D110: sparse: add a requirement when a repository uses sparse (BC)

[indygreg (Gregory Szorc)]

indygreg created this revision.
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Herald added a reviewer: hg-reviewers.

REVISION SUMMARY
  The presence of a sparse checkout can confuse legacy clients or
  clients without sparse enabled for reasons that should be obvious.
  
  This commit introduces a new repository requirement that tracks
  whether sparse is enabled. The requirement is added when a sparse
  config is activated and removed when the sparse config is reset.
  
  The localrepository constructor has been taught to not open repos
  with this requirement unless the sparse feature is enabled. It yields
  a more actionable error message than what you would get if the
  lockout were handled strictly at the requirements verification phase.
  Old clients that aren't sparse aware will see the generic
  "repository requires features unknown to this Mercurial" error,
  however.
  
  The new requirement has "exp" in its name to reflect the
  experimental nature of sparse. There's a chance that the eventual
  non-experimental feature won't change significantly and we could
  have squatted on the "sparse" requirement without ill effect. If
  that happens, we can teach new clients to still recognize the old
  name. But I suspect we'll sneak in some BC and we'll want a new
  requirement to convey new meaning.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D110

AFFECTED FILES
  mercurial/help/internals/requirements.txt
  mercurial/localrepo.py
  mercurial/sparse.py
  tests/test-sparse-requirement.t

CHANGE DETAILS

diff --git a/tests/test-sparse-requirement.t b/tests/test-sparse-requirement.t
new file mode 100644
--- /dev/null
+++ b/tests/test-sparse-requirement.t
@@ -0,0 +1,65 @@
+  $ hg init repo
+  $ cd repo
+
+  $ touch a.html b.html c.py d.py
+
+  $ cat > frontend.sparse << EOF
+  > [include]
+  > *.html
+  > EOF
+
+  $ hg -q commit -A -m initial
+
+  $ echo 1 > a.html
+  $ echo 1 > c.py
+  $ hg commit -m 'commit 1'
+
+Enable sparse profile
+
+  $ cat .hg/requires
+  dotencode
+  fncache
+  generaldelta
+  revlogv1
+  store
+
+  $ hg debugsparse --config extensions.sparse= --enable-profile frontend.sparse
+  $ ls
+  a.html
+  b.html
+
+Requirement for sparse added when sparse is enabled
+
+  $ cat .hg/requires
+  dotencode
+  exp-sparse
+  fncache
+  generaldelta
+  revlogv1
+  store
+
+Client without sparse enabled reacts properly
+
+  $ hg files
+  abort: repository is using sparse feature but sparse is not enabled; enable the "sparse" extensions to access!
+  [255]
+
+Requirement for sparse is removed when sparse is disabled
+
+  $ hg debugsparse --reset --config extensions.sparse=
+
+  $ cat .hg/requires
+  dotencode
+  fncache
+  generaldelta
+  revlogv1
+  store
+
+And client without sparse can access
+
+  $ hg files
+  a.html
+  b.html
+  c.py
+  d.py
+  frontend.sparse
diff --git a/mercurial/sparse.py b/mercurial/sparse.py
--- a/mercurial/sparse.py
+++ b/mercurial/sparse.py
@@ -18,6 +18,7 @@
     match as matchmod,
     merge as mergemod,
     pycompat,
+    scmutil,
     util,
 )
 
@@ -522,13 +523,14 @@
     prunetemporaryincludes(repo)
 
 def _updateconfigandrefreshwdir(repo, includes, excludes, profiles,
-                                force=False):
+                                force=False, removing=False):
     """Update the sparse config and working directory state."""
     raw = repo.vfs.tryread('sparse')
     oldincludes, oldexcludes, oldprofiles = parseconfig(repo.ui, raw)
 
     oldstatus = repo.status()
     oldmatch = matcher(repo)
+    oldrequires = set(repo.requirements)
 
     # TODO remove this try..except once the matcher integrates better
     # with dirstate. We currently have to write the updated config
@@ -538,11 +540,21 @@
     # updated. But this requires massive rework to matcher() and its
     # consumers.
 
-    writeconfig(repo, includes, excludes, profiles)
+    if 'exp-sparse' in oldrequires and removing:
+        repo.requirements.discard('exp-sparse')
+        scmutil.writerequires(repo.vfs, repo.requirements)
+    elif 'exp-sparse' not in oldrequires:
+        repo.requirements.add('exp-sparse')
+        scmutil.writerequires(repo.vfs, repo.requirements)
 
     try:
+        writeconfig(repo, includes, excludes, profiles)
         return refreshwdir(repo, oldstatus, oldmatch, force=force)
     except Exception:
+        if repo.requirements != oldrequires:
+            repo.requirements.clear()
+            repo.requirements |= oldrequires
+            scmutil.writerequires(repo.vfs, repo.requirements)
         writeconfig(repo, oldincludes, oldexcludes, oldprofiles)
         raise
 
@@ -647,7 +659,8 @@
                         len(oldexclude - newexclude))
 
         fcounts = map(len, _updateconfigandrefreshwdir(
-            repo, newinclude, newexclude, newprofiles, force=force))
+            repo, newinclude, newexclude, newprofiles, force=force,
+            removing=reset))
 
         printchanges(repo.ui, opts, profilecount, includecount,
                      excludecount, *fcounts)
diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -288,6 +288,7 @@
         'shared',
         'relshared',
         'dotencode',
+        'exp-sparse',
     }
     openerreqs = {
         'revlogv1',
@@ -419,6 +420,11 @@
             if inst.errno != errno.ENOENT:
                 raise
 
+        if 'exp-sparse' in self.requirements and not sparse.enabled:
+            raise error.RepoError(_('repository is using sparse feature but '
+                                    'sparse is not enabled; enable the '
+                                    '"sparse" extensions to access'))
+
         self.store = store.store(
                 self.requirements, self.sharedpath, vfsmod.vfs)
         self.spath = self.store.path
diff --git a/mercurial/help/internals/requirements.txt b/mercurial/help/internals/requirements.txt
--- a/mercurial/help/internals/requirements.txt
+++ b/mercurial/help/internals/requirements.txt
@@ -117,3 +117,14 @@
 Support for this requirement was added in Mercurial 3.4 (released
 August 2015). The requirement is currently experimental and is
 disabled by default.
+
+exp-sparse
+==========
+
+The working directory is sparse (only contains a subset of files).
+
+Support for this requirement was added in Mercurial 4.3 (released
+August 2017). This requirement and feature are experimental and may
+disappear in a future Mercurial release. The requirement will only
+be present on repositories that have opted in to a sparse working
+directory.



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