sidedata: add a 'side-data' repository feature and use it

sidedata: add a 'side-data' repository feature and use it

Most code don't really care how sidedata support is added, but it needs to know
if it is present. To achieve this. we use the `repo.features` attributes with a
new dedicated features".

Having such centralised information is more robust and will help us to remove the
sidedata requirements in a later changesets.

Differential Revision: https://phab.mercurial-scm.org/D10617

--- a/mercurial/bundle2.py	Mon May 03 12:29:41 2021 +0200
+++ b/mercurial/bundle2.py	Mon May 03 12:29:52 2021 +0200
@@ -180,6 +180,7 @@
     stringutil,
     urlutil,
 )
+from .interfaces import repository
 
 urlerr = util.urlerr
 urlreq = util.urlreq
@@ -1729,8 +1730,8 @@
             part.addparam(
                 b'targetphase', b'%d' % phases.secret, mandatory=False
             )
-        if b'exp-sidedata-flag' in repo.requirements:
-            part.addparam(b'exp-sidedata', b'1')
+    if repository.REPO_FEATURE_SIDE_DATA in repo.features:
+        part.addparam(b'exp-sidedata', b'1')
 
     if opts.get(b'streamv2', False):
         addpartbundlestream2(bundler, repo, stream=True)
@@ -2579,9 +2580,9 @@
         part.addparam(b'version', cgversion)
         if scmutil.istreemanifest(repo):
             part.addparam(b'treemanifest', b'1')
-        if b'exp-sidedata-flag' in repo.requirements:
-            part.addparam(b'exp-sidedata', b'1')
-            wanted = format_remote_wanted_sidedata(repo)
-            part.addparam(b'exp-wanted-sidedata', wanted)
+    if repository.REPO_FEATURE_SIDE_DATA in repo.features:
+        part.addparam(b'exp-sidedata', b'1')
+        wanted = format_remote_wanted_sidedata(repo)
+        part.addparam(b'exp-wanted-sidedata', wanted)
 
     return bundler

--- a/mercurial/exchange.py	Mon May 03 12:29:41 2021 +0200
+++ b/mercurial/exchange.py	Mon May 03 12:29:52 2021 +0200
@@ -43,6 +43,7 @@
     stringutil,
     urlutil,
 )
+from .interfaces import repository
 
 urlerr = util.urlerr
 urlreq = util.urlreq
@@ -893,7 +894,7 @@
         cgpart.addparam(b'version', version)
     if scmutil.istreemanifest(pushop.repo):
         cgpart.addparam(b'treemanifest', b'1')
-    if b'exp-sidedata-flag' in pushop.repo.requirements:
+    if repository.REPO_FEATURE_SIDE_DATA in pushop.repo.features:
         cgpart.addparam(b'exp-sidedata', b'1')
 
     def handlereply(op):
@@ -2427,7 +2428,7 @@
     if scmutil.istreemanifest(repo):
         part.addparam(b'treemanifest', b'1')
 
-    if b'exp-sidedata-flag' in repo.requirements:
+    if repository.REPO_FEATURE_SIDE_DATA in repo.features:
         part.addparam(b'exp-sidedata', b'1')
         sidedata = bundle2.format_remote_wanted_sidedata(repo)
         part.addparam(b'exp-wanted-sidedata', sidedata)

--- a/mercurial/interfaces/repository.py	Mon May 03 12:29:41 2021 +0200
+++ b/mercurial/interfaces/repository.py	Mon May 03 12:29:52 2021 +0200
@@ -21,6 +21,8 @@
 REPO_FEATURE_LFS = b'lfs'
 # Repository supports being stream cloned.
 REPO_FEATURE_STREAM_CLONE = b'streamclone'
+# Repository supports (at least) some sidedata to be stored
+REPO_FEATURE_SIDE_DATA = b'side-data'
 # Files storage may lack data for all ancestors.
 REPO_FEATURE_SHALLOW_FILE_STORAGE = b'shallowfilestorage'
 

--- a/mercurial/localrepo.py	Mon May 03 12:29:41 2021 +0200
+++ b/mercurial/localrepo.py	Mon May 03 12:29:52 2021 +0200
@@ -737,6 +737,9 @@
     storevfs = store.vfs
     storevfs.options = resolvestorevfsoptions(ui, requirements, features)
 
+    if requirementsmod.REVLOGV2_REQUIREMENT in requirements:
+        features.add(repository.REPO_FEATURE_SIDE_DATA)
+
     # The cache vfs is used to manage cache files.
     cachevfs = vfsmod.vfs(cachepath, cacheaudited=True)
     cachevfs.createmode = store.createmode