vi: allow ctrl-D to reduce indentation

When whitespace has been automatically added to a new line due to
autoindent entering ctrl-D should reduce the level of indentation.

Implement an approximation of this by treating ctrl-D as backspace.
For the common case of indentation using tabs this is good enough.
My attempt at a full implementation was three times bigger.

function                                             old     new   delta
char_insert                                          476     531     +55
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/0 up/down: 55/0)               Total: 55 bytes

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

1 files changed, 14 insertions, 2 deletions

diff --git a/editors/vi.c b/editors/vi.c
index 780c81234..0a82f9e38 100644
--- a/editors/vi.c
+++ b/editors/vi.c
@@ -2072,6 +2072,11 @@ static uintptr_t stupid_insert(char *p, char c) // stupidly insert the char c at
 #endif
 static char *char_insert(char *p, char c, int undo) // insert the char c at 'p'
 {
+#if ENABLE_FEATURE_VI_SETOPTS
+                char *q;
+                size_t len;
+#endif
+
         if (c == 22) {          // Is this an ctrl-V?
                 p += stupid_insert(p, '^');     // use ^ to indicate literal next
                 refresh(FALSE); // show the ^
@@ -2092,6 +2097,15 @@ 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);
+                }
+#endif
         } else if (c == term_orig.c_cc[VERASE] || c == 8 || c == 127) { // Is this a BS
                 if (p > text) {
                         p--;
@@ -2116,8 +2130,6 @@ static char *char_insert(char *p, char c, int undo) // insert the char c at 'p'
                         showmatching(p - 1);
                 }
                 if (autoindent && c == '\n') {  // auto indent the new line
-                        char *q;
-                        size_t len;
                         q = prev_line(p);       // use prev line as template
                         len = strspn(q, " \t"); // space or tab
                         if (len) {