threads / rfc / 31739

RFC patchattr: allow pattern escape using backslash

Subject: [PATCH/RFC] attr: allow pattern escape using backslash

## tl;dr

3 messages between Oct 6, 2012 and Oct 6, 2012. Diffs are folded; open one to read it.

replies: 2people: 2as markdown or json

Nguyễn Thái Ngọc Duy· Oct 6, 2012, 07:22 UTC · lore

.gitattributes pattern syntax is supposed to be the same as .gitignore (except a few things that do not make sense in attr context, but that's a different issue). .gitignore uses fnmatch() as the matching machinery and "\" is accepted as an escape code. In theory the pattern 'foo\ bar' should match path 'foo bar' in .gitignore. Granted, no one would write 'foo\ bar' in .gitignore when 'foo bar' should suffice.

Regardless, 'foo\ bar attr' does not (but should) attach "attr" to path "foo bar" because pattern/attr parse code does not understand backslash escape. It parses the line as path 'foo\' and attributes 'bar' and 'attr'. This patch teaches attr code to recognize the backslash in patterns (not macro names) and pass 'foo\ bar' down to fnmatch().

This changes the attr behavior. "foo\ attr", if exists in the field, would match nothing because path "foo\" is invalid in UNIX and is a directory in Windows, which we do not accept attaching attributes to. With this patch, that line becomes invalid and is rejected. So it's not really bad (i.e. no silent changes in behavior).

Other subtle behavioral changes may happen. Still, I think we should do this as it seems like a correct thing to do.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 We discussed the "spaces in path names in attr" before and I remember
 using quotes or double quotes, even substituting spaces with
 dots, were raised. I don't remember if backslashes were mentioned.

 attr.c                | 12 +++++++++++-
 t/t0003-attributes.sh |  5 +++++
 2 files changed, 16 insertions(+), 1 deletion(-)

Show changes to 2 files +16 −1

attr.c, t/t0003-attributes.sh

diff --git a/attr.c b/attr.c
index 887a9ae..173d51d 100644
--- a/attr.c
+++ b/attr.c
@@ -221,8 +221,18 @@ static struct match_attr *parse_attr_line(const char *line, const char *src,
 			return NULL;
 		}
 	}
-	else
+	else {
 		is_macro = 0;
+		namelen = 0;
+		while (name[namelen] != '\0' &&
+		       !strchr(blank, name[namelen])) {
+			if (name[namelen] == '\\' &&
+			    name[namelen + 1] != '\0')
+				namelen += 2;
+			else
+				namelen++;
+		}
+	}
 
 	states = name + namelen;
 	states += strspn(states, blank);
diff --git a/t/t0003-attributes.sh b/t/t0003-attributes.sh
index febc45c..16b419e 100755
--- a/t/t0003-attributes.sh
+++ b/t/t0003-attributes.sh
@@ -24,6 +24,7 @@ test_expect_success 'setup' '
 		echo "offon -test test"
 		echo "no notest"
 		echo "A/e/F test=A/e/F"
+		echo "A\\ b test=space"
 	) >.gitattributes &&
 	(
 		echo "g test=a/g" &&
@@ -196,6 +197,10 @@ test_expect_success 'root subdir attribute test' '
 	attr_check subdir/a/i unspecified
 '
 
+test_expect_success 'quoting in pattern' '
+	attr_check "A b" space
+'
+
 test_expect_success 'setup bare' '
 	git clone --bare . bare.git &&
 	cd bare.git

-- 
1.7.12.1.406.g6ab07c4

Junio C Hamano· Oct 6, 2012, 07:54 UTC · re: Nguyễn Thái Ngọc Duy · lore

Re: [PATCH/RFC] attr: allow pattern escape using backslash

Nguyễn Thái Ngọc Duy  <pclouds@gmail.com> writes:

Show 29 quoted lines

> .gitattributes pattern syntax is supposed to be the same as .gitignore
> (except a few things that do not make sense in attr context, but
> that's a different issue). .gitignore uses fnmatch() as the matching
> machinery and "\" is accepted as an escape code. In theory the pattern
> 'foo\ bar' should match path 'foo bar' in .gitignore. Granted, no one
> would write 'foo\ bar' in .gitignore when 'foo bar' should
> suffice.
>
> Regardless, 'foo\ bar attr' does not (but should) attach "attr" to
> path "foo bar" because pattern/attr parse code does not understand
> backslash escape. It parses the line as path 'foo\' and attributes
> 'bar' and 'attr'. This patch teaches attr code to recognize the
> backslash in patterns (not macro names) and pass 'foo\ bar' down to
> fnmatch().
>
> This changes the attr behavior. "foo\ attr", if exists in the field,
> would match nothing because path "foo\" is invalid in UNIX and is a
> directory in Windows, which we do not accept attaching attributes
> to. With this patch, that line becomes invalid and is rejected. So
> it's not really bad (i.e. no silent changes in behavior).
>
> Other subtle behavioral changes may happen. Still, I think we should
> do this as it seems like a correct thing to do.
>
> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
> ---
>  We discussed the "spaces in path names in attr" before and I remember
>  using quotes or double quotes, even substituting spaces with
>  dots, were raised. I don't remember if backslashes were mentioned.

My knee-jerk reaction, without thinking things through, is that this makes sense and doing the same for .gitignore would, too (even though the one-item-per-line nature of .gitignore makes "\ " and " " practically equivalent).

Shouldn't we do the same for quoting fnmatch(3) metacharacters? To match a path component 'a' followed by an asterisk followed by 'b', you could then write 'a\*b'. Same for quoting the backslash itself.

Nguyen Thai Ngoc Duy· Oct 6, 2012, 08:02 UTC · re: Junio C Hamano · lore

Re: [PATCH/RFC] attr: allow pattern escape using backslash

On Sat, Oct 6, 2012 at 2:54 PM, Junio C Hamano <gitster@pobox.com> wrote:

> Shouldn't we do the same for quoting fnmatch(3) metacharacters?  To
> match a path component 'a' followed by an asterisk followed by 'b',
> you could then write 'a\*b'.  Same for quoting the backslash itself.

I think my patch does that too. The thing it does not do is optimize this case so that we can do strcmp() instead of fnmatch() if the entire pattern does not contain any metacharacters but backslashes. I don't think it'll become popular enough to deserve an optimization.

-- 
Duy