Re: [PATCH 2/4] config: really keep value-internal whitespace verbatim

On 2024-03-15 18:46, Junio C Hamano wrote:

Dragan Simic [off-list ref] writes:

quoted

Fixes: ebdaae372b46 ("config: Keep inner whitespace verbatim")

No need for this line.  You mentioned it in the text already, and
more importantly, grepping for trailers is not the right thing to do
because we may think we fixed all bugs in ebdaae372b46 did with this
patch, which may in 6 months turn out to be false but we cannot undo
the trailer.  On the other hand, the discussion of the problem in
the proposed log message gives readers a richer context and the
future developers can understand that this fixed one thing in
ebdaae372b46 but didn't even know about other bugs introduced by
that old commit and make more intelligent decision based on that
better understanding.

Got it, and I agree that the discussions linked in the patch description
provide much better ways for understanding what brought us to the 
current
situation, and what led to the proposed bugfixes.

It's simply that I'm kind of used to providing "Fixes" tags for patches
in other projects;  I'll make a mental note not to do that for git.

I'll also send the v2 with no "Fixes" tag, after the v1 spends a few 
days
on the mailing list.

quoted

Signed-off-by: Dragan Simic <redacted>
---
 config.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/config.c b/config.c
index a86a20cdf5cb..5072f12e62e4 100644
--- a/config.c
+++ b/config.c

@@ -817,33 +817,38 @@ static int get_next_char(struct config_source 

*cs)

 static char *parse_value(struct config_source *cs)
 {
-	int quote = 0, comment = 0, space = 0;
+	int quote = 0, comment = 0;
+	size_t trim_len = 0;

quoted

 	strbuf_reset(&cs->value);
 	for (;;) {
 		int c = get_next_char(cs);
 		if (c == '\n') {
 			if (quote) {
 				cs->linenr--;
 				return NULL;
 			}
+			if (trim_len)
+				strbuf_setlen(&cs->value, trim_len);
 			return cs->value.buf;

So the idea is that we copy everything we read verbatim in cs->value
but keep track of the beginning of the run of whitespace characters
at the end of the line in trim_len so that we can rtrim it?  That
should be the most straight-forward implementation.

Yes, that's it.  It's as simple as it can be.  A different, somewhat
more complex approach of putting the encountered whitespace in a 
separate
buffer may be warranted if we expected _a lot_ of whitespace, i.e. much
more whitespace than the other characters, but that shouldn't be the 
case,
which makes the simple approach a good choice.

quoted

 		}
 		if (comment)
 			continue;
 		if (isspace(c) && !quote) {
+			if (!trim_len)
+				trim_len = cs->value.len;
 			if (cs->value.len)
+				strbuf_addch(&cs->value, c);
 			continue;

While we are not inside a dq-pair, we keep ignoring a whitespace
character at the beginning (i.e. cs->value.len == 0).

Yes, that "eats up" any leading whitespace.

If we have some value in cs->value, however, we add the whitespace
character to cs->value verbatim.  trim_len==0 signals that the last
character we processed was not a whitespace character, and we copy
the current length of cs->value there---this is so that we can rtrim
away the run of whitespaces at the end of the input, including the
byte we are adding here, if it turns out that we are looking at the
first whitespace character of such trailing blanks.

Exactly.  By the way, please know that I _really_ appreciate your
highly detailed patch reviews!

quoted

 		}
 		if (!quote) {
 			if (c == ';' || c == '#') {
 				comment = 1;
 				continue;
 			}
 		}

quoted

+		if (trim_len)
+			trim_len = 0;

If we are outside a dq-pair, we reach here only when we are looking
at a non-whitespace character.  If we are counting a run of unquoted
whitespaces, we can reset trim_len here to record that we do not
have to trim.

Exactly.  It resets the "need to rtrim flag", so to speak.

But can we be seeing a whitespace that is inside quote here?  Is
resetting trim_len to zero what we want in such a case?  Let's see.
Inside dq, we'd want to accumulate bytes, possibly after unwrapping
their backslash escapes, to cs->value, and these bytes include the
whitespace characters---we want to keep them literally without
trimming.  OK.

Yes, any whitespace inside a quoted option value is to be taken
verbatim, so we basically reset the "need to rtrim flag" in that case,
because value-internal whitespace isn't to be rtrimmed.

Looking good.  We should already demonstrate that this works well
with a new test in the same patch, can't we?  If we can, we should.

Sorry, this sounds a bit confusing to me?  I think there are already
more than enough new tests in the 3/4 patch I sent?

Could you, please, clarify a bit?

quoted

 		if (c == '\\') {
 			c = get_next_char(cs);
 			switch (c) {