[PATCH 0/3] Improve consistency of git-var

["Sean Allred via GitGitGadget" <gitgitgadget@gmail.com>]

This patch series makes a few distinct improvements to git-var to support
the change to git_editor() prompted here
[https://lore.kernel.org/git/xmqq1qpwwwxg.fsf@gitster.g/] and ultimately
support that patch to introduce GIT_SEQUENCE_EDITOR as a handled logical
variable.

We first have to pull apart the errors of 'the given logical variable is
unknown/meaningless' and 'the given logical variable is known, but its value
is undefined'. For example, if GIT_EDITOR (and its fallbacks) was completely
unset, git var GIT_EDITOR would end up inappropriately printing a usage
message. This is fixed in var.c by returning the git_var struct itself in
the search on git_vars (to see if the variable is known) and then calling
git_var->read() -- allowing us to handle the cases of 'git_var is null' and
'read() returned null' separately.

After this is done, we're able to remove the handling in var.c:editor()
that's been duplicated in editor.c -- allowing editor() to return NULL and
follow the logic prepared above.

Sean Allred (3):
  var: do not print usage() with a correct invocation
  var: remove read_var
  var: allow GIT_EDITOR to return null

 Documentation/git-var.txt |  3 +-
 builtin/var.c             | 26 +++++++--------
 t/t0007-git-var.sh        | 69 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 83 insertions(+), 15 deletions(-)


base-commit: a0789512c5a4ae7da935cd2e419f253cb3cb4ce7
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1434%2Fvermiculus%2Fsa%2Fvar-improvements-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1434/vermiculus/sa/var-improvements-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1434
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