Improve #? conditional expression in formats:

1) add support for else if, so
   #{?cond1,value1,#{?cond2,value2,else-value}} can be changed to
   #{?cond1,value1,cond2,value2,else-value};

2) add default empty string if there's no else value, so
   #{?cond1,value1,} can be changed to #{?cond1,value1}.

From David Mandelberg in GitHub issue 4451.

format.c

@@ -4514,7 +4514,8 @@ format_replace(struct format_expand_state *es, const char *key, size_t keylen,
 {
 	struct format_tree		 *ft = es->ft;
 	struct window_pane		 *wp = ft->wp;
-	const char			 *errstr, *copy, *cp, *marker = NULL;
+	const char			 *errstr, *copy, *cp, *cp2;
+	const char			 *marker = NULL;
 	const char			 *time_format = NULL;
 	char				 *copy0, *condition, *found, *new;
 	char				 *value, *left, *right;
@@ -4777,53 +4778,81 @@ format_replace(struct format_expand_state *es, const char *key, size_t keylen,
 		free(right);
 		free(left);
 	} else if (*copy == '?') {
-		/* Conditional: check first and choose second or third. */
+		/*
-		cp = format_skip(copy + 1, ",");
+		 * Conditional: For each pair of (condition, value), check the
-		if (cp == NULL) {
+		 * condition and return the value if true. If no condition
-			format_log(es, "condition syntax error: %s", copy + 1);
+		 * matches, return the last unpaired arg if there is one, or the
-			goto fail;
+		 * empty string if not.
-		}
+		 */
-		condition = xstrndup(copy + 1, cp - (copy + 1));
+		cp = copy + 1;
-		format_log(es, "condition is: %s", condition);
+		while (1) {
-
+			cp2 = format_skip(cp, ",");
-		found = format_find(ft, condition, modifiers, time_format);
+			if (cp2 == NULL) {
-		if (found == NULL) {
-			/*
-			 * If the condition not found, try to expand it. If
-			 * the expansion doesn't have any effect, then assume
-			 * false.
-			 */
-			found = format_expand1(es, condition);
-			if (strcmp(found, condition) == 0) {
-				free(found);
-				found = xstrdup("");
 				format_log(es,
-				    "condition '%s' not found; assuming false",
+				    "no condition matched in '%s'; using last "
+				    "arg", copy + 1);
+				value = format_expand1(es, cp);
+				break;
+			}
+
+			condition = xstrndup(cp, cp2 - cp);
+			format_log(es, "condition is: %s", condition);
+
+			found = format_find(ft, condition, modifiers,
+			    time_format);
+			if (found == NULL) {
+				/*
+				 * If the condition not found, try to expand it.
+				 * If the expansion doesn't have any effect,
+				 * then assume false.
+				 */
+				found = format_expand1(es, condition);
+				if (strcmp(found, condition) == 0) {
+					free(found);
+					found = xstrdup("");
+					format_log(es,
+					    "condition '%s' not found; "
+					    "assuming false",
+					    condition);
+				}
+			} else {
+				format_log(es, "condition '%s' found: %s",
+				    condition, found);
+			}
+
+			cp = cp2 + 1;
+			cp2 = format_skip(cp, ",");
+			if (format_true(found)) {
+				format_log(es, "condition '%s' is true",
+				    condition);
+				if (cp2 == NULL)
+					value = format_expand1(es, cp);
+				else {
+					right = xstrndup(cp, cp2 - cp);
+					value = format_expand1(es, right);
+					free(right);
+				}
+				free(condition);
+				free(found);
+				break;
+			} else {
+				format_log(es, "condition '%s' is false",
 				    condition);
 			}
-		} else {
-			format_log(es, "condition '%s' found: %s", condition,
-			    found);
-		}
 
-		if (format_choose(es, cp + 1, &left, &right, 0) != 0) {
+			free(condition);
-			format_log(es, "condition '%s' syntax error: %s",
-			    condition, cp + 1);
 			free(found);
-			goto fail;
-		}
-		if (format_true(found)) {
-			format_log(es, "condition '%s' is true", condition);
-			value = format_expand1(es, left);
-		} else {
-			format_log(es, "condition '%s' is false", condition);
-			value = format_expand1(es, right);
-		}
-		free(right);
-		free(left);
 
