[PATCH v4 0/3] completion of 'git [-C <dir>] diff'

The primary motivation for this topic is that the command-line completion of 'git diff' does not handle paths (unlike 'git status' and 'git add') and instead relies on the default behavior of Bash command-line completion, which completes files in $PWD; this does not work at all with the '-C <directory>' option.

This series teaches the completion machinery to complete revisions (unless '--' exists), then tracked paths, and then untracked paths, before letting the Bash default kick in. This way, we correctly complete 'git diff' command line even when '-C <directory>' is in effect.

The tests are the only changes relative to v2. In the step where tracked paths are completed, v2 did not demonstrate that untracked ones are *not* completed at the same time. Now we do by having untracked 'file3' next to 'file1' and 'file2' that are tracked. In the last step, we demonstrate untracked paths that do not share prefix with refs or tracked paths are completed, with or without the "-C <dir>" option.

 1/3: completion: no-op refactoring of diff completion
 2/3: completion: complete tracked paths for 'git diff'
 3/3: completion: 'git diff' completes untracked paths as a last
        resort

 contrib/completion/git-completion.bash | 69 +++++++++++++++-----------
 t/t9902-completion.sh                  | 49 ++++++++++++++++++
 2 files changed, 90 insertions(+), 28 deletions(-)

Range-diff against v3:
1:  d3c51c042c = 1:  3b99b45fee completion: no-op refactoring of diff completion
2:  c3658d6ca2 ! 2:  bcc24b6bda completion: complete tracked paths for 'git diff'
    @@ contrib/completion/git-completion.bash: _git_diff ()
      __git_mergetools_common="diffuse diffmerge ecmerge emerge kdiff3 meld opendiff
     
      ## t/t9902-completion.sh ##
    +@@ t/t9902-completion.sh: test_expect_success 'setup for integration tests' '
    + 	echo content >file1 &&
    + 	echo more >file2 &&
    + 	git add file1 file2 &&
    ++	echo untracked >file3 &&
    + 	git commit -m one &&
    + 	git branch mybranch &&
    + 	git tag mytag
     @@ t/t9902-completion.sh: test_expect_success 'git -C <path> checkout uses the right repo' '
      	EOF
      '
      
     +test_expect_success 'git diff completes tracked paths when no refs match' '
     +	# file1 and file2 are tracked but file3 is not
    -+	test_completion "git diff f" <<-\EOF
    ++	# there is no ref that begins with f
    ++	test_completion "git diff f" <<-\EOF &&
     +	file1
     +	file2
     +	EOF
    -+'
    -+
    -+test_expect_success 'git diff -- completes tracked paths' '
    -+	# file1 and file2 are tracked but file3 is not
     +	test_completion "git diff -- f" <<-\EOF
     +	file1
     +	file2
     +	EOF
     +'
     +
    -+test_expect_success 'git -C <path> diff completes tracked paths in specified repo' '
    ++test_expect_success 'git -C <path> diff completes in the specified repo' '
     +	test_when_finished "rm -rf repo-for-diff" &&
     +	git init repo-for-diff &&
    ++
    ++	# otherfile is tracked, oops is untracked
     +	echo content >repo-for-diff/otherfile &&
     +	git -C repo-for-diff add otherfile &&
    -+	echo untracked >repo-for-diff/oops &&
     +	git -C repo-for-diff commit -m otherfile &&
    -+	test_completion "git -C repo-for-diff diff o" <<-\EOF
    ++	echo untracked >repo-for-diff/oops &&
    ++	test_completion "git -C repo-for-diff diff o" <<-\EOF &&
     +	otherfile
     +	EOF
    -+'
    -+
    -+test_expect_success 'git -C <path> diff -- completes pathspecs in specified repo' '
    -+	test_when_finished "rm -rf repo-for-diff" &&
    -+	git init repo-for-diff &&
    -+	echo content >repo-for-diff/otherfile &&
    -+	git -C repo-for-diff add otherfile &&
    -+	git -C repo-for-diff commit -m otherfile &&
     +	test_completion "git -C repo-for-diff diff -- o" <<-\EOF
     +	otherfile
     +	EOF
3:  ba5dc6f164 ! 3:  34720a30ab completion: 'git diff' completes untracked paths as a last resort
    @@ contrib/completion/git-completion.bash: _git_diff ()
     
      ## t/t9902-completion.sh ##
     @@ t/t9902-completion.sh: test_expect_success 'setup for integration tests' '
    - 	echo content >file1 &&
      	echo more >file2 &&
      	git add file1 file2 &&
    + 	echo untracked >file3 &&
     +	echo untracked >ufile &&
      	git commit -m one &&
      	git branch mybranch &&
      	git tag mytag
    -@@ t/t9902-completion.sh: test_expect_success 'git diff -- completes tracked paths' '
    +@@ t/t9902-completion.sh: test_expect_success 'git diff completes tracked paths when no refs match' '
      	EOF
      '
      
     +test_expect_success 'git diff [--] completes untracked paths, too' '
    ++	# there is no ref or tracked path that begin with u
     +	test_completion "git diff u" <<-\EOF &&
     +	ufile
     +	EOF
    @@ t/t9902-completion.sh: test_expect_success 'git diff -- completes tracked paths'
     +	EOF
     +'
     +
    - test_expect_success 'git -C <path> diff completes tracked paths in specified repo' '
    - 	test_when_finished "rm -rf repo-for-diff" &&
    - 	git init repo-for-diff &&
    -@@ t/t9902-completion.sh: test_expect_success 'git -C <path> diff -- completes pathspecs in specified repo
    + test_expect_success 'git -C <path> diff completes in the specified repo' '
      	test_when_finished "rm -rf repo-for-diff" &&
      	git init repo-for-diff &&
    + 
    +-	# otherfile is tracked, oops is untracked
    ++	# otherfile is tracked, oops and ufile are untracked
      	echo content >repo-for-diff/otherfile &&
    -+	echo untracked >repo-for-diff/untracked &&
      	git -C repo-for-diff add otherfile &&
      	git -C repo-for-diff commit -m otherfile &&
    + 	echo untracked >repo-for-diff/oops &&
    ++	echo untracked >repo-for-diff/ufile &&
    + 	test_completion "git -C repo-for-diff diff o" <<-\EOF &&
    + 	otherfile
    + 	EOF
     -	test_completion "git -C repo-for-diff diff -- o" <<-\EOF
    -+	test_completion "git -C repo-for-diff diff o" <<-\EOF &&
    -+	otherfile
    -+	EOF
     +	test_completion "git -C repo-for-diff diff -- o" <<-\EOF &&
      	otherfile
      	EOF
     +	test_completion "git -C repo-for-diff diff u" <<-\EOF &&
    -+	untracked
    ++	ufile
     +	EOF
     +	test_completion "git -C repo-for-diff diff -- u" <<-\EOF
    -+	untracked
    ++	ufile
     +	EOF
      '