gdb/python/guile: check if styling is disabled in Color.escape_sequence

I noticed that the gdb.Color.escape_sequence() method would produce an
escape sequence even when styling is disabled.

I think this is the wrong choice.  Ideally, when styling is
disabled (e.g. with 'set style enabled off'), GDB should not be
producing styled output.

If a GDB extension is using gdb.Color to apply styling to the output,
then currently, the extension should be checking 'show style enabled'
any time Color.escape_sequence() is used.  This means lots of code
duplication, and the possibility that some locations will be missed,
which means disabling styling no longer does what it says.

I propose that Color.escape_sequence() should return the empty string
if styling is disabled.  A Python extension can then do:

  python
  c_none = gdb.Color('none')
  c_red = gdb.Color('red')
  print(c_red.escape_sequence(True)
        + "Text in red."
        + c_none.escape_sequence(True))
  end

If styling is enable this will print some red text.  And if styling is
disabled, then it will print text in the terminal's default color.

I have applied the same fix to the guile API.

I have extended the tests to cover this case.

Approved-By: Tom Tromey <tom@tromey.com>

2 files changed, 6 insertions, 0 deletions

diff --git a/gdb/doc/guile.texi b/gdb/doc/guile.texi
index c6808ef..c6d889f 100644
--- a/gdb/doc/guile.texi
+++ b/gdb/doc/guile.texi
@@ -3899,6 +3899,9 @@ Return string to change terminal's color to this.
 If @var{is_foreground} is @code{#t}, then the returned sequence will change
 foreground color.  Otherwise, the returned sequence will change background
 color.
+
+If styling is currently disabled (@pxref{Output Styling,,@kbd{set style
+enabled}}), then this procedure will return an empty string.
 @end deffn
 
 When color is initialized, its color space must be specified.  The
diff --git a/gdb/doc/python.texi b/gdb/doc/python.texi
index afbd62f..7bb6503 100644
--- a/gdb/doc/python.texi
+++ b/gdb/doc/python.texi
@@ -7101,6 +7101,9 @@ Returns string to change terminal's color to this.
 If @var{is_foreground} is @code{True}, then the returned sequence will change
 foreground color.  Otherwise, the returned sequence will change background
 color.
+
+If styling is currently disabled (@pxref{Output Styling,,@kbd{set style
+enabled}}), then this method will return an empty string.
 @end defun
 
 When color is initialized, its color space must be specified.  The