[Bug fortran/58001] New: Make it possible to silence "Extension: Tab character in format" warning

[Bug fortran/58001] New: Make it possible to silence "Extension: Tab character in format" warning

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58001

            Bug ID: 58001
           Summary: Make it possible to silence "Extension: Tab character
                    in format" warning
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: burnus at gcc dot gnu.org

For indenting the source code, gfortran warns only with -std=f* or with -Wtab.

However, for format strings, it always warns - and with -std=f* it even turns
the warning into an error! (see io.c's next_char_not_space)

Example:

1894  format(   '123')
      end

(The tab is before '123'. A tab in the string itself is not warned for.)

Maybe the best would be to disable this warning with -std=legacy - and refer to
-std=legacy in the -std=gnu warning?

[Bug fortran/58001] Make it possible to silence "Extension: Tab character in format" warning

[kargl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58001

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kargl at gcc dot gnu.org

--- Comment #1 from kargl at gcc dot gnu.org ---
(In reply to Tobias Burnus from comment #0)
> For indenting the source code, gfortran warns only with -std=f* or with
> -Wtab.

Please, check the archive.  At one time gfortran would issue a warning
if a tab was used in a nonconforming context.  Too many people were
upset about this, so the -W[no-]tab option, which has a convoluted history,
was the compromise.

> However, for format strings, it always warns - and with -std=f* it even
> turns the warning into an error! (see io.c's next_char_not_space)
> 
> Example:
> 
> 1894  format(   '123')
>       end
> 
> (The tab is before '123'. A tab in the string itself is not warned for.)
> 
> Maybe the best would be to disable this warning with -std=legacy - and refer
> to -std=legacy in the -std=gnu warning?

Tab is not and never has been a member of the Fortran character set.
The above line of code is nonconforming.  Gfortran, IMNSHO, should
always issue an error, but I lost that battle years ago.

[Bug fortran/58001] Make it possible to silence "Extension: Tab character in format" warning

[dominiq at lps dot ens.fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58001

Dominique d'Humieres <dominiq at lps dot ens.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-07-30
     Ever confirmed|0                           |1

--- Comment #2 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
Compiling the following code with -Wtabs

      print *, "A    string    with    Tabs    instead    of    spaces"
    print 1894
1894  format(    '123')
      end

gives

pr58001.f90:3.14:

1894  format( '123')
              1
Warning: Extension: Tab character in format at (1)

If compiled with -Wno-tabs, it gives

pr58001.f90:2.1:

 print 1894
 1
Warning: Nonconforming tab character at (1)
pr58001.f90:3.14:

1894  format( '123')
              1
Warning: Nonconforming tab character at (1)
pr58001.f90:3.14:

1894  format( '123')
              1
Warning: Extension: Tab character in format at (1)

Is this the expected behavior?-(I was expecting the later output for -Wtabs,
and no warning with -Wno-tabs: on most options Wno-* suppress the warnings for
the corresponding option.)

[Bug fortran/58001] Make it possible to silence "Extension: Tab character in format" warning

[sgk at troutmask dot apl.washington.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58001

--- Comment #3 from Steve Kargl <sgk at troutmask dot apl.washington.edu> ---
On Tue, Jul 30, 2013 at 12:59:00PM +0000, dominiq at lps dot ens.fr wrote:
> 
>       print *, "A    string    with    Tabs    instead    of    spaces"
>     print 1894
> 1894  format(    '123')
>       end
> 

According to both vi and nedit, there are no tabs in the
above code.  I assume that this is cut-n-paste from an
xterm term.

[Bug fortran/58001] Make it possible to silence "Extension: Tab character in format" warning

[dominiq at lps dot ens.fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58001

--- Comment #4 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
> According to both vi and nedit, there are no tabs in the
> above code.  I assume that this is cut-n-paste from an
> xterm term.

With Safari I see the tabs in comment #2, but not in what has been pasted in
comment #3. I am attaching the code.

[Bug fortran/58001] Make it possible to silence "Extension: Tab character in format" warning

[dominiq at lps dot ens.fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58001

--- Comment #5 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
Created attachment 30573
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=30573&action=edit
test case with tabs

[Bug fortran/58001] Make it possible to silence "Extension: Tab character in format" warning

[sgk at troutmask dot apl.washington.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58001

--- Comment #6 from Steve Kargl <sgk at troutmask dot apl.washington.edu> ---
On Tue, Jul 30, 2013 at 12:59:00PM +0000, dominiq at lps dot ens.fr wrote:
> 
> If compiled with -Wno-tabs, it gives
> 
> pr58001.f90:2.1:
> 
>  print 1894
>  1
> Warning: Nonconforming tab character at (1)
> pr58001.f90:3.14:
> 
> 1894  format( '123')
>               1
> Warning: Nonconforming tab character at (1)
> pr58001.f90:3.14:
> 
> 1894  format( '123')
>               1
> Warning: Extension: Tab character in format at (1)
> 
> Is this the expected behavior?

