Add option to tune diff highlighting

The new option `diff-column-highlight` can be set to highlight all
changed lines, only empty added/removed lines, or to not highlight in
any special way.

This option is only in effect when `diff-show-signs` is turned off.
Default is to only highlight empty lines.

Author: andebjor

doc/tigrc.5.adoc

@@ -277,6 +277,16 @@ The following variables can be set:
 	that disabling signs only makes sense when coloring is used to
 	distinguish added and removed lines. On by default.
 
+'diff-column-highlight' (enum) [no|all|only-empty]::
+
+	Highlight the left-most column in diff views visually when the option
+	'diff-show-signs' is not in effect. All added/removed lines can be
+	highlighted, or only empty lines. Changed lines are indicated in the
+	first column by a space highlighted by the color `diff-add-highlight` or
+	`diff-del-highlight`, respectively. Keeping the `standout` (reverse)
+	property set for these is suggested, as white space is otherwise
+	invisible. Default is to highlight only empty lines.
+
 'diff-highlight' (mixed)::
 
 	Whether to highlight diffs using Git's 'diff-highlight' program. Defaults

include/tig/options.h

@@ -38,6 +38,7 @@ typedef struct view_column *view_settings;
 	_(diff_context,			int,			VIEW_DIFF_LIKE) \
 	_(diff_noprefix,		bool,			VIEW_NO_FLAGS) \
 	_(diff_show_signs,		bool,			VIEW_NO_FLAGS) \
+	_(diff_column_highlight,	enum diff_column_highlight,	VIEW_NO_FLAGS) \
 	_(diff_options,			const char **,		VIEW_DIFF_LIKE) \
 	_(diff_highlight,		const char *,		VIEW_DIFF_LIKE) \
 	_(diff_view,			view_settings,		VIEW_NO_FLAGS) \

include/tig/types.h

@@ -161,6 +161,11 @@ bool map_enum_do(const struct enum_map_entry *map, size_t map_size, int *value,
 	_(REFRESH_MODE, AFTER_COMMAND), \
 	_(REFRESH_MODE, PERIODIC),
 
+#define DIFF_COLUMN_HIGHLIGHT_ENUM(_) \
+	_(DIFF_COLUMN_HIGHLIGHT, NO), \
+	_(DIFF_COLUMN_HIGHLIGHT, ALL), \
+	_(DIFF_COLUMN_HIGHLIGHT, ONLY_EMPTY)
+
 #define ENUM_INFO(_) \
 	_(author, AUTHOR_ENUM) \
 	_(commit_order, COMMIT_ORDER_ENUM) \
@@ -176,6 +181,7 @@ bool map_enum_do(const struct enum_map_entry *map, size_t map_size, int *value,
 	_(reference_type, REFERENCE_ENUM) \
 	_(refresh_mode, REFRESH_MODE_ENUM) \
 	_(status_label, STATUS_LABEL_ENUM) \
+	_(diff_column_highlight, DIFF_COLUMN_HIGHLIGHT_ENUM) \
 
 #define DEFINE_ENUMS(name, macro) DEFINE_ENUM(name, macro)
 ENUM_INFO(DEFINE_ENUMS)

src/draw.c

@@ -82,6 +82,20 @@ draw_chars(struct view *view, enum line_type type, const char *string, int lengt
 		    (type == LINE_DIFF_ADD || type == LINE_DIFF_DEL || type == LINE_DEFAULT) &&
 		    (string[0] == ' ' || string[0] == '+' || string[0] == '-') 
 		   ) {
+			if ( opt_diff_column_highlight == DIFF_COLUMN_HIGHLIGHT_ALL ||
+			    (opt_diff_column_highlight == DIFF_COLUMN_HIGHLIGHT_ONLY_EMPTY && len == 1)
+			   ) {
+				if (type == LINE_DIFF_ADD) {
+					set_view_attr(view, LINE_DIFF_ADD_HIGHLIGHT);
+					waddch(view->win, ' ');
+				} else if (type == LINE_DIFF_DEL) {
+					set_view_attr(view, LINE_DIFF_DEL_HIGHLIGHT);
+					waddch(view->win, ' ');
+				}
+
+				set_view_attr(view, type);
+			}
+
 			waddnstr(view->win, string+1, len-1);
 		} else {
 			waddnstr(view->win, string, len);

tigrc

@@ -115,6 +115,7 @@ set show-notes			= yes		# When non-bool passed as `--show-notes=...` (diff)
 #set diff-highlight		= true		# String (or bool): Path to diff-highlight script,
 						#                   defaults to `diff-highlight`.
 set diff-show-signs		= yes		# Show diff signs (+ and -) at the start of diff lines
+set diff-column-highlight	= only-empty	# Enum: no, all, only-empty
 #set blame-options		= -C -C -C	# User-defined options for `tig blame` (git-blame)
 #set log-options		= --pretty=raw	# User-defined options for `tig log` (git-log)
 #set main-options		= -n 1000	# User-defined options for `tig` (git-log)