Remove tracking of environment from osenv.nim v2 (#18575)

* Remove unnecessary environment tracking

* try to fix windows

* fix delEnv

* make putEnv work on windows even with empty values; improve tests: add tests, add js, vm testing

* [skip ci] fix changelog

Co-authored-by: Caden Haustein <code@brightlysalty.33mail.com>

lib/std/private/win_setenv.nim

@@ -0,0 +1,92 @@
+#[
+Copyright (c) Facebook, Inc. and its affiliates.
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+    http://www.apache.org/licenses/LICENSE-2.0
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+Adapted `setenv` from https://github.com/facebook/folly/blob/master/folly/portability/Stdlib.cpp
+translated from C to nim.
+]#
+
+#[
+Introduced in https://github.com/facebook/folly/commit/5d8ca09a3f96afefb44e35808f03651a096ab9c7
+
+TODO:
+check errno_t vs cint
+]#
+
+when not defined(windows): discard
+else:
+  proc setEnvironmentVariableA*(lpName, lpValue: cstring): int32 {.
+    stdcall, dynlib: "kernel32", importc: "SetEnvironmentVariableA", sideEffect.}
+    # same as winlean.setEnvironmentVariableA
+
+  proc c_getenv(env: cstring): cstring {.importc: "getenv", header: "<stdlib.h>".}
+  proc c_putenv_s(envname: cstring, envval: cstring): cint {.importc: "_putenv_s", header: "<stdlib.h>".}
+  proc c_wgetenv(varname: WideCString): WideCString {.importc: "_wgetenv", header: "<stdlib.h>".}
+
+  var errno {.importc, header: "<errno.h>".}: cint
+  type wchar_t  {.importc: "wchar_t".} = int16
+  var gWenviron {.importc:"_wenviron".}: ptr ptr wchar_t
+    # xxx `ptr UncheckedArray[WideCString]` did not work
+
+  proc mbstowcs_s(pReturnValue: ptr csize_t, wcstr: WideCString, sizeInWords: csize_t, mbstr: cstring, count: csize_t): cint {.importc: "mbstowcs_s", header: "<stdlib.h>".}
+    # xxx cint vs errno_t?
+
+  proc setEnvImpl*(name: cstring, value: cstring, overwrite: cint): cint =
+    const EINVAL = cint(22)
+    const MAX_ENV = 32767
+      # xxx get it from: `var MAX_ENV {.importc: "_MAX_ENV", header:"<stdlib.h>".}: cint`
+    if overwrite == 0 and c_getenv(name) != nil: return 0
+    if value[0] != '\0':
+      let e = c_putenv_s(name, value)
+      if e != 0:
+        errno = e
+        return -1
+      return 0
+    #[
+    We are trying to set the value to an empty string, but `_putenv_s` deletes
+    entries if the value is an empty string, and just calling
+    SetEnvironmentVariableA doesn't update `_environ`,
+    so we have to do these terrible things.
+    ]#
+    if c_putenv_s(name, "  ") != 0:
+      errno = EINVAL
+      return -1
+    # Here lies the documentation we blatently ignore to make this work.
+    var s = c_getenv(name)
+    s[0] = '\0'
+    #[
+    This would result in a double null termination, which normally signifies the
+    end of the environment variable list, so we stick a completely empty
+    environment variable into the list instead.
+    ]#
+    s[1] = '='
+    #[
+    If gWenviron is null, the wide environment has not been initialized
+    yet, and we don't need to try to update it. We have to do this otherwise
+    we'd be forcing the initialization and maintenance of the wide environment
+    even though it's never actually used in most programs.
+    ]#
+    if gWenviron != nil:
+      # var buf: array[MAX_ENV + 1, WideCString]
+      var buf: array[MAX_ENV + 1, Utf16Char]
+      let buf2 = cast[WideCString](buf[0].addr)
+      var len: csize_t
+      if mbstowcs_s(len.addr, buf2, buf.len.csize_t, name, MAX_ENV) != 0:
+        errno = EINVAL
+        return -1
+      c_wgetenv(buf2)[0] = '\0'.Utf16Char
+      c_wgetenv(buf2)[1] = '='.Utf16Char
+
+    # And now, we have to update the outer environment to have a proper empty value.
+    if setEnvironmentVariableA(name, value) == 0:
+      errno = EINVAL
+      return -1
+    return 0