On 6/11/26 8:58 AM, [email protected] wrote:
A naïve Fortran user would think that if the thing being stringified contains a
quote but not an apostrophe, it should use quotes as the delimiter.
i.e. CPP_STRINGIFY(key .eq. "x")
should produce 'key .eq. "x"'
It's not wrong to blindly double the quotes, though. Just better to use
apostrophes in some cases.
I appreciate the feedback. The patch is safe and follows a principle of least
surprise. In this case, before the patch, all code appeared to be fortran
conforming and gave the appearance that there was a problem somewhere else.
I need to know if the patch is approved or not? If not, is there a concern that
I not understand and if so, what?
Regards,
Jerry
Cheers,
--
..................Malcolm Cohen, NAG Oxford/Tokyo.
-----Original Message-----
From: Jerry D <[email protected]>
Sent: Thursday, June 11, 2026 8:36 AM
To: Jason Merrill <[email protected]>; Malcolm Cohen <[email protected]>
Cc: gfortran <[email protected]>
Subject: Fwd: [PATCH] PR125533 fortran/libcpp: CPP stringify operator emits \"
for double-quotes in Fortran mode
Jason and Malcolm,
Can either of you review the attached patch. It touches on libcpp and fixes a
sneaky glitch for gfortran.
Much appreciated,
Jerry
-------- Forwarded Message --------
Subject: [PATCH] PR125533 fortran/libcpp: CPP stringify operator emits \" for
double-quotes in Fortran mode
Date: Fri, 5 Jun 2026 12:47:12 -0700
From: Jerry D <[email protected]>
To: gfortran <[email protected]>, gcc-patches <[email protected]>
CC: Jakub Jelinek <[email protected]>
See attached patch. This one was a surprise and a subtle problem.
See the explanation in the commit message. Since this touches on libcpp I am
not sure who else should review this.
Regression tested on x86_64.
OK for mainline and backport to 16 later.
Regards,
Jerry
---
The traditional-mode CPP stringification operator escaped double-quote
characters in macro argument tokens with a backslash (e.g.
CPP_STRINGIFY(key .eq. "x") expanded to "key .eq. \"x\""). This is correct for C but not
valid Fortran: Fortran represents an embedded double-quote with a doubled quote (""), not a backslash-quote
(\").
The backslash-escaped output was rejected by the Fortran scanner with a
spurious syntax error.
Fix: add a new flag fortran_string_escaping to struct cpp_options. When set,
traditional.cc emits a doubled quote instead of a backslash-quote when escaping
a double-quote character inside a stringified argument, and suppresses the
extra backslash before a literal backslash in that context.
Set the flag in gfc_cpp_post_options, which configures the CPP reader for
Fortran.
PR fortran/125533
Assisted by: Claude Sonnet 4.6
gcc/fortran/ChangeLog:
* cpp.cc (gfc_cpp_post_options): Set fortran_string_escaping in
cpp_options so traditional-mode stringification uses doubled-quote
escaping instead of backslash-quote.
gcc/testsuite/ChangeLog:
* gfortran.dg/cpp_stringify_quote_1.F90: New test.
libcpp/ChangeLog:
* include/cpplib.h (cpp_options): Add fortran_string_escaping flag.
* traditional.cc (replace_args_and_push): When
fortran_string_escaping is set, escape double-quote with a doubled
quote rather than a backslash; suppress the extra backslash before a
backslash inside a quoted argument.
---
