git_handler: fix hgsubstate generation

Before this patch, in the git to hg conversion, .hgsubstate once created is
never deleted, even if no submodules are any longer present. This is broken
state, as shown by the test for which the SHA changes. Fix that by looking at
the diff instead of just what submodules are present.

Since 'gitlinks' now contains *changed* gitlinks, not *all* gitlinks, it no
longer makes sense to gate gitmodules checks on that.

This patch simply demonstrates that the test was broken; an upcoming patch will
introduce more tests.

Bonus: this also makes the import process faster because we no longer need to
walk the entire tree to collect gitlinks.

This will cause the SHAs of repos that have submodules added and then removed
to change.

hggit/git_handler.py

@@ -685,25 +685,39 @@ class GitHandler(object):
         # get a list of the changed, added, removed files and gitlinks
         files, gitlinks = self.get_files_changed(commit)
 
-        # Handle gitlinks: collect
-        gitlinks = self.collect_gitlinks(commit.tree)
         git_commit_tree = self.git[commit.tree]
 
-        # Analyze hgsubstate and build an updated version
-        # using SHAs from gitlinks
-        hgsubstate = None
-        if gitlinks:
-            hgsubstate = util.parse_hgsubstate(self.git_file_readlines(git_commit_tree, '.hgsubstate'))
-            for path, sha in gitlinks:
+        # Analyze hgsubstate and build an updated version using SHAs from
+        # gitlinks. Order of application:
+        # - preexisting .hgsubstate in git tree
+        # - .hgsubstate from hg parent
+        # - changes in gitlinks
+        hgsubstate = util.parse_hgsubstate(
+            self.git_file_readlines(git_commit_tree, '.hgsubstate'))
+        parentsubdata = ''
+        if gparents:
+            p1ctx = self.repo.changectx(gparents[0])
+            if '.hgsubstate' in p1ctx:
+                parentsubdata = p1ctx.filectx('.hgsubstate').data().splitlines()
+                parentsubstate = util.parse_hgsubstate(parentsubdata)
+                for path, sha in parentsubstate.iteritems():
+                    hgsubstate[path] = sha
+        for path, sha in gitlinks.iteritems():
+            if sha is None:
+                hgsubstate.pop(path, None)
+            else:
                 hgsubstate[path] = sha
         # in case .hgsubstate wasn't among changed files
         # force its inclusion
-            files['.hgsubstate'] = (False, 0100644, None)
+        if not hgsubstate and parentsubdata:
+            files['.hgsubstate'] = True, None, None
+        elif util.serialize_hgsubstate(hgsubstate) != parentsubdata:
+            files['.hgsubstate'] = False, 0100644, None
 
         # Analyze .hgsub and merge with .gitmodules
         hgsub = None
         gitmodules = self.parse_gitmodules(git_commit_tree)
-        if gitmodules or gitlinks:
+        if gitmodules:
             hgsub = util.parse_hgsub(self.git_file_readlines(git_commit_tree, '.hgsub'))
             for (sm_path, sm_url, sm_name) in gitmodules:
                 hgsub[sm_path] = '[git]' + sm_url

tests/test-git-submodules.t

@@ -51,9 +51,9 @@ while older git will use the full normalized path for .)
 
   $ hg clone gitrepo2 hgrepo | grep -v '^updating'
   importing git objects into hg
-  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ hg -R hgrepo log --graph  | grep -v ': *master'
-  @  changeset:   2:76fda365fbbb
+  @  changeset:   2:8f93c04eafda
   |  tag:         default/master
   |  tag:         tip
   |  user:        test <test@example.org>
@@ -73,4 +73,8 @@ while older git will use the full normalized path for .)
 
 we should have some bookmarks
   $ hg -R hgrepo book
-   * master                    2:76fda365fbbb
+   * master                    2:8f93c04eafda
+
+check that .hgsubstate and .hgsub aren't present
+  $ hg -R hgrepo manifest
+  alpha