Built-in merge tools contain a hard-coded assumption about
whether or not a tool's exit code can be trusted to determine
the success or failure of a merge.  Tools whose exit codes are
not trusted contain calls to check_unchanged() in their
merge_cmd() functions.

A problem with this is that the trustExitCode configuration is
not honored for built-in tools.

Teach built-in tools to honor the trustExitCode configuration.
Extend run_merge_cmd() so that it is responsible for calling
check_unchanged() when a tool's exit code cannot be trusted.
Remove check_unchanged() calls from scriptlets since they are no
longer responsible for calling it.

When no configuration is present, exit_code_trustable() is
checked to see whether the exit code should be trusted.
The default implementation returns false.

Tools whose exit codes can be trusted override
exit_code_trustable() to true.

Reported-by: Dun Peal <dunpealer@gmail.com>
Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

UI consistency improvements.

* nf/mergetool-prompt:
  difftool/mergetool: make the form of yes/no questions consistent

Every yes/no question in difftool/mergetool scripts has slightly
different form, and none of them is consistent with the form git
itself uses.

Make the form of all the questions consistent with the form used
by git.

Reviewed-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Nikola Forró <nforro@redhat.com>
Acked-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Signed-off-by: Jacob Nisnevich <jacob.nisnevich@gmail.com>
Acked-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

When no diff nor merge tool is specified (config, option), mergetool-lib
is supposed to choose a default tool from a set of tools. That set is
constructed dynamically depending on the environment (graphical, editor
setting) as a space separated string of tool names.

719518f (mergetool--lib: set IFS for difftool and mergetool, 2015-05-20)
introduced a newline as IFS which breaks the parsing of the space
separated list into items, resulting in a failed search for an available
tool.

Set IFS to a space locally for the tool search.

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-sh-setup sets IFS but it is not used by git-difftool--helper.
Set IFS in git-mergetool--lib so that the mergetool scriptlets,
difftool, and mergetool do not need to do so.

Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Remove return statements and rework check_unchanged() so that the exit
status from the last evaluated expression bubbles up to the callers.

Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Even though setup_user_tool assigns the exit status from "eval
$merge_tool_cmd" to $status, the variable is overwritten by the
function it calls next, check_unchanged, without ever getting looked
at by anybody.  And "return $status" at the end of this function
returns the value check_unchanged assigned to it (which is the same
as the value the function returns).  Which makes the assignment a
no-op.

Remove it.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Fix-up to a new feature in 'master'.

* da/difftool:
  difftool: honor --trust-exit-code for builtin tools

run_merge_tool() was not setting $status, which prevented the
exit code for builtin tools from being forwarded to the caller.

Capture the exit status and add a test to guarantee the behavior.

Reported-by: Adria Farres <14farresa@gmail.com>
Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>