diffpkg: allow to set column width for side-by-side view

The magic values `columns` and `auto` allow to set specific aspects,
with 'auto' as the default value:

- auto: Set width to the maximum line length of all input files
- columns: Set width to the shell defined $COLUMNS env var

Furthermore any number can be passed to set a static width.

3 files changed, 57 insertions, 11 deletions

diff --git a/contrib/completion/zsh/_devtools.in b/contrib/completion/zsh/_devtools.in
index 46e04fb..b93e510 100644
--- a/contrib/completion/zsh/_devtools.in
+++ b/contrib/completion/zsh/_devtools.in
@@ -51,6 +51,7 @@ _diffpkg_args=(
 	'(-u -U --unified)'{-u,-U,--unified}'[Output 3 lines of unified context]'
 	'(-y --side-by-side)'{-y,--side-by-side}'[Output in two columns]'
 	'--color=[Color output]:when:($_colors[*])'
+	'(-W --width=)'{-W,--width=}'[Output at most NUM print columns]:num:(auto columns)'
 	'(-v --verbose)'{-v,--verbose}'[Provide more detailed/unfiltered output]'
 	'(-h --help)'{-h,--help}'[Display usage]'
 	'*:packages:_devtools_completions_all_packages'
diff --git a/doc/man/diffpkg.1.asciidoc b/doc/man/diffpkg.1.asciidoc
index ec89f89..69e0c27 100644
--- a/doc/man/diffpkg.1.asciidoc
+++ b/doc/man/diffpkg.1.asciidoc
@@ -48,6 +48,10 @@ Output Options
 *-y, --side-by-side*::
 	Output in two columns
 
+*-W, --width*[='NUM']::
+	Output at most 'NUM' (default `'auto'`) print columns; 'NUM' can be `'auto'`, `'columns'` or a number.
+	`'auto'` will be resolved to the maximum line length of both files, guaranteeing the diff to be uncut.
+
 Modes
 -----
 
diff --git a/src/diffpkg.in b/src/diffpkg.in
index ce8b030..baeb546 100644
--- a/src/diffpkg.in
+++ b/src/diffpkg.in
@@ -32,6 +32,8 @@ usage() {
 		                         Plain --color means --color='auto'
 		    -u, -U, --unified    Output 3 lines of unified context
 		    -y, --side-by-side   Output in two columns
+		    -W, --width=NUM      Output at most NUM (default 'auto') print columns
+		                         NUM can be 'auto', 'columns' or a number
 
 		MODES
 		    -l, --list           Activate content list diff mode (default)
@@ -50,6 +52,7 @@ BUILDINFO=0
 
 DIFFMODE=--side-by-side
 DIFFCOLOR=--color
+DIFFWIDTH=--width=auto
 DIFFOPTIONS=(--expand-tabs)
 
 # option checking
@@ -100,6 +103,15 @@ while (( $# )); do
 			DIFFCOLOR="$1"
 			shift
 			;;
+		-W|--width)
+			(( $# <= 1 )) && die "missing argument for %s" "$1"
+			DIFFWIDTH="--width=$2"
+			shift 2
+			;;
+		--width=*)
+			DIFFWIDTH="$1"
+			shift
+			;;
 		--)
 			shift
 			break
@@ -113,6 +125,7 @@ while (( $# )); do
 	esac
 done
 
+# Set options based on flags or magic values
 if (( VERBOSE )); then
 	if [[ $DIFFMODE == --unified ]]; then
 		DIFFMODE="--unified=99999"
@@ -120,6 +133,12 @@ if (( VERBOSE )); then
 else
 	DIFFOPTIONS+=(--suppress-common-lines)
 fi
+if [[ $DIFFWIDTH == --width=columns ]]; then
+	DIFFWIDTH="--width=${COLUMNS:-130}"
+fi
+if [[ $DIFFWIDTH != --width=auto ]]; then
+	DIFFOPTIONS+=("${DIFFWIDTH}")
+fi
 DIFFOPTIONS+=("${DIFFMODE}" "${DIFFCOLOR}")
 
 if ! (( DIFFOSCOPE || TARLIST || PKGINFO || BUILDINFO )); then
@@ -156,6 +175,19 @@ tar_list() {
 	fi | sort
 }
 
+file_line_length() {
+	path="$1"
+	wc -L "${path}" | tail -n1 | sed -E 's/^ +//g' | cut -d' ' -f1
+}
+
+file_diff_columns() {
+	file1="$1"
+	file2="$2"
+	file1_length=$(file_line_length "$file1")
+	file2_length=$(file_line_length "$file2")
+	echo $(( file1_length + file2_length + 3 ))
+}
+
 diff_pkgs() {
 	local oldpkg newpkg
 	oldpkg=$(readlink -m "$1")
@@ -167,24 +199,33 @@ diff_pkgs() {
 	DIFFOPTIONS+=(--label "${oldpkg}" --label "${newpkg}")
 
 	if (( TARLIST )); then
-		tar_list "$oldpkg" > "$TMPDIR/filelist-old"
-		tar_list "$newpkg" > "$TMPDIR/filelist"
-
-		diff "${DIFFOPTIONS[@]}" "$TMPDIR/filelist-old" "$TMPDIR/filelist"
+		tar_list "$oldpkg" > "$TMPDIR/old"
+		tar_list "$newpkg" > "$TMPDIR/new"
 	fi
 
 	if (( PKGINFO )); then
-		bsdtar xOqf "$oldpkg" .PKGINFO > "$TMPDIR/pkginfo-old"
-		bsdtar xOqf "$newpkg" .PKGINFO > "$TMPDIR/pkginfo"
-
-		diff "${DIFFOPTIONS[@]}" "$TMPDIR/pkginfo-old" "$TMPDIR/pkginfo"
+		bsdtar xOqf "$oldpkg" .PKGINFO > "$TMPDIR/old"
+		bsdtar xOqf "$newpkg" .PKGINFO > "$TMPDIR/new"
 	fi
 
 	if (( BUILDINFO )); then
-		bsdtar xOqf "$oldpkg" .BUILDINFO > "$TMPDIR/buildinfo-old"
-		bsdtar xOqf "$newpkg" .BUILDINFO > "$TMPDIR/buildinfo"
+		bsdtar xOqf "$oldpkg" .BUILDINFO > "$TMPDIR/old"
+		bsdtar xOqf "$newpkg" .BUILDINFO > "$TMPDIR/new"
+	fi
+
+	if (( TARLIST || PKGINFO || BUILDINFO )); then
+		# Resolve dynamic auto width one we know the content to diff
+		if [[ $DIFFWIDTH == --width=auto ]]; then
+			AUTOLENGTH=$(file_diff_columns "$TMPDIR/old" "$TMPDIR/new")
+			DIFFOPTIONS+=("--width=${AUTOLENGTH}")
+		fi
+
+		# Print a header for side-by-side view as it lacks labels
+		if [[ $DIFFMODE == --side-by-side ]]; then
+			printf -- "--- %s\n+++ %s\n" "${oldpkg}" "${newpkg}"
+		fi
 
-		diff "${DIFFOPTIONS[@]}" "$TMPDIR/buildinfo-old" "$TMPDIR/buildinfo"
+		diff "${DIFFOPTIONS[@]}" "$TMPDIR/old" "$TMPDIR/new"
 	fi
 
 	if (( DIFFOSCOPE )); then