With -Wno-tabs, gfortran should report a warning for the
occurence of every tab used in the context of a character
from the Fortran character set.  Taking your code, which I've
deleted here, and replace all whitespace by tabs, I get the
expected number of warnings.  Historically, I wanted to use
-Wtabs as you expected, but there was too much wailing on 
the gfortran lists, so it was changed to -Wno-tabs with the
meaning that "no tabs are allowed" in the context of the
Fortran character set.  You'll notice that tabs within
a literal character string are not flagged.  The history
of -Wtabs verse -Wno-tabs can be found in the mailinglist
archive.

Now, for the problem at hand, it seems that there is a
bug in io.c.   Here the code in question:


/* Eat up the spaces and return a character.  */

static char
next_char_not_space (bool *error)
{
  char c;
  do
    {
      error_element = c = next_char (NONSTRING);
      if (c == '\t')
    {
      if (gfc_option.allow_std & GFC_STD_GNU)
        gfc_warning ("Extension: Tab character in format at %C");
      else
        {
          gfc_error ("Extension: Tab character in format at %C");
          *error = true;
          return c;
        }
    }
    }
  while (gfc_is_whitespace (c));
  return c;
}

Notice that there is no check for gfc_option.warn_tabs.

[Bug fortran/58001] Make it possible to silence "Extension: Tab character in format" warning

[dominiq at lps dot ens.fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58001

--- Comment #7 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
> With -Wno-tabs, gfortran should report a warning for the
> occurence of every tab used in the context of a character
> from the Fortran character set.  Taking your code, which I've
> deleted here, and replace all whitespace by tabs, I get the
> expected number of warnings.  Historically, I wanted to use
> -Wtabs as you expected, but there was too much wailing on 
> the gfortran lists, so it was changed to -Wno-tabs with the
> meaning that "no tabs are allowed" in the context of the
> Fortran character set.  You'll notice that tabs within
> a literal character string are not flagged.

I cannot understand the rationale of this choice, but I guess it's too late to
change it!-(

> The history of -Wtabs verse -Wno-tabs can be found in the mailinglist
> archive.

No interest to dig the archives on this issue.

[Bug fortran/58001] Make it possible to silence "Extension: Tab character in format" warning

[sgk at troutmask dot apl.washington.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58001

--- Comment #8 from Steve Kargl <sgk at troutmask dot apl.washington.edu> ---
On Tue, Jul 30, 2013 at 06:16:27PM +0000, dominiq at lps dot ens.fr wrote:
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58001
> 
> --- Comment #7 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
> > With -Wno-tabs, gfortran should report a warning for the
> > occurence of every tab used in the context of a character
> > from the Fortran character set.  Taking your code, which I've
> > deleted here, and replace all whitespace by tabs, I get the
> > expected number of warnings.  Historically, I wanted to use
> > -Wtabs as you expected, but there was too much wailing on 
> > the gfortran lists, so it was changed to -Wno-tabs with the
> > meaning that "no tabs are allowed" in the context of the
> > Fortran character set.  You'll notice that tabs within
> > a literal character string are not flagged.
> 
> I cannot understand the rationale of this choice, but I guess it's too late to
> change it!-(
> 
> > The history of -Wtabs verse -Wno-tabs can be found in the mailinglist
> > archive.
> 
> No interest to dig the archives on this issue.

http://gcc.gnu.org/ml/fortran/2006-03/msg00226.html

[Bug fortran/58001] Make it possible to silence "Extension: Tab character in format" warning

[sgk at troutmask dot apl.washington.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58001

--- Comment #9 from Steve Kargl <sgk at troutmask dot apl.washington.edu> ---
The following patch causes gfortran to treat a tab within
a FORMAT statement that same as it does elsewhere for the
appearance of a nonconforming use of tab.  The two tet
cases have been adjusted.

