[TopGit PATCH] hooks/pre-commit: check for cycles in dependencies

[Bert Wesarg <bert.wesarg@googlemail.com>]

Only newly added dependencies needs to be considered.  For each of these deps
check if there is a path from this dep to the current HEAD.

Use recursive_dep() for this task.  Even if recursive_dep() uses a DFS-like
traversal it will not run into an infty-loop if there would be a cycle, because
recursive_dep() takes .topdeps only from committed trees.  And it is required
that the committed dependency graph is acyclic.

Signed-off-by: Bert Wesarg <bert.wesarg@googlemail.com>

---
 hooks/pre-commit.sh |   30 ++++++++++++++++++++++++++++--
 1 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/hooks/pre-commit.sh b/hooks/pre-commit.sh
index 9d677e9..8e05a4e 100644
--- a/hooks/pre-commit.sh
+++ b/hooks/pre-commit.sh
@@ -20,7 +20,8 @@ tg_util
 if head_=$(git symbolic-ref -q HEAD); then
 	case "$head_" in
 		refs/heads/*)
-			git rev-parse -q --verify "refs/top-bases${head_#refs/heads}" >/dev/null || exit 0;;
+			head_="${head_#refs/heads/}"
+			git rev-parse -q --verify "refs/top-bases/$head_" >/dev/null || exit 0;;
 		*)
 			exit 0;;
 	esac
@@ -35,4 +36,29 @@ fi
 [ -s "$root_dir/.topmsg" ] ||
 	die ".topmsg is missing"
 
-# TODO: Verify .topdeps for valid branch names and against cycles
+check_cycle_name()
+{
+	[ "$head_" != "$_dep" ] ||
+		die "TopGit dependencies form a cycle: perpetrator is $_name"
+}
+
+# only check newly added deps
+# check if a path exists to the current HEAD
+git diff --cached "$root_dir/.topdeps" |
+	awk '
+BEGIN      { in_hunk = 0; }
+/^@@ /     { in_hunk = 1; }
+/^\+/      { if (in_hunk == 1) printf("%s\n", substr($0, 2)); }
+/^[^@ +-]/ { in_hunk = 0; }
+' |
+	while read newly_added; do
+		# deps can be non-tgish but we can't run recurse_deps() on them
+		ref_exists "refs/top-bases/$newly_added" ||
+			continue
+		# recurse_deps uses dfs but takes the .topdeps from the tree,
+		# therefor no infty-loop in the cycle-check
+		no_remotes=1 recurse_deps check_cycle_name "$newly_added"
+	done
+
+
+# TODO: Verify .topdeps for valid branch names
-- 
tg: (99f2ef6..) bw/check-for-dep-cycle (depends on: master)