vim-patch:8.1.0973: pattern with syntax error gives threee error messages

Problem:    Pattern with syntax error gives threee error messages. (Kuang-che
            Wu)
Solution:   Remove outdated internal error.  Don't fall back to other engine
            after an error.
https://github.com/vim/vim/commit/cd62512c5595fa1f7a7f2c6ec1a90ea6bde3ad50

3 files changed, 16 insertions, 12 deletions

diff --git a/src/nvim/regexp.c b/src/nvim/regexp.c
index 7c8d228d45..3b3ca29dad 100644
--- a/src/nvim/regexp.c
+++ b/src/nvim/regexp.c
@@ -7090,6 +7090,7 @@ regprog_T *vim_regcomp(char_u *expr_arg, int re_flags)
 {
   regprog_T   *prog = NULL;
   char_u      *expr = expr_arg;
+  int          save_called_emsg;
 
   regexp_engine = p_re;
 
@@ -7116,9 +7117,11 @@ regprog_T *vim_regcomp(char_u *expr_arg, int re_flags)
   bt_regengine.expr = expr;
   nfa_regengine.expr = expr;
 
-  /*
-   * First try the NFA engine, unless backtracking was requested.
-   */
+  //
+  // First try the NFA engine, unless backtracking was requested.
+  //
+  save_called_emsg = called_emsg;
+  called_emsg = false;
   if (regexp_engine != BACKTRACKING_ENGINE) {
     prog = nfa_regengine.regcomp(expr,
         re_flags + (regexp_engine == AUTOMATIC_ENGINE ? RE_AUTO : 0));
@@ -7143,11 +7146,13 @@ regprog_T *vim_regcomp(char_u *expr_arg, int re_flags)
     // If the NFA engine failed, try the backtracking engine. The NFA engine
     // also fails for patterns that it can't handle well but are still valid
     // patterns, thus a retry should work.
-    if (regexp_engine == AUTOMATIC_ENGINE) {
+    // But don't try if an error message was given.
+    if (regexp_engine == AUTOMATIC_ENGINE && !called_emsg) {
       regexp_engine = BACKTRACKING_ENGINE;
       prog = bt_regengine.regcomp(expr, re_flags);
     }
   }
+  called_emsg |= save_called_emsg;
 
   if (prog != NULL) {
     // Store the info needed to call regcomp() again when the engine turns out
diff --git a/src/nvim/regexp_nfa.c b/src/nvim/regexp_nfa.c
index d1369e4532..95030974d8 100644
--- a/src/nvim/regexp_nfa.c
+++ b/src/nvim/regexp_nfa.c
@@ -6476,16 +6476,10 @@ static regprog_T *nfa_regcomp(char_u *expr, int re_flags)
 
   nfa_regcomp_start(expr, re_flags);
 
-  /* Build postfix form of the regexp. Needed to build the NFA
-   * (and count its size). */
+  // Build postfix form of the regexp. Needed to build the NFA
+  // (and count its size).
   postfix = re2post();
   if (postfix == NULL) {
-    // TODO(vim): only give this error for debugging?
-    if (post_ptr >= post_end) {
-      IEMSGN("Internal error: estimated max number "
-             "of states insufficient: %" PRId64,
-             post_end - post_start);
-    }
     goto fail;              // Cascaded (syntax?) error
   }
 
diff --git a/src/nvim/testdir/test_search.vim b/src/nvim/testdir/test_search.vim
index 8eec1f7a1e..08ccc8d4fe 100644
--- a/src/nvim/testdir/test_search.vim
+++ b/src/nvim/testdir/test_search.vim
@@ -580,3 +580,8 @@ func Test_large_hex_chars2()
   endtry
   set re&
 endfunc
+
+func Test_one_error_msg()
+  " This  was also giving an internal error
+  call assert_fails('call search(" \\((\\v[[=P=]]){185}+             ")', 'E871:')
+endfunc