revert: only pre-fetch files that needs to be touched

Summary:
With recent version of mercurial (>= 3.2, 4dfcf21a6aa7), revert uses status
information to determine the files that needs to be touched. It then offer a
simple handle for extensions that needs prefetch.

Test Plan:
Ran the tests. Certain tests depended on the old revert behavior (of
prefetching everything), so they required slight changes.

Reviewers: pyd, sid0, davidsp

Differential Revision: https://phabricator.fb.com/D1551059

remotefilelog/__init__.py

@@ -309,7 +309,10 @@ def onetimeclientsetup(ui):
             pass
     wrapfunction(verify, '_verify', _verify)
 
-    wrapfunction(cmdutil, 'revert', revert)
+    if util.safehasattr(cmdutil, '_revertprefetch'):
+        wrapfunction(cmdutil, '_revertprefetch', _revertprefetch)
+    else:
+        wrapfunction(cmdutil, 'revert', revert)
 
 def getrenamedfn(repo, endrev=None):
     rcache = {}
@@ -535,6 +538,7 @@ def pull(orig, ui, repo, *pats, **opts):
 
 def revert(orig, ui, repo, ctx, parents, *pats, **opts):
     # prefetch prior to reverting
+    # used for old mercurial version
     if shallowrepo.requirement in repo.requirements:
         files = []
         m = scmutil.match(ctx, pats, opts)
@@ -546,6 +550,18 @@ def revert(orig, ui, repo, ctx, parents, *pats, **opts):
 
     return orig(ui, repo, ctx, parents, *pats, **opts)
 
+def _revertprefetch(orig, repo, ctx, *files):
+    # prefetch data that needs to be reverted
+    # used for new mercurial version
+    if shallowrepo.requirement in repo.requirements:
+        allfiles = []
+        mf = ctx.manifest()
+        for f in files:
+            for path in f:
+                allfiles.append((path, hex(mf[path])))
+        repo.fileservice.prefetch(allfiles)
+    return orig(repo, ctx, *files)
+
 commands.norepo += " debugremotefilelog"
 
 @command('debugremotefilelog', [

tests/test-local.t

@@ -120,7 +120,8 @@
 
   $ clearcache
   $ hg revert -r .~2 y z
-  3 files fetched over 2 fetches - (3 misses, 0.00% hit ratio) over *s (glob)
+  no changes needed to z
+  2 files fetched over 2 fetches - (2 misses, 0.00% hit ratio) over *s (glob)
   $ hg checkout -C -r . -q
 
 # explicit bundle should produce full bundle file
@@ -131,6 +132,7 @@
   $ cd ..
 
   $ hgcloneshallow ssh://user@dummy/master shallow2 -q
+  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over *s (glob)
   $ cd shallow2
   $ hg unbundle ../local.bundle
   adding changesets

tests/test-prefetch.t

@@ -71,7 +71,7 @@
   updating bookmark foo
   (run 'hg update' to get a working copy)
   prefetching file contents
-  3 files fetched over 1 fetches - (3 misses, 0.00% hit ratio) over 0.09s
+  3 files fetched over 1 fetches - (3 misses, 0.00% hit ratio) over *s (glob)
 
   $ hg up tip
   3 files updated, 0 files merged, 0 files removed, 0 files unresolved