More index cleanups

This is based on ds/cache-tree-basics.

Here are a few more cleanups that are vaguely related to the index. I discovered these while preparing my sparse-index RFC that I intend to send early next week.

The biggest patch is the final one, which creates a test script for comparing sparse-checkouts to full checkouts. There are some commands that do not behave similarly. This script will be the backbone of my testing strategy for the sparse-index by adding a new mode to compare sparse-checkouts with the two index types (full and sparse).

UPDATES IN V3
=============

* Callers to cache_tree_update() no longer initialize the cache_tree in advance.

* Added a patch to update verify_cache() prototype.

* Added missing "pos + 1" in fsmonitor.c.

* Added a BUG() statement when repo->istate->repo is already populated, but not equal to repo.

* Cleaned up test_region pattern quoting. Thanks, Junio!

Thanks, -Stolee

Derrick Stolee (9):
cache-tree: clean up cache_tree_update()
cache-tree: simplify verify_cache() prototype
cache-tree: extract subtree_pos()
fsmonitor: de-duplicate BUG()s around dirty bits
repository: add repo reference to index_state
name-hash: use trace2 regions for init
sparse-checkout: load sparse-checkout patterns
test-lib: test_region looks for trace2 regions
t1092: test interesting sparse-checkout scenarios

 builtin/checkout.c                       |   3 -
 builtin/sparse-checkout.c                |   5 -
 cache-tree.c                             |  38 +--
 cache-tree.h                             |   2 +
 cache.h                                  |   1 +
 dir.c                                    |  17 ++
 dir.h                                    |   2 +
 fsmonitor.c                              |  27 +-
 name-hash.c                              |   3 +
 repository.c                             |   6 +
 sequencer.c                              |   3 -
 t/t0500-progress-display.sh              |   3 +-
 t/t1092-sparse-checkout-compatibility.sh | 301 +++++++++++++++++++++++
 t/test-lib-functions.sh                  |  42 ++++
 unpack-trees.c                           |   8 +-
 15 files changed, 408 insertions(+), 53 deletions(-)
 create mode 100755 t/t1092-sparse-checkout-compatibility.sh

base-commit: a4b6d202caad83c6dc29abe9b17e53a1b3fb54a0
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-839%2Fderrickstolee%2Fmore-index-cleanups-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-839/derrickstolee/more-index-cleanups-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/839

Range-diff vs v2:

1: f9dccaed0ac ! 1: bdc8ecca3d2 cache-tree: clean up cache_tree_update()
@@ Commit message
BUG() statement or returning with an error because future callers will want to populate an empty cache-tree using this method.

- Also drop local variables that are used exactly once and can be found
- directly from the 'istate' parameter.
+ Callers can also remove their conditional allocations of cache_tree.
+
+ Also drop local variables that can be found directly from the 'istate'
+ parameter.

+ ## builtin/checkout.c ##
+@@ builtin/checkout.c: static int merge_working_tree(const struct checkout_opts *opts,
+ }
+ }
+
+- if (!active_cache_tree)
+- active_cache_tree = cache_tree();
+-
+ if (!cache_tree_fully_valid(active_cache_tree))
+ cache_tree_update(&the_index, WRITE_TREE_SILENT | WRITE_TREE_REPAIR);
+
+
## cache-tree.c ##
@@ cache-tree.c: static int update_one(struct cache_tree *it,

@@ cache-tree.c: static int update_one(struct cache_tree *it,
trace2_region_leave("cache_tree", "update", the_repository); trace_performance_leave("cache_tree_update");
if (i < 0)
+@@ cache-tree.c: static int write_index_as_tree_internal(struct object_id *oid,
+ cache_tree_valid = 0;
+ }
+
+- if (!index_state->cache_tree)
+- index_state->cache_tree = cache_tree();
+-
+ if (!cache_tree_valid && cache_tree_update(index_state, flags) < 0)
+ return WRITE_TREE_UNMERGED_INDEX;
+
+
+ ## sequencer.c ##
+@@ sequencer.c: static int do_recursive_merge(struct repository *r,
+
+ static struct object_id *get_cache_tree_oid(struct index_state *istate)
+ {
+- if (!istate->cache_tree)
+- istate->cache_tree = cache_tree();
+-
+ if (!cache_tree_fully_valid(istate->cache_tree))
+ if (cache_tree_update(istate, 0)) {
+ error(_("unable to update cache tree"));
+
+ ## unpack-trees.c ##
+@@ unpack-trees.c: int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
+ if (!ret) {
+ if (git_env_bool("GIT_TEST_CHECK_CACHE_TREE", 0))
+ cache_tree_verify(the_repository, &o->result);
+- if (!o->result.cache_tree)
+- o->result.cache_tree = cache_tree();
+ if (!cache_tree_fully_valid(o->result.cache_tree))
+ cache_tree_update(&o->result,
+ WRITE_TREE_SILENT |

