fix: add support for negative enum values

Copilot review identified that negative values like -1 were being
incorrectly parsed as 0. Added UnaryExpr handling in processExplicitValue
to properly support negative number literals.

Also fixed test expectation for SQL NULL handling with Priority enum
where PriorityLow (0) is the zero value, not PriorityNone (-1).

Author: umputun

enum

@@ -249,6 +249,18 @@ func (g *Generator) processExplicitValue(expr ast.Expr, state *constParseState)
 			state.iotaOp = nil
 			return val
 		}
+	case *ast.UnaryExpr:
+		// handle negative numbers like -1
+		if e.Op == token.SUB {
+			if lit, ok := e.X.(*ast.BasicLit); ok {
+				if val, err := ConvertLiteralToInt(lit); err == nil {
+					state.lastExprType = exprTypePlain
+					state.lastValue = -val
+					state.iotaOp = nil
+					return -val
+				}
+			}
+		}
 	}
 	return 0
 }

internal/generator/generator.go

@@ -97,8 +97,8 @@ func TestGeneratedEnumWithSQL(t *testing.T) {
 	row = db.QueryRow("SELECT status, priority FROM records WHERE id = ?", 2)
 	err = row.Scan(&status, &priority)
 	require.NoError(t, err)
-	assert.Equal(t, StatusUnknown, status)  // zero value
-	assert.Equal(t, PriorityNone, priority) // zero value for priority (-1)
+	assert.Equal(t, StatusUnknown, status) // zero value
+	assert.Equal(t, PriorityLow, priority) // zero value for priority (0)
 }
 
 func TestGeneratedEnumWithYAML(t *testing.T) {