[PATCH] ignores: handle non UTF-8 exclude files

[PATCH] ignores: handle non UTF-8 exclude files

[Matthieu Beauchamp-Boulay via GitGitGadget]

From: Matthieu Beauchamp-Boulay <matthieu.beauchamp.boulay@gmail.com>

When reading exclude files, git assumes it is encoded in UTF-8 and will
fail to apply patterns if it isn't. This is a silent failure as no warning
or errors are shown to the users. This is a problem that can take a while
to diagnose as many users will not think of checking the encoding of their
file and may believe their patterns are wrong instead. Users may also
accidentally commit undesired files.

On Windows, this happens if a user uses Windows PowerShell to create the
file, which results in a UTF-16LE file with a BOM. This issue was discussed
here https://github.com/git-for-windows/git/issues/3329. An example of
where a user was confused that his exclude file was not working is cited
https://github.com/git-for-windows/git/issues/3227.

A minimal fix should at least warn the user if git cannot properly decode
the exclude file. Ideally, git would handle any given Unicode file.

First, check if a BOM is present. If it is, decode the file to UTF-8.
If no BOM is detected, then try to parse the file as UTF-8. If that fails,
attempt to decode the file using the working tree encoding of the file,
if any. If that fails, print a warning to tell the user that the exclude
file could not be decoded and skip the file.

This raises the issue that if the entire tree is encoded in, for example
UTF-16BE (no BOM), then even if the encoding is given in .gitattributes,
git would not be able to decode it. I believe that this is still
acceptable since a warning will be emitted for the file (since it has no
BOM, is not valid UTF-8 and no working tree encoding could be found).

One case that isn't handled is if a wrong encoding is given in the
attributes and the exclude file has no BOM and is not UTF-8. Using
iconv to convert an UTF16BE file to UTF-8 while specifying UTF-16LE
yields gibberish without an error and so this case is a silent failure
where no patterns will match.

Signed-off-by: Matthieu Beauchamp-Boulay <matthieu.beauchamp.boulay@gmail.com>
---
    ignores: handle non UTF-8 exclude files

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2157%2FMatthieu-Beauchamp%2Funicode-support-gitignore-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2157/Matthieu-Beauchamp/unicode-support-gitignore-v1
Pull-Request: https://github.com/git/git/pull/2157

 dir.c              |  29 +++++++++++++
 t/lib-encoding.sh  |   8 ++++
 t/t0008-ignores.sh | 102 +++++++++++++++++++++++++++++++++++++++++++++
 utf8.c             |  29 +++++++++++++
 utf8.h             |  12 ++++++
 5 files changed, 180 insertions(+)

diff --git a/dir.c b/dir.c
index b00821f294..895d476253 100644
--- a/dir.c
+++ b/dir.c
@@ -1154,7 +1154,9 @@ static int add_patterns(const char *fname, const char *base, int baselen,
 	int r;
 	int fd;
 	size_t size = 0;
+	size_t reencoded_size = 0;
 	char *buf;
+	char *reencoded = NULL;
 
 	if (flags & PATTERN_NOFOLLOW)
 		fd = open_nofollow(fname, O_RDONLY);
@@ -1190,7 +1192,34 @@ static int add_patterns(const char *fname, const char *base, int baselen,
 			close(fd);
 			return -1;
 		}
+
+		if (!try_reencode_to_utf8(buf, size, &reencoded, &reencoded_size) && !is_valid_utf8(buf, size)) {
+			struct conv_attrs ca;
+			convert_attrs(istate, &ca, fname);
+
+			if (ca.working_tree_encoding) {
+				reencoded = reencode_string_len(buf, size, "UTF-8", ca.working_tree_encoding, &reencoded_size);
+				if (!reencoded) {
+					warning(_("Failed to decode exclude file %s from encoding %s"), pl->src, ca.working_tree_encoding);
+					free(buf);
+					return -1;
+				}
+			} else {
+				warning(_("Ignoring exclude file with unknown encoding: %s"), pl->src);
+				free(buf);
+				return -1;
+			}
+		}
+
+		if (reencoded) {
+			size = reencoded_size;
+			free(buf);
+			buf = xmallocz(size);
+			memcpy(buf, reencoded, size);
+			free(reencoded);
+		}
 		buf[size++] = '\n';
+
 		close(fd);
 		if (oid_stat) {
 			int pos;
diff --git a/t/lib-encoding.sh b/t/lib-encoding.sh
index 2dabc8c73e..1b1cc357ba 100644
--- a/t/lib-encoding.sh
+++ b/t/lib-encoding.sh
@@ -23,3 +23,11 @@ write_utf32 () {
 	fi &&
 	iconv -f UTF-8 -t UTF-32
 }
+
+write_encoded () {
+  iconv -f UTF-8 -t "$1"
+}
+
+write_bom () {
+  echo "$@" | perl -pe 's/\s+//g; $_=pack("H*", $_)'
+}
\ No newline at end of file
diff --git a/t/t0008-ignores.sh b/t/t0008-ignores.sh
index db8bde280e..d5a3002ffb 100755
--- a/t/t0008-ignores.sh
+++ b/t/t0008-ignores.sh
@@ -4,6 +4,7 @@ test_description=check-ignore
 
 TEST_CREATE_REPO_NO_TEMPLATE=1
 . ./test-lib.sh
+. "$TEST_DIRECTORY/lib-encoding.sh"
 
 init_vars () {
 	global_excludes="global-excludes"
@@ -963,4 +964,105 @@ test_expect_success EXPENSIVE 'large exclude file ignored in tree' '
 	test_cmp expect err
 '
 
