[PATCH v5 00/11] Fix the early config

These patches are an attempt to make Git's startup sequence a bit less surprising.

The idea here is to discover the .git/ directory gently (i.e. without changing the current working directory, nor any global variables), and to use it to read the .git/config file early, before we actually called setup_git_directory() (if we ever do that).

This also allows us to fix the early config e.g. to determine the pager or to resolve aliases in a non-surprising manner.

My own use case: in the GVFS Git fork, we need to execute pre-command and post-command hooks before and after *every* Git command. A previous version of the pre-command/post-command hook support was broken, as it used run_hook() which implicitly called setup_git_directory() too early. The discover_git_directory() function (and due to core.hooksPath also the read_early_config() function) helped me fix this.

Notable notes:

- Even if it can cause surprising problems, `init` and `clone` are not
  special-cased. Rationale: it would introduce technical debt and
  violate the Principle Of Least Astonishment.

- The read_early_config() function does not cache Git directory
  discovery nor read values. This is left for another patch series, if
  it ever becomes necessary.

- The alias handling in git.c could possibly benefit from this work, but
  again, this is a separate topic from the current patch series.

Changes since v4:

- plugged memory leaks in setup_git_directory() (thanks, Brandon)

- added some tests that demonstrate how early config currently can fail
  in undesired ways

- fixed indentation (this change was snuck into gitster/git's
  js/early-config branch, and I happened to notice the difference by
  pure random chance)

Johannes Schindelin (11):
  t7006: replace dubious test
  setup_git_directory(): use is_dir_sep() helper
  Prepare setup_discovered_git_directory() the root directory
  setup_git_directory_1(): avoid changing global state
  Introduce the discover_git_directory() function
  Make read_early_config() reusable
  read_early_config(): avoid .git/config hack when unneeded
  read_early_config(): really discover .git/
  Test read_early_config()
  setup_git_directory_gently_1(): avoid die()ing
  t1309: document cases where we would want early config not to die()

 cache.h                 |   8 ++
 config.c                |  25 +++++
 pager.c                 |  31 ------
 setup.c                 | 252 +++++++++++++++++++++++++++++++++---------------
 t/helper/test-config.c  |  15 +++
 t/t1309-early-config.sh |  75 ++++++++++++++
 t/t7006-pager.sh        |  18 +++-
 7 files changed, 313 insertions(+), 111 deletions(-)
 create mode 100755 t/t1309-early-config.sh

base-commit: e0688e9b28f2c5ff711460ee8b62077be5df2360
Published-As: https://github.com/dscho/git/releases/tag/early-config-v5
Fetch-It-Via: git fetch https://github.com/dscho/git early-config-v5

Interdiff vs v4:

 diff --git a/setup.c b/setup.c
 index 9118b48590a..b0a28f609e2 100644
 --- a/setup.c
 +++ b/setup.c
 @@ -903,7 +903,7 @@ static enum discovery_result setup_git_directory_gently_1(struct strbuf *dir,
  			if (die_on_error ||
  			    error_code == READ_GITFILE_ERR_NOT_A_FILE) {
  				if (is_git_directory(dir->buf))
 -				    gitdirenv = DEFAULT_GIT_DIR_ENVIRONMENT;
 +					gitdirenv = DEFAULT_GIT_DIR_ENVIRONMENT;
  			} else if (error_code &&
  				   error_code != READ_GITFILE_ERR_STAT_FAILED)
  				return GIT_DIR_INVALID_GITFILE;
 @@ -979,7 +979,8 @@ const char *discover_git_directory(struct strbuf *gitdir)
  
  const char *setup_git_directory_gently(int *nongit_ok)
  {
 -	struct strbuf cwd = STRBUF_INIT, dir = STRBUF_INIT, gitdir = STRBUF_INIT;
 +	static struct strbuf cwd = STRBUF_INIT;
 +	struct strbuf dir = STRBUF_INIT, gitdir = STRBUF_INIT;
  	const char *prefix;
  
  	/*
 @@ -1027,6 +1028,8 @@ const char *setup_git_directory_gently(int *nongit_ok)
  	case GIT_DIR_HIT_MOUNT_POINT:
  		if (nongit_ok) {
  			*nongit_ok = 1;
 +			strbuf_release(&cwd);
 +			strbuf_release(&dir);
  			return NULL;
  		}
  		die(_("Not a git repository (or any parent up to mount point %s)\n"
 @@ -1044,6 +1047,9 @@ const char *setup_git_directory_gently(int *nongit_ok)
  	startup_info->have_repository = !nongit_ok || !*nongit_ok;
  	startup_info->prefix = prefix;
  
 +	strbuf_release(&dir);
 +	strbuf_release(&gitdir);
 +
  	return prefix;
  }
  
 diff --git a/t/t1309-early-config.sh b/t/t1309-early-config.sh
 index 0c55dee514c..027eca63a3c 100755
 --- a/t/t1309-early-config.sh
 +++ b/t/t1309-early-config.sh
 @@ -47,4 +47,29 @@ test_expect_success 'ceiling #2' '
  	test xdg = "$(cat output)"
  '
  
 +test_with_config ()
 +{
 +	rm -rf throwaway &&
 +	git init throwaway &&
 +	(
 +		cd throwaway &&
 +		echo "$*" >.git/config &&
 +		test-config read_early_config early.config
 +	)
 +}
 +
 +test_expect_success 'ignore .git/ with incompatible repository version' '
 +	test_with_config "[core]repositoryformatversion = 999999" 2>err &&
 +	grep "warning:.* Expected git repo version <= [1-9]" err
 +'
 +
 +test_expect_failure 'ignore .git/ with invalid repository version' '
 +	test_with_config "[core]repositoryformatversion = invalid"
 +'
 +
 +
 +test_expect_failure 'ignore .git/ with invalid config' '
 +	test_with_config "["
 +'
 +
  test_done