Re: [PATCH 4/4] mergetools/meld: Use '--output' when available

On Thu, Aug 18, 2011 at 03:13:10AM -0500, Jonathan Nieder wrote:

David Aguilar wrote:

quoted

use the '--output' option when available.

Yay. :)

quoted

--- a/mergetools/meld
+++ b/mergetools/meld

@@ -4,6 +4,37 @@ diff_cmd () {
 
 merge_cmd () {
 	touch "$BACKUP"
-	"$merge_tool_path" "$LOCAL" "$MERGED" "$REMOTE"
+	if test "$meld_has_output_option" = true
+	then
+		"$merge_tool_path" --output "$MERGED" \
+			"$BASE" "$LOCAL" "$REMOTE"

Shouldn't this be "$LOCAL" "$BASE" "$REMOTE"?

Yup, thanks.

quoted

+	else
+		"$merge_tool_path" "$LOCAL" "$MERGED" "$REMOTE"
+	fi
 	check_unchanged

I wonder if the version test could be made a little simpler (perhaps
to cope better if future versions use a different numbering system):

	if "$merge_tool_path" --output /dev/null --help >/dev/null 2>&1
	then
		"$merge_tool_path" --output ...
	else
		"$merge_tool_path" "$LOCAL" ...
	fi

Forgive my ignorance: is this function likely to be called in a loop?
If so, it makes sense to precompute or cache the result of detection,
like you already do.

Yes, it is called in a loop...

	check_meld_for_output_option () {
		if ...
		then
			meld_has_output_option=true
		else
			meld_has_output_option=false
		fi
	}

	merge_cmd () {
		if test -z "${meld_has_output_option:+set}"
		then
			check_meld_for_output_option
		fi

		if test "$meld_has_output_option" = true
		then
			...


[...]

quoted

+	# Filter meld --version to contain numbers and dots only
+	meld="$(meld --version 2>/dev/null | sed -e 's/[^0-9.]\+//g')"

\+ is not a BRE.  If parsing version numbers seems like the right
thing to do, maybe "tr -cd 0-9."?

quoted

+	meld="${meld:-0.0.0}"
+
+	meld_major="$(expr "$meld" : '\([0-9]\{1,\}\)' || echo 0)"
+	meld_minor="$(expr "$meld" : '[0-9]\{1,\}\.\([0-9]\{1,\}\)' || echo 0)"

I think git avoids \{m,n\} ranges where possible (for portability).
This could be:

	meld_major=${meld%%.*}
	meld_nonmajor=${meld#${meld_major}.}
	meld_minor=${meld_nonmajor%%.*}

or:

	case $meld in
	[2-9].* | [1-9][0-9]* | 1.[5-9]* | 1.[1-9][0-9]*)	# >= 1.5.0
		meld_has_output_option=true ;;
	*)
		meld_has_output_option=false ;;
	esac

It's nice how self-contained this can be now that it's in its own
file.  Thanks.

Right, I was using \{1,\} since that's what CodingStyle said to
use instead of \+ (which I forgot to fixup above as you saw).

The case statement is nice and simple enough to understand.
By doing meld --output /dev/null --help we're relying on
older versions blowing up with --output and --help returning
exit status 0.  That seems pretty reasonable.
The case statement does seem sufficient but just trying
--output and seeing what happens is even simpler.
Your example also uses $merge_tool_path, which I forgot to do,
so I'll be sure to include that too.

I'll wait until tomorrow to see if there are any more comments
and reroll.

Thanks,
-- 
					David