Re: [PATCH v6 3/7] eoie: add End of Index Entry (EOIE) extension

[SZEDER Gábor <szeder.dev@gmail.com>]

On Wed, Sep 26, 2018 at 03:54:38PM -0400, Ben Peart wrote:
> The End of Index Entry (EOIE) is used to locate the end of the variable

Nit: perhaps start with: 

  The End of Index Entry (EOIE) optional extension can be used to ...

to make it clearer for those who don't immediately realize the
significance of the upper case 'E' in the extension's signature.

> length index entries and the beginning of the extensions. Code can take
> advantage of this to quickly locate the index extensions without having
> to parse through all of the index entries.
> 
> Because it must be able to be loaded before the variable length cache
> entries and other index extensions, this extension must be written last.
> The signature for this extension is { 'E', 'O', 'I', 'E' }.
> 
> The extension consists of:
> 
> - 32-bit offset to the end of the index entries
> 
> - 160-bit SHA-1 over the extension types and their sizes (but not
> their contents).  E.g. if we have "TREE" extension that is N-bytes
> long, "REUC" extension that is M-bytes long, followed by "EOIE",
> then the hash would be:
> 
> SHA-1("TREE" + <binary representation of N> +
> 	"REUC" + <binary representation of M>)
> 
> Signed-off-by: Ben Peart <Ben.Peart@microsoft.com>
> ---
>  Documentation/technical/index-format.txt |  23 ++++
>  read-cache.c                             | 151 +++++++++++++++++++++--
>  t/README                                 |   5 +
>  t/t1700-split-index.sh                   |   1 +
>  4 files changed, 172 insertions(+), 8 deletions(-)
> 

> diff --git a/t/README b/t/README
> index 3ea6c85460..aa33ac4f26 100644
> --- a/t/README
> +++ b/t/README
> @@ -327,6 +327,11 @@ GIT_TEST_COMMIT_GRAPH=<boolean>, when true, forces the commit-graph to
>  be written after every 'git commit' command, and overrides the
>  'core.commitGraph' setting to true.
>  
> +GIT_TEST_DISABLE_EOIE=<boolean> disables writing the EOIE extension.
> +This is used to allow tests 1, 4-9 in t1700-split-index.sh to succeed
> +as they currently hard code SHA values for the index which are no longer
> +valid due to the addition of the EOIE extension.

Is this extension enabled by default?  The commit message doesn't
explicitly say so, but I don't see any way to turn it on or off, while
there is this new GIT_TEST environment variable to disable it for one
particular test, so it seems so.  If that's indeed the case, then
wouldn't it be better to update those hard-coded SHA1 values in t1700
instead?

>  Naming Tests
>  ------------
>  
> diff --git a/t/t1700-split-index.sh b/t/t1700-split-index.sh
> index be22398a85..1f168378c8 100755
> --- a/t/t1700-split-index.sh
> +++ b/t/t1700-split-index.sh
> @@ -7,6 +7,7 @@ test_description='split index mode tests'
>  # We need total control of index splitting here
>  sane_unset GIT_TEST_SPLIT_INDEX
>  sane_unset GIT_FSMONITOR_TEST
> +GIT_TEST_DISABLE_EOIE=true; export GIT_TEST_DISABLE_EOIE
>  
>  test_expect_success 'enable split index' '
>  	git config splitIndex.maxPercentChange 100 &&
> -- 
> 2.18.0.windows.1
>