[RFC] Fix pager bugs with style output

  >>>>> "Joel" == Joel Brobecker <brobecker@adacore.com> writes:

Joel> Thanks for this! I haven't looked at the patch itself (and got
Joel> a bit scared by the "hard to reason about" part...),

:)

Here's an updated version that fixes these problems.

Tom

commit 38209a5a87bd7532e61b386fa858b1b9011de7b9
Author: Tom Tromey <tom@tromey.com>
Date:   Thu Feb 7 06:23:40 2019 -0700

    Fix pager bugs with style output
    
    I believe this fixes all the pager output problems with styling that
    Philippe pointed out, plus at least one more.  The patch is somewhat
    hard to reason about, so you may wish to give it a try.  Even writing
    the tests was hard.
    
    This removes the style caching, because it was difficult to keep the
    style cache correct in all cases.  Since this would cause more style
    escapes to be emitted, instead it changes fputs_styled to try to avoid
    unnecessary changes.
    
    Another bug was that the wrap buffer was not flushed in the case where
    wrap_column==0.  In the old (pre-patch series) code, characters were
    directly emitted in this case; so flushing the wrap buffer here
    restores this behavior.
    
    On error the wrap buffer must be emptied.  Otherwise, interrupting
    output can leave characters in the buffer that will be emitted later.
    
    As discussed on gdb-patches, this fixes the ada-lang.c problem where
    filtered and unfiltered printing were mixed.  Now user_select_syms
    uses filtered printing, which is what its callees were already doing.
    
    Finally, it was possible for source line highlighting to be garbled
    (and invalid escape sequences emitted) if the pager was invoked at the
    wrong spot.  To fix this, the patch arranges for source line escapes
    to always be emitted as a unit.
    
    gdb/ChangeLog
    2019-02-12  Tom Tromey  <tom@tromey.com>
    
            * ada-lang.c (user_select_syms): Use filtered printing.
            * utils.c (wrap_style): New global.
            (desired_style): Remove.
            (emit_style_escape): Add stream parameter.
            (set_output_style, reset_terminal_style, prompt_for_continue):
            Update.
            (flush_wrap_buffer): Only flush gdb_stdout.
            (wrap_here): Set wrap_style.
            (fputs_maybe_filtered): Clear the wrap buffer on exception.  Don't
            treat escape sequences as a character.  Change when wrap buffer is
            flushed.
            (fputs_styled): Do not set the output style when the default is
            requested.
            * ui-style.h (struct ui_file_style) <is_default>: New method.
            * source.c (print_source_lines_base): Emit escape sequences in one
            piece.
    
    gdb/testsuite/ChangeLog
    2019-02-07  Tom Tromey  <tom@tromey.com>
    
            * gdb.base/style.exp: Add line-wrapping tests.
            * gdb.base/page.exp: Add test for quitting during pagination.
  

Hi Tom,

> Here's an updated version that fixes these problems.

Thanks Tom! This whole thing _is_ complex, and I understand now why
you took out the style caching..

