vi: make de-indentation with ctrl-D more like vim

Commit ac6495f6f (vi: allow ctrl-D to reduce indentation) treated
ctrl-D during autoindent as a backspace.  This was adequate for
indentation using tabs but doesn't work well with the expandtab
option.  In the latter case it's necessary to backspace over all
the spaces.

Make ctrl-D work correctly when spaces are present in the indent.

Also, make it behave more like vim:

- ctrl-D is independent of autoindent;
- indentation is reduced even when the cursor isn't positioned at
  the end of the indent.

function                                             old     new   delta
char_insert                                          679     717     +38
get_column                                             -      37     +37
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 1/0 up/down: 75/0)               Total: 75 bytes

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 21 insertions, 9 deletions

diff --git a/editors/vi.c b/editors/vi.c
index de7a43325..caf01acd3 100644
--- a/editors/vi.c
+++ b/editors/vi.c
@@ -763,6 +763,11 @@ static int next_tabstop(int col)
         return col + ((tabstop - 1) - (col % tabstop));
 }
 
+static int prev_tabstop(int col)
+{
+        return col - ((col % tabstop) ?: tabstop);
+}
+
 static int next_column(char c, int co)
 {
         if (c == '\t')
@@ -772,7 +777,6 @@ static int next_column(char c, int co)
         return co + 1;
 }
 
-#if ENABLE_FEATURE_VI_SETOPTS
 static int get_column(char *p)
 {
         const char *r;
@@ -782,7 +786,6 @@ static int get_column(char *p)
                 co = next_column(*r, co);
         return co;
 }
-#endif
 
 //----- Erase the Screen[] memory ------------------------------
 static void screen_erase(void)
@@ -2113,14 +2116,23 @@ static char *char_insert(char *p, char c, int undo) // insert the char c at 'p'
                 if ((p[-1] != '\n') && (dot > text)) {
                         p--;
                 }
-#if ENABLE_FEATURE_VI_SETOPTS
-        } else if (c == 4 && autoindent) {      // ctrl-D reduces indentation
-                q = begin_line(p);
-                len = strspn(q, " \t");
-                if (len && q + len == p) {
-                        p--;
-                        p = text_hole_delete(p, p, ALLOW_UNDO_QUEUED);
+        } else if (c == 4) {    // ctrl-D reduces indentation
+                int prev;
+                char *r, *bol;
+                bol = begin_line(p);
+                for (r = bol; r < end_line(p); ++r) {
+                        if (!isblank(*r))
+                                break;
                 }
+
+                prev = prev_tabstop(get_column(r));
+                while (r > bol && get_column(r) > prev) {
+                        if (p > bol)
+                                p--;
+                        r--;
+                        r = text_hole_delete(r, r, ALLOW_UNDO_QUEUED);
+                }
+#if ENABLE_FEATURE_VI_SETOPTS
         } else if (c == '\t' && expandtab) {    // expand tab
                 int col = get_column(p);
                 col = next_tabstop(col) - col + 1;