patch 8.2.2905: no error when defaults.vim cannot be loaded

Problem:    No error when defaults.vim cannot be loaded.
Solution:   Add an error message. (Christian Brabandt, closes #8248)

runtime/doc/starting.txt

@@ -1036,7 +1036,7 @@ giving the mapping.
 
 
 Defaults without a .vimrc file ~
-							*defaults.vim*
+							*defaults.vim* *E1187*
 If Vim is started normally and no user vimrc file is found, the
 $VIMRUNTIME/defaults.vim script is loaded.  This will set 'compatible' off,
 switch on syntax highlighting and a few more things.  See the script for

src/errors.h

@@ -413,3 +413,5 @@ EXTERN char e_missing_redir_end[]
 	INIT(= N_("E1185: Missing :redir END"));
 EXTERN char e_expression_does_not_result_in_value_str[]
 	INIT(= N_("E1186: Expression does not result in a value: %s"));
+EXTERN char e_failed_to_source_defaults[]
+	INIT(= N_("E1187: Failed to source defaults.vim"));

src/main.c

@@ -3128,7 +3128,11 @@ source_startup_scripts(mparm_T *parmp)
     if (parmp->use_vimrc != NULL)
     {
 	if (STRCMP(parmp->use_vimrc, "DEFAULTS") == 0)
-	    do_source((char_u *)VIM_DEFAULTS_FILE, FALSE, DOSO_NONE, NULL);
+	{
+	    if (do_source((char_u *)VIM_DEFAULTS_FILE, FALSE, DOSO_NONE, NULL)
+									 != OK)
+		emsg(e_failed_to_source_defaults);
+	}
 	else if (STRCMP(parmp->use_vimrc, "NONE") == 0
 				     || STRCMP(parmp->use_vimrc, "NORC") == 0)
 	{
@@ -3200,7 +3204,9 @@ source_startup_scripts(mparm_T *parmp)
 		&& !has_dash_c_arg)
 	    {
 		// When no .vimrc file was found: source defaults.vim.
-		do_source((char_u *)VIM_DEFAULTS_FILE, FALSE, DOSO_NONE, NULL);
+		if (do_source((char_u *)VIM_DEFAULTS_FILE, FALSE, DOSO_NONE,
+								 NULL) == FAIL)
+		    emsg(e_failed_to_source_defaults);
 	    }
 	}
 

src/testdir/test_startup.vim

@@ -276,6 +276,19 @@ func Test_V_arg()
    call assert_match("sourcing \"$VIMRUNTIME[\\/]defaults\.vim\"\r\nline 1: \" The default vimrc file\..*  verbose=15\n", out)
 endfunc
 
+" Test that an error is shown when the defaults.vim file could not be read
+func Test_defaults_error()
+  " Can't catch the output of gvim.
+  CheckNotGui
+  CheckNotMSWindows
+
+  let out = system('VIMRUNTIME=/tmp ' .. GetVimCommand() .. ' --clean -cq')
+  call assert_match("E1187: Failed to source defaults.vim", out)
+
+  let out = system('VIMRUNTIME=/tmp ' .. GetVimCommand() .. ' -u DEFAULTS -cq')
+  call assert_match("E1187: Failed to source defaults.vim", out)
+endfunc
+
 " Test the '-q [errorfile]' argument.
 func Test_q_arg()
   CheckFeature quickfix

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2905,
 /**/
     2904,
 /**/