> commit 38209a5a87bd7532e61b386fa858b1b9011de7b9
> Author: Tom Tromey <tom@tromey.com>
> Date:   Thu Feb 7 06:23:40 2019 -0700
> 
>     Fix pager bugs with style output
>     
>     I believe this fixes all the pager output problems with styling that
>     Philippe pointed out, plus at least one more.  The patch is somewhat
>     hard to reason about, so you may wish to give it a try.  Even writing
>     the tests was hard.
>     
>     This removes the style caching, because it was difficult to keep the
>     style cache correct in all cases.  Since this would cause more style
>     escapes to be emitted, instead it changes fputs_styled to try to avoid
>     unnecessary changes.
>     
>     Another bug was that the wrap buffer was not flushed in the case where
>     wrap_column==0.  In the old (pre-patch series) code, characters were
>     directly emitted in this case; so flushing the wrap buffer here
>     restores this behavior.
>     
>     On error the wrap buffer must be emptied.  Otherwise, interrupting
>     output can leave characters in the buffer that will be emitted later.
>     
>     As discussed on gdb-patches, this fixes the ada-lang.c problem where
>     filtered and unfiltered printing were mixed.  Now user_select_syms
>     uses filtered printing, which is what its callees were already doing.
>     
>     Finally, it was possible for source line highlighting to be garbled
>     (and invalid escape sequences emitted) if the pager was invoked at the
>     wrong spot.  To fix this, the patch arranges for source line escapes
>     to always be emitted as a unit.
>     
>     gdb/ChangeLog
>     2019-02-12  Tom Tromey  <tom@tromey.com>
>     
>             * ada-lang.c (user_select_syms): Use filtered printing.
>             * utils.c (wrap_style): New global.
>             (desired_style): Remove.
>             (emit_style_escape): Add stream parameter.
>             (set_output_style, reset_terminal_style, prompt_for_continue):
>             Update.
>             (flush_wrap_buffer): Only flush gdb_stdout.
>             (wrap_here): Set wrap_style.
>             (fputs_maybe_filtered): Clear the wrap buffer on exception.  Don't
>             treat escape sequences as a character.  Change when wrap buffer is
>             flushed.
>             (fputs_styled): Do not set the output style when the default is
>             requested.
>             * ui-style.h (struct ui_file_style) <is_default>: New method.
>             * source.c (print_source_lines_base): Emit escape sequences in one
>             piece.
>     
>     gdb/testsuite/ChangeLog
>     2019-02-07  Tom Tromey  <tom@tromey.com>
>     
>             * gdb.base/style.exp: Add line-wrapping tests.
>             * gdb.base/page.exp: Add test for quitting during pagination.

Good news: As far as I can tell, this patch fixes all issues detected
by the AdaCore testsuite :-).

I reviewed the patch as best as I could, and the changes make sense
to me. Ingesting more in detail how the pager and the line wrapping
works might yield a more throrough review; but between the new testcases
and AdaCore's testsuite, I think it's pretty good. If there are bugs
still left lurking, we can address them one by one, with corresponding
testcases.

One thought, perhaps: Would it make sense to call can_emit_style_escape
inside emit_style_escape? I'm not entirely sure whether this would
always work or not. On the one hand, the issue with relying on callers
of emit_style_escape to verify that it makes sense is that we're bound
to forget again in the future. On the other hand, I'm trying to think
what would happen is a user changed XTERM from xterm to dump, for
instance. Normally, we should always be in the normal style when the
user has the prompt, so there would be no need to reset it back to
the default style. One thing I did notice is that a couple of calls
to emit_style_escape are unprotected in prompt_for_continue: From
what I can tell, it seems like we'd be emitting ansi sequences when
in fact we shouldn't?

Other than that, everything looked OK for me.

