From: James McCoy <jamessan@debian.org>
Date: Tue, 6 Oct 2015 23:46:30 -0400
Subject: Support sourcing a vimrc.tiny when Vim is invoked as vi

This is used only in the vim-tiny package to allow a specific
configuration for vim-tiny's vi.  The vim-tiny package is substantially
different from other Vim packages, so it does not make sense to
share the same config.

Closes: #222138
Signed-off-by: Stefano Zacchiroli <zack@debian.org>
Signed-off-by: James Vega <jamessan@debian.org>
---
 src/main.c    | 23 ++++++++++++++++++++++-
 src/os_unix.h |  3 +++
 src/structs.h |  3 +++
 3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/src/main.c b/src/main.c
index d1c42ed..c3e6bda 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1929,6 +1929,10 @@ parse_command_name(mparm_T *parmp)
     }
     else if (STRNICMP(initstr, "vim", 3) == 0)
 	initstr += 3;
+#ifdef SYS_TINYRC_FILE
+    else if (STRNICMP(initstr, "vi", 2) == 0)
+	parmp->vi_mode = TRUE;
+#endif
 
     // Catch "[r][g]vimdiff" and "[r][g]viewdiff".
     if (STRICMP(initstr, "diff") == 0)
@@ -3224,7 +3228,12 @@ source_startup_scripts(mparm_T *parmp)
 	 * Get system wide defaults, if the file name is defined.
 	 */
 #ifdef SYS_VIMRC_FILE
-	(void)do_source((char_u *)SYS_VIMRC_FILE, FALSE, DOSO_NONE, NULL);
+# if defined(SYS_TINYRC_FILE) && defined(TINY_VIMRC)
+	if (parmp->vi_mode)
+	    (void)do_source((char_u *)SYS_TINYRC_FILE, FALSE, DOSO_NONE, NULL);
+	else
+# endif
+	    (void)do_source((char_u *)SYS_VIMRC_FILE, FALSE, DOSO_NONE, NULL);
 #endif
 #ifdef MACOS_X
 	(void)do_source((char_u *)"$VIMRUNTIME/macmap.vim", FALSE,
@@ -3263,13 +3272,25 @@ source_startup_scripts(mparm_T *parmp)
 #ifdef USR_EXRC_FILE2
 		&& do_source((char_u *)USR_EXRC_FILE2, FALSE,
 						       DOSO_NONE, NULL) == FAIL
+#endif
+#if defined(SYS_TINYRC_FILE) && defined(TINY_VIMRC)
+		&& !parmp->vi_mode
 #endif
 		&& !has_dash_c_arg)
 	    {
 		// When no .vimrc file was found: source defaults.vim.
 		if (do_source((char_u *)VIM_DEFAULTS_FILE, FALSE, DOSO_NONE,
 								 NULL) == FAIL)
+		{
+		    /*
+		     * If running as the vim.tiny executable, regardless how what argv[0] is, we
+		     * don't want to error due to missing defaults.vim.  That's provided by
+		     * vim-runtime, which isn't typically installed with vim-tiny.
+		     */
+#ifndef TINY_VIMRC
 		    emsg(e_failed_to_source_defaults);
+#endif
+		}
 	    }
 	}
 
diff --git a/src/os_unix.h b/src/os_unix.h
index d87ec90..3f5ce0f 100644
--- a/src/os_unix.h
+++ b/src/os_unix.h
@@ -205,6 +205,9 @@ typedef struct dsc$descriptor   DESC;
 /*
  * Unix system-dependent file names
  */
+#ifndef SYS_TINYRC_FILE
+# define SYS_TINYRC_FILE "$VIM/vimrc.tiny"
+#endif
 #ifndef SYS_VIMRC_FILE
 # define SYS_VIMRC_FILE "$VIM/vimrc"
 #endif
diff --git a/src/structs.h b/src/structs.h
index 46a71cb..ac661a6 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -4468,6 +4468,9 @@ typedef struct
 #ifdef FEAT_DIFF
     int		diff_mode;		// start with 'diff' set
 #endif
+#ifdef SYS_TINYRC_FILE
+    int		vi_mode;		/* started as "vi" */
+#endif
 } mparm_T;
 
 /*