[StGit PATCH 13/14] Log and undo external modifications

["Karl Hasselström" <kha@treskal.com>]

At the beginning of every StGit command, quickly check if the branch
head recorded in the log is the same as the actual branch head; if
it's not, conclude that some non-StGit tool has modified the stack,
and record a log entry that says so. (Additionally, if the log doesn't
exist yet, create it.)

This introduces the possibility that a log entry specifies a head and
a top that aren't equal. So teach undo, redo, and reset to deal with
that case.

Signed-off-by: Karl Hasselström <kha@treskal.com>

---

 stgit/commands/common.py     |    1 
 stgit/commands/redo.py       |    4 +-
 stgit/commands/reset.py      |    8 +++-
 stgit/commands/undo.py       |    4 +-
 stgit/lib/log.py             |   88 ++++++++++++++++++++++++++++--------------
 stgit/lib/transaction.py     |   39 ++++++++++++-------
 t/t3105-undo-external-mod.sh |   68 ++++++++++++++++++++++++++++++++
 7 files changed, 162 insertions(+), 50 deletions(-)
 create mode 100755 t/t3105-undo-external-mod.sh


diff --git a/stgit/commands/common.py b/stgit/commands/common.py
index fd02398..2689a42 100644
--- a/stgit/commands/common.py
+++ b/stgit/commands/common.py
@@ -525,6 +525,7 @@ class DirectoryAnywhere(_Directory):
 class DirectoryHasRepository(_Directory):
     def setup(self):
         self.git_dir # might throw an exception
+        log.compat_log_external_mods()
 
 class DirectoryInWorktree(DirectoryHasRepository):
     def setup(self):
diff --git a/stgit/commands/redo.py b/stgit/commands/redo.py
index 47221a5..a1075ec 100644
--- a/stgit/commands/redo.py
+++ b/stgit/commands/redo.py
@@ -46,7 +46,7 @@ def func(parser, options, args):
     trans = transaction.StackTransaction(stack, 'redo %d' % options.number,
                                          discard_changes = options.hard)
     try:
-        log.reset_stack(trans, stack.repository.default_iw, state, [])
+        log.reset_stack(trans, stack.repository.default_iw, state)
     except transaction.TransactionHalted:
         pass
-    return trans.run(stack.repository.default_iw)
+    return trans.run(stack.repository.default_iw, allow_bad_head = True)
diff --git a/stgit/commands/reset.py b/stgit/commands/reset.py
index 5ad9914..22d7731 100644
--- a/stgit/commands/reset.py
+++ b/stgit/commands/reset.py
@@ -57,7 +57,11 @@ def func(parser, options, args):
     trans = transaction.StackTransaction(stack, 'reset',
                                          discard_changes = options.hard)
     try:
-        log.reset_stack(trans, stack.repository.default_iw, state, patches)
+        if patches:
+            log.reset_stack_partially(trans, stack.repository.default_iw,
+                                      state, patches)
+        else:
+            log.reset_stack(trans, stack.repository.default_iw, state)
     except transaction.TransactionHalted:
         pass
-    return trans.run(stack.repository.default_iw)
+    return trans.run(stack.repository.default_iw, allow_bad_head = not patches)
diff --git a/stgit/commands/undo.py b/stgit/commands/undo.py
index b1d7de9..58f1da6 100644
--- a/stgit/commands/undo.py
+++ b/stgit/commands/undo.py
@@ -43,7 +43,7 @@ def func(parser, options, args):
     trans = transaction.StackTransaction(stack, 'undo %d' % options.number,
                                          discard_changes = options.hard)
     try:
-        log.reset_stack(trans, stack.repository.default_iw, state, [])
+        log.reset_stack(trans, stack.repository.default_iw, state)
     except transaction.TransactionHalted:
         pass
-    return trans.run(stack.repository.default_iw)
+    return trans.run(stack.repository.default_iw, allow_bad_head = True)
diff --git a/stgit/lib/log.py b/stgit/lib/log.py
index a8de06b..8c0516b 100644
--- a/stgit/lib/log.py
+++ b/stgit/lib/log.py
@@ -259,6 +259,7 @@ class Log(object):
             self.base = self.patches[self.applied[0]].data.parent
         else:
             self.base = self.head
+    all_patches = property(lambda self: self.applied + self.unapplied)
     @property
     def top(self):
         if self.applied:
@@ -297,34 +298,33 @@ def copy_log(repo, src_branch, dst_branch, msg):
 def default_repo():
     return stack.Repository.default()
 
-def reset_stack(trans, iw, state, only_patches):
-    """Reset the stack to a given previous state. If C{only_patches} is
-    not empty, touch only patches whose names appear in it.
+def reset_stack(trans, iw, state):
+    """Reset the stack to a given previous state."""
+    for pn in trans.all_patches:
+        trans.patches[pn] = None
+    for pn in state.all_patches:
+        trans.patches[pn] = state.patches[pn]
+    trans.applied = state.applied
+    trans.unapplied = state.unapplied
+    trans.base = state.base
+    trans.head = state.head
+
+def reset_stack_partially(trans, iw, state, only_patches):
+    """Reset the stack to a given previous state -- but only the given
+    patches, not anything else.
 