> diff --git a/gdb/ChangeLog b/gdb/ChangeLog
> index 4ab3af01982..b0bef57f52b 100644
> --- a/gdb/ChangeLog
> +++ b/gdb/ChangeLog
> @@ -1,3 +1,22 @@
> +2019-02-12  Tom Tromey  <tom@tromey.com>
> +
> +	* ada-lang.c (user_select_syms): Use filtered printing.
> +	* utils.c (wrap_style): New global.
> +	(desired_style): Remove.
> +	(emit_style_escape): Add stream parameter.
> +	(set_output_style, reset_terminal_style, prompt_for_continue):
> +	Update.
> +	(flush_wrap_buffer): Only flush gdb_stdout.
> +	(wrap_here): Set wrap_style.
> +	(fputs_maybe_filtered): Clear the wrap buffer on exception.  Don't
> +	treat escape sequences as a character.  Change when wrap buffer is
> +	flushed.
> +	(fputs_styled): Do not set the output style when the default is
> +	requested.
> +	* ui-style.h (struct ui_file_style) <is_default>: New method.
> +	* source.c (print_source_lines_base): Emit escape sequences in one
> +	piece.
> +
>  2019-02-11  Alan Hayward  <alan.hayward@arm.com>
>  
>  	* aarch64-linux-tdep.c (aarch64_linux_get_syscall_number): Check
> diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
> index a878d4d1af2..d33c7571a47 100644
> --- a/gdb/ada-lang.c
> +++ b/gdb/ada-lang.c
> @@ -3903,16 +3903,16 @@ user_select_syms (struct block_symbol *syms, int nsyms, int max_results)
>      error (_("\
>  canceled because the command is ambiguous\n\
>  See set/show multiple-symbol."));
> -  
> +
>    /* If select_mode is "all", then return all possible symbols.
>       Only do that if more than one symbol can be selected, of course.
>       Otherwise, display the menu as usual.  */
>    if (select_mode == multiple_symbols_all && max_results > 1)
>      return nsyms;
>  
> -  printf_unfiltered (_("[0] cancel\n"));
> +  printf_filtered (_("[0] cancel\n"));
>    if (max_results > 1)
> -    printf_unfiltered (_("[1] all\n"));
> +    printf_filtered (_("[1] all\n"));
>  
>    sort_choices (syms, nsyms);
>  
> @@ -3926,16 +3926,16 @@ See set/show multiple-symbol."));
>            struct symtab_and_line sal =
>              find_function_start_sal (syms[i].symbol, 1);
>  
> -	  printf_unfiltered ("[%d] ", i + first_choice);
> +	  printf_filtered ("[%d] ", i + first_choice);
>  	  ada_print_symbol_signature (gdb_stdout, syms[i].symbol,
>  				      &type_print_raw_options);
>  	  if (sal.symtab == NULL)
> -	    printf_unfiltered (_(" at <no source file available>:%d\n"),
> -			       sal.line);
> +	    printf_filtered (_(" at <no source file available>:%d\n"),
> +			     sal.line);
>  	  else
> -	    printf_unfiltered (_(" at %s:%d\n"),
> -			       symtab_to_filename_for_display (sal.symtab),
> -			       sal.line);
> +	    printf_filtered (_(" at %s:%d\n"),
> +			     symtab_to_filename_for_display (sal.symtab),
> +			     sal.line);
>            continue;
>          }
>        else
> @@ -3951,37 +3951,37 @@ See set/show multiple-symbol."));
>  
>            if (SYMBOL_LINE (syms[i].symbol) != 0 && symtab != NULL)
>  	    {
> -	      printf_unfiltered ("[%d] ", i + first_choice);
> +	      printf_filtered ("[%d] ", i + first_choice);
>  	      ada_print_symbol_signature (gdb_stdout, syms[i].symbol,
>  					  &type_print_raw_options);
> -	      printf_unfiltered (_(" at %s:%d\n"),
> -				 symtab_to_filename_for_display (symtab),
> -				 SYMBOL_LINE (syms[i].symbol));
> +	      printf_filtered (_(" at %s:%d\n"),
> +			       symtab_to_filename_for_display (symtab),
> +			       SYMBOL_LINE (syms[i].symbol));
>  	    }
>            else if (is_enumeral
>                     && TYPE_NAME (SYMBOL_TYPE (syms[i].symbol)) != NULL)
>              {
> -              printf_unfiltered (("[%d] "), i + first_choice);
> +              printf_filtered (("[%d] "), i + first_choice);
>                ada_print_type (SYMBOL_TYPE (syms[i].symbol), NULL,
>                                gdb_stdout, -1, 0, &type_print_raw_options);
> -              printf_unfiltered (_("'(%s) (enumeral)\n"),
> -                                 SYMBOL_PRINT_NAME (syms[i].symbol));
> +              printf_filtered (_("'(%s) (enumeral)\n"),
> +			       SYMBOL_PRINT_NAME (syms[i].symbol));
>              }
>  	  else
>  	    {
> -	      printf_unfiltered ("[%d] ", i + first_choice);
> +	      printf_filtered ("[%d] ", i + first_choice);
>  	      ada_print_symbol_signature (gdb_stdout, syms[i].symbol,
>  					  &type_print_raw_options);
>  
