func runReachable()

in cmd/viewcore/main.go [619:701]
73 lines of code
15 McCabe index (conditional complexity)

func runReachable(cmd *cobra.Command, args []string) {
	_, c, err := readCore()
	if err != nil {
		exitf("%v\n", err)
	}
	n, err := strconv.ParseInt(args[0], 16, 64)
	if err != nil {
		exitf("can't parse %q as an object address\n", args[1])
	}
	a := core.Address(n)
	obj, _ := c.FindObject(a)
	if obj == 0 {
		exitf("can't find object at address %s\n", args[1])
	}

	// Breadth-first search backwards until we reach a root.
	type hop struct {
		i int64         // offset in "from" object (the key in the path map) where the pointer is
		x gocore.Object // the "to" object
		j int64         // the offset in the "to" object
	}
	depth := map[gocore.Object]int{}
	depth[obj] = 0
	q := []gocore.Object{obj}
	done := false
	for !done {
		if len(q) == 0 {
			panic("can't find a root that can reach the object")
		}
		y := q[0]
		q = q[1:]
		c.ForEachReversePtr(y, func(x gocore.Object, r *gocore.Root, i, j int64) bool {
			if r != nil {
				// found it.
				if r.Frame == nil {
					// Print global
					fmt.Printf("%s", r.Name)
				} else {
					// Print stack up to frame in question.
					var frames []*gocore.Frame
					for f := r.Frame.Parent(); f != nil; f = f.Parent() {
						frames = append(frames, f)
					}
					for k := len(frames) - 1; k >= 0; k-- {
						fmt.Printf("%s\n", frames[k].Func().Name())
					}
					// Print frame + variable in frame.
					fmt.Printf("%s.%s", r.Frame.Func().Name(), r.Name)
				}
				fmt.Printf("%s → \n", typeFieldName(r.Type, i))

				z := y
				for {
					fmt.Printf("%x %s", c.Addr(z), typeName(c, z))
					if z == obj {
						fmt.Println()
						break
					}
					// Find an edge out of z which goes to an object
					// closer to obj.
					c.ForEachPtr(z, func(i int64, w gocore.Object, j int64) bool {
						if d, ok := depth[w]; ok && d < depth[z] {
							fmt.Printf(" %s → %s", objField(c, z, i), objRegion(c, w, j))
							z = w
							return false
						}
						return true
					})
					fmt.Println()
				}
				done = true
				return false
			}
			if _, ok := depth[x]; ok {
				// we already found a shorter path to this object.
				return true
			}
			depth[x] = depth[y] + 1
			q = append(q, x)
			return true
		})
	}
}