Bug #55413 mysqltest gives parse error for lines matching "^let.*\\.*;$"

Allow escaped quotes also in statements not starting with --
But will not support single unescaped ' or `

client/mysqltest.cc

@@ -5507,6 +5507,8 @@ int read_line(char *buf, int size)
   char c, UNINIT_VAR(last_quote);
   char *p= buf, *buf_end= buf + size - 1;
   int skip_char= 0;
+  my_bool have_slash= FALSE;
+  
   enum {R_NORMAL, R_Q, R_SLASH_IN_Q,
         R_COMMENT, R_LINE_START} state= R_LINE_START;
   DBUG_ENTER("read_line");
@@ -5577,10 +5579,14 @@ int read_line(char *buf, int size)
 	DBUG_RETURN(0);
       }
       else if (c == '\'' || c == '"' || c == '`')
+      {
+        if (! have_slash) 
         {
 	  last_quote= c;
 	  state= R_Q;
 	}
+      }
+      have_slash= (c == '\\');
       break;
 
     case R_COMMENT:

mysql-test/r/mysqltest.result

@@ -262,6 +262,9 @@ a long \$where variable content
 
 banana = banana
 Not a banana: ba\$cat\$cat
+with\`some"escaped\'quotes
+with\`some"escaped\'quotes
+single'tick`backtick
 mysqltest: At line 1: Missing arguments to let
 mysqltest: At line 1: Missing variable name in let
 mysqltest: At line 1: Missing assignment operator in let

mysql-test/t/mysqltest.test

@@ -701,6 +701,16 @@ echo banana = $cat;
 let $cat=ba\\\$cat\\\$cat;
 echo Not a banana: $cat;
 
+# Bug #55413 would cause this to fail
+let $escape= with\`some\"escaped\'quotes;
+echo $escape;
+
+--let $escape= with\`some\"escaped\'quotes
+echo $escape;
+
+# This only works with "--let" syntax
+--let $tick= single'tick`backtick
+echo $tick;
 
 # Test illegal uses of let