>  	      if (symtab != NULL)
> -		printf_unfiltered (is_enumeral
> -				   ? _(" in %s (enumeral)\n")
> -				   : _(" at %s:?\n"),
> -				   symtab_to_filename_for_display (symtab));
> +		printf_filtered (is_enumeral
> +				 ? _(" in %s (enumeral)\n")
> +				 : _(" at %s:?\n"),
> +				 symtab_to_filename_for_display (symtab));
>  	      else
> -		printf_unfiltered (is_enumeral
> -				   ? _(" (enumeral)\n")
> -				   : _(" at ?\n"));
> +		printf_filtered (is_enumeral
> +				 ? _(" (enumeral)\n")
> +				 : _(" at ?\n"));
>  	    }
>          }
>      }
> diff --git a/gdb/source.c b/gdb/source.c
> index c32b7c66b15..f99215f9810 100644
> --- a/gdb/source.c
> +++ b/gdb/source.c
> @@ -1249,7 +1249,6 @@ static void
>  print_source_lines_base (struct symtab *s, int line, int stopline,
>  			 print_source_lines_flags flags)
>  {
> -  int c;
>    scoped_fd desc;
>    int noprint = 0;
>    int nlines = stopline - line;
> @@ -1343,13 +1342,10 @@ print_source_lines_base (struct symtab *s, int line, int stopline,
>  	   line, symtab_to_filename_for_display (s), s->nlines);
>  
>    const char *iter = lines.c_str ();
> -  while (nlines-- > 0)
> +  while (nlines-- > 0 && *iter != '\0')
>      {
>        char buf[20];
>  
> -      c = *iter++;
> -      if (c == '\0')
> -	break;
>        last_line_listed = current_source_line;
>        if (flags & PRINT_SOURCE_LINES_FILENAME)
>          {
> @@ -1358,33 +1354,55 @@ print_source_lines_base (struct symtab *s, int line, int stopline,
>          }
>        xsnprintf (buf, sizeof (buf), "%d\t", current_source_line++);
>        uiout->text (buf);
> -      do
> +
> +      while (*iter != '\0')
>  	{
> -	  if (c < 040 && c != '\t' && c != '\n' && c != '\r' && c != '\033')
> +	  /* Find a run of characters that can be emitted at once.
> +	     This is done so that escape sequences are kept
> +	     together.  */
> +	  const char *start = iter;
> +	  while (true)
>  	    {
> -	      xsnprintf (buf, sizeof (buf), "^%c", c + 0100);
> -	      uiout->text (buf);
> +	      int skip_bytes;
> +
> +	      char c = *iter;
> +	      if (c == '\033' && skip_ansi_escape (iter, &skip_bytes))
> +		iter += skip_bytes;
> +	      else if (c < 040 && c != '\t')
> +		break;
> +	      else if (c == 0177)
> +		break;
> +	      else
> +		++iter;
>  	    }
> -	  else if (c == 0177)
> -	    uiout->text ("^?");
> -	  else if (c == '\r')
> +	  if (iter > start)
>  	    {
> -	      /* Skip a \r character, but only before a \n.  */
> -	      if (*iter != '\n')
> -		printf_filtered ("^%c", c + 0100);
> +	      std::string text (start, iter);
> +	      uiout->text (text.c_str ());
>  	    }
> -	  else
> +	  if (*iter == '\r')
>  	    {
> -	      xsnprintf (buf, sizeof (buf), "%c", c);
> +	      /* Treat either \r or \r\n as a single newline.  */
> +	      ++iter;
> +	      if (*iter == '\n')
> +		++iter;
> +	      break;
> +	    }
> +	  else if (*iter == '\n')
> +	    {
> +	      ++iter;
> +	      break;
> +	    }
> +	  else if (*iter > 0 && *iter < 040)
> +	    {
> +	      xsnprintf (buf, sizeof (buf), "^%c", *iter + 0100);
>  	      uiout->text (buf);
>  	    }
> +	  else if (*iter == 0177)
> +	    uiout->text ("^?");
>  	}
> -      while (c != '\n' && (c = *iter++) != '\0');
> -      if (c == '\0')
> -	break;
> +      uiout->text ("\n");
>      }
> -  if (!lines.empty() && lines.back () != '\n')
> -    uiout->text ("\n");
>  }
>  
>  
> diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
> index d963997d8bf..906b774c8ba 100644
> --- a/gdb/testsuite/ChangeLog
> +++ b/gdb/testsuite/ChangeLog
> @@ -1,3 +1,8 @@
> +2019-02-07  Tom Tromey  <tom@tromey.com>
> +
> +	* gdb.base/style.exp: Add line-wrapping tests.
> +	* gdb.base/page.exp: Add test for quitting during pagination.
> +
>  2019-02-10  Joel Brobecker  <brobecker@adacore.com>
>  
>  	* gdb.ada/mi_ref_changeable: New testcase.
> diff --git a/gdb/testsuite/gdb.base/page.exp b/gdb/testsuite/gdb.base/page.exp
> index 74615911d25..10ebf0d43b2 100644
> --- a/gdb/testsuite/gdb.base/page.exp
> +++ b/gdb/testsuite/gdb.base/page.exp
> @@ -80,6 +80,20 @@ gdb_expect_list "paged count remainder" "${gdb_prompt} " {
>      11
>  }
>  
> +set fours [string repeat 4 40]
> +set str "1\\n2\\n3\\n$fours\\n5\\n"
> +
> +# Avoid some confusing output from readline.
> +gdb_test_no_output "set editing off"
> +
> +gdb_test_no_output "set width 30"
> +send_gdb "printf \"$str\"\n"
