[PATCH v1 0/4] Remove obsolete Cygwin support from git-gui

=== This is an update, incorporating responses to Junio's and Eric's
comments:
  -- clarified what the "upstream" git-gui branch is
  -- Removed some changes from patch 2 as requested by Junio, reducing
     changes in patch 3 and patch 4
       All code is fixed only after applying patch 4
       Differences in patch 3 and 4 are minimimized
   -- updated comments to clarify G4w dedicated code.
   -- updated all comments to (hopefully) clarify points of confusion
===

git-gui has many snippets of code guarded by an is_Cygwin test, all of which target a problematic hybrid Cygwin/Windows 8.4.1 Tcl/Tk removed from the Cygwin project in March 2012. That is when Cygwin switched to a well-supported unix/X11 Tcl/Tk package. 64-bit Cygwin was released later so has always had the unix/X11 package. git-gui runs as-is on more recent Cygwin, treating it as a Linux variant, though two functions are disabled.

The old Tcl/Tk understands Windows pathnames but has incomplete support for unix pathnames (for instance, all pathnames output by that Tcl are Windows, not unix). The Cygwin git executables all use unix pathnames (though like all Cygwin executables have some capability to accept Windows pathnames). git-gui's Cygwin specific code causes git-gui to use Windows pathnames everywhere. The unix/X11 Tcl/Tk requires use of unix pathname, so none of the Cygwin specific code is compatible.

git-gui is maintained at https://github.com/prati0100/git-gui. The git-gui in Junio's tree corresponds to commit c0698df057, behind the current git-gui master which is a5005ded.

Fortunately, the git-gui/is_Cygwin function in Junio's tree relies upon the old Tcl/Tk that outputs Windows pathnames. As this fails to detect Cygwin, git-gui treats Cygwin as a unix variant with no platform specific code enabled and git-gui currently runs on Cygwin.

But, commit c5766eae6f on the git-gui master branch fixes is_Cygwin to work with the new Tcl/Tk's signature (which is not that of a Windows Tcl/Tk). Thus, Cygwin is detected, the incompatible Cygwin code is enabled, and git-gui no longer runs on Cygwin.

Also, there is Cygwin specific code in the Makefile, intended to allow a completely unsupported configuration with a Windows Tcl/Tk. However, the Makefile code mis-identifies the unix/X11 Tcl/Tk as Windows, triggering insertion of a hardcoded Windows path to the library directory into git-gui making it non-portable. The Cygwin git maintainer comments this code out, but the code should be removed as it is demonstrated to be incompatible with Cygwin and targets a configuration Cygwin does not support.

The existing code for file browsing and creating a desktop icon is shared with Git For Windows support, and supports only Windows pathnames. This code does not work on Cygwin and needs replacement or update. The menu items for these functions are enabled by is_Cygwin, so appear only after is_Cygwin is fixed as discussed above.

patch 1 removes the obsolete Makefile code
patch 2 removes obsolete git-gui.sh code, wrapped in is_Cygwin
     except for code fixed in patches 3 and 4
patch 3 implements Cygwin specific file browsing support
patch 4 implements Cygwin specific desktop icon support

The end result is that git-gui on Cygwin is restored to the full capabilities existing prior to the Tcl/Tk switch in 2012. Also, the remaining Cygwin specific code, updated in patches 3 and 4, no longer overlaps with Git For Windows support.

Any argument for keeping the old Cygwin code must address who is going to test and maintain that code, on what platform, and who the target audience is. The old Tcl/Tk was only on 32-bit Cygwin and only supported for the Insight debugger, 32-bit Cygwin is no longer supported, git-gui is not supported on 8.4.1 Tcl/Tk, and the Windows versions targeted by 2012'ish 32-bit Cygwin are no longer supported.

Mark Levedahl (4):
  git gui Makefile - remove Cygwin modifications
  git-gui - remove obsolete Cygwin specific code
  git-gui - use cygstart to browse on Cygwin
  git-gui - use mkshortcut on Cygwin

 Makefile                  |  21 +------
 git-gui.sh                | 118 +++-----------------------------------
 lib/choose_repository.tcl |  27 +--------
 lib/shortcut.tcl          |  31 +++++-----
 4 files changed, 27 insertions(+), 170 deletions(-)