Subject: Re: [PATCH v2 2/3] t7800: fix tests when difftool uses --no-symlinks

From: John Keeping <[email-masked]>
Date: Mon, 25 Mar 2013 10:42:19 +0000

On Mon, Mar 25, 2013 at 08:41:59AM +0100, Johannes Sixt wrote:
> Am 3/24/2013 16:15, schrieb John Keeping:
> > Subject: [PATCH] difftool: don't overwrite modified files
> > 
> > After running the user's diff tool, git-difftool will copy any files
> > that differ between the working tree and the temporary tree.  This is
> > useful when the user edits the file in their diff tool but is wrong if
> > they edit the working tree file while examining the diff.
> > 
> > Instead of copying unconditionally when the files differ, store the
> > initial hash of the working tree file and only copy the temporary file
> > back if it was modified and the working tree file was not.  If both
> > files have been modified, print a warning and exit with an error.
> > 
> > Signed-off-by: John Keeping <[email-masked]>
> > ---
> >  git-difftool.perl   | 35 +++++++++++++++++++++--------------
> >  t/t7800-difftool.sh | 26 ++++++++++++++++++++++++++
> >  2 files changed, 47 insertions(+), 14 deletions(-)
> > 
> > diff --git a/git-difftool.perl b/git-difftool.perl
> > index c433e86..be82b5a 100755
> > --- a/git-difftool.perl
> > +++ b/git-difftool.perl
> > @@ -15,7 +15,6 @@ use strict;
> >  use warnings;
> >  use File::Basename qw(dirname);
> >  use File::Copy;
> > -use File::Compare;
> >  use File::Find;
> >  use File::stat;
> >  use File::Path qw(mkpath rmtree);
> > @@ -123,7 +122,7 @@ sub setup_dir_diff
> >  	my $rindex = '';
> >  	my %submodule;
> >  	my %symlink;
> > -	my @working_tree = ();
> > +	my %working_tree;
> >  	my @rawdiff = split('\0', $diffrtn);
> >  
> >  	my $i = 0;
> > @@ -175,7 +174,9 @@ EOF
> >  
> >  		if ($rmode ne $null_mode) {
> >  			if (use_wt_file($repo, $workdir, $dst_path, $rsha1, $symlinks)) {
> > -				push(@working_tree, $dst_path);
> > +				$working_tree{$dst_path} =
> > +					$repo->command_oneline('hash-object',
> > +						"$workdir/$dst_path");
> >  			} else {
> >  				$rindex .= "$rmode $rsha1\t$dst_path\0";
> >  			}
> > @@ -227,7 +228,7 @@ EOF
> >  	# not part of the index. Remove any trailing slash from $workdir
> >  	# before starting to avoid double slashes in symlink targets.
> >  	$workdir =~ s|/$||;
> > -	for my $file (@working_tree) {
> > +	for my $file (keys %working_tree) {
> >  		my $dir = dirname($file);
> >  		unless (-d "$rdir/$dir") {
> >  			mkpath("$rdir/$dir") or
> > @@ -278,7 +279,7 @@ EOF
> >  		exit_cleanup($tmpdir, 1) if not $ok;
> >  	}
> >  
> > -	return ($ldir, $rdir, $tmpdir, @working_tree);
> > +	return ($ldir, $rdir, $tmpdir, %working_tree);
> >  }
> >  
> >  sub write_to_file
> > @@ -376,7 +377,7 @@ sub dir_diff
> >  	my $error = 0;
> >  	my $repo = Git->repository();
> >  	my $workdir = find_worktree($repo);
> > -	my ($a, $b, $tmpdir, @worktree) =
> > +	my ($a, $b, $tmpdir, %worktree) =
> >  		setup_dir_diff($repo, $workdir, $symlinks);
> >  
> >  	if (defined($extcmd)) {
> > @@ -390,19 +391,25 @@ sub dir_diff
> >  	# should be copied back to the working tree.
> >  	# Do not copy back files when symlinks are used and the
> >  	# external tool did not replace the original link with a file.
> > -	for my $file (@worktree) {
> > +	for my $file (keys %worktree) {
> >  		next if $symlinks && -l "$b/$file";
> >  		next if ! -f "$b/$file";
> >  
> > -		my $diff = compare("$b/$file", "$workdir/$file");
> > -		if ($diff == 0) {
> > -			next;
> > -		} elsif ($diff == -1) {
> > -			my $errmsg = "warning: Could not compare ";
> > -			$errmsg += "'$b/$file' with '$workdir/$file'\n";
> > +		my $wt_hash = $repo->command_oneline('hash-object',
> > +			"$workdir/$file");
> > +		my $tmp_hash = $repo->command_oneline('hash-object',
> > +			"$b/$file");
> 
> This is gross. Can't we do much better here? Difftool already keeps a
> GIT_INDEX of the files in the temporary tree ($tmpdir/rindex). Running
> git-diff-files should be sufficient to tell which ones where edited via
> the users's diff-tool. Then you can restrict calling hash-object to only
> those worktree files where an "edit collision" needs to be checked for.

That's only the case for files that are not copied from the working
tree, so the temporary index doesn't contain the files that are of
interest here.

> You could also keep a parallel index that keeps the state of the same set
> of files in the worktree. Then another git-diff-files call could replace
> the other half of hash-object calls.

I like the idea of creating an index from the working tree files and
using it here.  If we create a "starting state" index for these files,
we should be able to run git-diff-files against both the working tree
and the temporary tree at this point and compare the output.  I'll try
this approach this evening.

> > +		my $wt_modified = $wt_hash ne $worktree{$file};
> > +		my $tmp_modified = $tmp_hash ne $worktree{$file};
> > +
> > +		if ($wt_modified and $tmp_modified) {
> > +			my $errmsg = "warning: Both files modified: ";
> > +			$errmsg .= "'$workdir/$file' and '$b/$file'.\n";
> > +			$errmsg .= "warning: Working tree file has been left.\n";
> > +			$errmsg .= "warning:\n";
> >  			warn $errmsg;
> >  			$error = 1;
> > -		} elsif ($diff == 1) {
> > +		} elsif ($tmp_modified) {
> >  			my $mode = stat("$b/$file")->mode;
> >  			copy("$b/$file", "$workdir/$file") or
> >  			exit_cleanup($tmpdir, 1);