[Bug preprocessor/101628] New: Preprocessor errors on extended characters in #if 0 code block

[Bug preprocessor/101628] New: Preprocessor errors on extended characters in #if 0 code block

[david.post at ohyonghao dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101628

            Bug ID: 101628
           Summary: Preprocessor errors on extended characters in #if 0
                    code block
           Product: gcc
           Version: 10.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: preprocessor
          Assignee: unassigned at gcc dot gnu.org
          Reporter: david.post at ohyonghao dot com
  Target Milestone: ---

In a #if 0 code block, the presence of characters outside the extended
character set being used as an identifier still gets passed to the C++ compiler
and errors out with the message:

error: extended character ∂ is not valid in an identifier

Sample code:

int main(int argc, char **argv){
#if 0
    Q_∂(false)
#endif
    return 0;
}

The code within the #if 0 block should never be compiled which is the behavior
of other compilers such as clang++ which gleefully ignores bad code within #if
0 block. 

To clarify, with clang++ the code errors without the #if 0 block, which is
expected behavior, and compiles with the #if 0 block around the bad code. g++
errors in both cases.

[Bug preprocessor/101628] Preprocessor errors on extended characters in #if 0 code block

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101628

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Related to PR 62661 which was closed as invalid.
Basically the C++ standard says the tokens inside the #if blocks need to be
valid tokens still.

[Bug preprocessor/101628] Preprocessor errors on extended characters in #if 0 code block

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101628

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
thus dup

*** This bug has been marked as a duplicate of bug 62661 ***

[Bug preprocessor/101628] Preprocessor errors on extended characters in #if 0 code block

[david.post at ohyonghao dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101628

--- Comment #3 from David Post <david.post at ohyonghao dot com> ---
This seems to be implementation dependent. As per 15.1.6:
The implementation can process and skip sections of source files conditionally,
include other source files, import macros from header units, and replace
macros. These capabilities are called preprocessing, because conceptually they
occur before translation of the resulting translation unit.

and 15.2.14
Each directive's condition is checked in order. If it evaluates to false
(zero), the group that it controls is skipped: 

But what you are implying is that skipped means that you process it anyway,
then ignore the result, whereas other implementations take this to mean that
the group is skipped over and not processed.

This seems to be an implementation decision rather than a requirement by the
standard, or am I missing the part of the standard which states that those
tokens must still be valid?

[Bug preprocessor/101628] Preprocessor errors on extended characters in #if 0 code block

[schwab@linux-m68k.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101628

--- Comment #4 from Andreas Schwab <schwab@linux-m68k.org> ---
15.1.6 isn't about implementation options, it is the definition of the term
preprocessing.  The whole chapter always talks about sequences of preprocessing
tokens, whether skipped over or processed.