  -:  ----------- >  2:  1b8b5680094 cache-tree: simplify verify_cache() prototype
  2:  84323e04d08 =  3:  314b6b34f75 cache-tree: extract subtree_pos()
  3:  31095f9aa0e !  4:  4e688d25f8c fsmonitor: de-duplicate BUG()s around dirty bits

@@ Commit message
cannot simplify it too much. However, the error string is identical in each, so this simplifies things.

+ Be sure to add one when checking if a position if valid, since the
+ minimum is a bound on the expected size.
+
The end result is that the code is simpler to read while also preserving these assertions for developers in the FSMonitor space.

@@ fsmonitor.c
- if (pos >= istate->cache_nr)
- BUG("fsmonitor_dirty has more entries than the index (%"PRIuMAX" >= %u)",
- (uintmax_t)pos, istate->cache_nr);
-+ assert_index_minimum(istate, pos);
++ assert_index_minimum(istate, pos + 1);

ce = istate->cache[pos];
ce->ce_flags &= ~CE_FSMONITOR_VALID;
4: a0d89d7a973 ! 5: 6373997e05c repository: add repo reference to index_state
@@ Commit message
repository, add a 'repo' pointer to struct index_state that allows access to this repository.

+ Add a BUG() statement if the repo already has an index, and the index
+ already has a repo, but somehow the index points to a different repo.
+
This will prevent future changes from needing to pass an additional 'struct repository *repo' parameter and instead rely only on the 'struct index_state *istate' parameter.
@@ repository.c: int repo_read_index(struct repository *repo)
+ /* Complete the double-reference */
+ if (!repo->index->repo)
+ repo->index->repo = repo;
++ else if (repo->index->repo != repo)
++ BUG("repo's index should point back at itself");
+
return read_index_from(repo->index, repo->index_file, repo->gitdir);
}

  5:  bc092f5c703 =  6:  9b545d7dbec name-hash: use trace2 regions for init
  6:  04d1daf7222 =  7:  554cc7647e6 sparse-checkout: load sparse-checkout patterns
  7:  8832ce84623 !  8:  b37181bdec4 test-lib: test_region looks for trace2 regions
     @@ t/test-lib-functions.sh: test_subcommand () {
      +		shift
      +	fi
      +
     -+	grep -e "\"region_enter\".*\"category\":\"$1\",\"label\":\"$2\"" "$3"
     ++	grep -e	'"region_enter".*"category":"'"$1"'","label":"'"$2"\" "$3"
      +	exitcode=$?
      +
     -+	if test $exitcode != $expect_exit
     ++	if test $exitcode != $expect_exit = 1]
      +	then
      +		return 1
      +	fi
      +
     -+	grep -e "\"region_leave\".*\"category\":\"$1\",\"label\":\"$2\"" "$3"
     ++	grep -e	'"region_leave".*"category":"'"$1"'","label":"'"$2"\" "$3"
      +	exitcode=$?
      +
     -+	if test $exitcode != $expect_exit
     ++	if test $exitcode != $expect_exit = 1]
      +	then
      +		return 1
      +	fi
     ++
     ++	return 0
      +}
  8:  984458007ed !  9:  72f925353d3 t1092: test interesting sparse-checkout scenarios
     @@ t/t1092-sparse-checkout-compatibility.sh (new)
      +		echo a >a &&
      +		echo "after deep" >e &&
      +		echo "after folder1" >g &&
     ++		echo "after x" >z &&
      +		mkdir folder1 folder2 deep x &&
      +		mkdir deep/deeper1 deep/deeper2 &&
      +		mkdir deep/deeper1/deepest &&
     @@ t/t1092-sparse-checkout-compatibility.sh (new)
      +		echo "after deepest" >deep/deeper1/e &&
      +		cp a folder1 &&
      +		cp a folder2 &&
     ++		cp a x &&
      +		cp a deep &&
      +		cp a deep/deeper1 &&
      +		cp a deep/deeper2 &&
      +		cp a deep/deeper1/deepest &&
     ++		cp -r deep/deeper1/deepest deep/deeper2 &&
      +		git add . &&
      +		git commit -m "initial commit" &&
      +		git checkout -b base &&

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