action: do not expand env vars in Exec action

...<command> argument (but still resolve tilde).

This makes it easier to write sh -c '' constructs without turning labwc
into a shell parser in order to expand environment variables, whilst
respecting single quotes and escaped characters as well as ignoring
subshells syntax like $(foo) and backticks.

Also, fix bug where buffer length+alloc get out-of-sync

docs/labwc-actions.5.scd

@@ -19,6 +19,7 @@ Actions are used in menus and keyboard/mouse bindings.
 	Execute command.  Note that in the interest of backward compatibility,
 	labwc supports <execute> as an alternative to <command> even though
 	openbox documentation states that it is deprecated.
+	Note: Tilde (~) is expanded in the command before passing to execvp()
 
 *<action name="Exit" />*
 	Exit labwc.

docs/labwc-config.5.scd

@@ -32,6 +32,8 @@ variables accordingly. It is recommended to specify keyboard layout settings and
 cursor size/theme here; see environment variable section below for details. Note
 that the environment file is treated differently by openbox where it is simply
 sourced prior to running openbox.
+Note: Tilde (~) and environment variables in the value are expanded, but
+subshell syntax and apostrophes are ignored.
 
 The *menu.xml* file defines the context/root-menus and is described in
 labwc-menu(5).

include/common/buf.h

@@ -19,7 +19,13 @@ struct buf {
 };
 
 /**
- * buf_expand_shell_variables - expand $foo, ${foo} and ~ in buffer
+ * buf_expand_tilde - expand ~ in buffer
+ * @s: buffer
+ */
+void buf_expand_tilde(struct buf *s);
+
+/**
+ * buf_expand_shell_variables - expand $foo and ${foo} in buffer
  * @s: buffer
  * Note: $$ is not handled
  */

src/action.c

@@ -564,7 +564,7 @@ actions_run(struct view *activator, struct server *server,
 				struct buf cmd;
 				buf_init(&cmd);
 				buf_add(&cmd, action_str_from_arg(arg));
-				buf_expand_shell_variables(&cmd);
+				buf_expand_tilde(&cmd);
 				spawn_async_no_shell(cmd.buf);
 				free(cmd.buf);
 			}

src/common/buf.c

@@ -4,6 +4,35 @@
 #include "common/buf.h"
 #include "common/mem.h"
 
+static void
+buf_add_one_char(struct buf *s, char ch)
+{
+	if (s->alloc <= s->len + 1) {
+		s->alloc = s->alloc * 3 / 2 + 16;
+		s->buf = xrealloc(s->buf, s->alloc);
+	}
+	s->buf[s->len++] = ch;
+	s->buf[s->len] = '\0';
+}
+
+void
+buf_expand_tilde(struct buf *s)
+{
+	struct buf new;
+	buf_init(&new);
+	for (int i = 0 ; i < s->len ; i++) {
+		if (s->buf[i] == '~') {
+			buf_add(&new, getenv("HOME"));
+		} else {
+			buf_add_one_char(&new, s->buf[i]);
+		}
+	}
+	free(s->buf);
+	s->buf = new.buf;
+	s->len = new.len;
+	s->alloc = new.alloc;
+}
+
 static void
 strip_curly_braces(char *s)
 {
@@ -46,22 +75,15 @@ buf_expand_shell_variables(struct buf *s)
 			if (p) {
 				buf_add(&new, p);
 			}
-		} else if (s->buf[i] == '~') {
-			/* expand tilde */
-			buf_add(&new, getenv("HOME"));
 		} else {
-			/* just add one character at a time */
-			if (new.alloc <= new.len + 1) {
-				new.alloc = new.alloc * 3 / 2 + 16;
-				new.buf = xrealloc(new.buf, new.alloc);
-			}
-			new.buf[new.len++] = s->buf[i];
-			new.buf[new.len] = '\0';
+			buf_add_one_char(&new, s->buf[i]);
 		}
 	}
 	free(environment_variable.buf);
 	free(s->buf);
 	s->buf = new.buf;
+	s->len = new.len;
+	s->alloc = new.alloc;
 }
 
 void

src/config/session.c

@@ -38,6 +38,7 @@ process_line(char *line)
 	buf_init(&value);
 	buf_add(&value, string_strip(++p));
 	buf_expand_shell_variables(&value);
+	buf_expand_tilde(&value);
 	if (string_empty(key) || !value.len) {
 		goto error;
 	}