code review 163068: Add flag -tabindent to gofmt: forces use of

Add flag -tabindent to gofmt: forces use of
tabs for indentation even if -spaces is set.

Changes to gofmt:
- added -tabindent flag
- don't recompute parser and printer mode repeatedly

Changes to go/printer:
- provide new printing mode TabIndent

Changes to tabwriter:
- implement new mode TabIndent to use tabs independent
  of the actual padding character for leading empty columns
- distinguish between minimal cell width and tab width
  (tabwidth is only used if the output contains tabs,
  minwidth and padding are always considered)
- fixed and added more comments
- some additional factoring

By default, -tabindent is disabled and the default gofmt
behavior is unchanged. By setting -spaces and -tabindent,
gofmt will use tabs for indentation but do any other
alignment with spaces. This permits a user to change the
visible indentation by simply changing the editor's tab
width and the code will remain properly aligned without
the need to rerun gofmt.

[gri, 2009-12-02 04:57:08]

Hello rsc,

I'd like you to review the following change.

[rsc, 2009-12-03 00:51:45]

LGTM

This is going to be painful to roll out.

[gri, 2009-12-03 00:57:17]

*** Submitted as http://code.google.com/p/go/source/detail?r=17d3ac883eb2 ***

Add flag -tabindent to gofmt: forces use of
tabs for indentation even if -spaces is set.

Changes to gofmt:
- added -tabindent flag
- don't recompute parser and printer mode repeatedly

Changes to go/printer:
- provide new printing mode TabIndent

Changes to tabwriter:
- implement new mode TabIndent to use tabs independent
  of the actual padding character for leading empty columns
- distinguish between minimal cell width and tab width
  (tabwidth is only used if the output contains tabs,
  minwidth and padding are always considered)
- fixed and added more comments
- some additional factoring

By default, -tabindent is disabled and the default gofmt
behavior is unchanged. By setting -spaces and -tabindent,
gofmt will use tabs for indentation but do any other
alignment with spaces. This permits a user to change the
visible indentation by simply changing the editor's tab
width and the code will remain properly aligned without
the need to rerun gofmt.

R=rsc
http://codereview.appspot.com/163068

[gri, 2009-12-03 00:58:51]

I am suggesting that we don't change the default quite yet. There may
be some fine-tuning, and if we change the semicolon handling we should
combine the two. In the meantime, godoc can use the new mode.
- Robert

On Wednesday, December 2, 2009,  <rsc@golang.org> wrote:
> LGTM
>
> This is going to be painful to roll out.
>
>
> http://codereview.appspot.com/163068
>

[rsc, 2009-12-03 01:05:29]

On Wed, Dec 2, 2009 at 16:58, Robert Griesemer <gri@golang.org> wrote:
> I am suggesting that we don't change the default quite yet. There may
> be some fine-tuning, and if we change the semicolon handling we should
> combine the two. In the meantime, godoc can use the new mode.

good plan