[Bug c/104147] New: C preprocessor may remove the standard required whitespace between the preprocessing tokens

[pavel.morozkin at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104147

            Bug ID: 104147
           Summary: C preprocessor may remove the standard required
                    whitespace between the preprocessing tokens
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pavel.morozkin at gmail dot com
  Target Milestone: ---

Sample code:
#define X(x,y)  x y
#define STR_(x) #x
#define STR(x)  STR_(x)
STR(X(Y,Y))

Invocations:
$ gcc t222.c -std=c11 -pedantic -Wall -Wextra -E -P
"Y Y"

$ gcc t222.c -std=c11 -pedantic -Wall -Wextra -E -P -D"Y()"
"YY"

Also 1: Somehow gcc takes into account the whitespace between `,` and `Y`:
$ gcc t222.c -std=c11 -pedantic -Wall -Wextra -E -P -D"Y()" -D"Z=STR(X(Y,Y))"
"YY"

$ gcc t222.c -std=c11 -pedantic -Wall -Wextra -E -P -D"Y()" -D"Z=STR(X(Y, Y))"
"Y Y"

Also 2: This:
STR(X(Y,
Y))

leads to:
$ gcc t222.c -std=c11 -pedantic -Wall -Wextra -E -P -D"Y()"
"Y Y"

However, this:
STR(X(Y
,Y))

leads to:
$ gcc t222.c -std=c11 -pedantic -Wall -Wextra -E -P -D"Y()"
"YY"

The whitespace is required by the standard.