patch 8.2.2758: Vim9: wrong line number for autoload function with wrong name

Problem:    Vim9: wrong line number for autoload function with wrong name.
Solution:   Set and restore SOURCING_LNUM. (closes #8100)

src/testdir/test_vim9_func.vim

@@ -74,6 +74,30 @@ def TestCompilingErrorInTry()
   delete('Xdir', 'rf')
 enddef
 
+def Test_autoload_name_mismatch()
+  var dir = 'Xdir/autoload'
+  mkdir(dir, 'p')
+
+  var lines =<< trim END
+      vim9script
+      def scriptX#Function()
+        # comment
+        g:runtime = 'yes'
+      enddef
+  END
+  writefile(lines, dir .. '/script.vim')
+
+  var save_rtp = &rtp
+  exe 'set rtp=' .. getcwd() .. '/Xdir'
+  lines =<< trim END
+      call script#Function()
+  END
+  CheckScriptFailure(lines, 'E746:', 2)
+
+  &rtp = save_rtp
+  delete(dir, 'rf')
+enddef
+
 def CallRecursive(n: number): number
   return CallRecursive(n + 1)
 enddef

src/userfunc.c

@@ -4058,7 +4058,11 @@ define_function(exarg_T *eap, char_u *name_arg)
 	    }
 	    if (j == FAIL)
 	    {
+		linenr_T save_lnum = SOURCING_LNUM;
+
+		SOURCING_LNUM = sourcing_lnum_top;
 		semsg(_("E746: Function name does not match script file name: %s"), name);
+		SOURCING_LNUM = save_lnum;
 		goto erret;
 	    }
 	}

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2758,
 /**/
     2757,
 /**/