From 15f90ba1f0694f5b9b27358c6ef53ae332a692e9 Mon Sep 17 00:00:00 2001
From: Paul Jolly <paul@myitcv.io>
Date: Thu, 20 Aug 2020 15:27:43 +0100
Subject: [PATCH] Use github.com/rogpeppe/go-internal/fmtsort for stable map
 output

github.com/rogpeppe/go-internal factors out an opinionated selection of
internal packages and functionality from the Go standard library. One
such package is fmtsort:

    Package fmtsort provides a general stable ordering mechanism for
    maps, on behalf of the fmt and text/template packages. It is not
    guaranteed to be efficient and works only for types that are valid
    map keys.

Use this package to ensure the Formatter output for maps is stable.

Fixes #47
---
 formatter.go      | 7 ++++---
 formatter_test.go | 3 ++-
 go.mod            | 5 ++++-
 go.sum            | 5 +++++
 4 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/formatter.go b/formatter.go
index bf4b598..f3718ea 100644
--- a/formatter.go
+++ b/formatter.go
@@ -8,6 +8,7 @@ import (
 	"text/tabwriter"
 
 	"github.com/kr/text"
+	"github.com/rogpeppe/go-internal/fmtsort"
 )
 
 type formatter struct {
@@ -123,10 +124,10 @@ func (p *printer) printValue(v reflect.Value, showType, quote bool) {
 				writeByte(p, '\n')
 				pp = p.indent()
 			}
-			keys := v.MapKeys()
+			sm := fmtsort.Sort(v)
 			for i := 0; i < v.Len(); i++ {
-				k := keys[i]
-				mv := v.MapIndex(k)
+				k := sm.Key[i]
+				mv := sm.Value[i]
 				pp.printValue(k, false, true)
 				writeByte(pp, ':')
 				if expand {
diff --git a/formatter_test.go b/formatter_test.go
index c8c0b51..10ce57a 100644
--- a/formatter_test.go
+++ b/formatter_test.go
@@ -38,7 +38,7 @@ func (f F) Format(s fmt.State, c rune) {
 	fmt.Fprintf(s, "F(%d)", int(f))
 }
 
-type Stringer struct { i int }
+type Stringer struct{ i int }
 
 func (s *Stringer) String() string { return "foo" }
 
@@ -74,6 +74,7 @@ var gosyntax = []test{
 	//{make(chan int), "(chan int)(0x1234)"},
 	{unsafe.Pointer(uintptr(unsafe.Pointer(&long))), fmt.Sprintf("unsafe.Pointer(0x%02x)", uintptr(unsafe.Pointer(&long)))},
 	{func(int) {}, "func(int) {...}"},
+	{map[string]string{"a": "a", "b": "b"}, "map[string]string{\"a\":\"a\", \"b\":\"b\"}"},
 	{map[int]int{1: 1}, "map[int]int{1:1}"},
 	{int32(1), "int32(1)"},
 	{io.EOF, `&errors.errorString{s:"EOF"}`},
diff --git a/go.mod b/go.mod
index 9a27b6e..579209a 100644
--- a/go.mod
+++ b/go.mod
@@ -2,4 +2,7 @@ module github.com/kr/pretty
 
 go 1.12
 
-require github.com/kr/text v0.1.0
+require (
+	github.com/kr/text v0.1.0
+	github.com/rogpeppe/go-internal v1.6.1
+)
diff --git a/go.sum b/go.sum
index 714f82a..a0e55fc 100644
--- a/go.sum
+++ b/go.sum
@@ -1,3 +1,8 @@
+github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
 github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
+github.com/rogpeppe/go-internal v1.6.1 h1:/FiVV8dS/e+YqF2JvO3yXRFbBLTIuSDkuC7aBOAvL+k=
+github.com/rogpeppe/go-internal v1.6.1/go.mod h1:xXDCJY+GAPziupqXw64V24skbSoqbTEfhy4qGm1nDQc=
+gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/errgo.v2 v2.1.0/go.mod h1:hNsd1EY+bozCKY1Ytp96fpM3vjJbqLJn88ws8XvfDNI=