Fix gocognit output for generic receivers with multiple type params

When the receiver type was a generic type with multiple type parameters, the
output of recvString was "BADRECV". This was happening because expression for
generic type of one param has different type than expression for generic type
with multiple params.

gocognit.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"go/ast"
 	"go/token"
+	"strings"
 
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/passes/inspect"
@@ -59,6 +60,13 @@ func recvString(recv ast.Expr) string {
 		return "*" + recvString(t.X)
 	case *ast.IndexExpr:
 		return recvString(t.X) + "[" + recvString(t.Index) + "]"
+	case *ast.IndexListExpr:
+		targs := make([]string, 0, len(t.Indices))
+		for _, exp := range t.Indices {
+			targs = append(targs, recvString(exp))
+		}
+
+		return recvString(t.X) + "[" + strings.Join(targs, ", ") + "]"
 	}
 	return "BADRECV"
 }