Fix to swallow BOMs in sourced files

Fixes #1518

common.h

@@ -59,6 +59,9 @@ typedef std::vector<wcstring> wcstring_list_t;
 */
 #define BYTE_MAX 0xffu
 
+/** BOM value */
+#define UTF8_BOM_WCHAR 0xFEFFu
+
 /* Flags for unescape_string functions */
 enum
 {

reader.cpp

@@ -4205,7 +4205,7 @@ static int read_ni(int fd, const io_chain_t &io)
             acc.insert(acc.end(), buff, buff + c);
         }
 
-        const wcstring str = acc.empty() ? wcstring() : str2wcstring(&acc.at(0), acc.size());
+        wcstring str = acc.empty() ? wcstring() : str2wcstring(&acc.at(0), acc.size());
         acc.clear();
 
         if (fclose(in_stream))
@@ -4216,6 +4216,12 @@ static int read_ni(int fd, const io_chain_t &io)
             res = 1;
         }
 
+        /* Swallow a BOM (#1518) */
+        if (! str.empty() && str.at(0) == UTF8_BOM_WCHAR)
+        {
+            str.erase(0, 1);
+        }
+
         parse_error_list_t errors;
         if (! parse_util_detect_errors(str, &errors, false /* do not accept incomplete */))
         {

tests/test9.in

@@ -113,4 +113,7 @@ try_unbalanced_block 'if false'
 "while" false; end
 "wh"'ile' false; "e"nd
 
+# BOM checking (see #1518)
+echo \uFEFF"echo bom_test" | source
+
 false

tests/test9.out

@@ -17,3 +17,4 @@ foo
 bar
 baz
 psub file was deleted
+bom_test