From 3461d0f5d1d020865d0e68ece92ea58ef83a6bf9 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Thu, 8 Apr 2021 17:45:33 -0700
Subject: parser: fix poor diagnosis of \x invalid escape.

* parser.l (grammar): Because the \x pattern requires one or
more digits after it, if they are not present, we simply
report \x as an an unrecognized escape. It's better if we
diagnose it properly as a \x that is not followed by digits.
---
 parser.l | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/parser.l b/parser.l
index e310d1f7..778c632a 100644
--- a/parser.l
+++ b/parser.l
@@ -836,6 +836,10 @@ UONLY   {U2}{U}|{U3}{U}{U}|{U4}{U}{U}{U}
   return TEXT;
 }
 
+<SPECIAL>[\\]x {
+  yyerrorf(yyg, lit("\\x escape without digits"), nao);
+}
+
 <SPECIAL>[\\]. {
   yyerrorf(yyg, lit("unrecognized escape \\~a"), chr(yytext[1]), nao);
 }
@@ -919,7 +923,10 @@ UONLY   {U2}{U}|{U3}{U}{U}|{U4}{U}{U}{U}
     return REGCHAR;
   }
 
-  yyerrprepf(yyg, lit("unrecognized escape in regex"), nao);
+  if (yytext[1] == 'x')
+    yyerrprepf(yyg, lit("\\x escape without digits in regex"), nao);
+  else
+    yyerrprepf(yyg, lit("unrecognized escape in regex"), nao);
   return ERRTOK;
 }
 
@@ -1021,6 +1028,10 @@ UONLY   {U2}{U}|{U3}{U}{U}|{U4}{U}{U}{U}
   return LITCHAR;
 }
 
+<STRLIT,QSILIT,WLIT,QWLIT>[\\]x {
+  yyerrorf(yyg, lit("\\x escape without digits"), nao);
+}
+
 <STRLIT,QSILIT,WLIT,QWLIT>[\\]. {
   yyerrorf(yyg, lit("unrecognized escape: \\~a"), chr(yytext[1]), nao);
 }
-- 
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