Add use of Windows Wide CRT API for env. vars (#20084)

* Add use of Windows Wide CRT API for env. vars

Replaces use of CRT API `getenv` and `putenv` with respectively
`_wgetenv` and `_wputenv`. Motivation is to reliably convert environment
variables to UTF-8, and the wide API is best there, because it's
reliably UTF-16.

Changed the hack in `lib/std/private/win_setenv.nim` by switching the
order of the Unicode and MBCS environment update; Unicode first, MBCS
second. Because `_wgetenv`/`_wputenv` is now used, the Unicode
environment will be initialized, so it should always be updated.

Stop updating MBCS environment with the name of `getEnv`. It's not
necessarily true that MBCS encoding and the `string` encoding is the
same. Instead convert UTF-16 to current Windows code page with
`wcstombs`, and use that string to update MBCS.

Fixes regression in `6b3c77e` that caused `std/envvars.getEnv` or
`std/os.getEnv` on Windows to return non-UTF-8 encoded strings.

Add tests that test environment variables with Unicode characters in
their name or value.

* Fix test issues

Fixes

* `nim cpp` didn't compile the tests
* Nimscript import of `tosenv.nim` from `test_nimscript.nims` failed
  with "cannot importc"

* Fix missing error check on `wcstombs`

* Fix ANSI testing errors

* Separate ANSI-related testing to their own tests, and only executing
  them if running process has a specific code page
  * Setting locale with `setlocale` was not reliable and didn't work on
    certain machines
* Add handling of a "no character representation" error in second
  `wcstombs` call

* tests/newruntime_misc: Increment allocCount

Increments overall allocations in `tnewruntime_misc` test. This is
because `getEnv` now does an additional allocation: allocation of the
UTF-16 string used as parameter to `c_wgetenv`.

* Revert "tests/newruntime_misc: Increment allocCount"

This reverts commit 4d4fe8bd3edb1bfc6d600f247af797c7552f5477.

* tests/newruntime_misc: Increment allocCount on Windows

Increments overall allocations in `tnewruntime_misc` test for Windows.
This is because `getEnv` on Windows now does an additional allocation:
allocation of the UTF-16 string used as parameter to `c_wgetenv`.

* Refactor, adding suggestions from code review

Co-authored-by: Clay Sweetser <Varriount@users.noreply.github.com>

* Document, adding suggestions

Co-authored-by: Clay Sweetser <Varriount@users.noreply.github.com>

Co-authored-by: ringabout <43030857+ringabout@users.noreply.github.com>
Co-authored-by: Clay Sweetser <Varriount@users.noreply.github.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/lib/std/envvars.nim b/lib/std/envvars.nim
index 5b135cbd3..d7706c17d 100644
--- a/lib/std/envvars.nim
+++ b/lib/std/envvars.nim
@@ -57,15 +57,19 @@ when not defined(nimscript):
 
   else:
 
-    proc c_getenv(env: cstring): cstring {.
-      importc: "getenv", header: "<stdlib.h>".}
     when defined(windows):
       proc c_putenv(envstring: cstring): cint {.importc: "_putenv", header: "<stdlib.h>".}
       from std/private/win_setenv import setEnvImpl
       import winlean
+      proc c_wgetenv(varname: WideCString): WideCString {.importc: "_wgetenv",
+          header: "<stdlib.h>".}
+      proc getEnvImpl(env: cstring): WideCString = c_wgetenv(env.newWideCString)
     else:
+      proc c_getenv(env: cstring): cstring {.
+        importc: "getenv", header: "<stdlib.h>".}
       proc c_setenv(envname: cstring, envval: cstring, overwrite: cint): cint {.importc: "setenv", header: "<stdlib.h>".}
       proc c_unsetenv(env: cstring): cint {.importc: "unsetenv", header: "<stdlib.h>".}
+      proc getEnvImpl(env: cstring): cstring = c_getenv(env)
 
     proc getEnv*(key: string, default = ""): string {.tags: [ReadEnvEffect].} =
       ## Returns the value of the `environment variable`:idx: named `key`.
@@ -83,7 +87,7 @@ when not defined(nimscript):
         assert getEnv("unknownEnv") == ""
         assert getEnv("unknownEnv", "doesn't exist") == "doesn't exist"
 
-      let env = c_getenv(key)
+      let env = getEnvImpl(key)
       if env == nil: return default
       result = $env
 
@@ -99,7 +103,7 @@ when not defined(nimscript):
       runnableExamples:
         assert not existsEnv("unknownEnv")
 
-      return c_getenv(key) != nil
+      return getEnvImpl(key) != nil
 
     proc putEnv*(key, val: string) {.tags: [WriteEnvEffect].} =
       ## Sets the value of the `environment variable`:idx: named `key` to `val`.