Fix detection of unfinished Unicode surrogate pair at end of string.

The U&'...' and U&"..." syntaxes silently discarded a surrogate pair
start (that is, a code between U+D800 and U+DBFF) if it occurred at
the very end of the string.  This seems like an obvious oversight,
since we throw an error for every other invalid combination of surrogate
characters, including the very same situation in E'...' syntax.

This has been wrong since the pair processing was added (in 9.0),
so back-patch to all supported branches.

Discussion: https://postgr.es/m/19113.1482337898@sss.pgh.pa.us

diff --git a/src/backend/parser/scan.l b/src/backend/parser/scan.l
index ce2c84fd098d2d04f4ca14a1a1f7d79aa6596d2d..aa8299d69ef959d6d9d503cbf02bc80e5a9a1193 100644 (file)
--- a/src/backend/parser/scan.l
+++ b/src/backend/parser/scan.l
@@ -1428,7 +1428,15 @@ litbuf_udeescape(unsigned char escape, core_yyscan_t yyscanner)
                }
        }
 
+       /* unfinished surrogate pair? */
+       if (pair_first)
+       {
+               ADVANCE_YYLLOC(in - litbuf + 3);                                /* 3 for U&" */
+               yyerror("invalid Unicode surrogate pair");
+       }
+
        *out = '\0';
+
        /*
         * We could skip pg_verifymbstr if we didn't process any non-7-bit-ASCII
         * codes; but it's probably not worth the trouble, since this isn't