patch 8.2.5146: memory leak when substitute expression nests

Problem:    Memory leak when substitute expression nests.
Solution:   Use an array of expression results.

src/alloc.c

@@ -586,6 +586,9 @@ free_all_mem(void)
 # ifdef FEAT_QUICKFIX
     check_quickfix_busy();
 # endif
+# ifdef FEAT_EVAL
+    free_resub_eval_result();
+# endif
 }
 #endif
 

src/errors.h

@@ -3300,3 +3300,7 @@ EXTERN char e_could_not_reset_handler_for_timeout_str[]
 EXTERN char e_could_not_check_for_pending_sigalrm_str[]
 	INIT(= N_("E1289: Could not check for pending SIGALRM: %s"));
 #endif
+#ifdef FEAT_EVAL
+EXTERN char e_substitute_nesting_too_deep[]
+	INIT(= N_("E1290: substitute nesting too deep"));
+#endif

src/ex_cmds.c

@@ -3701,6 +3701,7 @@ ex_substitute(exarg_T *eap)
     int		start_nsubs;
 #ifdef FEAT_EVAL
     int		save_ma = 0;
+    int		save_sandbox = 0;
 #endif
 
     cmd = eap->arg;
@@ -4403,6 +4404,7 @@ ex_substitute(exarg_T *eap)
 		 */
 #ifdef FEAT_EVAL
 		save_ma = curbuf->b_p_ma;
+		save_sandbox = sandbox;
 		if (subflags.do_count)
 		{
 		    // prevent accidentally changing the buffer by a function
@@ -4416,7 +4418,8 @@ ex_substitute(exarg_T *eap)
 		// Disallow changing text or switching window in an expression.
 		++textlock;
 #endif
-		// get length of substitution part
+		// Get length of substitution part, including the NUL.
+		// When it fails sublen is zero.
 		sublen = vim_regsub_multi(&regmatch,
 				    sub_firstlnum - regmatch.startpos[0].lnum,
 			       sub, sub_firstline, 0,
@@ -4429,11 +4432,10 @@ ex_substitute(exarg_T *eap)
 		// the replacement.
 		// Don't keep flags set by a recursive call.
 		subflags = subflags_save;
-		if (aborting() || subflags.do_count)
+		if (sublen == 0 || aborting() || subflags.do_count)
 		{
 		    curbuf->b_p_ma = save_ma;
-		    if (sandbox > 0)
-			sandbox--;
+		    sandbox = save_sandbox;
 		    goto skip;
 		}
 #endif

src/proto/regexp.pro

@@ -10,6 +10,7 @@ void unref_extmatch(reg_extmatch_T *em);
 char_u *regtilde(char_u *source, int magic);
 int vim_regsub(regmatch_T *rmp, char_u *source, typval_T *expr, char_u *dest, int destlen, int flags);
 int vim_regsub_multi(regmmatch_T *rmp, linenr_T lnum, char_u *source, char_u *dest, int destlen, int flags);
+void free_resub_eval_result(void);
 char_u *reg_submatch(int no);
 list_T *reg_submatch_list(int no);
 int vim_regcomp_had_eol(void);

src/regexp.c

@@ -1922,6 +1922,23 @@ vim_regsub_multi(
     return result;
 }
 
+#if defined(FEAT_EVAL) || defined(PROTO)
+// When nesting more than a couple levels it's probably a mistake.
+# define MAX_REGSUB_NESTING 4
+static char_u   *eval_result[MAX_REGSUB_NESTING] = {NULL, NULL, NULL, NULL};
+
+# if defined(EXITFREE) || defined(PROTO)
+    void
+free_resub_eval_result(void)
+{
+    int i;
+
+    for (i = 0; i < MAX_REGSUB_NESTING; ++i)
+	VIM_CLEAR(eval_result[i]);
+}
+# endif
+#endif
+
     static int
 vim_regsub_both(
     char_u	*source,
@@ -1941,7 +1958,8 @@ vim_regsub_both(
     linenr_T	clnum = 0;	// init for GCC
     int		len = 0;	// init for GCC
 #ifdef FEAT_EVAL
-    static char_u   *eval_result = NULL;
+    static int  nesting = 0;
+    int		nested;
 #endif
     int		copy = flags & REGSUB_COPY;
 
@@ -1953,6 +1971,14 @@ vim_regsub_both(
     }
     if (prog_magic_wrong())
 	return 0;
+#ifdef FEAT_EVAL
+    if (nesting == MAX_REGSUB_NESTING)
+    {
+	emsg(_(e_substitute_nesting_too_deep));
+	return 0;
+    }
+    nested = nesting;
+#endif
     src = source;
     dst = dest;
 
