Print Go call tree

Question

Given a file like this:

package main

func A() {}

func B() {
   A()
}

func C() {
   A()
}

func D() {
   B()
}

func E() {
   B()
}

func F() {
   C()
}

func G() {
   C()
}

func main() {
   D()
   E()
   F()
   G()
}

I would like to print a call tree of the program, something like this:

main
   D
      B
         A
   E
      B
         A
   F
      C
         A
   G
      C
         A

I found the callgraph program [1], but it does not create a tree:

PS C:\prog> callgraph .
prog.A  --static-4:5--> prog.C
prog.A  --static-5:5--> prog.D
prog.main       --static-19:5-->        prog.A
prog.B  --static-9:5--> prog.E
prog.B  --static-10:5-->        prog.F
prog.main       --static-20:5-->        prog.B

Is some method available to do this?

1. https://github.com/golang/tools/blob/master/cmd/callgraph

Answer 1

So I did find a package that seems to handle printing a tree from a graph on the command line [1]. However I thought about it some more, and a printed tree might not be the best solution to my issue. What I want to do, is return an error from one of my functions. However to do that, I need to propagate the error all the way up to main. As this can be several layers, I thought it would be best if I start from main, and work my way down to the desired function. That way, I can the work in stages if need be. The issue is, how do I get an ordered list of these functions? I found a solution with tsort [2]:

PS C:\> callgraph -format digraph . | coreutils tsort
"init/test.main"
"init/test.D"
"init/test.E"
"init/test.F"
"init/test.G"
"init/test.B"
"init/test.C"
"init/test.A"

but I may not always want the entire call graph. Next I thought about just adding a panic:

func A() {
   panic(1)
}

but this will not give you all branches, only the first path to the target function:

main.A(...)
        C:/test.go:4
main.B(...)
        C:/test.go:8
main.D(...)
        C:/test.go:16
main.main()
        C:/test.go:32 +0x45

Finally I wrote my own sort function, that takes arbitrary destination as input, and prints all paths in order from main to the target function:

package main

func tsort(graph map[string][]string, end string) []string {
   var (
      b = make(map[string]bool)
      l []string
      s = []string{end}
   )
   for len(s) > 0 {
      n := s[len(s) - 1]
      b[n] = true
      for _, m := range graph[n] {
         if ! b[m] {
            s = append(s, m)
         }
      }
      if s[len(s) - 1] == n {
         s = s[:len(s) - 1]
         l = append(l, n)
      }
   }
   return l
}

Example:

package main

import (
   "bytes"
   "fmt"
   "os/exec"
)

func main() {
   b := new(bytes.Buffer)
   c := exec.Command("callgraph", "-format", "digraph", ".")
   c.Stdout = b
   c.Run()
   m := make(map[string][]string)
   for {
      var parent, child string
      _, e := fmt.Fscanln(b, &parent, &child)
      if e != nil { break }
      m[child] = append(m[child], parent)
   }
   for n, s := range tsort(m, `"init/test.A"`) {
      fmt.Print(n+1, ". ", s, "\n")
   }
}

Result:

1. "init/test.main"
2. "init/test.G"
3. "init/test.F"
4. "init/test.C"
5. "init/test.D"
6. "init/test.E"
7. "init/test.B"
8. "init/test.A"

1. https://github.com/soniakeys/graph/blob/master/treevis/treevis.go
2. https://github.com/uutils/coreutils