Graph from "main" callgraph.Node with depth control

[iNevd]

example: https://github.com/iNevd/go-callvis/commit/3aee0ac40d1a2b9e86993be5014958f0138d8f18

First, find the main function Node

    var newRoot *callgraph.Node
    for _, r := range cg.Nodes {
        if r.Func.Name() == "main" {
            newRoot = r
            break
        }
    }

Second, visit all the Node in depth-first order start from newRoot with set depth.

replace callgraph.GraphVisitEdges to GraphVisitNodeDFS

https://github.com/ofabry/go-callvis/blob/fbe7e9f07309d21b548a61ca04dda073234ec8d6/output.go#L132

func GraphVisitNodeDFS(maxDepth int, n *callgraph.Node, edge func(*callgraph.Edge) error) error {
  seen := make(map[*callgraph.Node]bool)
  var visit func(d int, n *callgraph.Node) error
  visit = func(d int, n *callgraph.Node) error {
      if maxDepth > 0 && d > maxDepth {
          return nil
      }
      if !seen[n] {
          seen[n] = true
          d += 1
          for _, e := range n.Out {
              if err := visit(d, e.Callee); err != nil {
                  return err
              }
              if err := edge(e); err != nil {
                  return err
              }
          }
      }
      return nil
  }
  for _, e := range n.Out {
      if err := visit(0, e.Callee); err != nil {
          return err
      }
      if err := edge(e); err != nil {
          return err
      }
  }
  return nil
}