test-sparse-revlog: commit the repo content in a single in-mem transaction

I don't like to use the internal API like that, but it make the whole generation
twice faster on my machine and suitable for always run during tests. However it
also mean the `--pure` version of the test will run this with the pure source
code and be unbearably slow. However if another flavor generated the file, pure
will be able to simply reuse it, so it seems fine.

tests/artifacts/scripts/generate-churning-bundle.py

@@ -14,8 +14,6
 # of the files always get updated while the rest of the lines get updated over
 # time. This update happens over many topological branches, some getting merged
 # back.
-#
-# Running with `chg` in your path and `CHGHG` set is recommended for speed.
 
 
 import hashlib
@@ -25,6 +23,10 import subprocess
 import sys
 import tempfile
 
+import mercurial.context
+import mercurial.hg
+import mercurial.ui
+
 BUNDLE_NAME = 'big-file-churn.hg'
 
 # constants for generating the repository
@@ -218,27 +220,47 def hg(command, *args):
     return subprocess.check_call(full_cmd, env=env)
 
 
+def write_repo(path):
+    """write repository content in memory"""
+    repo = mercurial.hg.repository(
+        mercurial.ui.ui.load(),
+        path=path.encode('utf-8'),
+    )
+    nodemap = {None: repo.nodeconstants.nullid}
+    with repo.lock(), repo.transaction(b'bundle-generation'):
+        for idx, (p1, p2) in GRAPH.items():
+            if sys.stdout.isatty():
+                print("generating commit #%d/%d" % (idx, NB_CHANGESET))
+
+            file_fn = lambda repo, memctx, path: mercurial.context.memfilectx(
+                repo,
+                memctx,
+                path,
+                data=b''.join(CONTENT.pop(idx)()),
+            )
+
+            mc = mercurial.context.memctx(
+                repo,
+                (nodemap[p1], nodemap[p2]),
+                b'commit #%d' % idx if idx else b'initial commit',
+                [FILENAME.encode('ascii')],
+                file_fn,
+                user=b"test",
+                date=(0, 0),
+            )
+            nodemap[idx] = repo.commitctx(mc)
+
+
 def run(target):
     tmpdir = tempfile.mkdtemp(prefix='tmp-hg-test-big-file-bundle-')
     try:
         os.chdir(tmpdir)
-        hg('init')
-        for idx, (p1, p2) in GRAPH.items():
-            if sys.stdout.isatty():
-                print("generating commit #%d/%d" % (idx, NB_CHANGESET))
-            if p1 is not None and p1 != idx - 1:
-                hg('update', "%d" % p1)
-            if p2 is not None:
-                hg('merge', "%d" % p2)
-            with open(FILENAME, 'wb') as f:
-                # pop the value to let it be garbage collection eventually.
-                for line in CONTENT.pop(idx)():
-                    f.write(line)
-            if idx == 0:
-                hg('add', FILENAME)
-                hg('commit', '--addremove', '--message', 'initial commit')
-            else:
-                hg('commit', '--message', 'commit #%d' % idx)
+        hg(
+            'init',
+            '--config',
+            'format.maxchainlen=%d' % NB_CHANGESET,
+        )
+        write_repo(tmpdir)
         hg('bundle', '--all', target, '--config', 'devel.bundle.delta=p1')
         with open(target, 'rb') as bundle:
             data = bundle.read()