[PATCH v2] read-cache: update TEST_GIT_INDEX_VERSION support

Rename TEST_GIT_INDEX_VERSION to GIT_TEST_INDEX_VERSION for consistency with the other GIT_TEST_ special setups and properly document its use.

Signed-off-by: Ben Peart <Ben.Peart@microsoft.com>
---

Notes:
    Base Ref: v2.19.0
    Web-Diff: https://github.com/benpeart/git/commit/e26ccb9004
    Checkout: git fetch https://github.com/benpeart/git git-test-index-version-v2 && git checkout e26ccb9004
    
    ### Interdiff (v1..v2):
    
    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
     ifdef GIT_INTEROP_MAKE_OPTS
     	@echo GIT_INTEROP_MAKE_OPTS=\''$(subst ','\'',$(subst ','\'',$(GIT_INTEROP_MAKE_OPTS)))'\' >>$@+
     endif
    -ifdef TEST_GIT_INDEX_VERSION
    -	@echo TEST_GIT_INDEX_VERSION=\''$(subst ','\'',$(subst ','\'',$(TEST_GIT_INDEX_VERSION)))'\' >>$@+
    +ifdef GIT_TEST_INDEX_VERSION
    +	@echo GIT_TEST_INDEX_VERSION=\''$(subst ','\'',$(subst ','\'',$(GIT_TEST_INDEX_VERSION)))'\' >>$@+
     endif
     	@if cmp $@+ $@ >/dev/null 2>&1; then $(RM) $@+; else mv $@+ $@; fi
    
    diff --git a/read-cache.c b/read-cache.c
    index d140ce9989..7b1354d759 100644
    --- a/read-cache.c
    +++ b/read-cache.c
    @@ -1570,45 +1570,26 @@ static unsigned int get_index_format_default(void)
     	char *envversion = getenv("GIT_INDEX_VERSION");
     	char *endp;
     	int value;
    -	unsigned int version = -1;
    +	unsigned int version = INDEX_FORMAT_DEFAULT;
    
    -	if (envversion) {
    -		version = strtoul(envversion, &endp, 10);
    -		if (*endp ||
    -			version < INDEX_FORMAT_LB || INDEX_FORMAT_UB < version) {
    -			warning(_("GIT_INDEX_VERSION set, but the value is invalid.\n"
    -				"Using version %i"), INDEX_FORMAT_DEFAULT);
    -			version = INDEX_FORMAT_DEFAULT;
    -		}
    -	}
    -
    -	if (version == -1) {
    -		if (!git_config_get_int("index.version", &value)) {
    +	if (!envversion) {
    +		if (!git_config_get_int("index.version", &value))
     			version = value;
     		if (version < INDEX_FORMAT_LB || INDEX_FORMAT_UB < version) {
     			warning(_("index.version set, but the value is invalid.\n"
     				  "Using version %i"), INDEX_FORMAT_DEFAULT);
    -				version = INDEX_FORMAT_DEFAULT;
    -			}
    +			return INDEX_FORMAT_DEFAULT;
     		}
    +		return version;
     	}
    
    -	if (version == -1) {
    -		envversion = getenv("GIT_TEST_INDEX_VERSION");
    -		if (envversion) {
     	version = strtoul(envversion, &endp, 10);
     	if (*endp ||
     	    version < INDEX_FORMAT_LB || INDEX_FORMAT_UB < version) {
    -				warning(_("GIT_TEST_INDEX_VERSION set, but the value is invalid.\n"
    +		warning(_("GIT_INDEX_VERSION set, but the value is invalid.\n"
     			  "Using version %i"), INDEX_FORMAT_DEFAULT);
     		version = INDEX_FORMAT_DEFAULT;
     	}
    -		}
    -	}
    -
    -	if (version == -1)
    -		version = INDEX_FORMAT_DEFAULT;
    -
     	return version;
     }
    
    diff --git a/t/README b/t/README
    index f872638a78..fb6359b17b 100644
    --- a/t/README
    +++ b/t/README
    @@ -320,8 +320,7 @@ 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.
    +for the index version specified.  Can be set to any valid version.
    
     Naming Tests
     ------------
    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
     GIT_TRACE_BARE=1
     export GIT_TRACE_BARE
    
    -if test -n "${TEST_GIT_INDEX_VERSION:+isset}"
    +if test -n "${GIT_TEST_INDEX_VERSION:+isset}"
     then
    -	GIT_INDEX_VERSION="$TEST_GIT_INDEX_VERSION"
    +	GIT_INDEX_VERSION="$GIT_TEST_INDEX_VERSION"
     	export GIT_INDEX_VERSION
     fi
    
    ### Patches

 Makefile      | 6 +++---
 t/README      | 5 ++++-
 t/test-lib.sh | 4 ++--
 3 files changed, 9 insertions(+), 6 deletions(-)