Re: [PATCH] index-format.txt: be more liberal on what can represent invalid cache tree

Nguyễn Thái Ngọc Duy  [off-list ref] writes:

We have been writing -1 as "invalid" since day 1. On that same day we
accept all negative entry counts as "invalid". So in theory all C Git
versions out there would be happy to accept any negative numbers. JGit
seems to do exactly the same.

I am of two minds here.

The existing code is being more lenient than specified when they
read stuff others wrote, but it still adheres to -1 when writing.
Allowing random implementations to write random negative values will
close the door for us to later update the specification to encode
more informatin about these invalid entries by using negative value
other than -1 here.

I am OK with a reword to say "negative means invalid, and writers
should write -1 for invalid entries", but without the latter half,
this change is not justified.

We have been writing -1 as "invalid" since day 1. On that same day we
accept all negative entry counts as "invalid". So in theory all C Git
versions out there would be happy to accept any negative numbers. JGit
seems to do exactly the same.

Correct the document to reflect the fact that -1 is not the only magic
number. At least one implementation, libgit2, is found to treat -1
this way.

Signed-off-by: Nguyễn Thái Ngọc Duy <redacted>
---
 On Thu, Dec 13, 2012 at 1:14 AM, Junio C Hamano [off-list ref] wrote:
 > Nguyễn Thái Ngọc Duy  [off-list ref] writes:
 >
 >> We have been writing -1 as "invalid" since day 1. On that same day we
 >> accept all negative entry counts as "invalid". So in theory all C Git
 >> versions out there would be happy to accept any negative numbers. JGit
 >> seems to do exactly the same.
 >
 > I am of two minds here.
 >
 > The existing code is being more lenient than specified when they
 > read stuff others wrote, but it still adheres to -1 when writing.
 > Allowing random implementations to write random negative values will
 > close the door for us to later update the specification to encode
 > more informatin about these invalid entries by using negative value
 > other than -1 here.

 How would that work with existing versions? If you write -2 in
 cache-tree, the next time 1.8.0 updates cache tree it writes -1 back.
 That loses whatever information you attach to -2. A new cache-tree
 extension is probably better.

 > I am OK with a reword to say "negative means invalid, and writers
 > should write -1 for invalid entries", but without the latter half,
 > this change is not justified.

 Done.

 Documentation/technical/index-format.txt | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Documentation/technical/index-format.txt b/Documentation/technical/index-format.txt
index 9d25b30..ce28a7a 100644
--- a/Documentation/technical/index-format.txt
+++ b/Documentation/technical/index-format.txt

@@ -161,8 +161,9 @@ GIT index format
     this span of index as a tree.
 
   An entry can be in an invalidated state and is represented by having
-  -1 in the entry_count field. In this case, there is no object name
-  and the next entry starts immediately after the newline.
+  a negative number in the entry_count field. In this case, there is no
+  object name and the next entry starts immediately after the newline.
+  When writing an invalid entry, -1 should always be used as entry_count.
 
   The entries are written out in the top-down, depth-first order.  The
   first entry represents the root level of the repository, followed by the

-- 
1.8.0.rc2.23.g1fb49df