hush: fix comment parsing in `cmd`, closes 10421

function                                             old     new   delta
parse_stream                                        2692    2690      -2

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

shell/ash_test/ash-parsing/comment2.right

@@ -0,0 +1,4 @@
+Ok1
+Ok2
+Ok5
+Ok6

shell/ash_test/ash-parsing/comment2.tests

@@ -0,0 +1,13 @@
+echo "`echo Ok1 #comment is ignored`"
+echo `echo Ok2 #comment is ignored`
+#
+# Surprisingly, bash does not handle comments in $()
+# the same way as in ``. "#" causes the rest of the line, _including_ )",
+# to be ignored. These lines would cause an error:
+#echo "$(echo Ok3 #comment is ignored)"
+#echo $(echo Ok4 #comment is ignored)
+#
+echo "$(echo Ok5 #comment is ignored
+)"
+echo $(echo Ok6 #comment is ignored
+)

shell/hush.c

@@ -5140,14 +5140,23 @@ static struct pipe *parse_stream(char **pstring,
 		case '#':
 			if (dest.length == 0 && !dest.has_quoted_part) {
 				/* skip "#comment" */
+				/* note: we do not add it to &ctx.as_string */
+/* TODO: in bash:
+ * comment inside $() goes to the next \n, even inside quoted string (!):
+ * cmd "$(cmd2 #comment)" - syntax error
+ * cmd "`cmd2 #comment`" - ok
+ * We accept both (comment ends where command subst ends, in both cases).
+ */
 				while (1) {
 					ch = i_peek(input);
-					if (ch == EOF || ch == '\n')
+					if (ch == '\n') {
+						nommu_addchr(&ctx.as_string, '\n');
+						break;
+					}
+					ch = i_getch(input);
+					if (ch == EOF)
 						break;
-					i_getch(input);
-					/* note: we do not add it to &ctx.as_string */
 				}
-				nommu_addchr(&ctx.as_string, '\n');
 				continue; /* back to top of while (1) */
 			}
 			break;

shell/hush_test/hush-parsing/comment2.right

@@ -0,0 +1,4 @@
+Ok1
+Ok2
+Ok5
+Ok6

shell/hush_test/hush-parsing/comment2.tests

@@ -0,0 +1,13 @@
+echo "`echo Ok1 #comment is ignored`"
+echo `echo Ok2 #comment is ignored`
+#
+# Surprisingly, bash does not handle comments in $()
+# the same way as in ``. "#" causes the rest of the line, _including_ )",
+# to be ignored. These lines would cause an error:
+#echo "$(echo Ok3 #comment is ignored)"
+#echo $(echo Ok4 #comment is ignored)
+#
+echo "$(echo Ok5 #comment is ignored
+)"
+echo $(echo Ok6 #comment is ignored
+)