+############################################################################
+#
+# test handling of unicode for .gitignore when BOM is preset or worktree encoding is set for the file
+
+supports_encoding () {
+  encoding="$1" &&
+  d="support-bom-$encoding" &&
+  shift &&
+	mkdir -p "$d" &&
+	touch "$d/file" "$d/excluded" &&
+	write_bom "$@" > "$d/.gitignore" &&
+  echo excluded | write_encoded "$encoding" >> "$d/.gitignore"
+	git check-ignore "$d/excluded" > "$d/actual" &&
+	echo "$d/excluded" > expect &&
+	test_cmp expect "$d/actual"
+}
+
+test_expect_success ICONV 'Can read gitignore in UTF-8 with BOM' '
+  supports_encoding "UTF-8" EF BB BF
+'
+
+test_expect_success ICONV 'Can read gitignore in UTF-16LE when given a BOM' '
+  supports_encoding "UTF-16LE" FF FE
+'
+
+test_expect_success ICONV 'Can read gitignore in UTF-16BE when given a BOM' '
+  supports_encoding "UTF-16BE" FE FF
+'
+
+test_expect_success ICONV 'Can read gitignore in UTF-32LE when given a BOM' '
+  supports_encoding "UTF-32LE" FF FE 00 00
+'
+
+test_expect_success ICONV 'Can read gitignore in UTF-32BE when given a BOM' '
+  supports_encoding "UTF-32BE" 00 00 FE FF
+'
+
+supports_reading_ignore_in_working_tree_encoding () {
+  encoding="$1" &&
+  d="support-wt-$encoding" &&
+	mkdir -p "$d" &&
+	touch "$d/file" "$d/excluded" &&
+  echo ".gitignore		text working-tree-encoding=$encoding" > "$d/.gitattributes" &&
+  echo excluded | write_encoded "$encoding" > "$d/.gitignore"
+	git check-ignore "$d/excluded" > "$d/actual" &&
+	echo "$d/excluded" > expect &&
+	test_cmp expect "$d/actual"
+}
+
+test_expect_success ICONV 'Can read gitignore in UTF-8 when it is set as working tree encoding' '
+  supports_reading_ignore_in_working_tree_encoding "UTF-8"
+'
+
+test_expect_success ICONV 'Can read gitignore in UTF-16LE when it is set as working tree encoding' '
+  supports_reading_ignore_in_working_tree_encoding "UTF-16LE"
+'
+
+test_expect_success ICONV 'Can read gitignore in UTF-16BE when it is set as working tree encoding' '
+  supports_reading_ignore_in_working_tree_encoding "UTF-16BE"
+'
+
+test_expect_success ICONV 'Can read gitignore in UTF-32LE when it is set as working tree encoding' '
+  supports_reading_ignore_in_working_tree_encoding "UTF-32LE"
+'
+
+test_expect_success ICONV 'Can read gitignore in UTF-32BE when it is set as working tree encoding' '
+  supports_reading_ignore_in_working_tree_encoding "UTF-32BE"
+'
+
+test_expect_success ICONV 'Issues a warning if encoding cannot be deduced' '
+  d="warn-unknown-encoding" &&
+	mkdir -p "$d" &&
+	touch "$d/file" "$d/excluded" &&
+	echo excluded | write_encoded "UTF-16BE" > "$d/.gitignore" &&
+	test_must_fail git check-ignore "$d/excluded" > actual 2>&1 &&
+	echo "warning: Ignoring exclude file with unknown encoding: $d/.gitignore" > expect &&
+	test_cmp expect actual
+'
+
+test_expect_success ICONV 'Warns if the exclude file cannot be decoded due to encoded attributes' '
+  d="warn-cant-decode-attributes" &&
+	mkdir -p "$d" &&
+	touch "$d/file" "$d/excluded" &&
+	echo excluded | write_encoded "UTF-16BE" > "$d/.gitignore" &&
+  echo ".gitignore		text working-tree-encoding=UTF-16BE" | write_encoded "UTF-16BE" > "$d/.gitattributes" &&
+	test_must_fail git check-ignore "$d/excluded" > actual 2>&1 &&
+	echo "warning: Ignoring exclude file with unknown encoding: $d/.gitignore" > expect &&
+	test_cmp expect actual
+'
+
+test_expect_failure ICONV 'Issues a warning if the wrong encoding is given' '
+  d="warn-wrong-encoding" &&
+	mkdir -p "$d" &&
+	touch "$d/file" "$d/excluded" &&
+	echo excluded | write_encoded "UTF-16BE" > "$d/.gitignore" &&
+  echo ".gitignore		text working-tree-encoding=UTF-16LE" > "$d/.gitattributes" &&
+	test_must_fail git check-ignore "$d/excluded" > actual 2>&1 &&
+	echo "warning: Ignoring exclude file with unknown encoding: $d/.gitignore" > expect &&
+	test_cmp expect actual
+'
+
 test_done
diff --git a/utf8.c b/utf8.c
index 35a0251939..904cf20f97 100644
--- a/utf8.c
+++ b/utf8.c
@@ -252,6 +252,17 @@ int is_utf8(const char *text)
 	return 1;
 }
 
