1 files changed, 69 insertions, 0 deletions
diff --git a/src/internal/testlog/log.go b/src/internal/testlog/log.go
new file mode 100644
index 0000000..3c5f780
--- /dev/null
+++ b/src/internal/testlog/log.go
@@ -0,0 +1,69 @@
+// 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 file.
+
+// Package testlog provides a back-channel communication path
+// between tests and package os, so that cmd/go can see which
+// environment variables and files a test consults.
+package testlog
+
+import "sync/atomic"
+
+// Interface is the interface required of test loggers.
+// The os package will invoke the interface's methods to indicate that
+// it is inspecting the given environment variables or files.
+// Multiple goroutines may call these methods simultaneously.
+type Interface interface {
+	Getenv(key string)
+	Stat(file string)
+	Open(file string)
+	Chdir(dir string)
+}
+
+// logger is the current logger Interface.
+// We use an atomic.Value in case test startup
+// is racing with goroutines started during init.
+// That must not cause a race detector failure,
+// although it will still result in limited visibility
+// into exactly what those goroutines do.
+var logger atomic.Value
+
+// SetLogger sets the test logger implementation for the current process.
+// It must be called only once, at process startup.
+func SetLogger(impl Interface) {
+	if logger.Load() != nil {
+		panic("testlog: SetLogger must be called only once")
+	}
+	logger.Store(&impl)
+}
+
+// Logger returns the current test logger implementation.
+// It returns nil if there is no logger.
+func Logger() Interface {
+	impl := logger.Load()
+	if impl == nil {
+		return nil
+	}
+	return *impl.(*Interface)
+}
+
+// Getenv calls Logger().Getenv, if a logger has been set.
+func Getenv(name string) {
+	if log := Logger(); log != nil {
+		log.Getenv(name)
+	}
+}
+
+// Open calls Logger().Open, if a logger has been set.
+func Open(name string) {
+	if log := Logger(); log != nil {
+		log.Open(name)
+	}
+}
+
+// Stat calls Logger().Stat, if a logger has been set.
+func Stat(name string) {
+	if log := Logger(); log != nil {
+		log.Stat(name)
+	}
+}