pkg/eval/vals: Make Repr sort map keys before printing.

This addresses #1495.

0.20.0-release-notes.md

@@ -4,6 +4,8 @@ Draft release notes for Elvish 0.20.0.
 
 -   A new `os:` module providing access to operating system functionality.
 
+-   Maps now have their keys sorted when printed.
+
 -   The `peach` command now has a `&num-workers` option
     ([#648](https://github.com/elves/elvish/issues/648)).
 

pkg/eval/vals/repr.go

@@ -5,6 +5,7 @@ import (
 	"math"
 	"math/big"
 	"reflect"
+	"sort"
 	"strconv"
 
 	"src.elv.sh/pkg/parse"
@@ -67,8 +68,19 @@ func Repr(v any, indent int) string {
 		return b.String()
 	case Map:
 		builder := NewMapReprBuilder(indent)
+		// Collect all the key-value pairs.
+		pairs := make([][2]any, 0, v.Len())
 		for it := v.Iterator(); it.HasElem(); it.Next() {
 			k, v := it.Elem()
+			pairs = append(pairs, [2]any{k, v})
+		}
+		// Sort the pairs. See the godoc of CmpTotal for the sorting algorithm.
+		sort.Slice(pairs, func(i, j int) bool {
+			return CmpTotal(pairs[i][0], pairs[j][0]) == CmpLess
+		})
+		// Print the pairs.
+		for _, pair := range pairs {
+			k, v := pair[0], pair[1]
 			builder.WritePair(Repr(k, indent+1), indent+2, Repr(v, indent+2))
 		}
 		return builder.String()

pkg/eval/vals/repr_test.go

@@ -38,8 +38,28 @@ func TestReprPlain(t *testing.T) {
 
 		Args(EmptyMap).Rets("[&]"),
 		Args(MakeMap("foo", "bar")).Rets("[&foo=bar]"),
+		// Keys of the same type are sorted.
+		Args(MakeMap("b", "second", "a", "first", "c", "third")).
+			Rets("[&a=first &b=second &c=third]"),
+		Args(MakeMap(2, "second", 1, "first", 3, "third")).
+			Rets("[&(num 1)=first &(num 2)=second &(num 3)=third]"),
+		// Keys of mixed types tested in a different test.
 
 		Args(reprer{}).Rets("<reprer>"),
 		Args(nonReprer{}).Rets("<unknown {}>"),
 	})
 }
+
+func TestReprPlain_MapWithKeysOfMixedTypes(t *testing.T) {
+	m := MakeMap(
+		"b", "second", "a", "first", "c", "third",
+		2, "second", 1, "first", 3, "third")
+	strPart := "&a=first &b=second &c=third"
+	numPart := "&(num 1)=first &(num 2)=second &(num 3)=third"
+	want1 := "[" + strPart + " " + numPart + "]"
+	want2 := "[" + numPart + " " + strPart + "]"
+	got := ReprPlain(m)
+	if got != want1 && got != want2 {
+		t.Errorf("got %q, want %q or %q", got, want1, want2)
+	}
+}