> +gdb_expect_list "paged count for interrupt" \
> +    ".*$pagination_prompt" \
> +    [list 1\r\n 2\r\n 3\r\n 444444444444444444444444444444]
> +
> +gdb_test "q" "Quit" "quit while paging"
> +
>  gdb_exit
>  return 0
>  
> diff --git a/gdb/testsuite/gdb.base/style.exp b/gdb/testsuite/gdb.base/style.exp
> index 78d04b02903..010d9592f34 100644
> --- a/gdb/testsuite/gdb.base/style.exp
> +++ b/gdb/testsuite/gdb.base/style.exp
> @@ -45,6 +45,24 @@ save_vars { env(TERM) } {
>  
>      gdb_test "print &main" " = .* \033\\\[34m$hex\033\\\[m <$main_expr>"
>  
> +    # Regression test for a bug where line-wrapping would occur at the
> +    # wrong spot with styling.  There were different bugs at different
> +    # widths, so try two.
> +    foreach width {20 30} {
> +	gdb_test_no_output "set width $width"
> +	# There was also a bug where the styling could be wrong in the
> +	# line listing; this is why the words from the source code are
> +	# spelled out in the final result line of the test.
> +	gdb_test "frame" \
> +	    [multi_line \
> +		 "#0 *$main_expr.*$arg_expr.*" \
> +		 ".*$arg_expr.*" \
> +		 ".* at .*$file_expr.*" \
> +		 "\[0-9\]+.*return.* break here .*"
> +	    ] \
> +	    "frame when width=$width"
> +    }
> +
>      gdb_exit
>      gdb_spawn
>  
> diff --git a/gdb/ui-style.h b/gdb/ui-style.h
> index d719438c726..04a1d448ba9 100644
> --- a/gdb/ui-style.h
> +++ b/gdb/ui-style.h
> @@ -163,6 +163,16 @@ struct ui_file_style
>    /* Return the ANSI escape sequence for this style.  */
>    std::string to_ansi () const;
>  
> +  /* Return true if this style is the default style; false
> +     otherwise.  */
> +  bool is_default () const
> +  {
> +    return (m_foreground == NONE
> +	    && m_background == NONE
> +	    && m_intensity == NORMAL
> +	    && !m_reverse);
> +  }
> +
>    /* Return true if this style specified reverse display; false
>       otherwise.  */
>    bool is_reverse () const
> diff --git a/gdb/utils.c b/gdb/utils.c
> index 6fb5736abb5..c383a4bff06 100644
> --- a/gdb/utils.c
> +++ b/gdb/utils.c
> @@ -72,6 +72,7 @@
>  #include <algorithm>
>  #include "common/pathstuff.h"
>  #include "cli/cli-style.h"
> +#include "common/scope-exit.h"
>  
>  void (*deprecated_error_begin_hook) (void);
>  
> @@ -1282,6 +1283,9 @@ static const char *wrap_indent;
>  /* Column number on the screen where wrap_buffer begins, or 0 if wrapping
>     is not in effect.  */
>  static int wrap_column;
> +
> +/* The style applied at the time that wrap_here was called.  */
> +static ui_file_style wrap_style;
>  
>  
>  /* Initialize the number of lines per page and chars per line.  */
> @@ -1427,21 +1431,19 @@ set_screen_width_and_height (int width, int height)
>  
>  static ui_file_style applied_style;
>  
> -/* The currently desired style.  This can differ from the applied
> -   style when showing the pagination prompt.  */
> -
> -static ui_file_style desired_style;
> -
> -/* Emit an ANSI style escape for STYLE to the wrap buffer.  */
> +/* Emit an ANSI style escape for STYLE.  If STREAM is nullptr, emit to
> +   the wrap buffer; otherwise emit to STREAM.  */
>  
>  static void
> -emit_style_escape (const ui_file_style &style)
> +emit_style_escape (const ui_file_style &style,
> +		   struct ui_file *stream = nullptr)
>  {
> -  if (applied_style == style)
> -    return;
>    applied_style = style;
>  
> -  wrap_buffer.append (style.to_ansi ());
> +  if (stream == nullptr)
> +    wrap_buffer.append (style.to_ansi ());
> +  else
> +    fputs_unfiltered (style.to_ansi ().c_str (), stream);
>  }
>  
>  /* See utils.h.  */
> @@ -1465,11 +1467,9 @@ can_emit_style_escape (struct ui_file *stream)
>  static void
>  set_output_style (struct ui_file *stream, const ui_file_style &style)
>  {
> -  if (!can_emit_style_escape (stream)
> -      || style == desired_style)
> +  if (!can_emit_style_escape (stream))
>      return;
>  
> -  desired_style = style;
>    emit_style_escape (style);
>  }
>  
> @@ -1482,9 +1482,8 @@ reset_terminal_style (struct ui_file *stream)
>      {
>        /* Force the setting, regardless of what we think the setting
>  	 might already be.  */
> -      desired_style = ui_file_style ();
> -      applied_style = desired_style;
> -      wrap_buffer.append (desired_style.to_ansi ());
> +      applied_style = ui_file_style ();
> +      wrap_buffer.append (applied_style.to_ansi ());
>      }
>  }
