internal/godebug: remove dependency on os

The immediate reason is that we want to use godebug from math/rand,
and math/rand importing godebug importing os causes an import cycle
in package testing.

More generally, the new approach to backward compatibility outlined
in discussion #55090 will require using this package from other similarly
sensitive places, perhaps even package os itself. Best to remove all
dependencies.

Preparation for #54880.

Change-Id: Ia01657a2d90e707a8121a336c9db3b7247c0198f
Reviewed-on: https://go-review.googlesource.com/c/go/+/439418
Auto-Submit: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>

3 files changed, 14 insertions, 9 deletions

diff --git a/src/syscall/env_unix.go b/src/syscall/env_unix.go
index 67e6c5fbe2..6d917da208 100644
--- a/src/syscall/env_unix.go
+++ b/src/syscall/env_unix.go
@@ -31,11 +31,6 @@ var (
 
 func runtime_envs() []string // in package runtime
 
-// setenv_c and unsetenv_c are provided by the runtime but are no-ops
-// if cgo isn't loaded.
-func setenv_c(k, v string)
-func unsetenv_c(k string)
-
 func copyenv() {
 	env = make(map[string]int)
 	for i, s := range envs {
@@ -67,7 +62,7 @@ func Unsetenv(key string) error {
 		envs[i] = ""
 		delete(env, key)
 	}
-	unsetenv_c(key)
+	runtimeUnsetenv(key)
 	return nil
 }
 
@@ -124,7 +119,7 @@ func Setenv(key, value string) error {
 		envs = append(envs, kv)
 	}
 	env[key] = i
-	setenv_c(key, value)
+	runtimeSetenv(key, value)
 	return nil
 }
 
@@ -135,7 +130,7 @@ func Clearenv() {
 	defer envLock.Unlock()
 
 	for k := range env {
-		unsetenv_c(k)
+		runtimeUnsetenv(k)
 	}
 	env = make(map[string]int)
 	envs = []string{}
diff --git a/src/syscall/env_windows.go b/src/syscall/env_windows.go
index 74b154ec15..cd085a9e44 100644
--- a/src/syscall/env_windows.go
+++ b/src/syscall/env_windows.go
@@ -42,6 +42,7 @@ func Setenv(key, value string) error {
 	if e != nil {
 		return e
 	}
+	runtimeSetenv(key, value)
 	return nil
 }
 
@@ -50,7 +51,12 @@ func Unsetenv(key string) error {
 	if err != nil {
 		return err
 	}
-	return SetEnvironmentVariable(keyp, nil)
+	e := SetEnvironmentVariable(keyp, nil)
+	if e != nil {
+		return e
+	}
+	runtimeUnsetenv(key)
+	return nil
 }
 
 func Clearenv() {
diff --git a/src/syscall/syscall.go b/src/syscall/syscall.go
index 62bfa449cf..446a299f57 100644
--- a/src/syscall/syscall.go
+++ b/src/syscall/syscall.go
@@ -100,3 +100,7 @@ func (tv *Timeval) Nano() int64 {
 
 func Getpagesize() int
 func Exit(code int)
+
+// runtimeSetenv and runtimeUnsetenv are provided by the runtime.
+func runtimeSetenv(k, v string)
+func runtimeUnsetenv(k string)