git difftool: No such file or directory

git difftool: No such file or directory

[Alan Blotz]

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Thank you for filling out a Git bug report!
Please answer the following questions to help us understand your issue.

What did you do before the bug happened? (Steps to reproduce your issue)

mkdir broken-diff
cd broken-diff
git init
mkdir dir1
mkdir dir2
touch dir1/orig
cd dir2/
ln -s ../dir1/orig sym
cd ..
git add dir*
git ci -m "init"
git checkout -b b
git rm dir2/sym 
git ci -m "remove"
git difftool -d master HEAD

What did you expect to happen? (Expected behavior)

git difftool shall compare both branches.

What happened instead? (Actual behavior)

git difftool prints an error:

fatal: could not open '/tmp/git-difftool.l4UM7e/left/dir2/sym' for writing: No such file or directory

Please review the rest of the bug report below.
You can delete any lines you don't wish to share.


[System Info]
git version:
git version 2.31.1
cpu: x86_64
no commit associated with this build
sizeof-long: 8
sizeof-size_t: 8
shell-path: /bin/sh
uname: Linux 5.12.12-300.fc34.x86_64 #1 SMP Fri Jun 18 14:30:51 UTC 2021 x86_64
compiler info: gnuc: 11.0
libc info: glibc: 2.33
$SHELL (typically, interactive shell): /bin/bash


[Enabled Hooks]

Re: git difftool: No such file or directory

[Đoàn Trần Công Danh]

On 2021-06-30 11:38:21+0200, Alan Blotz <work@blotz.org> wrote:

> Thank you for filling out a Git bug report!
> Please answer the following questions to help us understand your issue.
> 
> What did you do before the bug happened? (Steps to reproduce your issue)
> 
> mkdir broken-diff
> cd broken-diff
> git init
> mkdir dir1
> mkdir dir2
> touch dir1/orig
> cd dir2/
> ln -s ../dir1/orig sym
> cd ..
> git add dir*
> git ci -m "init"
> git checkout -b b
> git rm dir2/sym 
> git ci -m "remove"
> git difftool -d master HEAD
> 
> What did you expect to happen? (Expected behavior)
> 
> git difftool shall compare both branches.
> 
> What happened instead? (Actual behavior)
> 
> git difftool prints an error:
> 
> fatal: could not open '/tmp/git-difftool.l4UM7e/left/dir2/sym' for writing: No such file or directory

It looks like this behaviour was there from the time difftool was
re-written in C in 03831ef7b5, (difftool: implement the functionality
in the builtin, 2017-01-19). The perl version didn't have this
problem.

The perl version create a file in place of that symlink and write the
symlink's target into that file. The C version tries to write (and
follow?) the symlink.

This hack can fix the problem but I'm not sure it's correct:
----8<---

diff --git a/builtin/difftool.c b/builtin/difftool.c
index 2115e548a5..737ebb5b1a 100644
--- a/builtin/difftool.c
+++ b/builtin/difftool.c
@@ -492,12 +492,14 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 		if (*entry->left) {
 			add_path(&ldir, ldir_len, entry->path);
 			ensure_leading_directories(ldir.buf);
-			write_file(ldir.buf, "%s", entry->left);
+			unlink(ldir.buf);
+			write_file_buf(ldir.buf, entry->left, strlen(entry->left));
 		}
 		if (*entry->right) {
 			add_path(&rdir, rdir_len, entry->path);
 			ensure_leading_directories(rdir.buf);
-			write_file(rdir.buf, "%s", entry->right);
+			unlink(rdir.buf);
+			write_file_buf(rdir.buf, entry->right, strlen(entry->right));
 		}
 	}
---->8----- 

+Cc: Dscho, who wrote the C version.

-- 
Danh

Re: git difftool: No such file or directory

[David Aguilar]

On Wed, Jun 30, 2021 at 5:38 PM Đoàn Trần Công Danh
<congdanhqx@gmail.com> wrote:
>
> On 2021-06-30 11:38:21+0200, Alan Blotz <work@blotz.org> wrote:
>
> > Thank you for filling out a Git bug report!
> > Please answer the following questions to help us understand your issue.
> >
> > What did you do before the bug happened? (Steps to reproduce your issue)
> >
> > mkdir broken-diff
> > cd broken-diff
> > git init
> > mkdir dir1
> > mkdir dir2
> > touch dir1/orig
> > cd dir2/
> > ln -s ../dir1/orig sym
> > cd ..
> > git add dir*
> > git ci -m "init"
> > git checkout -b b
> > git rm dir2/sym
> > git ci -m "remove"
> > git difftool -d master HEAD
> >
> > What did you expect to happen? (Expected behavior)
> >
> > git difftool shall compare both branches.
> >
> > What happened instead? (Actual behavior)
> >
> > git difftool prints an error:
> >
> > fatal: could not open '/tmp/git-difftool.l4UM7e/left/dir2/sym' for writing: No such file or directory
>
> It looks like this behaviour was there from the time difftool was
> re-written in C in 03831ef7b5, (difftool: implement the functionality
> in the builtin, 2017-01-19). The perl version didn't have this
> problem.
>
> The perl version create a file in place of that symlink and write the
> symlink's target into that file. The C version tries to write (and
> follow?) the symlink.
>
> This hack can fix the problem but I'm not sure it's correct:
> ----8<---
>
> diff --git a/builtin/difftool.c b/builtin/difftool.c
> index 2115e548a5..737ebb5b1a 100644
> --- a/builtin/difftool.c
> +++ b/builtin/difftool.c
> @@ -492,12 +492,14 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
>                 if (*entry->left) {
>                         add_path(&ldir, ldir_len, entry->path);
>                         ensure_leading_directories(ldir.buf);
> -                       write_file(ldir.buf, "%s", entry->left);
> +                       unlink(ldir.buf);
> +                       write_file_buf(ldir.buf, entry->left, strlen(entry->left));
>                 }
>                 if (*entry->right) {
>                         add_path(&rdir, rdir_len, entry->path);
>                         ensure_leading_directories(rdir.buf);
> -                       write_file(rdir.buf, "%s", entry->right);
> +                       unlink(rdir.buf);
> +                       write_file_buf(rdir.buf, entry->right, strlen(entry->right));
>                 }
>         }
> ---->8-----
>
> +Cc: Dscho, who wrote the C version.

Thank you for tracking this down!

I re-read the original perl version and this indeed looks like it
should do the trick since it's doing the same thing we did in perl.

I'm a little ashamed that we didn't have a test case to cover this use
case but the reproduction recipe you included looks like a great
start. We already have a few tests that use the SYMLINKS test prereq
so this would slot in well there.
-- 
David