archive: use the internal zlib-based gzip compression by default

We just introduced support for compressing `.tar.gz` archives in the
`git archive` process itself, using zlib directly instead of spawning
`gzip`.

While this takes less CPU time overall, on multi-core machines, this is
slightly slower in terms of wall clock time (it seems to be in the
ballpark of 15%).

It does reduce the number of dependencies by one, though, which makes it
desirable to turn that mode on by default.

Changing the default benefits most notably the MinGit flavor of Git for
Windows (which intends to support 3rd-party applications that want to
use Git and want to bundle a minimal set of files for that purpose, i.e.
stripping out all non-essential files such as interactive commands,
Perl, and yes, also `gzip`).

We also can now remove the `GZIP` prerequisite from quite a number of
test cases in `t/t5000-tar-tree.sh`.

This closes git-for-windows#1970

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

Documentation/git-archive.txt

@@ -116,7 +116,8 @@ tar.<format>.command::
 	format is given.
 +
 The "tar.gz" and "tgz" formats are defined automatically and default to
-`gzip -cn`. You may override them with custom commands.
+`:zlib`, triggering an in-process gzip compression. You may override
+them with custom commands, e.g. `gzip -cn` or `pigz -cn`.
 
 tar.<format>.remote::
 	If true, enable `<format>` for use by remote clients via

archive-tar.c

@@ -514,9 +514,9 @@ void init_tar_archiver(void)
 	int i;
 	register_archiver(&tar_archiver);
 
-	tar_filter_config("tar.tgz.command", "gzip -cn", NULL);
+	tar_filter_config("tar.tgz.command", ":zlib", NULL);
 	tar_filter_config("tar.tgz.remote", "true", NULL);
-	tar_filter_config("tar.tar.gz.command", "gzip -cn", NULL);
+	tar_filter_config("tar.tar.gz.command", ":zlib", NULL);
 	tar_filter_config("tar.tar.gz.remote", "true", NULL);
 	git_config(git_tar_config, NULL);
 	for (i = 0; i < nr_tar_filters; i++) {

t/t5000-tar-tree.sh

@@ -291,36 +291,41 @@ test_expect_success 'only enabled filters are available remotely' '
 	test_cmp_bin remote.bar config.bar
 '
 
-test_expect_success GZIP 'git archive --format=tgz' '
+test_expect_success 'git archive --format=tgz' '
 	git archive --format=tgz HEAD >j.tgz
 '
 
-test_expect_success GZIP 'git archive --format=tar.gz' '
+test_expect_success 'git archive --format=tar.gz' '
 	git archive --format=tar.gz HEAD >j1.tar.gz &&
 	test_cmp_bin j.tgz j1.tar.gz
 '
 
-test_expect_success GZIP 'infer tgz from .tgz filename' '
+test_expect_success 'infer tgz from .tgz filename' '
 	git archive --output=j2.tgz HEAD &&
 	test_cmp_bin j.tgz j2.tgz
 '
 
-test_expect_success GZIP 'infer tgz from .tar.gz filename' '
+test_expect_success 'infer tgz from .tar.gz filename' '
 	git archive --output=j3.tar.gz HEAD &&
 	test_cmp_bin j.tgz j3.tar.gz
 '
 
+test_expect_success 'use `archive.tgz.command=:zlib` explicitly' '
+	git -c archive.tgz.command=:zlib archive --output=j4.tgz HEAD &&
+	test_cmp_bin j.tgz j4.tgz
+'
+
 test_expect_success GZIP 'extract tgz file' '
 	gzip -d -c <j.tgz >j.tar &&
 	test_cmp_bin b.tar j.tar
 '
 
-test_expect_success GZIP 'remote tar.gz is allowed by default' '
+test_expect_success 'remote tar.gz is allowed by default' '
 	git archive --remote=. --format=tar.gz HEAD >remote.tar.gz &&
 	test_cmp_bin j.tgz remote.tar.gz
 '
 
-test_expect_success GZIP 'remote tar.gz can be disabled' '
+test_expect_success 'remote tar.gz can be disabled' '
 	git config tar.tar.gz.remote false &&
 	test_must_fail git archive --remote=. --format=tar.gz HEAD \
 		>remote.tar.gz