #4710: Return empty slice instead of nil in getTableAndConnectionSuggestions (#4734)

pkg/interactive/interactive_client.go

@@ -647,6 +647,9 @@ func (c *InteractiveClient) getTableAndConnectionSuggestions(word string) []prom
 
 	connection := strings.TrimSpace(parts[0])
 	t := c.suggestions.tablesBySchema[connection]
+	if t == nil {
+		return []prompt.Suggest{}
+	}
 	return t
 }
 

pkg/interactive/interactive_client_test.go

@@ -0,0 +1,70 @@
+package interactive
+
+import (
+	"testing"
+
+	"github.com/c-bata/go-prompt"
+)
+
+// TestGetTableAndConnectionSuggestions_ReturnsEmptySliceNotNil tests that
+// getTableAndConnectionSuggestions returns an empty slice instead of nil
+// when no matching connection is found in the schema.
+//
+// This is important for proper API contract - functions that return slices
+// should return empty slices rather than nil to avoid unexpected nil pointer
+// issues in calling code.
+//
+// Bug: #4710
+// PR: #4734
+func TestGetTableAndConnectionSuggestions_ReturnsEmptySliceNotNil(t *testing.T) {
+	tests := []struct {
+		name     string
+		word     string
+		expected bool // true if we expect non-nil result
+	}{
+		{
+			name:     "empty word should return non-nil",
+			word:     "",
+			expected: true,
+		},
+		{
+			name:     "unqualified table should return non-nil",
+			word:     "table",
+			expected: true,
+		},
+		{
+			name:     "non-existent connection should return non-nil",
+			word:     "nonexistent.table",
+			expected: true,
+		},
+		{
+			name:     "qualified table with dot should return non-nil",
+			word:     "aws.instances",
+			expected: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Create a minimal InteractiveClient with empty suggestions
+			c := &InteractiveClient{
+				suggestions: &autoCompleteSuggestions{
+					schemas:          []prompt.Suggest{},
+					unqualifiedTables: []prompt.Suggest{},
+					tablesBySchema:    make(map[string][]prompt.Suggest),
+				},
+			}
+
+			result := c.getTableAndConnectionSuggestions(tt.word)
+
+			if tt.expected && result == nil {
+				t.Errorf("getTableAndConnectionSuggestions(%q) returned nil, expected non-nil empty slice", tt.word)
+			}
+
+			// Additional check: even if not nil, should be empty in these test cases
+			if result != nil && len(result) != 0 {
+				t.Errorf("getTableAndConnectionSuggestions(%q) returned non-empty slice %v, expected empty slice", tt.word, result)
+			}
+		})
+	}
+}