perf: add functions to get vfs-like object for Mercurial earlier than 2.3

perf: add functions to get vfs-like object for Mercurial earlier than 2.3

Before this patch, using svfs prevents perf.py from measuring
performance of Mercurial earlier than 2.3 (or 7034365089bf), because
svfs isn't available in such Mercurial, even though there are some
code paths for Mercurial earlier than 2.3 in perf.py.

For example, setting "_prereadsize" attribute in perfindex() and
perfnodelookup() is effective only with hg earlier than 1.8 (or
61c9bc3da402).

To get appropriate vfs-like object to access files under .hg/store,
this patch adds getsvfs() (and also getvfs(), for future use).

To avoid examining existence of attribute at each repetition while
measuring performance, getsvfs() is invoked outside the function to be
called repeatedly.

This patch also adds check-perf-code.py an extra check entry to detect
direct usage of repo.(vfs|svfs|opener|sopener) in perf.py.

--- a/contrib/perf.py	Sun Oct 09 01:03:17 2016 +0900
+++ b/contrib/perf.py	Sun Oct 09 01:03:18 2016 +0900
@@ -232,6 +232,28 @@
     raise error.Abort(("perfbranchmap not available with this Mercurial"),
                       hint="use 2.5 or later")
 
+def getsvfs(repo):
+    """Return appropriate object to access files under .hg/store
+    """
+    # for "historical portability":
+    # repo.svfs has been available since 2.3 (or 7034365089bf)
+    svfs = getattr(repo, 'svfs', None)
+    if svfs:
+        return svfs
+    else:
+        return getattr(repo, 'sopener')
+
+def getvfs(repo):
+    """Return appropriate object to access files under .hg
+    """
+    # for "historical portability":
+    # repo.vfs has been available since 2.3 (or 7034365089bf)
+    vfs = getattr(repo, 'vfs', None)
+    if vfs:
+        return vfs
+    else:
+        return getattr(repo, 'opener')
+
 # perf commands
 
 @command('perfwalk', formatteropts)
@@ -302,9 +324,10 @@
     import mercurial.changelog
     import mercurial.manifest
     timer, fm = gettimer(ui, opts)
+    svfs = getsvfs(repo)
     def t():
-        repo.changelog = mercurial.changelog.changelog(repo.svfs)
-        repo.manifest = mercurial.manifest.manifest(repo.svfs)
+        repo.changelog = mercurial.changelog.changelog(svfs)
+        repo.manifest = mercurial.manifest.manifest(svfs)
         repo._tags = None
         return len(repo.tags())
     timer(t)
@@ -483,8 +506,9 @@
     timer, fm = gettimer(ui, opts)
     mercurial.revlog._prereadsize = 2**24 # disable lazy parser in old hg
     n = repo["tip"].node()
+    svfs = getsvfs(repo)
     def d():
-        cl = mercurial.revlog.revlog(repo.svfs, "00changelog.i")
+        cl = mercurial.revlog.revlog(svfs, "00changelog.i")
         cl.rev(n)
     timer(d)
     fm.end()
@@ -556,7 +580,7 @@
     import mercurial.revlog
     mercurial.revlog._prereadsize = 2**24 # disable lazy parser in old hg
     n = repo[rev].node()
-    cl = mercurial.revlog.revlog(repo.svfs, "00changelog.i")
+    cl = mercurial.revlog.revlog(getsvfs(repo), "00changelog.i")
     def d():
         cl.rev(n)
         clearcaches(cl)
@@ -903,7 +927,8 @@
 
     Result is the number of markers in the repo."""
     timer, fm = gettimer(ui)
-    timer(lambda: len(obsolete.obsstore(repo.svfs)))
+    svfs = getsvfs(repo)
+    timer(lambda: len(obsolete.obsstore(svfs)))
     fm.end()
 
 @command('perflrucachedict', formatteropts +

--- a/tests/check-perf-code.py	Sun Oct 09 01:03:17 2016 +0900
+++ b/tests/check-perf-code.py	Sun Oct 09 01:03:18 2016 +0900
@@ -12,6 +12,8 @@
   [
     (r'(branchmap|repoview)\.subsettable',
      "use getbranchmapsubsettable() for early Mercurial"),
+    (r'\.(vfs|svfs|opener|sopener)',
+     "use getvfs()/getsvfs() for early Mercurial"),
   ],
   # warnings
   [