-    @param only_patches: Reset only these patches
+    @param only_patches: Touch only these patches
     @type only_patches: iterable"""
     only_patches = set(only_patches)
-    def mask(s):
-        if only_patches:
-            return s & only_patches
-        else:
-            return s
-    patches_to_reset = mask(set(state.applied + state.unapplied))
+    patches_to_reset = set(state.applied + state.unapplied) & only_patches
     existing_patches = set(trans.all_patches)
     original_applied_order = list(trans.applied)
-    to_delete = mask(existing_patches - patches_to_reset)
-
-    # If we have to change the stack base, we need to pop all patches
-    # first.
-    if not only_patches and trans.base != state.base:
-        trans.pop_patches(lambda pn: True)
-        out.info('Setting stack base to %s' % state.base.sha1)
-        trans.base = state.base
+    to_delete = (existing_patches - patches_to_reset) & only_patches
 
     # In one go, do all the popping we have to in order to pop the
     # patches we're going to delete or modify.
     def mod(pn):
-        if only_patches and not pn in only_patches:
+        if not pn in only_patches:
             return False
         if pn in to_delete:
             return True
@@ -347,17 +347,12 @@ def reset_stack(trans, iw, state, only_patches):
             out.info('Resurrecting %s' % pn)
         trans.patches[pn] = state.patches[pn]
 
-    # Push/pop patches as necessary.
-    if only_patches:
-        # Push all the patches that we've popped, if they still
-        # exist.
-        pushable = set(trans.unapplied)
-        for pn in original_applied_order:
-            if pn in pushable:
-                trans.push_patch(pn, iw)
-    else:
-        # Recreate the exact order specified by the goal state.
-        trans.reorder_patches(state.applied, state.unapplied, iw)
+    # Push all the patches that we've popped, if they still
+    # exist.
+    pushable = set(trans.unapplied)
+    for pn in original_applied_order:
+        if pn in pushable:
+            trans.push_patch(pn, iw)
 
 def undo_state(stack, undo_steps):
     """Find the log entry C{undo_steps} steps in the past. (Successive
@@ -396,3 +391,36 @@ def undo_state(stack, undo_steps):
             raise LogException('Not enough undo information available')
         log = Log(stack.repository, log.parents[0].sha1, log.parents[0])
     return log
+
+def log_external_mods(stack):
+    ref = log_ref(stack.name)
+    try:
+        log_commit = stack.repository.refs.get(ref)
+    except KeyError:
+        # No log exists yet.
+        log_entry(stack, 'start of log')
+        return
+    try:
+        log = Log(stack.repository, ref, log_commit)
+    except LogException:
+        # Something's wrong with the log, so don't bother.
+        return
+    if log.head == stack.head:
+        # No external modifications.
+        return
+    log_entry(stack, '\n'.join([
+                'external modifications', '',
+                'Modifications by tools other than StGit (e.g. git).']))
+
+def compat_log_external_mods():
+    try:
+        repo = default_repo()
+    except git.RepositoryException:
+        # No repository, so we couldn't log even if we wanted to.
+        return
+    try:
+        stack = repo.get_stack(repo.current_branch_name)
+    except exception.StgException:
+        # Stack doesn't exist, so we can't log.
+        return
+    log_external_mods(stack)
diff --git a/stgit/lib/transaction.py b/stgit/lib/transaction.py
index 2003105..0c8d9a5 100644
--- a/stgit/lib/transaction.py
+++ b/stgit/lib/transaction.py
@@ -91,6 +91,7 @@ class StackTransaction(object):
         self.__current_tree = self.__stack.head.data.tree
         self.__base = self.__stack.base
         self.__discard_changes = discard_changes
+        self.__bad_head = None
         if isinstance(allow_conflicts, bool):
             self.__allow_conflicts = lambda trans: allow_conflicts
         else:
@@ -109,8 +110,22 @@ class StackTransaction(object):
                 or self.patches[self.applied[0]].data.parent == val)
         self.__base = val
     base = property(lambda self: self.__base, __set_base)
-    def __checkout(self, tree, iw):
-        if not self.__stack.head_top_equal():
+    @property
+    def top(self):
+        if self.__applied:
+            return self.__patches[self.__applied[-1]]
+        else:
+            return self.__base
+    def __get_head(self):
+        if self.__bad_head:
+            return self.__bad_head
+        else:
+            return self.top
+    def __set_head(self, val):
+        self.__bad_head = val
+    head = property(__get_head, __set_head)
+    def __checkout(self, tree, iw, allow_bad_head):
+        if not (allow_bad_head or self.__stack.head_top_equal()):
             out.error(
                 'HEAD and top are not the same.',
                 'This can happen if you modify a branch with git.',
@@ -143,26 +158,22 @@ class StackTransaction(object):
                 assert self.__stack.patches.exists(pn)
             else:
                 assert pn in remaining
-    @property
-    def __head(self):
-        if self.__applied:
-            return self.__patches[self.__applied[-1]]
-        else:
-            return self.__base
     def abort(self, iw = None):
         # The only state we need to restore is index+worktree.
         if iw:
-            self.__checkout(self.__stack.head.data.tree, iw)
-    def run(self, iw = None):
+            self.__checkout(self.__stack.head.data.tree, iw,
+                            allow_bad_head = True)
+    def run(self, iw = None, allow_bad_head = False):
         """Execute the transaction. Will either succeed, or fail (with an
         exception) and do nothing."""
         self.__check_consistency()
-        new_head = self.__head
+        log.log_external_mods(self.__stack)
+        new_head = self.head
 
