multi-repo setup tool: add pragma to transfrom file roots to git

... and in this way enable them to present themselves to our tool
als fully specified content (which will be useful once we add target
caching). If that file root is under git anyway (like the rules or
external target files in this repository) computing that git root
is also a relatively cheap operation.

1 files changed, 24 insertions, 3 deletions

diff --git a/bin/just-mr.py b/bin/just-mr.py
index f71bbefe..472131d2 100755
--- a/bin/just-mr.py
+++ b/bin/just-mr.py
@@ -73,6 +73,8 @@ def read_config(configfile):
 def git_root(*, upstream):
     if upstream in GIT_CHECKOUT_LOCATIONS:
         return GIT_CHECKOUT_LOCATIONS[upstream]
+    elif upstream and os.path.isabs(upstream):
+        return upstream
     else:
         return os.path.join(ROOT, "git")
 
@@ -293,8 +295,27 @@ def archive_checkout(desc, repo_type="archive", *, fetch_only=False):
             git_subtree(tree=tree, subdir=desc.get("subdir", "."), upstream=None),
             git_root(upstream=None)]
 
-def describe_file(desc):
-    fpath = desc["path"]
+def file_as_git(fpath):
+    root_result = subprocess.run(["git", "rev-parse", "--show-toplevel"],
+                                 cwd=fpath,
+                                 stdout=subprocess.PIPE,
+                                 stderr=subprocess.DEVNULL)
+    if not root_result.returncode == 0:
+        # Fall back to file root
+        return ["file", fpath]
+    root = root_result.stdout.decode('utf-8').rstrip()
+    subdir = os.path.relpath(fpath, root)
+    root_tree = subprocess.run(["git", "log", "-n", "1", "--format=%T"],
+                               cwd = root, stdout=subprocess.PIPE
+                               ).stdout.decode('utf-8').strip()
+    return ["git tree",
+            git_subtree(tree=root_tree, subdir=subdir, upstream=root),
+            root]
+
+def file_checkout(desc):
+    fpath = os.path.abspath(desc["path"])
+    if desc.get("pragma", {}).get("to_git") and not ALWAYS_FILE:
+        return file_as_git(fpath)
     return ["file", os.path.abspath(fpath)]
 
 def resolve_repo(desc, *, seen=None, repos):
@@ -314,7 +335,7 @@ def checkout(desc, *, name, repos):
     if repo_type in ["archive", "zip"]:
         return archive_checkout(repo_desc, repo_type=repo_type)
     if repo_type == "file":
-        return describe_file(repo_desc)
+        return file_checkout(repo_desc)
     fail("Unknown repository type %s for %s"
          % (repo_type, name))