>  
> @@ -1551,7 +1550,7 @@ prompt_for_continue (void)
>    pagination_disabled_for_command = disable_pagination;
>  
>    /* Restore the current styling.  */
> -  emit_style_escape (desired_style);
> +  emit_style_escape (applied_style);
>  
>    dont_repeat ();		/* Forget prev cmd -- CR won't repeat it.  */
>  }
> @@ -1589,7 +1588,7 @@ reinitialize_more_filter (void)
>  static void
>  flush_wrap_buffer (struct ui_file *stream)
>  {
> -  if (!wrap_buffer.empty ())
> +  if (stream == gdb_stdout && !wrap_buffer.empty ())
>      {
>        fputs_unfiltered (wrap_buffer.c_str (), stream);
>        wrap_buffer.clear ();
> @@ -1644,6 +1643,7 @@ wrap_here (const char *indent)
>  	wrap_indent = "";
>        else
>  	wrap_indent = indent;
> +      wrap_style = applied_style;
>      }
>  }
>  
> @@ -1743,6 +1743,14 @@ fputs_maybe_filtered (const char *linebuffer, struct ui_file *stream,
>        return;
>      }
>  
> +  auto buffer_clearer
> +    = make_scope_exit ([&] ()
> +		       {
> +			 wrap_buffer.clear ();
> +			 wrap_column = 0;
> +			 wrap_indent = "";
> +		       });
> +
>    /* Go through and output each character.  Show line extension
>       when this is necessary; prompt user for new page when this is
>       necessary.  */
> @@ -1759,6 +1767,8 @@ fputs_maybe_filtered (const char *linebuffer, struct ui_file *stream,
>  
>        while (*lineptr && *lineptr != '\n')
>  	{
> +	  int skip_bytes;
> +
>  	  /* Print a single line.  */
>  	  if (*lineptr == '\t')
>  	    {
> @@ -1769,6 +1779,14 @@ fputs_maybe_filtered (const char *linebuffer, struct ui_file *stream,
>  	      chars_printed = ((chars_printed >> 3) + 1) << 3;
>  	      lineptr++;
>  	    }
> +	  else if (*lineptr == '\033'
> +		   && skip_ansi_escape (lineptr, &skip_bytes))
> +	    {
> +	      wrap_buffer.append (lineptr, skip_bytes);
> +	      /* Note that we don't consider this a character, so we
> +		 don't increment chars_printed here.  */
> +	      lineptr += skip_bytes;
> +	    }
>  	  else
>  	    {
>  	      wrap_buffer.push_back (*lineptr);
> @@ -1782,15 +1800,18 @@ fputs_maybe_filtered (const char *linebuffer, struct ui_file *stream,
>  
>  	      chars_printed = 0;
>  	      lines_printed++;
> -	      /* If we aren't actually wrapping, don't output newline --
> -	         if chars_per_line is right, we probably just overflowed
> -	         anyway; if it's wrong, let us keep going.  */
>  	      if (wrap_column)
>  		{
> -		  emit_style_escape (ui_file_style ());
> -		  flush_wrap_buffer (stream);
> +		  if (can_emit_style_escape (stream))
> +		    emit_style_escape (ui_file_style (), stream);
> +		  /* If we aren't actually wrapping, don't output
> +		     newline -- if chars_per_line is right, we
> +		     probably just overflowed anyway; if it's wrong,
> +		     let us keep going.  */
>  		  fputc_unfiltered ('\n', stream);
>  		}
> +	      else
> +		flush_wrap_buffer (stream);
>  
>  	      /* Possible new page.  Note that
>  		 PAGINATION_DISABLED_FOR_COMMAND might be set during
> @@ -1803,8 +1824,8 @@ fputs_maybe_filtered (const char *linebuffer, struct ui_file *stream,
>  	      if (wrap_column)
>  		{
>  		  fputs_unfiltered (wrap_indent, stream);
> -		  emit_style_escape (desired_style);
> -		  flush_wrap_buffer (stream);
> +		  if (can_emit_style_escape (stream))
> +		    emit_style_escape (wrap_style, stream);
>  		  /* FIXME, this strlen is what prevents wrap_indent from
>  		     containing tabs.  However, if we recurse to print it
>  		     and count its chars, we risk trouble if wrap_indent is
> @@ -1828,6 +1849,8 @@ fputs_maybe_filtered (const char *linebuffer, struct ui_file *stream,
>  	  lineptr++;
>  	}
>      }
> +
> +  buffer_clearer.release ();
>  }
>  
>  void
> @@ -1842,9 +1865,16 @@ void
>  fputs_styled (const char *linebuffer, const ui_file_style &style,
>  	      struct ui_file *stream)
>  {
> -  set_output_style (stream, style);
> -  fputs_maybe_filtered (linebuffer, stream, 1);
> -  set_output_style (stream, ui_file_style ());
> +  /* This just makes it so we emit somewhat fewer escape
> +     sequences.  */
> +  if (style.is_default ())
> +    fputs_maybe_filtered (linebuffer, stream, 1);
> +  else
> +    {
> +      set_output_style (stream, style);
> +      fputs_maybe_filtered (linebuffer, stream, 1);
> +      set_output_style (stream, ui_file_style ());
> +    }
>  }
>  
>  int
  