+int is_valid_utf8(const char *text, size_t len)
+{
+	while (text && len > 0) {
+		ucs_char_t ch = pick_one_utf8_char(&text, &len);
+		if (text && ch == 0 && len > 0)
+			return 0;
+	}
+
+	return text != NULL;
+}
+
 static void strbuf_add_indented_text(struct strbuf *buf, const char *text,
 				     int indent, int indent2)
 {
@@ -643,6 +654,24 @@ int is_missing_required_utf_bom(const char *enc, const char *data, size_t len)
 	);
 }
 
+int try_reencode_to_utf8(const char *text, size_t len, char **out_text, size_t *out_len)
+{
+	const char *in_encoding;
+	if (has_bom_prefix(text, len, utf32_be_bom, sizeof(utf32_be_bom)))
+		in_encoding = "UTF-32BE";
+	else if (has_bom_prefix(text, len, utf32_le_bom, sizeof(utf32_le_bom)))
+		in_encoding = "UTF-32LE";
+	else if (has_bom_prefix(text, len, utf16_be_bom, sizeof(utf16_be_bom)))
+		in_encoding = "UTF-16BE";
+	else if (has_bom_prefix(text, len, utf16_le_bom, sizeof(utf16_le_bom)))
+		in_encoding = "UTF-16LE";
+	else
+		return 0;
+
+	*out_text = reencode_string_len(text, len, "UTF-8", in_encoding, out_len);
+	return *out_text != NULL;
+}
+
 /*
  * Returns first character length in bytes for multi-byte `text` according to
  * `encoding`.
diff --git a/utf8.h b/utf8.h
index cf8ecb0f21..e52e4f7c06 100644
--- a/utf8.h
+++ b/utf8.h
@@ -10,6 +10,12 @@ int utf8_width(const char **start, size_t *remainder_p);
 int utf8_strnwidth(const char *string, size_t len, int skip_ansi);
 int utf8_strwidth(const char *string);
 int is_utf8(const char *text);
+
+/*
+ * Checks that the string is valid UTF-8 that does not contain the null byte
+ * except at the end of the string
+ */
+int is_valid_utf8(const char *text, size_t len);
 int is_encoding_utf8(const char *name);
 int same_encoding(const char *, const char *);
 __attribute__((format (printf, 2, 3)))
@@ -48,6 +54,12 @@ static inline char *reencode_string(const char *in,
 				   NULL);
 }
 
+/*
+ * Returns true if an unicode BOM is detected and the string can be reencoded to UTF-8.
+ * In that case the string is reencoded to UTF-8 in *out_text.
+ */
+int try_reencode_to_utf8(const char *text, size_t len, char **out_text, size_t *out_len);
+
 int mbs_chrlen(const char **text, size_t *remainder_p, const char *encoding);
 
 /*

base-commit: c4a0c8845e2426375ad257b6c221a3a7d92ecfda
-- 
gitgitgadget

Re: [PATCH] ignores: handle non UTF-8 exclude files

[Junio C Hamano]

"Matthieu Beauchamp-Boulay via GitGitGadget"
<gitgitgadget@gmail.com> writes:

> From: Matthieu Beauchamp-Boulay <matthieu.beauchamp.boulay@gmail.com>
>
> When reading exclude files, git assumes it is encoded in UTF-8 and will
> fail to apply patterns if it isn't.

Is it true?  I thought we assume that the exclude patters are
written in such a way to match the encoding of the pathnames,
whatever used on the platform that our calls to readdir(3) returns.
Some platforms may have compat/ code to convert these paths and
force use of UTF-8, but please do not write such platform local
conventions as if it were universal characteristics of our system.

"ignores" -> "exclude" on the title, as that is the canonical word
we use in the codebase to refer to the ignore mechanism.

Re: [PATCH] ignores: handle non UTF-8 exclude files

[Torsten Bögershausen]

On Sat, Jan 03, 2026 at 10:16:57PM +0000, Matthieu Beauchamp-Boulay via GitGitGadget wrote:
> From: Matthieu Beauchamp-Boulay <matthieu.beauchamp.boulay@gmail.com>
Thanks for contributing - some comments inlie
> 
> When reading exclude files, git assumes it is encoded in UTF-8 and will
Question: The report citet below talks about ignore files.

> fail to apply patterns if it isn't. This is a silent failure as no warning
> or errors are shown to the users. This is a problem that can take a while
> to diagnose as many users will not think of checking the encoding of their
> file and may believe their patterns are wrong instead. Users may also
> accidentally commit undesired files.
Note:
git status is your friend.
Blindly commiting without checking what is staged or not may
lead to unwanted results.

> 
> On Windows, this happens if a user uses Windows PowerShell to create the
> file, which results in a UTF-16LE file with a BOM.
>  This issue was discussed
> here https://github.com/git-for-windows/git/issues/3329. An example of
> where a user was confused that his exclude file was not working is cited
> https://github.com/git-for-windows/git/issues/3227.
A very short research indicates that powershell can be configured
to use UTF-8. I am not a powershell user, please correct if I am wrong.

> 
> A minimal fix should at least warn the user if git cannot properly decode
> the exclude file.
I think that reading an ignore file that contains a '\0' could/should
Git to complain. If someone asks my, most users are tempted to ignore
warnings for different reasons. Bailing out may feel more unpolite
but more clear that somethinh is wrong.

>Ideally, git would handle any given Unicode file.
That is debatable.

