submodule--helper: advise on fatal alternate error

When recursively cloning a superproject with some shallow modules
defined in its .gitmodules, then recloning with "--reference=<path>", an
error occurs. For example:

  git clone --recurse-submodules --branch=master -j8 \
    https://android.googlesource.com/platform/superproject \
    master
  git clone --recurse-submodules --branch=master -j8 \
    https://android.googlesource.com/platform/superproject \
    --reference master master2

fails with:

  fatal: submodule '<snip>' cannot add alternate: reference repository
  '<snip>' is shallow

When a alternate computed from the superproject's alternate cannot be
added, whether in this case or another, advise about configuring the
"submodule.alternateErrorStrategy" configuration option and using
"--reference-if-able" instead of "--reference" when cloning.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/advice.h b/advice.h
index d015404843..b706780614 100644
--- a/advice.h
+++ b/advice.h
@@ -30,6 +30,7 @@ extern int advice_waiting_for_editor;
 extern int advice_graft_file_deprecated;
 extern int advice_checkout_ambiguous_remote_branch_name;
 extern int advice_nested_tag;
+extern int advice_submodule_alternate_error_strategy_die;
 
 int git_default_advice_config(const char *var, const char *value);
 __attribute__((format (printf, 1, 2)))