vendor/github.com/google/go-cmp/cmp/report.go

// Copyright 2017, The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE.md file.

package cmp

// defaultReporter implements the reporter interface.
//
// As Equal serially calls the PushStep, Report, and PopStep methods, the
// defaultReporter constructs a tree-based representation of the compared value
// and the result of each comparison (see valueNode).
//
// When the String method is called, the FormatDiff method transforms the
// valueNode tree into a textNode tree, which is a tree-based representation
// of the textual output (see textNode).
//
// Lastly, the textNode.String method produces the final report as a string.
type defaultReporter struct {
	root *valueNode
	curr *valueNode
}

func (r *defaultReporter) PushStep(ps PathStep) {
	r.curr = r.curr.PushStep(ps)
	if r.root == nil {
		r.root = r.curr
	}
}
func (r *defaultReporter) Report(rs Result) {
	r.curr.Report(rs)
}
func (r *defaultReporter) PopStep() {
	r.curr = r.curr.PopStep()
}

// String provides a full report of the differences detected as a structured
// literal in pseudo-Go syntax. String may only be called after the entire tree
// has been traversed.
func (r *defaultReporter) String() string {
	assert(r.root != nil && r.curr == nil)
	if r.root.NumDiff == 0 {
		return ""
	}
	return formatOptions{}.FormatDiff(r.root).String()
}

func assert(ok bool) {
	if !ok {
		panic("assertion failure")
	}
}