test-sparse-revlog: make the large bundle generation more robust and useful

We do the following:
- adding a `--lazy` flag that skip the bundle generation if it already has the
  right content.
- adding a `--validate` flag that make sure the generated bundle match the
  expected content

Generate it on the fly with all this flag during the tests.

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

@@ -14,6 +14,10
 # 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.
+#
+# --lazy     will skip generating the file if one exist with the right content
+#            already.
+# --validate make sure the generated bundle has the expected content.
 
 
 import hashlib
@@ -251,7 +255,33 def write_repo(path):
             nodemap[idx] = repo.commitctx(mc)
 
 
-def run(target):
+def compute_md5(target):
+    with open(target, 'rb') as bundle:
+        data = bundle.read()
+        return hashlib.md5(data).hexdigest()
+
+
+def write_md5(target, md5):
+    with open(target + '.md5', 'wb') as md5file:
+        md5file.write(md5.encode('ascii') + b'\n')
+
+
+def read_md5(target):
+    with open(target + '.md5', 'rb') as md5file:
+        return md5file.read().strip().decode('ascii')
+
+
+def up_to_date_target(target):
+    """return true if the file already exist at the right"""
+    try:
+        found = compute_md5(target)
+        expected = read_md5(target)
+    except OSError:
+        return False
+    return found == expected
+
+
+def run(target, validate=False):
     tmpdir = tempfile.mkdtemp(prefix='tmp-hg-test-big-file-bundle-')
     try:
         os.chdir(tmpdir)
@@ -262,14 +292,17 def run(target):
         )
         write_repo(tmpdir)
         hg('bundle', '--all', target, '--config', 'devel.bundle.delta=p1')
-        with open(target, 'rb') as bundle:
-            data = bundle.read()
-            digest = hashlib.md5(data).hexdigest()
-        with open(target + '.md5', 'wb') as md5file:
-            md5file.write(digest.encode('ascii') + b'\n')
-        if sys.stdout.isatty():
-            print('bundle generated at "%s" md5: %s' % (target, digest))
-
+        digest = compute_md5(target)
+        if not validate:
+            write_md5(target, digest)
+        else:
+            expected = read_md5(target)
+            if expected != digest:
+                msg = "bundle generated does not match the expected content\n"
+                msg += "    expected: %s\n" % expected
+                msg += "    got:      %s" % digest
+                print(msg, file=sys.stderr)
+                return 1
     finally:
         shutil.rmtree(tmpdir)
     return 0
@@ -278,4 +311,8 def run(target):
 if __name__ == '__main__':
     orig = os.path.realpath(os.path.dirname(sys.argv[0]))
     target = os.path.join(orig, os.pardir, 'cache', BUNDLE_NAME)
-    sys.exit(run(target))
+    lazy = '--lazy' in sys.argv[1:]
+    validate = '--validate' in sys.argv[1:]
+    if lazy and up_to_date_target(target):
+        sys.exit(0)
+    sys.exit(run(target, validate=validate))

tests/test-sparse-revlog.t

@@ -11,28 +11,32 repeatedly while some of it changes rare
 
   $ bundlepath="$TESTDIR/artifacts/cache/big-file-churn.hg"
 
+#if pure
   $ expectedhash=`cat "$bundlepath".md5`
-
-#if slow
-
-  $ if [ ! -f "$bundlepath" ]; then
-  >     "$TESTDIR"/artifacts/scripts/generate-churning-bundle.py > /dev/null
-  > fi
-
-#else
-
   $ if [ ! -f "$bundlepath" ]; then
   >     echo 'skipped: missing artifact, run "'"$TESTDIR"'/artifacts/scripts/generate-churning-bundle.py"'
   >     exit 80
   > fi
-
-#endif
-
   $ currenthash=`f -M "$bundlepath" | cut -d = -f 2`
   $ if [ "$currenthash" != "$expectedhash" ]; then
   >     echo 'skipped: outdated artifact, md5 "'"$currenthash"'" expected "'"$expectedhash"'" run "'"$TESTDIR"'/artifacts/scripts/generate-churning-bundle.py"'
   >     exit 80
   > fi
+#else
+
+#if slow
+  $ LAZY_GEN=""
+
+#else
+  $ LAZY_GEN="--lazy"
+#endif
+
+#endif
+
+If the validation fails, either something is broken or the expected md5 need updating.
+To update the md5, invoke the script without --validate
+
+  $ "$TESTDIR"/artifacts/scripts/generate-churning-bundle.py --validate $LAZY_GEN > /dev/null
 
   $ cat >> $HGRCPATH << EOF
   > [format]