-# Figure out where to get the other repositories from,
-# based on where this GHC repo came from.
-my $branch = `git branch | grep "\* " | sed "s/^\* //"`; chomp $branch;
-my $remote = `git config branch.$branch.remote`; chomp $remote;
-my $defaultrepo = `git config remote.$remote.url`; chomp $defaultrepo;
-
-my $defaultrepo_base;
-my $checked_out_tree;
-
-if ($defaultrepo =~ /^...*:/) {
- # HTTP or SSH
- # Above regex says "at least two chars before the :", to avoid
- # catching Win32 drives ("C:\").
- $defaultrepo_base = $defaultrepo;
- $defaultrepo_base =~ s#/[^/]+/?$##;
- $checked_out_tree = 0;
-}
-elsif ($defaultrepo =~ /^\/|\.\.\/|.:(\/|\\)/) {
- # Local filesystem, either absolute or relative path
- # (assumes a checked-out tree):
- $defaultrepo_base = $defaultrepo;
- $checked_out_tree = 1;
-}
-else {
- die "Couldn't work out defaultrepo";
-}
+# Usage:
+#
+# ./sync-all [-q] [-s] [--ignore-failure] [-r repo]
+# [--nofib] [--testsuite] [--checked-out] cmd [git flags]
+#
+# Applies the command "cmd" to each repository in the tree.
+# sync-all will try to do the right thing for both git and darcs repositories.
+#
+# e.g.
+# ./sync-all -r http://darcs.haskell.org/ghc get
+# To get any repos which do not exist in the local tree
+#
+# ./sync-all pull
+# To pull everything from the default repos
+#
+# -------------- Flags -------------------
+# -q says to be quite, and -s to be silent.
+#
+# --ignore-failure says to ignore errors and move on to the next repository
+#
+# -r repo says to use repo as the location of package repositories
+#
+# --checked-out says that the remote repo is in checked-out layout, as
+# opposed to the layout used for the main repo. By default a repo on
+# the local filesystem is assumed to be checked-out, and repos accessed
+# via HTTP or SSH are assumed to be in the main repo layout; use
+# --checked-out to override the latter.
+#
+# --nofib, --testsuite also get the nofib and testsuite repos respectively
+#
+# ------------ Which repos to use -------------
+# sync-all uses the following algorithm to decide which remote repos to use
+#
+# It always computes the remote repos from a single base, $repo_base
+# How is $repo_base set?
+# If you say "-r repo", then that's $repo_base
+# otherwise $repo_base is set by asking git where the ghc repo came
+# from, and removing the last component (e.g. /ghc.git/ of /ghc/).
+#
+# Then sync-all iterates over the package found in the file
+# ./packages; see that file for a description of the contents.
+#
+# If $repo_base looks like a local filesystem path, or if you give
+# the --checked-out flag, sync-all works on repos of form
+# $repo_base/<local-path>
+# otherwise sync-all works on repos of form
+# $repo_base/<remote-path>
+# This logic lets you say
+# both sync-all -r http://darcs.haskell.org/ghc-6.12 pull
+# and sync-all -r ../HEAD pull
+# The latter is called a "checked-out tree".