Quotes around command-line argument that has unicode characters are not removed

["Dmitry Katsubo via cygwin" <cygwin@cygwin.com>]

Dear Cygwin community,

I observe the following on my Cygwin: when I put quotes around file that has
non-ASCII symbols, these quotes are passed to argv of the process literally,
otherwise they are removed. I would expect that there is a consistency.

I have written a small C program that displays arguments, and run it three
times:

#1 For the file with space, taken into quotes ("the file.txt") -- OK
#2 For the file with non-ASCII characters (Château.txt) -- OK
#3 For the file with non-ASCII characters, taken into quotes ("Château.txt") -- WRONG

d:\cli> uname -a
CYGWIN_NT-6.1-WOW PC 2.9.0(0.318/5/3) 2017-09-12 10:41 i686 Cygwin

D:\cli> chcp
Active code page: 866

D:\cli> dir
...cut...
2018-03-22  00:43                 0 Château.txt
2018-03-22  00:01               393 test.c
2018-03-22  00:01           150,230 test.exe
2018-03-21  00:15               186 test.pl
2018-03-22  00:43                 0 the file.txt
2018-03-22  00:40                16 текст плюс.txt
               6 File(s)        150,825 bytes
               2 Dir(s)  41,972,293,632 bytes free

D:\cli> test "the file.txt"
param 0 = test
param 1 = the file.txt
File 'the file.txt' was opened

D:\cli> test Château.txt
param 0 = test
param 1 = Château.txt
File 'Château.txt' was opened

D:\cli> test "Château.txt"
param 0 = test
param 1 = "Château.txt"
Failed to open '"Château.txt"': No such file or directory

As one can see, the last run fails. I am a bit puzzled: how can I pass the name
of the file with space and Unicode symbols? I need to do it in uniform way, as I
am calling a Cygwin program from native Windows program, as in [1].

D:\cli> test "текст плюс.txt"
param 0 = test
param 1 = "текст плюс.txt"
Failed to open '"текст плюс.txt"': No such file or directory

I have search a bit, but I couldn't find a direct answer. From post [1] and [2]
I see that compiler inserts the code to do some argument pre-processing like
@pathnames [3], but what are exactly the rules? Is quote pre-processing done in
dcrt0.cc:177 [4]?

Any feedback is appreciated.

[1] https://sourceware.org/ml/cygwin/2016-05/msg00082.html
[2] http://daviddeley.com/autohotkey/parameters/parameters.htm
[3] https://cygwin.com/cygwin-ug-net/using-specialnames.html#pathnames-at
[4] https://github.com/openunix/cygwin/blob/master/winsup/cygwin/dcrt0.cc#L177

=== test.c ===
#include <stdio.h>
#include <errno.h>
#include <string.h>

int main(int argc, char* argv[])
{
	for (int i = 0; i < argc; i++)
	{
		printf("param %d = %s\n", i, argv[i]);
	}
	FILE* f = fopen(argv[1], "r");
	if (f != NULL)
	{
		printf("File '%s' was opened\n", argv[1]);
		fclose(f);
	} else {
		printf("Failed to open '%s': %s\n", argv[1], strerror(errno));
	}
	return 0;
}

-- 
With best regards,
Dmitry

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