> 
> First, check if a BOM is present. If it is, decode the file to UTF-8.
> If no BOM is detected, then try to parse the file as UTF-8. If that fails,
> attempt to decode the file using the working tree encoding of the file,
> if any. If that fails, print a warning to tell the user that the exclude
> file could not be decoded and skip the file.
> 
> This raises the issue that if the entire tree is encoded in, for example
> UTF-16BE (no BOM), then even if the encoding is given in .gitattributes,
> git would not be able to decode it.
"able to decode: Yes. But willing to do so: not with the patch, right ?
> I believe that this is still
> acceptable since a warning will be emitted for the file (since it has no
> BOM, is not valid UTF-8 and no working tree encoding could be found).
> 
> One case that isn't handled is if a wrong encoding is given in the
> attributes and the exclude file has no BOM and is not UTF-8. Using
> iconv to convert an UTF16BE file to UTF-8 while specifying UTF-16LE
> yields gibberish without an error and so this case is a silent failure
> where no patterns will match.
One question is, if we should look at working_tree_encoding at all.
The other one is, how much UTF-16 handling of ignore or
other file should we have have in Git ?
It seems that this fix is for a very special case only ?

From
https://github.com/git-for-windows/git/issues/3329
we read:
/******/
if (size > 1 && buf[0] == 0xff && buf[1] == 0xfe) {
    char *reencoded = reencode_string_len(buf, size, "UTF-8", "UTF16-LE-BOM", &size);
    if (!reencoded)
        die(_("could not convert contents of '%s' from UTF-16"), fname);
    free(buf);
    buf = reencoded;
}
/******/
(Which seems a simpler suggestion)
However,  there is no UTF-16-LE-BOM in iconv 
(at least in the majority of implementations), 
so a better approach, totaly untested, may be:

if (size >= 2 && buf[0] == 0xff && buf[1] == 0xfe) {
    char *reencoded = reencode_string_len(buf+2, size-2, "UTF-8", "UTF16", &size);
    if (!reencoded)
        die(_("could not convert contents of '%s' from UTF-16"), fname);
    free(buf);
    buf = reencoded;
}

This leads to some free thinking, especially when we look at
other implementations of Git:
Would it be better to simply bail out on UTF-16 files ?
Techically all files with a '\0'.
[snip] 

Re: [PATCH] ignores: handle non UTF-8 exclude files

[brian m. carlson]

[-- Attachment #1: Type: text/plain, Size: 3337 bytes --]

On 2026-01-03 at 22:16:57, Matthieu Beauchamp-Boulay via GitGitGadget wrote:
> When reading exclude files, git assumes it is encoded in UTF-8 and will
> fail to apply patterns if it isn't. This is a silent failure as no warning
> or errors are shown to the users. This is a problem that can take a while
> to diagnose as many users will not think of checking the encoding of their
> file and may believe their patterns are wrong instead. Users may also
> accidentally commit undesired files.

This isn't actually true.  Git allows arbitrary byte sequences in the
file because Git allows filenames to have arbitrary byte sequences, just
like Unix.

> On Windows, this happens if a user uses Windows PowerShell to create the
> file, which results in a UTF-16LE file with a BOM. This issue was discussed
> here https://github.com/git-for-windows/git/issues/3329. An example of
> where a user was confused that his exclude file was not working is cited
> https://github.com/git-for-windows/git/issues/3227.

Ah, yes, here's the problem.  UTF-16LE is used on Windows, and on
Windows, Git stores pathnames as if they were converted into UTF-8, so
you do need to write the filenames in UTF-8 in the ignore file.

> A minimal fix should at least warn the user if git cannot properly decode
> the exclude file. Ideally, git would handle any given Unicode file.

As I mentioned, the file isn't necessarily in UTF-8 or Unicode.  Here's
an example shell script to demonstrate (requires a non-macOS Unix):

----
#!/bin/sh

rm -fr test-repo
git init --object-format=sha256 test-repo
cd test-repo
touch abc.txt
touch "$(printf '\220')"
printf '\220\n' >.gitignore
git add .
git status
git ls-files -io --exclude-standard
----

I'll point out that all of this is also true for things like config
files (which are also used in `.gitmodules`) and `.gitattributes` files.
If we wanted to make a change, we would be wise to make it everywhere.

However, if we wanted to force `.gitignore` to UTF-8, we'd need to have
an escape mechanism to write non-UTF-8 sequences, and as far as I know,
we don't.

> First, check if a BOM is present. If it is, decode the file to UTF-8.
> If no BOM is detected, then try to parse the file as UTF-8. If that fails,
> attempt to decode the file using the working tree encoding of the file,
> if any. If that fails, print a warning to tell the user that the exclude
> file could not be decoded and skip the file.

We do not accept and strip BOMs in UTF-8 files elsewhere (including in
things like `git diff` output), so we should not do so here, either.
For Unicode files, if there is no BOM, then the standard is that it's
assumed to automatically be UTF-8, so a BOM is superfluous and not
recommended.

