fix(inccommand): parse the command to check if it is previewable

Free regprog if command isn't previewable

Co-authored-by: zeertzjq <zeertzjq@outlook.com>

src/nvim/api/command.c

@@ -13,6 +13,7 @@
 #include "nvim/ex_docmd.h"
 #include "nvim/lua/executor.h"
 #include "nvim/ops.h"
+#include "nvim/regexp.h"
 #include "nvim/window.h"
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
@@ -94,6 +95,7 @@ Dictionary nvim_parse_cmd(String str, Dictionary opts, Error *err)
     }
     goto end;
   }
+  vim_regfree(cmdinfo.cmdmod.cmod_filter_regmatch.regprog);
 
   // Parse arguments
   Array args = ARRAY_DICT_INIT;

src/nvim/ex_docmd.c

@@ -1405,6 +1405,8 @@ bool is_cmd_ni(cmdidx_T cmdidx)
 }
 
 /// Parse command line and return information about the first command.
+/// If parsing is done successfully, need to free cmod_filter_regmatch.regprog after calling,
+/// usually done using undo_cmdmod() or execute_cmd().
 ///
 /// @param cmdline Command line string
 /// @param[out] eap Ex command arguments
@@ -1432,6 +1434,7 @@ bool parse_cmdline(char *cmdline, exarg_T *eap, CmdParseInfo *cmdinfo, char **er
 
   // Parse command modifiers
   if (parse_command_modifiers(eap, errormsg, &cmdinfo->cmdmod, false) == FAIL) {
+    vim_regfree(cmdinfo->cmdmod.cmod_filter_regmatch.regprog);
     return false;
   }
   after_modifier = eap->cmd;
@@ -10040,44 +10043,6 @@ static void ex_terminal(exarg_T *eap)
   do_cmdline_cmd(ex_cmd);
 }
 
-/// Checks if `cmd` is "previewable" (i.e. supported by 'inccommand').
-///
-/// @param[in] cmd Commandline to check. May start with a range or modifier.
-///
-/// @return true if `cmd` is previewable
-bool cmd_can_preview(char *cmd)
-{
-  if (cmd == NULL) {
-    return false;
-  }
-
-  // Ignore additional colons at the start...
-  cmd = skip_colon_white(cmd, true);
-
-  // Ignore any leading modifiers (:keeppatterns, :verbose, etc.)
-  for (int len = modifier_len(cmd); len != 0; len = modifier_len(cmd)) {
-    cmd += len;
-    cmd = skip_colon_white(cmd, true);
-  }
-
-  exarg_T ea;
-  memset(&ea, 0, sizeof(ea));
-  // parse the command line
-  ea.cmd = skip_range(cmd, NULL);
-  if (*ea.cmd == '*') {
-    ea.cmd = skipwhite(ea.cmd + 1);
-  }
-
-  if (find_ex_command(&ea, NULL) == NULL || ea.cmdidx == CMD_SIZE) {
-    return false;
-  } else if (!IS_USER_CMDIDX(ea.cmdidx)) {
-    // find_ex_command sets the flags for user commands automatically
-    ea.argt = cmdnames[(int)ea.cmdidx].cmd_argt;
-  }
-
-  return (ea.argt & EX_PREVIEW);
-}
-
 /// Gets a map of maps describing user-commands defined for buffer `buf` or
 /// defined globally if `buf` is NULL.
 ///

src/nvim/ex_getln.c

@@ -2372,7 +2372,7 @@ static void cmdpreview_close_win(void)
   }
 }
 
-/// Show 'inccommand' preview. It works like this:
+/// Show 'inccommand' preview if command is previewable. It works like this:
 ///    1. Store current undo information so we can revert to current state later.
 ///    2. Execute the preview callback with the parsed command, preview buffer number and preview
 ///       namespace number as arguments. The preview callback sets the highlight and does the
@@ -2385,12 +2385,15 @@ static void cmdpreview_close_win(void)
 ///    5. If the return value of the preview callback is not 0, update the screen while the effects
 ///       of the preview are still in place.
 ///    6. Revert all changes made by the preview callback.
-static void cmdpreview_show(CommandLineState *s)
+///
+/// @return whether preview is shown or not.
+static bool cmdpreview_may_show(CommandLineState *s)
 {
   // Parse the command line and return if it fails.
   exarg_T ea;
   CmdParseInfo cmdinfo;
   // Copy the command line so we can modify it.
+  int cmdpreview_type = 0;
   char *cmdline = xstrdup((char *)ccline.cmdbuff);
   char *errormsg = NULL;
   emsg_off++;  // Block errors when parsing the command line, and don't update v:errmsg
@@ -2400,6 +2403,12 @@ static void cmdpreview_show(CommandLineState *s)
   }
   emsg_off--;
 
+  // Check if command is previewable, if not, don't attempt to show preview
+  if (!(ea.argt & EX_PREVIEW)) {
+    vim_regfree(cmdinfo.cmdmod.cmod_filter_regmatch.regprog);
+    goto end;
+  }
+
   // Swap invalid command range if needed
   if ((ea.argt & EX_RANGE) && ea.line1 > ea.line2) {
     linenr_T lnum = ea.line1;
@@ -2454,7 +2463,7 @@ static void cmdpreview_show(CommandLineState *s)
   // the preview.
   Error err = ERROR_INIT;
   try_start();
-  int cmdpreview_type = execute_cmd(&ea, &cmdinfo, true);
+  cmdpreview_type = execute_cmd(&ea, &cmdinfo, true);
   if (try_end(&err)) {
     api_clear_error(&err);
     cmdpreview_type = 0;
@@ -2518,14 +2527,9 @@ static void cmdpreview_show(CommandLineState *s)
   update_topline(curwin);
 
   redrawcmdline();
-
-  // If preview callback returned 0, update screen to clear remnants of an earlier preview.
-  if (cmdpreview_type == 0) {
-    cmdpreview = false;
-    update_screen(SOME_VALID);
-  }
 end:
   xfree(cmdline);
+  return cmdpreview_type != 0;
 }
 
 static int command_line_changed(CommandLineState *s)
@@ -2564,9 +2568,9 @@ static int command_line_changed(CommandLineState *s)
       && *p_icm != NUL       // 'inccommand' is set
       && curbuf->b_p_ma      // buffer is modifiable
       && cmdline_star == 0   // not typing a password
-      && cmd_can_preview((char *)ccline.cmdbuff)
-      && !vpeekc_any()) {
-    cmdpreview_show(s);
+      && !vpeekc_any()
+      && cmdpreview_may_show(s)) {
+    // 'inccommand' preview has been shown.
   } else if (cmdpreview) {
     cmdpreview = false;
     update_screen(SOME_VALID);  // Clear 'inccommand' preview.

test/functional/ui/inccommand_spec.lua

@@ -3008,3 +3008,16 @@ it('long :%s/ with inccommand does not collapse cmdline', function()
     AAAAAAA^     |
   ]])
 end)
+
+it("with 'inccommand' typing :filter doesn't segfault or leak memory #19057", function()
+  clear()
+  common_setup(nil, 'nosplit')
+  feed(':filter s')
+  assert_alive()
+  feed(' ')
+  assert_alive()
+  feed('h')
+  assert_alive()
+  feed('i')
+  assert_alive()
+end)