just-mr: Correct handling of remotes with respect to compatibility mode

In order to set up roots, just-mr is able to interrogate, if given,
serve and/or remote-execution endpoints. However, just-mr operates
only with Git hashes, i.e., with a native mode CAS.

This commit ensures the correct interactions occur between just-mr
and the provided endpoints not only in native mode, but also in
comaptible mode, where a serve endpoint might be present even if
one cannot make use of its associated remote-exection endpoint.
The user always gets informed if any incompatibilities are
detected.

1 files changed, 9 insertions, 0 deletions

diff --git a/src/other_tools/root_maps/commit_git_map.cpp b/src/other_tools/root_maps/commit_git_map.cpp
index 04f14023..d97f33be 100644
--- a/src/other_tools/root_maps/commit_git_map.cpp
+++ b/src/other_tools/root_maps/commit_git_map.cpp
@@ -108,6 +108,15 @@ void EnsureRootAsAbsent(
                               /*fatal=*/true);
                     return;
                 }
+                if (not remote_api) {
+                    (*logger)(
+                        fmt::format("Missing or incompatible remote-execution "
+                                    "endpoint needed to sync workspace root {} "
+                                    "with the serve endpoint.",
+                                    tree_id),
+                        /*fatal=*/true);
+                    return;
+                }
                 // the tree is known locally, so we can upload it to remote CAS
                 // for the serve endpoint to retrieve it and set up the root
                 if (not EnsureAbsentRootOnServe(tree_id,