> diff --git a/t/lib-encoding.sh b/t/lib-encoding.sh
> index 2dabc8c73e..1b1cc357ba 100644
> --- a/t/lib-encoding.sh
> +++ b/t/lib-encoding.sh
> @@ -23,3 +23,11 @@ write_utf32 () {
>  	fi &&
>  	iconv -f UTF-8 -t UTF-32
>  }
> +
> +write_encoded () {
> +  iconv -f UTF-8 -t "$1"
> +}
> +
> +write_bom () {
> +  echo "$@" | perl -pe 's/\s+//g; $_=pack("H*", $_)'
> +}
> \ No newline at end of file

We place newlines at the end of our text files unless there's a good
reason no to.
-- 
brian m. carlson (they/them)
Toronto, Ontario, CA

[-- Attachment #2: signature.asc --]
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Re: [PATCH] ignores: handle non UTF-8 exclude files

[Matthieu Beauchamp]

On Sat, Jan 3, 2026 at 9:54 PM Junio C Hamano <gitster@pobox.com> wrote:
>
> "Matthieu Beauchamp-Boulay via GitGitGadget"
> <gitgitgadget@gmail.com> writes:
>
> > From: Matthieu Beauchamp-Boulay <matthieu.beauchamp.boulay@gmail.com>
> >
> > When reading exclude files, git assumes it is encoded in UTF-8 and will
> > fail to apply patterns if it isn't.
>
> Is it true?  I thought we assume that the exclude patters are
> written in such a way to match the encoding of the pathnames,
> whatever used on the platform that our calls to readdir(3) returns.
> Some platforms may have compat/ code to convert these paths and
> force use of UTF-8, but please do not write such platform local
> conventions as if it were universal characteristics of our system.

I believe you are correct, I wrongly assumed git would always
manipulate UTF-8 paths.
The revision will need to take the platform into consideration.

> "ignores" -> "exclude" on the title, as that is the canonical word
> we use in the codebase to refer to the ignore mechanism.

Thank you, I will update in the revision.

Re: [PATCH] ignores: handle non UTF-8 exclude files

[Matthieu Beauchamp]

On Sun, Jan 4, 2026 at 12:35 PM Torsten Bögershausen <tboegi@web.de> wrote:
>
> On Sat, Jan 03, 2026 at 10:16:57PM +0000, Matthieu Beauchamp-Boulay via GitGitGadget wrote:
> > From: Matthieu Beauchamp-Boulay <matthieu.beauchamp.boulay@gmail.com>
> Thanks for contributing - some comments inlie
> >
> > When reading exclude files, git assumes it is encoded in UTF-8 and will
> Question: The report citet below talks about ignore files.
>
> > fail to apply patterns if it isn't. This is a silent failure as no warning
> > or errors are shown to the users. This is a problem that can take a while
> > to diagnose as many users will not think of checking the encoding of their
> > file and may believe their patterns are wrong instead. Users may also
> > accidentally commit undesired files.
> Note:
> git status is your friend.
> Blindly commiting without checking what is staged or not may
> lead to unwanted results.

Yes of course, I'll remove that last line as it is not the problem I'm
really trying to fix.

> >
> > On Windows, this happens if a user uses Windows PowerShell to create the
> > file, which results in a UTF-16LE file with a BOM.
> >  This issue was discussed
> > here https://github.com/git-for-windows/git/issues/3329. An example of
> > where a user was confused that his exclude file was not working is cited
> > https://github.com/git-for-windows/git/issues/3227.
> A very short research indicates that powershell can be configured
> to use UTF-8. I am not a powershell user, please correct if I am wrong.
>

Yes you are correct, but I want to address the issues for users who may not
realize that they used the wrong encoding when creating their exclude file.
For that case I don't see how the fact that powershell can be configured to
UTF-8 helps, aside from preventing repeating the same mistake.

> >
> > A minimal fix should at least warn the user if git cannot properly decode
> > the exclude file.
> I think that reading an ignore file that contains a '\0' could/should
> Git to complain. If someone asks my, most users are tempted to ignore
> warnings for different reasons. Bailing out may feel more unpolite
> but more clear that somethinh is wrong.

While I agree that warnings may be ignored, I feel like a wrongly encoded
exclude file is not an error that warrants stopping git entirely.

As other reviewers mentioned, I wrongly assumed that the encoding would
be UTF-8. The idea of looking for the null byte in the exclude file
may be helpful
since any d_name from readdir (3) is null terminated. Checking for a null byte
before the end of the file could be a simple check to detect a bad exclude file.

> >Ideally, git would handle any given Unicode file.
> That is debatable.

Of course, I'll rephrase that part.

> >
> > First, check if a BOM is present. If it is, decode the file to UTF-8.
> > If no BOM is detected, then try to parse the file as UTF-8. If that fails,
> > attempt to decode the file using the working tree encoding of the file,
> > if any. If that fails, print a warning to tell the user that the exclude
> > file could not be decoded and skip the file.
> >
> > This raises the issue that if the entire tree is encoded in, for example
> > UTF-16BE (no BOM), then even if the encoding is given in .gitattributes,
> > git would not be able to decode it.
> "able to decode: Yes. But willing to do so: not with the patch, right ?
> > I believe that this is still
> > acceptable since a warning will be emitted for the file (since it has no
> > BOM, is not valid UTF-8 and no working tree encoding could be found).
> >
> > One case that isn't handled is if a wrong encoding is given in the
> > attributes and the exclude file has no BOM and is not UTF-8. Using
> > iconv to convert an UTF16BE file to UTF-8 while specifying UTF-16LE
> > yields gibberish without an error and so this case is a silent failure
> > where no patterns will match.
> One question is, if we should look at working_tree_encoding at all.
> The other one is, how much UTF-16 handling of ignore or
> other file should we have have in Git ?
> It seems that this fix is for a very special case only ?
>
> From
> https://github.com/git-for-windows/git/issues/3329
> we read:
> /******/
> if (size > 1 && buf[0] == 0xff && buf[1] == 0xfe) {
>     char *reencoded = reencode_string_len(buf, size, "UTF-8", "UTF16-LE-BOM", &size);
>     if (!reencoded)
>         die(_("could not convert contents of '%s' from UTF-16"), fname);
>     free(buf);
>     buf = reencoded;
> }
> /******/
> (Which seems a simpler suggestion)
> However,  there is no UTF-16-LE-BOM in iconv
> (at least in the majority of implementations),
> so a better approach, totaly untested, may be:
>
> if (size >= 2 && buf[0] == 0xff && buf[1] == 0xfe) {
>     char *reencoded = reencode_string_len(buf+2, size-2, "UTF-8", "UTF16", &size);
>     if (!reencoded)
>         die(_("could not convert contents of '%s' from UTF-16"), fname);
>     free(buf);
>     buf = reencoded;
> }
>
> This leads to some free thinking, especially when we look at
> other implementations of Git:
> Would it be better to simply bail out on UTF-16 files ?
> Techically all files with a '\0'.
> [snip]