>>>>> "Joel" == Joel Brobecker <brobecker@adacore.com> writes:

Joel> One thought, perhaps: Would it make sense to call can_emit_style_escape
Joel> inside emit_style_escape? I'm not entirely sure whether this would
Joel> always work or not. On the one hand, the issue with relying on callers
Joel> of emit_style_escape to verify that it makes sense is that we're bound
Joel> to forget again in the future. On the other hand, I'm trying to think
Joel> what would happen is a user changed XTERM from xterm to dump, for
Joel> instance. Normally, we should always be in the normal style when the
Joel> user has the prompt, so there would be no need to reset it back to
Joel> the default style. One thing I did notice is that a couple of calls
Joel> to emit_style_escape are unprotected in prompt_for_continue: From
Joel> what I can tell, it seems like we'd be emitting ansi sequences when
Joel> in fact we shouldn't?

This is all more subtle than I would like :(

The call to emit_style_escape in set_output_style deliberately does not
pass the stream argument.  But, it does test can_emit_style_escape on
the stream.  Changing this causes regressions because now the output
won't end up in the wrap buffer.  I added a comment to set_output_style.

The calls to in prompt_for_continue do indeed need protection now that
the caching is gone.  I've fixed these.  Also they were emitting to the
wrap buffer, which seems wrong (at least for the first one), because the
wrap buffer isn't flushed here.

There are still mysteries in here to me, too, like why one call to
prompt_for_continue checks "filter" but the other does not.

Tom