os: implement CreateTemp

Until tinygo implements fastrand(), use a placeholder RNG here.

src/os/tempfile_test.go

@@ -0,0 +1,79 @@
+// Copyright 2010 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 file.
+
+package os_test
+
+import (
+	"errors"
+	. "os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestCreateTemp(t *testing.T) {
+	nonexistentDir := filepath.Join("_also_not_exists_", "_not_exists_")
+	f, err := CreateTemp(nonexistentDir, "foo")
+	if f != nil || err == nil {
+		t.Errorf("CreateTemp(%q, `foo`) = %v, %v", nonexistentDir, f, err)
+	}
+}
+
+func TestCreateTempPattern(t *testing.T) {
+	tests := []struct{ pattern, prefix, suffix string }{
+		{"tempfile_test", "tempfile_test", ""},
+		{"tempfile_test*", "tempfile_test", ""},
+		{"tempfile_test*xyz", "tempfile_test", "xyz"},
+	}
+	for _, test := range tests {
+		f, err := CreateTemp("", test.pattern)
+		if err != nil {
+			t.Errorf("CreateTemp(..., %q) error: %v", test.pattern, err)
+			continue
+		}
+		defer Remove(f.Name())
+		base := filepath.Base(f.Name())
+		f.Close()
+		if !(strings.HasPrefix(base, test.prefix) && strings.HasSuffix(base, test.suffix)) {
+			t.Errorf("CreateTemp pattern %q created bad name %q; want prefix %q & suffix %q",
+				test.pattern, base, test.prefix, test.suffix)
+		}
+	}
+}
+
+func TestCreateTempBadPattern(t *testing.T) {
+	tmpDir := TempDir()
+
+	const sep = string(PathSeparator)
+	tests := []struct {
+		pattern string
+		wantErr bool
+	}{
+		{"ioutil*test", false},
+		{"tempfile_test*foo", false},
+		{"tempfile_test" + sep + "foo", true},
+		{"tempfile_test*" + sep + "foo", true},
+		{"tempfile_test" + sep + "*foo", true},
+		{sep + "tempfile_test" + sep + "*foo", true},
+		{"tempfile_test*foo" + sep, true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.pattern, func(t *testing.T) {
+			tmpfile, err := CreateTemp(tmpDir, tt.pattern)
+			if tmpfile != nil {
+				defer tmpfile.Close()
+			}
+			if tt.wantErr {
+				if err == nil {
+					t.Errorf("CreateTemp(..., %#q) succeeded, expected error", tt.pattern)
+				}
+				if !errors.Is(err, ErrPatternHasSeparator) {
+					t.Errorf("CreateTemp(..., %#q): %v, expected ErrPatternHasSeparator", tt.pattern, err)
+				}
+			} else if err != nil {
+				t.Errorf("CreateTemp(..., %#q): %v", tt.pattern, err)
+			}
+		})
+	}
+}