I was trying to cover more possible use cases, but this may not be a desired
behavior after all. Other reviewers pointed out that the exclude file may have
an abitrary encoding that needs to match the encoding of the paths as read
by git when using readdir (3).

You are correct, UTF-16-LE-BOM is a 'fictional' encoding handled by git. Git
handles the BOM and iconv will be passed the UTF-16LE encoding instead.

I would've liked to be able to handle any wrongly encoded exclude files, but
it's more complicated than I originally thought. Checking for a null byte
could be a simple way to detect some wrong encodings.

Re: [PATCH] ignores: handle non UTF-8 exclude files

[Matthieu Beauchamp]

On Sun, Jan 4, 2026 at 2:40 PM brian m. carlson
<sandals@crustytoothpaste.net> wrote:
>
> On 2026-01-03 at 22:16:57, Matthieu Beauchamp-Boulay via GitGitGadget wrote:
> > When reading exclude files, git assumes it is encoded in UTF-8 and will
> > fail to apply patterns if it isn't. This is a silent failure as no warning
> > or errors are shown to the users. This is a problem that can take a while
> > to diagnose as many users will not think of checking the encoding of their
> > file and may believe their patterns are wrong instead. Users may also
> > accidentally commit undesired files.
>
> This isn't actually true.  Git allows arbitrary byte sequences in the
> file because Git allows filenames to have arbitrary byte sequences, just
> like Unix.

Yes thank you for pointing that out, I had some wrong assumptions about the
encodings.

> > On Windows, this happens if a user uses Windows PowerShell to create the
> > file, which results in a UTF-16LE file with a BOM. This issue was discussed
> > here https://github.com/git-for-windows/git/issues/3329. An example of
> > where a user was confused that his exclude file was not working is cited
> > https://github.com/git-for-windows/git/issues/3227.
>
> Ah, yes, here's the problem.  UTF-16LE is used on Windows, and on
> Windows, Git stores pathnames as if they were converted into UTF-8, so
> you do need to write the filenames in UTF-8 in the ignore file.
>

Yes, the conversion from UTF16-LE to UTF-8 would need to be platform
specific.

> > A minimal fix should at least warn the user if git cannot properly decode
> > the exclude file. Ideally, git would handle any given Unicode file.
>
> As I mentioned, the file isn't necessarily in UTF-8 or Unicode.  Here's
> an example shell script to demonstrate (requires a non-macOS Unix):
>
> ----
> #!/bin/sh
>
> rm -fr test-repo
> git init --object-format=sha256 test-repo
> cd test-repo
> touch abc.txt
> touch "$(printf '\220')"
> printf '\220\n' >.gitignore
> git add .
> git status
> git ls-files -io --exclude-standard
> ----
>
> I'll point out that all of this is also true for things like config
> files (which are also used in `.gitmodules`) and `.gitattributes` files.
> If we wanted to make a change, we would be wise to make it everywhere.
>
> However, if we wanted to force `.gitignore` to UTF-8, we'd need to have
> an escape mechanism to write non-UTF-8 sequences, and as far as I know,
> we don't.

Right, I don't think forcing UTF-8 everywhere is worth it for a relatively
simple issue. If I can find a portable way to determine that an encoding
is incorrect (and possibly reencode it), I could apply it to those other files
as well.

> > First, check if a BOM is present. If it is, decode the file to UTF-8.
> > If no BOM is detected, then try to parse the file as UTF-8. If that fails,
> > attempt to decode the file using the working tree encoding of the file,
> > if any. If that fails, print a warning to tell the user that the exclude
> > file could not be decoded and skip the file.
>
> We do not accept and strip BOMs in UTF-8 files elsewhere (including in
> things like `git diff` output), so we should not do so here, either.
> For Unicode files, if there is no BOM, then the standard is that it's
> assumed to automatically be UTF-8, so a BOM is superfluous and not
> recommended.

I meant checking for UTF-16 and UTF-32 BOMs and then converting to UTF-8,
I will clarify if this part is still in the revision.

> > diff --git a/t/lib-encoding.sh b/t/lib-encoding.sh
> > index 2dabc8c73e..1b1cc357ba 100644
> > --- a/t/lib-encoding.sh
> > +++ b/t/lib-encoding.sh
> > @@ -23,3 +23,11 @@ write_utf32 () {
> >       fi &&
> >       iconv -f UTF-8 -t UTF-32
> >  }
> > +
> > +write_encoded () {
> > +  iconv -f UTF-8 -t "$1"
> > +}
> > +
> > +write_bom () {
> > +  echo "$@" | perl -pe 's/\s+//g; $_=pack("H*", $_)'
> > +}
> > \ No newline at end of file
>
> We place newlines at the end of our text files unless there's a good
> reason no to.
> --
> brian m. carlson (they/them)
> Toronto, Ontario, CA

I will fix it, I would've assumed that clang-format would fix that.

