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Re: [PATCH v1] read-cache: add GIT_TEST_INDEX_VERSION support

On 9/12/2018 6:31 PM, Thomas Gummerer wrote:
On 09/12, Ben Peart wrote:
Teach get_index_format_default() to support running the test suite
with specific index versions.  In particular, this enables the test suite
to be run using index version 4 which is not the default so gets less testing.

I found this commit message slightly misleading.  Running the test
suite with specific index versions is already supported, by defining
TEST_GIT_INDEX_VERSION in 'config.mak'.  What we're doing here is
introduce an additional environment variable that can also be used to
set the index format in tests.

Even setting TEST_GIT_INDEX_VERSION=4 in the environment does run the
test suite with index-v4.  Admittedly the name is a bit strange
compared to our usual GIT_TEST_* environment variable names, and it
should probably be documented better (it's only documented in the
Makefile currently), but I'm not sure we should introduce another
environment variable for this purpose?

TEST_GIT_INDEX_VERSION enables the testing I was looking for but you're right, it isn't well documented and the atypical naming and implementation don't help either.

I checked the documentation and code but didn't see any way to test the V4 index code path so wrote this patch. I wonder if we can improve the discoverability of TEST_GIT_INDEX_VERSION through better naming and documentation.

How about this as an alternative?

diff --git a/Makefile b/Makefile
index 5a969f5830..9e84ef02f7 100644
--- a/Makefile
+++ b/Makefile
@@ -400,7 +400,7 @@ all::
 # (defaults to "man") if you want to have a different default when
 # "git help" is called without a parameter specifying the format.
-# Define TEST_GIT_INDEX_VERSION to 2, 3 or 4 to run the test suite
+# Define GIT_TEST_INDEX_VERSION to 2, 3 or 4 to run the test suite
 # with a different indexfile format version.  If it isn't set the index
 # file format used is index-v[23].
@@ -2599,8 +2599,8 @@ endif
@echo GIT_INTEROP_MAKE_OPTS=\''$(subst ','\'',$(subst ','\'',$(GIT_INTEROP_MAKE_OPTS)))'\' >>$@+
- @echo TEST_GIT_INDEX_VERSION=\''$(subst ','\'',$(subst ','\'',$(TEST_GIT_INDEX_VERSION)))'\' >>$@+
+ @echo GIT_TEST_INDEX_VERSION=\''$(subst ','\'',$(subst ','\'',$(GIT_TEST_INDEX_VERSION)))'\' >>$@+

        @if cmp $@+ $@ >/dev/null 2>&1; then $(RM) $@+; else mv $@+ $@; fi

diff --git a/t/test-lib.sh b/t/test-lib.sh
index 44288cbb59..31698c01c4 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -134,9 +134,9 @@ export EDITOR

-if test -n "${TEST_GIT_INDEX_VERSION:+isset}"
+if test -n "${GIT_TEST_INDEX_VERSION:+isset}"
        export GIT_INDEX_VERSION

diff --git a/t/README b/t/README
index 9028b47d92..f872638a78 100644
--- a/t/README
+++ b/t/README
@@ -315,10 +315,14 @@ packs on demand. This normally only happens when the object size is
  over 2GB. This variable forces the code path on any object larger than
  <n> bytes.

-GIT_TEST_OE_DELTA_SIZE=<n> exercises the uncomon pack-objects code
+GIT_TEST_OE_DELTA_SIZE=<n> exercises the uncommon pack-objects code
  path where deltas larger than this limit require extra memory
  allocation for bookkeeping.

+GIT_TEST_INDEX_VERSION=<n> exercises the index read/write code path
+for the index version specified.  Can be set to any valid version
+but the non-default version 4 is probably the most beneficial.
  Naming Tests