hush: fix handling of empty heredoc EOF marker

function                                             old     new   delta
parse_stream                                        2609    2634     +25

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

shell/ash_test/ash-heredoc/heredoc_empty2.right

@@ -0,0 +1,4 @@
+OK1
+Ok:0
+OK2
+Ok:0

shell/ash_test/ash-heredoc/heredoc_empty2.tests

@@ -0,0 +1,14 @@
+unset a
+
+# Heredoc with empty delimiter
+cat <<- ""
+	OK1
+
+echo Ok:$?
+
+# Heredoc with empty delimiter
+cat <<- ""
+	OK2
+	
+
+echo Ok:$?

shell/hush.c

@@ -4001,24 +4001,34 @@ static char *fetch_till_str(o_string *as_string,
 		ch = i_getch(input);
 		if (ch != EOF)
 			nommu_addchr(as_string, ch);
-		if ((ch == '\n' || ch == EOF)
-		 && ((heredoc_flags & HEREDOC_QUOTED) || prev != '\\')
-		) {
-			if (strcmp(heredoc.data + past_EOL, word) == 0) {
-				heredoc.data[past_EOL] = '\0';
-				debug_printf_parse("parsed heredoc '%s'\n", heredoc.data);
-				return heredoc.data;
-			}
-			while (ch == '\n') {
-				o_addchr(&heredoc, ch);
-				prev = ch;
+		if (ch == '\n' || ch == EOF) {
+ check_heredoc_end:
+			if ((heredoc_flags & HEREDOC_QUOTED) || prev != '\\') {
+				if (strcmp(heredoc.data + past_EOL, word) == 0) {
+					heredoc.data[past_EOL] = '\0';
+					debug_printf_parse("parsed heredoc '%s'\n", heredoc.data);
+					return heredoc.data;
+				}
+				if (ch == '\n') {
+					/* This is a new line.
+					 * Remember position and backslash-escaping status.
+					 */
+					o_addchr(&heredoc, ch);
+					prev = ch;
  jump_in:
-				past_EOL = heredoc.length;
-				do {
-					ch = i_getch(input);
-					if (ch != EOF)
-						nommu_addchr(as_string, ch);
-				} while ((heredoc_flags & HEREDOC_SKIPTABS) && ch == '\t');
+					past_EOL = heredoc.length;
+					/* Get 1st char of next line, possibly skipping leading tabs */
+					do {
+						ch = i_getch(input);
+						if (ch != EOF)
+							nommu_addchr(as_string, ch);
+					} while ((heredoc_flags & HEREDOC_SKIPTABS) && ch == '\t');
+					/* If this immediately ended the line,
+					 * go back to end-of-line checks.
+					 */
+					if (ch == '\n')
+						goto check_heredoc_end;
+				}
 			}
 		}
 		if (ch == EOF) {

shell/hush_test/hush-heredoc/heredoc_empty2.right

@@ -0,0 +1,4 @@
+OK1
+Ok:0
+OK2
+Ok:0

shell/hush_test/hush-heredoc/heredoc_empty2.tests

@@ -0,0 +1,14 @@
+unset a
+
+# Heredoc with empty delimiter
+cat <<- ""
+	OK1
+
+echo Ok:$?
+
+# Heredoc with empty delimiter
+cat <<- ""
+	OK2
+	
+
+echo Ok:$?