Re: [PATCH] ignores: handle non UTF-8 exclude files

[brian m. carlson]

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On 2026-01-06 at 20:45:56, Matthieu Beauchamp wrote:
> On Sun, Jan 4, 2026 at 2:40 PM brian m. carlson
> <sandals@crustytoothpaste.net> wrote:
> > Ah, yes, here's the problem.  UTF-16LE is used on Windows, and on
> > Windows, Git stores pathnames as if they were converted into UTF-8, so
> > you do need to write the filenames in UTF-8 in the ignore file.
> >
> 
> Yes, the conversion from UTF16-LE to UTF-8 would need to be platform
> specific.

We typically don't want platform-specific behaviour in Git.  Many Git
contributors do not work on Windows but we want things to work as much
as possible identically across all platforms because it makes
development easier, as well as making it easier for users to reason
about the project.  I, for one, don't have a Windows system (nor do I
want one) but I do want my Git code to just work there.

As an example, we still use a POSIX shell in aliases and other settings
on Windows despite the fact that PowerShell is built into Windows
because it means that aliases and similar functionality just work
correctly regardless of platform and it allows users to write a config
file that works everywhere.

Instead of trying to force Git to gracefully handle UTF-16 in its config
files, my strong recommendation is to adjust your PowerShell scripts to
use UTF-8 instead[0] or use a POSIX shell.  I'll note that Microsoft's
new Edit text editor[1] defaults to UTF-8 (and, except on Windows, LF
line endings), so I know that Microsoft understands that UTF-8 is the
proper encoding to use on the Internet today.

[0] https://stackoverflow.com/questions/5596982/using-powershell-to-write-a-file-in-utf-8-without-the-bom
[1] Available at https://github.com/microsoft/edit and apparently
shipped with Windows.  I will say that I was impressed at its
functionality for a 231 KiB binary footprint.
-- 
brian m. carlson (they/them)
Toronto, Ontario, CA

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Re: [PATCH] ignores: handle non UTF-8 exclude files

[Collin Funk]

"brian m. carlson" <sandals@crustytoothpaste.net> writes:

> Instead of trying to force Git to gracefully handle UTF-16 in its config
> files, my strong recommendation is to adjust your PowerShell scripts to
> use UTF-8 instead[0] or use a POSIX shell.  I'll note that Microsoft's
> new Edit text editor[1] defaults to UTF-8 (and, except on Windows, LF
> line endings), so I know that Microsoft understands that UTF-8 is the
> proper encoding to use on the Internet today.
>
> [1] Available at https://github.com/microsoft/edit and apparently
> shipped with Windows.  I will say that I was impressed at its
> functionality for a 231 KiB binary footprint.

Does it handle text that is not UTF-8 encoded?

An unfortunate trend that I have seen with Rust programs is that they
completely disregard the systems locale. E.g. using
LC_ALL=en_US.ISO-8859-1 and passing an "À" character as an option will
typically fail since it is encoded as 0xC0 which is not a valid UTF-8
character.

I figured it was worth bringing up since Git may wany to think about it
some before introducing more Rust. I think it can be worked around by
using OsString [1], but I guess many people choose not to.

Collin

[1] https://doc.rust-lang.org/std/ffi/struct.OsString.html

Re: [PATCH] ignores: handle non UTF-8 exclude files

[Phillip Wood]

On 07/01/2026 01:35, Collin Funk wrote:
> 
> An unfortunate trend that I have seen with Rust programs is that they
> completely disregard the systems locale. E.g. using
> LC_ALL=en_US.ISO-8859-1 and passing an "À" character as an option will
> typically fail since it is encoded as 0xC0 which is not a valid UTF-8
> character.
> 
> I figured it was worth bringing up since Git may wany to think about it
> some before introducing more Rust. I think it can be worked around by
> using OsString [1], but I guess many people choose not to.

Git will certainly want to continue to support non-utf8 encodings. 
That's perfectly possible in rust but in my (rather limited) experience 
it does take a bit more effort than the equivalent code using the 
standard library's String type. I find it particularly annoying that 
"cargo run" refuses to pass non-utf8 arguments to the program being run 
when the program has been carefully written to support them.

Thanks

Phillip

Re: [PATCH] ignores: handle non UTF-8 exclude files

[Phillip Wood]

On 06/01/2026 20:32, Matthieu Beauchamp wrote:
> 
> Yes you are correct, but I want to address the issues for users who may not
> realize that they used the wrong encoding when creating their exclude file.
> For that case I don't see how the fact that powershell can be configured to
> UTF-8 helps, aside from preventing repeating the same mistake.

My concern with that is that it ends up hampering collaboration with 
people using bash on Windows or a native shell on other platforms. If 
they append to a UTF-16 encoded .gitignore with "echo path >>.gitignore" 
you'll end up with a mix of encodings in the same file. Similarly if you 
use powershell to append to an existing file that is UTF-8 encoded with 
"echo hello >>.gitignore" is the appended text UTF-16 encoded resulting 
in mixed encodings in the same file?

