discovery: avoid dropping remote heads hidden locally

An extra post processing was added to recognize remote heads that are hidden
locally as "common" instead of "unknown". However, this processing was
removing such hidden heads from the remote heads sets.

It had no impact because we used to pull phase information from all remote
heads.

This series will replace the phase pulling operation to a more efficient
process but requires the unmodified pulled set information.

mercurial/exchange.py

@@ -1313,8 +1313,7 b' def _pulldiscoverychangegroup(pullop):'
     common, fetch, rheads = tmp
     nm = pullop.repo.unfiltered().changelog.nodemap
     if fetch and rheads:
-        # If a remote heads in filtered locally, lets drop it from the unknown
-        # remote heads and put in back in common.
+        # If a remote heads is filtered locally, put in back in common.
         #
         # This is a hackish solution to catch most of "common but locally
         # hidden situation".  We do not performs discovery on unfiltered
@@ -1324,16 +1323,12 b' def _pulldiscoverychangegroup(pullop):'
         # If a set of such "common but filtered" changeset exist on the server
         # but are not including a remote heads, we'll not be able to detect it,
         scommon = set(common)
-        filteredrheads = []
         for n in rheads:
             if n in nm:
                 if n not in scommon:
                     common.append(n)
-            else:
-                filteredrheads.append(n)
-        if not filteredrheads:
+        if set(rheads).issubset(set(common)):
             fetch = []
-        rheads = filteredrheads
     pullop.common = common
     pullop.fetch = fetch
     pullop.rheads = rheads

tests/test-treediscovery.t

@@ -520,7 +520,7 b' Both have new stuff in existing named br'
   "GET /?cmd=heads HTTP/1.1" 200 - x-hgproto-1:0.1 0.2 comp=zstd,zlib,none,bzip2
   "GET /?cmd=branches HTTP/1.1" 200 - x-hgarg-1:nodes=d8f638ac69e9ae8dea4f09f11d696546a912d961 x-hgproto-1:0.1 0.2 comp=zstd,zlib,none,bzip2
   "GET /?cmd=between HTTP/1.1" 200 - x-hgarg-1:pairs=d8f638ac69e9ae8dea4f09f11d696546a912d961-d57206cc072a18317c1e381fb60aa31bd3401785 x-hgproto-1:0.1 0.2 comp=zstd,zlib,none,bzip2
-  "GET /?cmd=changegroupsubset HTTP/1.1" 200 - x-hgarg-1:bases=d8f638ac69e9ae8dea4f09f11d696546a912d961&heads=d8f638ac69e9ae8dea4f09f11d696546a912d961 x-hgproto-1:0.1 0.2 comp=zstd,zlib,none,bzip2
+  "GET /?cmd=changegroupsubset HTTP/1.1" 200 - x-hgarg-1:bases=d8f638ac69e9ae8dea4f09f11d696546a912d961&heads=d8f638ac69e9ae8dea4f09f11d696546a912d961+2c8d5d5ec612be65cdfdeac78b7662ab1696324a x-hgproto-1:0.1 0.2 comp=zstd,zlib,none,bzip2
   "GET /?cmd=listkeys HTTP/1.1" 200 - x-hgarg-1:namespace=phases x-hgproto-1:0.1 0.2 comp=zstd,zlib,none,bzip2
   "GET /?cmd=capabilities HTTP/1.1" 200 -
   "GET /?cmd=heads HTTP/1.1" 200 - x-hgproto-1:0.1 0.2 comp=zstd,zlib,none,bzip2