patch 8.2.3146: Vim9: line number wrong for :execute argument

Problem:    Vim9: line number wrong for :execute argument.
Solution:   Use the line number of the :execute command itself. (closes #8537)

src/eval.c

@@ -6191,6 +6191,7 @@ ex_execute(exarg_T *eap)
     char_u	*p;
     garray_T	ga;
     int		len;
+    long	start_lnum = SOURCING_LNUM;
 
     ga_init2(&ga, 1, 80);
 
@@ -6244,6 +6245,9 @@ ex_execute(exarg_T *eap)
 
     if (ret != FAIL && ga.ga_data != NULL)
     {
+	// use the first line of continuation lines for messages
+	SOURCING_LNUM = start_lnum;
+
 	if (eap->cmdidx == CMD_echomsg || eap->cmdidx == CMD_echoerr)
 	{
 	    // Mark the already saved text as finishing the line, so that what

src/testdir/test_vim9_script.vim

@@ -4167,6 +4167,16 @@ def Test_option_modifier()
   set hlsearch&
 enddef
 
+" This must be called last, it may cause following :def functions to fail
+def Test_xxx_echoerr_line_number()
+  var lines =<< trim END
+      echoerr 'some'
+         .. ' error'
+         .. ' continued'
+  END
+  CheckDefExecAndScriptFailure(lines, 'some error continued', 1)
+enddef
+
 def ProfiledFunc()
   var n = 3
   echo [[1, 2], [3, 4]]->filter((_, l) => l[0] == n)

src/version.c

@@ -755,6 +755,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3146,
 /**/
     3145,
 /**/