[PATCH v2 0/4] Sparse checkout completion fixes

This fixes a few issues with tab completion for the sparse-checkout command, specifically with the "add" and "set" subcommands.

As noted in v1, the 4th patch implements a somewhat suboptimal solution that at least improves the situation, while also documenting with a code comment a much more involved alternative solution that we could consider in the future.

Changes since v1:

 * Use __git wrapper function to squelch errors, as suggested by SZEDER
   Gábor
 * note that we could use the index or HEAD for the more involved solution
   in patch 4.

[1] https://lore.kernel.org/git/xmqqv8yjz5us.fsf@gitster.g/

Elijah Newren (4):
  completion: squelch stray errors in sparse-checkout completion
  completion: fix logic for determining whether cone mode is active
  completion: avoid misleading completions in cone mode
  completion: avoid user confusion in non-cone mode

 contrib/completion/git-completion.bash | 96 +++++++++++++++++++++++++-
 1 file changed, 93 insertions(+), 3 deletions(-)

base-commit: 564d0252ca632e0264ed670534a51d18a689ef5d
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1349%2Fnewren%2Fsparse-checkout-completion-fixes-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1349/newren/sparse-checkout-completion-fixes-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/1349

Range-diff vs v1:

 1:  591c7b8d73b ! 1:  97e20e3b99d completion: squelch stray errors in sparse-checkout completion
     @@ Commit message
              fatal: ../: '../' is outside repository at '/home/newren/floss/git'
      
          is written to stderr, which munges the users view of their own command.
     -    Squelch such messages.
     +    Squelch such messages by using the __git() wrapper, designed for this
     +    purpose; see commit e15098a314 (completion: consolidate silencing errors
     +    from git commands, 2017-02-03) for more on the wrapper.
      
          Signed-off-by: Elijah Newren <newren@gmail.com>
      
     @@ contrib/completion/git-completion.bash: __gitcomp_directories ()
       			_found=1
       		fi
      -	done < <(git ls-tree -z -d --name-only HEAD $_tmp_dir)
     -+	done < <(git ls-tree -z -d --name-only HEAD $_tmp_dir 2>/dev/null)
     ++	done < <(__git ls-tree -z -d --name-only HEAD $_tmp_dir)
       
       	if [[ $_found == 0 ]] && [[ "$cur" =~ /$ ]]; then
       		# No possible further completions any deeper, so assume we're at
 2:  a15fb054579 = 2:  212ba35ed46 completion: fix logic for determining whether cone mode is active
 3:  e8cc5c54e60 = 3:  1cbbcd9097c completion: avoid misleading completions in cone mode
 4:  fe8669a3f4f ! 4:  604f21dc827 completion: avoid user confusion in non-cone mode
     @@ contrib/completion/git-completion.bash: _git_sparse_checkout ()
      +			# completion function which:
      +			#
      +			#     1. Provides completions based on
     -+			#        files/directories that exist in HEAD, not
     -+			#        just those currently present in the working
     -+			#        tree.  Bash's default file and directory
     -+			#        completion is totally useless for "git
     -+			#        sparse-checkout add" because of this.  It is
     -+			#        likewise problematic for "git
     -+			#        sparse-checkout set" except in those subset
     -+			#        of cases when trying to narrow scope to a
     -+			#        strict subset of what you already have
     -+			#        checked out.
     ++			#        files/directories that exist in HEAD (or in
     ++			#        the index since sparse-index isn't possible
     ++			#        in non-cone mode), not just those currently
     ++			#        present in the working tree.  Bash's
     ++			#        default file and directory completion is
     ++			#        totally useless for "git sparse-checkout
     ++			#        add" because of this.  It is likewise
     ++			#        problematic for "git sparse-checkout set"
     ++			#        except in those subset of cases when trying
     ++			#        to narrow scope to a strict subset of what
     ++			#        you already have checked out.
      +			#
      +			#     2. Always provides file/directory completions
      +			#        with a prepended leading '/', so that