@@ -1969,11 +1995,11 @@ vim_regsub_both(
 	// "flags & REGSUB_COPY" != 0.
 	if (copy)
 	{
-	    if (eval_result != NULL)
+	    if (eval_result[nested] != NULL)
 	    {
-		STRCPY(dest, eval_result);
-		dst += STRLEN(eval_result);
-		VIM_CLEAR(eval_result);
+		STRCPY(dest, eval_result[nested]);
+		dst += STRLEN(eval_result[nested]);
+		VIM_CLEAR(eval_result[nested]);
 	    }
 	}
 	else
@@ -1981,7 +2007,7 @@ vim_regsub_both(
 	    int		    prev_can_f_submatch = can_f_submatch;
 	    regsubmatch_T   rsm_save;
 
-	    VIM_CLEAR(eval_result);
+	    VIM_CLEAR(eval_result[nested]);
 
 	    // The expression may contain substitute(), which calls us
 	    // recursively.  Make sure submatch() gets the text from the first
@@ -1995,6 +2021,11 @@ vim_regsub_both(
 	    rsm.sm_maxline = rex.reg_maxline;
 	    rsm.sm_line_lbr = rex.reg_line_lbr;
 
+	    // Although unlikely, it is possible that the expression invokes a
+	    // substitute command (it might fail, but still).  Therefore keep
+	    // an array if eval results.
+	    ++nesting;
+
 	    if (expr != NULL)
 	    {
 		typval_T	argv[2];
@@ -2034,26 +2065,27 @@ vim_regsub_both(
 
 		if (rettv.v_type == VAR_UNKNOWN)
 		    // something failed, no need to report another error
-		    eval_result = NULL;
+		    eval_result[nested] = NULL;
 		else
 		{
-		    eval_result = tv_get_string_buf_chk(&rettv, buf);
-		    if (eval_result != NULL)
-			eval_result = vim_strsave(eval_result);
+		    eval_result[nested] = tv_get_string_buf_chk(&rettv, buf);
+		    if (eval_result[nested] != NULL)
+			eval_result[nested] = vim_strsave(eval_result[nested]);
 		}
 		clear_tv(&rettv);
 	    }
 	    else if (substitute_instr != NULL)
 		// Execute instructions from ISN_SUBSTITUTE.
-		eval_result = exe_substitute_instr();
+		eval_result[nested] = exe_substitute_instr();
 	    else
-		eval_result = eval_to_string(source + 2, TRUE);
+		eval_result[nested] = eval_to_string(source + 2, TRUE);
+	    --nesting;
 
-	    if (eval_result != NULL)
+	    if (eval_result[nested] != NULL)
 	    {
 		int had_backslash = FALSE;
 
-		for (s = eval_result; *s != NUL; MB_PTR_ADV(s))
+		for (s = eval_result[nested]; *s != NUL; MB_PTR_ADV(s))
 		{
 		    // Change NL to CR, so that it becomes a line break,
 		    // unless called from vim_regexec_nl().
@@ -2077,15 +2109,15 @@ vim_regsub_both(
 		if (had_backslash && (flags & REGSUB_BACKSLASH))
 		{
 		    // Backslashes will be consumed, need to double them.
-		    s = vim_strsave_escaped(eval_result, (char_u *)"\\");
+		    s = vim_strsave_escaped(eval_result[nested], (char_u *)"\\");
 		    if (s != NULL)
 		    {
-			vim_free(eval_result);
-			eval_result = s;
+			vim_free(eval_result[nested]);
+			eval_result[nested] = s;
 		    }
 		}
 
-		dst += STRLEN(eval_result);
+		dst += STRLEN(eval_result[nested]);
 	    }
 
 	    can_f_submatch = prev_can_f_submatch;

src/testdir/test_substitute.vim

@@ -995,7 +995,7 @@ func Test_using_old_sub()
     ~
     s/
   endfunc
-  silent!  s/\%')/\=Repl()
+  silent! s/\%')/\=Repl()
 
   delfunc Repl
   bwipe!
@@ -1359,4 +1359,14 @@ func Test_substitute_short_cmd()
   bw!
 endfunc
 
+" This should be done last to reveal a memory leak when vim_regsub_both() is
+" called to evaluate an expression but it is not used in a second call.
+func Test_z_substitute_expr_leak()
+  func SubExpr()
+    ~n
+  endfunc
+  silent! s/\%')/\=SubExpr()
+  delfunc SubExpr
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -734,6 +734,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    5146,
 /**/
     5145,
 /**/