Thanks

Phillip

Re: [PATCH] ignores: handle non UTF-8 exclude files

[brian m. carlson]

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On 2026-01-07 at 01:35:11, Collin Funk wrote:
> An unfortunate trend that I have seen with Rust programs is that they
> completely disregard the systems locale. E.g. using
> LC_ALL=en_US.ISO-8859-1 and passing an "À" character as an option will
> typically fail since it is encoded as 0xC0 which is not a valid UTF-8
> character.

Git does not usually directly read input and then convert it to other
encodings unless specifically asked to (e.g., `working-tree-encoding`),
so I fully expect that nothing will change there.  However, in many
cases, Git also currently does not honour LC_ALL, such as for commit
messages.

> I figured it was worth bringing up since Git may wany to think about it
> some before introducing more Rust. I think it can be worked around by
> using OsString [1], but I guess many people choose not to.

The people who have been working on Rust have been very careful to not
make assumptions that all data is UTF-8, and I don't expect that to
change.

OsString is slightly problematic because it is effectively UTF-8-ish (on
Windows, it's actually WTF-8 and on Unix it allows arbitrary bytes) but
there is no portable way to get any consistent byte encoding out of it.
(In versions of Rust too new for us to use, there is a function that
provides a byte encoding but it's not guaranteed to be stable across
versions.)  I have some custom code in one of my branches to handle the
conversion to and from OsString to a consistent byte encoding using some
traits to paper over the operating system differences.

In general, I expect we will continue to use some C-based interfaces
(possibly called via Rust wrappers) because Rust also does not expose
things like file descriptors on Windows or the full range of stat or
other information we need.

One assumption I do think is safe to make is that arbitrary Unicode can
be printed to the terminal, such as in error messages.  Considering that
virtually everybody sets IUTF8 in Unix terminals and we effectively do
that right now with localized text, I think that's okay.
-- 
brian m. carlson (they/them)
Toronto, Ontario, CA

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Re: [PATCH] ignores: handle non UTF-8 exclude files

[Collin Funk]

"brian m. carlson" <sandals@crustytoothpaste.net> writes:

> On 2026-01-07 at 01:35:11, Collin Funk wrote:
>> An unfortunate trend that I have seen with Rust programs is that they
>> completely disregard the systems locale. E.g. using
>> LC_ALL=en_US.ISO-8859-1 and passing an "À" character as an option will
>> typically fail since it is encoded as 0xC0 which is not a valid UTF-8
>> character.
>
> Git does not usually directly read input and then convert it to other
> encodings unless specifically asked to (e.g., `working-tree-encoding`),
> so I fully expect that nothing will change there.  However, in many
> cases, Git also currently does not honour LC_ALL, such as for commit
> messages.

That makes sense.

>> I figured it was worth bringing up since Git may wany to think about it
>> some before introducing more Rust. I think it can be worked around by
>> using OsString [1], but I guess many people choose not to.
>
> The people who have been working on Rust have been very careful to not
> make assumptions that all data is UTF-8, and I don't expect that to
> change.

Great, glad that it was considered. I guess you have to worry about
crates, but I think I recall wide agreement that Git was going to be
careful with what it decides to use.

> OsString is slightly problematic because it is effectively UTF-8-ish (on
> Windows, it's actually WTF-8 and on Unix it allows arbitrary bytes) but
> there is no portable way to get any consistent byte encoding out of it.
> (In versions of Rust too new for us to use, there is a function that
> provides a byte encoding but it's not guaranteed to be stable across
> versions.)  I have some custom code in one of my branches to handle the
> conversion to and from OsString to a consistent byte encoding using some
> traits to paper over the operating system differences.

Interesting, good to know. Thanks.

Unrelated to encoding, but two other things I noticed about Rust. Before
main() SIGPIPE is set to SIG_IGN which can be seen with the programs
below:

    $ cat main.rs 
    use std::io::{self, Write};
    fn main() -> io::Result<()> {
        io::stdout().write_all(b"hello world\n")?;
        Ok(())
    }
    $ cat main.c
    #include <unistd.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <errno.h>
    int
    main (void)
    {
      static const char message[] = "hello world\n";
      if (write (STDOUT_FILENO, message, sizeof message - 1) < 0)
        {
          fprintf (stderr, "%s\n", strerror (errno));
          return EXIT_FAILURE;
        }
      return EXIT_SUCCESS;
    }
    $ rustc main.rs
    $ gcc main.c
    $ ./main | :
    Error: Os { code: 32, kind: BrokenPipe, message: "Broken pipe" }
    $ echo ${PIPESTATUS[@]}
    1 0
    $ ./a.out | :
    $ echo ${PIPESTATUS[@]}
    141 0

Before executing a program using the standard library, SIGPIPE will be
set to SIG_DFL. That is better than not doing that, but both behaviors
mean that the typical behavior of inheriting signal actions from the
parent process is impossible without hacks or an unstable feature that
has been unfortunately stagnant for years [1].

Before main() all standard file descriptors are also opened. While
reasonable in many cases, is not the desired behavior for all programs.
Using the same example programs:

    $ ./main >&-
    $ echo $?
    0
    $ ./a.out >&-
    Bad file descriptor
    $ echo $?
    1

I'm not sure if either of those will affect 'git' at all, assuming it is
mostly library code that is called from C.

But it will likely have to be considered if someone wants to write a
program that goes in libexec that is executed by 'git'.

Collin

[1] https://dev-doc.rust-lang.org/beta/unstable-book/language-features/unix-sigpipe.html