go/internal/xmaps: New package that complements standard package maps

Currently with the only utility to retrieve map keys in sorted order.

We will need this in several tests in follow-up patches.

go/internal/xmaps/xmaps.go

+// Copyright (C) 2024  Nexedi SA and Contributors.
+//                     Kirill Smelkov <kirr@nexedi.com>
+//
+// This program is free software: you can Use, Study, Modify and Redistribute
+// it under the terms of the GNU General Public License version 3, or (at your
+// option) any later version, as published by the Free Software Foundation.
+//
+// You can also Link and Combine this program with other software covered by
+// the terms of any of the Free Software licenses or any of the Open Source
+// Initiative approved licenses and Convey the resulting work. Corresponding
+// source of such a combination shall include the source code for all other
+// software used.
+//
+// This program is distributed WITHOUT ANY WARRANTY; without even the implied
+// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+//
+// See COPYING file for full licensing terms.
+// See https://www.nexedi.com/licensing for rationale and options.
+
+// Package xmaps complements standard package maps.
+package xmaps
+
+import (
+	"cmp"
+	"slices"
+)
+
+// SortedKeys returns all keys of map m in their ascending order.
+func SortedKeys[M ~map[K]V, K cmp.Ordered, V any](m M) []K {
+	keyv := make([]K, 0, len(m))
+	for k := range m {
+		keyv = append(keyv, k)
+	}
+	slices.Sort(keyv)
+	return keyv
+}

go/internal/xmaps/xmaps_test.go

+// Copyright (C) 2024  Nexedi SA and Contributors.
+//                     Kirill Smelkov <kirr@nexedi.com>
+//
+// This program is free software: you can Use, Study, Modify and Redistribute
+// it under the terms of the GNU General Public License version 3, or (at your
+// option) any later version, as published by the Free Software Foundation.
+//
+// You can also Link and Combine this program with other software covered by
+// the terms of any of the Free Software licenses or any of the Open Source
+// Initiative approved licenses and Convey the resulting work. Corresponding
+// source of such a combination shall include the source code for all other
+// software used.
+//
+// This program is distributed WITHOUT ANY WARRANTY; without even the implied
+// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+//
+// See COPYING file for full licensing terms.
+// See https://www.nexedi.com/licensing for rationale and options.
+
+package xmaps
+
+import (
+	"slices"
+	"testing"
+)
+
+func TestSortedKeys(t *testing.T) {
+	m := map[string]int{
+		"c":   1,
+		"b":   2,
+		"a":   3,
+		"zzz": 4,
+		"rr":  5,
+		"p":   6,
+		"j":   7,
+	}
+
+	kok := []string{"a", "b", "c", "j", "p", "rr", "zzz"}
+
+	for i := 0; i < 100; i++ {
+		keyv := SortedKeys(m)
+		if !slices.Equal(keyv, kok) {
+			t.Fatalf("SortedKeys:\nhave: %s\nwant: %s", keyv, kok)
+		}
+	}
+}