         # Set branch head.
         if iw:
             try:
-                self.__checkout(new_head.data.tree, iw)
+                self.__checkout(new_head.data.tree, iw, allow_bad_head)
             except git.CheckoutException:
                 # We have to abort the transaction.
                 self.abort(iw)
@@ -257,7 +268,7 @@ class StackTransaction(object):
         cd = orig_cd.set_committer(None)
         s = ['', ' (empty)'][cd.is_nochange()]
         oldparent = cd.parent
-        cd = cd.set_parent(self.__head)
+        cd = cd.set_parent(self.top)
         base = oldparent.data.tree
         ours = cd.parent.data.tree
         theirs = cd.tree
@@ -267,7 +278,7 @@ class StackTransaction(object):
             if iw == None:
                 self.__halt('%s does not apply cleanly' % pn)
             try:
-                self.__checkout(ours, iw)
+                self.__checkout(ours, iw, allow_bad_head = False)
             except git.CheckoutException:
                 self.__halt('Index/worktree dirty')
             try:
diff --git a/t/t3105-undo-external-mod.sh b/t/t3105-undo-external-mod.sh
new file mode 100755
index 0000000..289a42a
--- /dev/null
+++ b/t/t3105-undo-external-mod.sh
@@ -0,0 +1,68 @@
+#!/bin/sh
+
+test_description='Undo external modifications of the stack'
+
+. ./test-lib.sh
+
+# Ignore our own output files.
+cat > .git/info/exclude <<EOF
+/expected.txt
+/head?.txt
+EOF
+
+test_expect_success 'Initialize StGit stack' '
+    stg init &&
+    echo 000 >> a &&
+    git add a &&
+    git commit -m p0 &&
+    echo 111 >> a &&
+    git add a &&
+    git commit -m p1 &&
+    stg uncommit -n 1
+'
+
+cat > expected.txt <<EOF
+000
+111
+222
+EOF
+test_expect_success 'Make a git commit and turn it into a patch' '
+    git rev-parse HEAD > head0.txt &&
+    echo 222 >> a &&
+    git add a &&
+    git commit -m p2 &&
+    git rev-parse HEAD > head1.txt &&
+    stg repair &&
+    test "$(echo $(stg applied))" = "p1 p2" &&
+    test "$(echo $(stg unapplied))" = "" &&
+    test_cmp expected.txt a
+'
+
+cat > expected.txt <<EOF
+000
+111
+222
+EOF
+test_expect_success 'Undo the patchification' '
+    stg undo &&
+    git rev-parse HEAD > head2.txt &&
+    test_cmp head1.txt head2.txt &&
+    test "$(echo $(stg applied))" = "p1" &&
+    test "$(echo $(stg unapplied))" = "" &&
+    test_cmp expected.txt a
+'
+
+cat > expected.txt <<EOF
+000
+111
+EOF
+test_expect_success 'Undo the commit' '
+    stg undo &&
+    git rev-parse HEAD > head3.txt &&
+    test_cmp head0.txt head3.txt &&
+    test "$(echo $(stg applied))" = "p1" &&
+    test "$(echo $(stg unapplied))" = "" &&
+    test_cmp expected.txt a
+'
+
+test_done