Hi Paul,
I'm trying to understand the meaning of 'in_position' and 'out_position' in
function 'print_half_line'. While doing this, I spotted a bug:
$ cat foo1.txt
a
ab
abc
$ cat foo2.txt
ab
abcd
$ src/diff -t -y foo1.txt foo2.txt
a <
ab ab
abc | abcd
This is obviously not how it's intended to be. The attached patch fixes it.
The cause is that in the case of a character of width 1, the assignment
out_position = in_position;
was lost in commit 05cdf3102ef3fb261db311a3e5d090fb63dbc792 (yesterday).
With this patch, the result is again as it should be:
$ src/diff -t -y foo1.txt foo2.txt
a <
ab ab
abc | abcd
The patch also improves comments in this function. So that next time,
I (or anyone else) don't spent 30 minutes to understand the difference
between 'in_position' and 'out_position'.
Bruno
>From 9826aa322e65815288ae63c3a0bb81c1c1267cd8 Mon Sep 17 00:00:00 2001
From: Bruno Haible <br...@clisp.org>
Date: Wed, 5 Jul 2023 19:26:52 +0200
Subject: [PATCH] diff: Fix "diff -y" output
This fixes a regression from 2023-07-04.
* src/side.c (print_half_line): Restore the assignment to out_position.
---
src/side.c | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)
diff --git a/src/side.c b/src/side.c
index 8404c3a..49c7fe5 100644
--- a/src/side.c
+++ b/src/side.c
@@ -66,14 +66,19 @@ tab_from_to (intmax_t from, intmax_t to)
}
/* Print the text for half an sdiff line. This means truncate to
- width observing tabs, and trim a trailing newline. Return the
- last column written (not the number of chars). */
+ OUT_BOUND columns, observing tabs, and trim a trailing newline.
+ Return the presumed column position on the output device after
+ the write (not the number of chars). */
static intmax_t
print_half_line (char const *const *line, intmax_t indent, intmax_t out_bound)
{
FILE *out = outfile;
+ /* IN_POSITION is the current column position if we were outputting the
+ entire line, i.e. ignoring OUT_BOUND. */
intmax_t in_position = 0;
+ /* OUT_POSITION is the current column position. It stays <= OUT_BOUND
+ at any moment. */
intmax_t out_position = 0;
char const *text_pointer = line[0];
char const *text_limit = line[1];
@@ -188,9 +193,14 @@ print_half_line (char const *const *line, intmax_t indent, intmax_t out_bound)
case 'z': case '{': case '|': case '}': case '~':
if (ckd_add (&in_position, in_position, 1))
return out_position;
- FALLTHROUGH;
+ if (in_position <= out_bound)
+ {
+ out_position = in_position;
+ putc (c, out);
+ }
+ break;
- /* Print width already handled. */
+ /* Print width 0. */
case '\0': case '\f': case '\v':
if (in_position <= out_bound)
putc (c, out);
--
2.34.1
