upgrade: support upgrade to/from zstd storage (issue6088)

upgrade: support upgrade to/from zstd storage (issue6088)

Now that we have an official config option for a shiny format improvement, we
better make it simple to migrate to/from it.

--- a/mercurial/upgrade.py	Wed Mar 27 18:27:03 2019 +0100
+++ b/mercurial/upgrade.py	Fri Feb 01 15:51:02 2019 +0100
@@ -24,6 +24,10 @@
     vfs as vfsmod,
 )
 
+from .utils import (
+    compression,
+)
+
 def requiredsourcerequirements(repo):
     """Obtain requirements required to be present to upgrade a repo.
 
@@ -61,9 +65,16 @@
     the dropped requirement must appear in the returned set for the upgrade
     to be allowed.
     """
-    return {
+    supported = {
         localrepo.SPARSEREVLOG_REQUIREMENT,
     }
+    for name in compression.compengines:
+        engine = compression.compengines[name]
+        if engine.available() and engine.revlogheader():
+            supported.add(b'exp-compression-%s' % name)
+            if engine.name() == 'zstd':
+                supported.add(b'revlog-compression-zstd')
+    return supported
 
 def supporteddestrequirements(repo):
     """Obtain requirements that upgrade supports in the destination.
@@ -73,7 +84,7 @@
 
     Extensions should monkeypatch this to add their custom requirements.
     """
-    return {
+    supported = {
         'dotencode',
         'fncache',
         'generaldelta',
@@ -81,6 +92,13 @@
         'store',
         localrepo.SPARSEREVLOG_REQUIREMENT,
     }
+    for name in compression.compengines:
+        engine = compression.compengines[name]
+        if engine.available() and engine.revlogheader():
+            supported.add(b'exp-compression-%s' % name)
+            if engine.name() == 'zstd':
+                supported.add(b'revlog-compression-zstd')
+    return supported
 
 def allowednewrequirements(repo):
     """Obtain requirements that can be added to a repository during upgrade.
@@ -92,12 +110,19 @@
     bad additions because the whitelist approach is safer and will prevent
     future, unknown requirements from accidentally being added.
     """
-    return {
+    supported = {
         'dotencode',
         'fncache',
         'generaldelta',
         localrepo.SPARSEREVLOG_REQUIREMENT,
     }
+    for name in compression.compengines:
+        engine = compression.compengines[name]
+        if engine.available() and engine.revlogheader():
+            supported.add(b'exp-compression-%s' % name)
+            if engine.name() == 'zstd':
+                supported.add(b'revlog-compression-zstd')
+    return supported
 
 def preservedrequirements(repo):
     return set()

--- a/tests/test-upgrade-repo.t	Wed Mar 27 18:27:03 2019 +0100
+++ b/tests/test-upgrade-repo.t	Fri Feb 01 15:51:02 2019 +0100
@@ -854,4 +854,78 @@
   generaldelta
   revlogv1
   store
+
+#if zstd
+
+Check upgrading to a zstd revlog
+--------------------------------
+
+upgrade
+
+  $ hg --config format.revlog-compression=zstd debugupgraderepo --run  --no-backup >/dev/null
+  $ hg debugformat -v
+  format-variant    repo config default
+  fncache:           yes    yes     yes
+  dotencode:         yes    yes     yes
+  generaldelta:      yes    yes     yes
+  sparserevlog:      yes    yes     yes
+  plain-cl-delta:    yes    yes     yes
+  compression:       zstd   zlib    zlib
+  compression-level: default default default
+  $ cat .hg/requires
+  dotencode
+  fncache
+  generaldelta
+  revlog-compression-zstd
+  revlogv1
+  sparserevlog
+  store
+
+downgrade
+
+  $ hg debugupgraderepo --run --no-backup > /dev/null
+  $ hg debugformat -v
+  format-variant    repo config default
+  fncache:           yes    yes     yes
+  dotencode:         yes    yes     yes
+  generaldelta:      yes    yes     yes
+  sparserevlog:      yes    yes     yes
+  plain-cl-delta:    yes    yes     yes
+  compression:       zlib   zlib    zlib
+  compression-level: default default default
+  $ cat .hg/requires
+  dotencode
+  fncache
+  generaldelta
+  revlogv1
+  sparserevlog
+  store
+
+upgrade from hgrc
+
+  $ cat >> .hg/hgrc << EOF
+  > [format]
+  > revlog-compression=zstd
+  > EOF
+  $ hg debugupgraderepo --run --no-backup > /dev/null
+  $ hg debugformat -v
+  format-variant    repo config default
+  fncache:           yes    yes     yes
+  dotencode:         yes    yes     yes
+  generaldelta:      yes    yes     yes
+  sparserevlog:      yes    yes     yes
+  plain-cl-delta:    yes    yes     yes
+  compression:       zstd   zstd    zlib
+  compression-level: default default default
+  $ cat .hg/requires
+  dotencode
+  fncache
+  generaldelta
+  revlog-compression-zstd
+  revlogv1
+  sparserevlog
+  store
+
   $ cd ..
+
+#endif