patch 9.0.0047: using freed memory with recursive substitute

Problem:    Using freed memory with recursive substitute.
Solution:   Always make a copy for reg_prev_sub.

src/ex_cmds.c

@@ -3994,7 +3994,16 @@ ex_substitute(exarg_T *eap)
 	sub_copy = sub;
     }
     else
-	sub = regtilde(sub, magic_isset());
+    {
+	char_u *newsub = regtilde(sub, magic_isset());
+
+	if (newsub != sub)
+	{
+	    // newsub was allocated, free it later.
+	    sub_copy = newsub;
+	    sub = newsub;
+	}
+    }
 
     /*
      * Check for a match on each line.

src/regexp.c

@@ -1766,11 +1766,11 @@ regtilde(char_u *source, int magic)
 	}
     }
 
+    // Store a copy of newsub  in reg_prev_sub.  It is always allocated,
+    // because recursive calls may make the returned string invalid.
     vim_free(reg_prev_sub);
-    if (newsub != source)	// newsub was allocated, just keep it
+    reg_prev_sub = vim_strsave(newsub);
-	reg_prev_sub = newsub;
+
-    else			// no ~ found, need to save newsub
-	reg_prev_sub = vim_strsave(newsub);
     return newsub;
 }
 

src/testdir/test_regexp_latin.vim

@@ -1114,4 +1114,15 @@ func Test_using_two_engines_pattern()
   bwipe!
 endfunc
 
+func Test_recursive_substitute_expr()
+  new
+  func Repl()
+    s
+  endfunc
+  silent! s/\%')/~\=Repl()
+
+  bwipe!
+  delfunc Repl
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -735,6 +735,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    47,
 /**/
     46,
 /**/