-		free(condition);
+			if (cp2 == NULL) {
-		free(found);
+				format_log(es,
+				    "no condition matched in '%s'; using empty "
+				    "string", copy + 1);
+				value = xstrdup("");
+				break;
+			}
+
+			cp = cp2 + 1;
+		}
 	} else if (mexp != NULL) {
 		value = format_replace_expression(mexp, es, copy);
 		if (value == NULL)

window-buffer.c

@@ -44,12 +44,8 @@ static void		 window_buffer_key(struct window_mode_entry *,
 #define WINDOW_BUFFER_DEFAULT_KEY_FORMAT \
 	"#{?#{e|<:#{line},10}," \
 		"#{line}" \
-	"," \
+	",#{e|<:#{line},36},"	\
-		"#{?#{e|<:#{line},36},"	\
+		"M-#{a:#{e|+:97,#{e|-:#{line},10}}}" \
-	        	"M-#{a:#{e|+:97,#{e|-:#{line},10}}}" \
-		"," \
-	        	"" \
-		"}" \
 	"}"
 
 static const struct menu_item window_buffer_menu_items[] = {

window-client.c

@@ -43,12 +43,8 @@ static void		 window_client_key(struct window_mode_entry *,
 #define WINDOW_CLIENT_DEFAULT_KEY_FORMAT \
 	"#{?#{e|<:#{line},10}," \
 		"#{line}" \
-	"," \
+	",#{e|<:#{line},36},"	\
-		"#{?#{e|<:#{line},36},"	\
+		"M-#{a:#{e|+:97,#{e|-:#{line},10}}}" \
-	        	"M-#{a:#{e|+:97,#{e|-:#{line},10}}}" \
-		"," \
-	        	"" \
-		"}" \
 	"}"
 
 static const struct menu_item window_client_menu_items[] = {

window-tree.c

@@ -41,30 +41,24 @@ static void		 window_tree_key(struct window_mode_entry *,
 		"#{?pane_marked,#[reverse],}" \
 		"#{pane_current_command}#{?pane_active,*,}#{?pane_marked,M,}" \
 		"#{?#{&&:#{pane_title},#{!=:#{pane_title},#{host_short}}},: \"#{pane_title}\",}" \
+	",window_format," \
+		"#{?window_marked_flag,#[reverse],}" \
+		"#{window_name}#{window_flags}" \
+		"#{?#{&&:#{==:#{window_panes},1},#{&&:#{pane_title},#{!=:#{pane_title},#{host_short}}}},: \"#{pane_title}\",}" \
 	"," \
-		"#{?window_format," \
+		"#{session_windows} windows" \
-			"#{?window_marked_flag,#[reverse],}" \
+		"#{?session_grouped, " \
-			"#{window_name}#{window_flags}" \
+			"(group #{session_group}: " \
-			"#{?#{&&:#{==:#{window_panes},1},#{&&:#{pane_title},#{!=:#{pane_title},#{host_short}}}},: \"#{pane_title}\",}" \
+			"#{session_group_list})," \
-		"," \
-			"#{session_windows} windows" \
-			"#{?session_grouped, " \
-				"(group #{session_group}: " \
-				"#{session_group_list})," \
-			"}" \
-			"#{?session_attached, (attached),}" \
 		"}" \
+		"#{?session_attached, (attached),}" \
 	"}"
 
 #define WINDOW_TREE_DEFAULT_KEY_FORMAT \
 	"#{?#{e|<:#{line},10}," \
 		"#{line}" \
-	"," \
+	",#{e|<:#{line},36},"	\
-		"#{?#{e|<:#{line},36},"	\
+	        "M-#{a:#{e|+:97,#{e|-:#{line},10}}}" \
-	        	"M-#{a:#{e|+:97,#{e|-:#{line},10}}}" \
-		"," \
-	        	"" \
-		"}" \
 	"}"
 
 static const struct menu_item window_tree_menu_items[] = {