vim-patch:8.2.2121: internal error when using \ze before \zs in a pattern

Problem:    Internal error when using \ze before \zs in a pattern.
Solution:   Check the end is never before the start. (closes vim/vim#7442)
a7a691cc14

src/nvim/regexp.c

@@ -3605,6 +3605,22 @@ theend:
   if (backpos.ga_maxlen > BACKPOS_INITIAL)
     ga_clear(&backpos);
 
+  // Make sure the end is never before the start.  Can happen when \zs and
+  // \ze are used.
+  if (REG_MULTI) {
+    const lpos_T *const start = &rex.reg_mmatch->startpos[0];
+    const lpos_T *const end = &rex.reg_mmatch->endpos[0];
+
+    if (end->lnum < start->lnum
+        || (end->lnum == start->lnum && end->col < start->col)) {
+      rex.reg_mmatch->endpos[0] = rex.reg_mmatch->startpos[0];
+    }
+  } else {
+    if (rex.reg_match->endp[0] < rex.reg_match->startp[0]) {
+      rex.reg_match->endp[0] = rex.reg_match->startp[0];
+    }
+  }
+
   return retval;
 }
 

src/nvim/regexp_nfa.c

@@ -6591,6 +6591,22 @@ static long nfa_regexec_both(char_u *line, colnr_T startcol,
 #endif
 
 theend:
+  // Make sure the end is never before the start.  Can happen when \zs and
+  // \ze are used.
+  if (REG_MULTI) {
+    const lpos_T *const start = &rex.reg_mmatch->startpos[0];
+    const lpos_T *const end = &rex.reg_mmatch->endpos[0];
+
+    if (end->lnum < start->lnum
+        || (end->lnum == start->lnum && end->col < start->col)) {
+      rex.reg_mmatch->endpos[0] = rex.reg_mmatch->startpos[0];
+    }
+  } else {
+    if (rex.reg_match->endp[0] < rex.reg_match->startp[0]) {
+      rex.reg_match->endp[0] = rex.reg_match->startp[0];
+    }
+  }
+
   return retval;
 }
 

src/nvim/testdir/test_regexp_latin.vim

@@ -755,6 +755,13 @@ func Test_start_end_of_buffer_match()
   bwipe!
 endfunc
 
+func Test_ze_before_zs()
+  call assert_equal('', matchstr(' ', '\%#=1\ze \zs'))
+  call assert_equal('', matchstr(' ', '\%#=2\ze \zs'))
+  call assert_equal(repeat([''], 10), matchlist(' ', '\%#=1\ze \zs'))
+  call assert_equal(repeat([''], 10), matchlist(' ', '\%#=2\ze \zs'))
+endfunc
+
 " Check for detecting error
 func Test_regexp_error()
   set regexpengine=2