shelve: refactor shelvestate loading

shelve: refactor shelvestate loading

This is a preparatory patch which separates file reading from the
minimal validation we have (like turning version into int and
checking that this version is supported). The purpose of this patch
is to be able to read statefile form simplekeyvaluefile, which is
implemented in the following patch.

--- a/hgext/shelve.py	Thu May 11 22:33:45 2017 -0400
+++ b/hgext/shelve.py	Sun May 14 14:15:07 2017 -0700
@@ -176,39 +176,47 @@
 
     @classmethod
     def load(cls, repo):
+        # Order is important, because old shelvestate file uses it
+        # to detemine values of fields (i.g. version is on the first line,
+        # name is on the second and so forth). Please do not change.
+        keys = ['version', 'name', 'originalwctx', 'pendingctx', 'parents',
+                'nodestoremove', 'branchtorestore', 'keep', 'activebook']
+        d = {}
         fp = repo.vfs(cls._filename)
         try:
-            version = int(fp.readline().strip())
-
-            if version != cls._version:
-                raise error.Abort(_('this version of shelve is incompatible '
-                                   'with the version used in this repo'))
-            name = fp.readline().strip()
-            wctx = nodemod.bin(fp.readline().strip())
-            pendingctx = nodemod.bin(fp.readline().strip())
-            parents = [nodemod.bin(h) for h in fp.readline().split()]
-            nodestoremove = [nodemod.bin(h) for h in fp.readline().split()]
-            branchtorestore = fp.readline().strip()
-            keep = fp.readline().strip() == cls._keep
-            activebook = fp.readline().strip()
-        except (ValueError, TypeError) as err:
-            raise error.CorruptedState(str(err))
+            for key in keys:
+                d[key] = fp.readline().strip()
         finally:
             fp.close()
 
+        # some basic syntactic verification and transformation
+        try:
+            d['version'] = int(d['version'])
+            if d['version'] != cls._version:
+                raise error.Abort(_('this version of shelve is incompatible '
+                                    'with the version used in this repo'))
+            d['originalwctx'] = nodemod.bin(d['originalwctx'])
+            d['pendingctx'] = nodemod.bin(d['pendingctx'])
+            d['parents'] = [nodemod.bin(h)
+                            for h in d['parents'].split(' ')]
+            d['nodestoremove'] = [nodemod.bin(h)
+                                  for h in d['nodestoremove'].split(' ')]
+        except (ValueError, TypeError, KeyError) as err:
+            raise error.CorruptedState(str(err))
+
         try:
             obj = cls()
-            obj.name = name
-            obj.wctx = repo[wctx]
-            obj.pendingctx = repo[pendingctx]
-            obj.parents = parents
-            obj.nodestoremove = nodestoremove
-            obj.branchtorestore = branchtorestore
-            obj.keep = keep
+            obj.name = d['name']
+            obj.wctx = repo[d['originalwctx']]
+            obj.pendingctx = repo[d['pendingctx']]
+            obj.parents = d['parents']
+            obj.nodestoremove = d['nodestoremove']
+            obj.branchtorestore = d.get('branchtorestore', '')
+            obj.keep = d.get('keep') == cls._keep
             obj.activebookmark = ''
-            if activebook != cls._noactivebook:
-                obj.activebookmark = activebook
-        except error.RepoLookupError as err:
+            if d.get('activebook', '') != cls._noactivebook:
+                obj.activebookmark = d.get('activebook', '')
+        except (error.RepoLookupError, KeyError) as err:
             raise error.CorruptedState(str(err))
 
         return obj