Index: gcc/fortran/io.c
===================================================================
--- gcc/fortran/io.c    (revision 201382)
+++ gcc/fortran/io.c    (working copy)
@@ -192,23 +192,14 @@ unget_char (void)
 /* Eat up the spaces and return a character.  */

 static char
-next_char_not_space (bool *error)
+next_char_not_space ()
 {
   char c;
   do
     {
       error_element = c = next_char (NONSTRING);
-      if (c == '\t')
-    {
-      if (gfc_option.allow_std & GFC_STD_GNU)
-        gfc_warning ("Extension: Tab character in format at %C");
-      else
-        {
-          gfc_error ("Extension: Tab character in format at %C");
-          *error = true;
-          return c;
-        }
-    }
+      if (!gfc_option.warn_tabs && c == '\t')
+      gfc_warning ("Nonconforming tab character in FORMAT at %C");
     }
   while (gfc_is_whitespace (c));
   return c;
@@ -226,7 +217,6 @@ format_lex (void)
   char c, delim;
   int zflag;
   int negative_flag;
-  bool error = false;

   if (saved_token != FMT_NONE)
     {
@@ -235,7 +225,7 @@ format_lex (void)
       return token;
     }

-  c = next_char_not_space (&error);
+  c = next_char_not_space ();

   negative_flag = 0;
   switch (c)
@@ -245,7 +235,7 @@ format_lex (void)
       /* Falls through.  */

     case '+':
-      c = next_char_not_space (&error);
+      c = next_char_not_space ();
       if (!ISDIGIT (c))
     {
       token = FMT_UNKNOWN;
@@ -256,7 +246,7 @@ format_lex (void)

       do
     {
-      c = next_char_not_space (&error);
+      c = next_char_not_space ();
       if (ISDIGIT (c))
         value = 10 * value + c - '0';
     }
@@ -286,7 +276,7 @@ format_lex (void)

       do
     {
-      c = next_char_not_space (&error);
+      c = next_char_not_space ();
       if (ISDIGIT (c))
         {
           value = 10 * value + c - '0';
@@ -321,7 +311,7 @@ format_lex (void)
       break;

     case 'T':
-      c = next_char_not_space (&error);
+      c = next_char_not_space ();
       switch (c)
     {
     case 'L':
@@ -349,7 +339,7 @@ format_lex (void)
       break;

     case 'S':
-      c = next_char_not_space (&error);
+      c = next_char_not_space ();
       if (c != 'P' && c != 'S')
     unget_char ();

@@ -357,7 +347,7 @@ format_lex (void)
       break;

     case 'B':
-      c = next_char_not_space (&error);
+      c = next_char_not_space ();
       if (c == 'N' || c == 'Z')
     token = FMT_BLANK;
       else
@@ -419,7 +409,7 @@ format_lex (void)
       break;

     case 'E':
-      c = next_char_not_space (&error);
+      c = next_char_not_space ();
       if (c == 'N' )
     token = FMT_EN;
       else if (c == 'S')
@@ -449,7 +439,7 @@ format_lex (void)
       break;

     case 'D':
-      c = next_char_not_space (&error);
+      c = next_char_not_space ();
       if (c == 'P')
     {
       if (!gfc_notify_std (GFC_STD_F2003, "DP format "
@@ -472,7 +462,7 @@ format_lex (void)
       break;

     case 'R':
-      c = next_char_not_space (&error);
+      c = next_char_not_space ();
       switch (c)
     {
     case 'C':
@@ -513,9 +503,6 @@ format_lex (void)
       break;
     }

-  if (error)
-    return FMT_ERROR;
-
   return token;
 }

Index: gcc/testsuite/gfortran.dg/fmt_tab_1.f90
===================================================================
--- gcc/testsuite/gfortran.dg/fmt_tab_1.f90    (revision 201382)
+++ gcc/testsuite/gfortran.dg/fmt_tab_1.f90    (working copy)
@@ -1,6 +1,9 @@
-! { dg-do run }
+! { dg-do compile }
+! { dg-options "-Wtabs" }
 ! PR fortran/32987
       program TestFormat
         write (*, 10)
- 10     format ('Hello ',    'bug!') ! { dg-warning "Extension: Tab character
in format" }
+        ! There is a tab character before 'bug'.  This is accepted without
+        ! the -Wno-tabs option or a -std= option.
+ 10     format ('Hello ',    'bug!')
       end
Index: gcc/testsuite/gfortran.dg/fmt_tab_2.f90
===================================================================
--- gcc/testsuite/gfortran.dg/fmt_tab_2.f90    (revision 201382)
+++ gcc/testsuite/gfortran.dg/fmt_tab_2.f90    (working copy)
@@ -2,6 +2,6 @@
 ! { dg-options "-std=f2003" }
 ! PR fortran/32987
       program TestFormat
-        write (*, 10) ! { dg-error "FORMAT label 10 at .1. not defined" }
- 10     format ('Hello ',    'bug!') ! { dg-error "Extension: Tab character in
format" }
+        write (*, 10)
+ 10     format ('Hello ',    'bug!') ! { dg-warning "tab character in FORMAT"
}
       end