Remove string exception from remaster.

[wizard.git] / wizard / app / __init__.py

diff --git a/wizard/app/__init__.py b/wizard/app/__init__.py
index 83954396562bf08747a8f0e4813fb43ffb0abbd8..6a5ee6a05ac00588e33df8af2961cf9e5020dfa6 100644 (file)
--- a/wizard/app/__init__.py
+++ b/wizard/app/__init__.py
@@ -6,6 +6,23 @@ You'll need to know how to overload the :class:`Application` class
 and use some of the functions in this module in order to specify
 new applications.
 
 and use some of the functions in this module in order to specify
 new applications.
 

+To specify custom applications as plugins,  add the following ``entry_points``
+configuration::
+
+    [wizard.app]
+    yourappname = your.module:Application
+    otherappname = your.other.module:Application
+
+.. note::
+
+    Wizard will complain loudly if ``yourappname`` conflicts with an
+    application name defined by someone else.
+
+There are some submodules for programming languages that define common
+functions and data that may be used by applications in that language.  See:
+
+* :mod:`wizard.app.php`
+

 .. testsetup:: *
 
     import re
 .. testsetup:: *
 
     import re


@@ -16,31 +33,57 @@ new applications.
 """
 
 import os.path
 """
 
 import os.path

+import subprocess

 import re
 import distutils.version
 import decorator
 import shlex
 import logging
 import shutil
 import re
 import distutils.version
 import decorator
 import shlex
 import logging
 import shutil

+import sqlalchemy
+import sqlalchemy.exc
+import string
+import urlparse
+import tempfile
+import pkg_resources
+import traceback

 
 import wizard
 
 import wizard

-from wizard import resolve, scripts, shell, util
-
-_application_list = [
-    "mediawiki", "wordpress", "joomla", "e107", "gallery2",
-    "phpBB", "advancedbook", "phpical", "trac", "turbogears", "django",
-    # these are technically deprecated
-    "advancedpoll", "gallery",
-]
-_applications = None
+from wizard import plugin, resolve, shell, sql, util

 
 

+_applications = None

 def applications():
     """Hash table for looking up string application name to instance"""
     global _applications
     if not _applications:
 def applications():
     """Hash table for looking up string application name to instance"""
     global _applications
     if not _applications:

-        _applications = dict([(n,Application.make(n)) for n in _application_list ])
+        _applications = dict()
+        for dist in pkg_resources.working_set:
+            for appname, entry in dist.get_entry_map("wizard.app").items():
+                if appname in _applications:
+                    newname = dist.key + ":" + appname
+                    if newname in _applications:
+                        raise Exception("Unrecoverable application name conflict for %s from %s", appname, dist.key)
+                    logging.warning("Could not overwrite %s, used %s instead", appname, newname)
+                    appname = newname
+                appclass = entry.load()
+                _applications[appname] = appclass(appname)
+        # setup dummy apps
+        for entry in pkg_resources.iter_entry_points("wizard.dummy_apps"):
+            appfun = entry.load()
+            dummy_apps = appfun()
+            for appname in dummy_apps:
+                # a dummy app that already exists is not a fatal error
+                if appname in _applications:
+                    continue
+                _applications[appname] = Application(appname)

     return _applications
 
     return _applications
 

+def getApplication(appname):
+    """Retrieves application instance given a name"""
+    try:
+        return applications()[appname]
+    except KeyError:
+        raise NoSuchApplication(appname)

 
 class Application(object):
     """
 
 class Application(object):
     """


@@ -61,7 +104,12 @@ class Application(object):
     parametrized_files = []
     #: Keys that are used in older versions of the application, but
     #: not for the most recent version.
     parametrized_files = []
     #: Keys that are used in older versions of the application, but
     #: not for the most recent version.

-    deprecated_keys = []
+    deprecated_keys = set()
+    #: Keys that we can simply generate random strings for if they're missing
+    random_keys = set()
+    #: Values that are not sufficiently random for a random key.  This can
+    #: include default values for a random configuration option,
+    random_blacklist = set()

     #: Dictionary of variable names to extractor functions.  These functions
     #: take a :class:`wizard.deploy.Deployment` as an argument and return the value of
     #: the variable, or ``None`` if it could not be found.
     #: Dictionary of variable names to extractor functions.  These functions
     #: take a :class:`wizard.deploy.Deployment` as an argument and return the value of
     #: the variable, or ``None`` if it could not be found.


@@ -76,6 +124,17 @@ class Application(object):
     #: a conflict marker string and a result list.  See :mod:`wizard.resolve`
     #: for more information.
     resolutions = {}
     #: a conflict marker string and a result list.  See :mod:`wizard.resolve`
     #: for more information.
     resolutions = {}

+    #: Instance of :class:`wizard.install.ArgSchema` that defines the arguments
+    #: this application requires.
+    install_schema = None
+    #: Name of the database that this application uses, i.e. ``mysql`` or
+    #: ``postgres``.  If we end up supporting multiple databases for a single
+    #: application, there should also be a value for this in
+    #: :class:`wizard.deploy.Deployment`; the value here is merely the preferred
+    #: value.
+    database = None
+    #: Indicates whether or not a web stub is necessary.
+    needs_web_stub = False

     def __init__(self, name):
         self.name = name
         self.versions = {}
     def __init__(self, name):
         self.name = name
         self.versions = {}


@@ -109,21 +168,111 @@ class Application(object):
         result = {}
         for k,extractor in self.extractors.items():
             result[k] = extractor(deployment)
         result = {}
         for k,extractor in self.extractors.items():
             result[k] = extractor(deployment)

+        # XXX: ugh... we have to do quoting
+        for k in self.random_keys:
+            if result[k] is None or result[k] in self.random_blacklist:
+                result[k] = "'%s'" % util.random_key()

         return result
         return result

+    def dsn(self, deployment):
+        """
+        Returns the deployment specific database URL.  Uses the override file
+        in :file:`.wizard` if it exists, and otherwise attempt to extract the
+        variables from the source files.
+
+        Under some cases, the database URL will contain only the database
+        property, and no other values.  This indicates that the actual DSN
+        should be determined from the environment.
+
+        This function might return ``None``.
+
+        .. note::
+
+            We are allowed to batch these two together, because the full precedence
+            chain for determining the database of an application combines these
+            two together.  If this was not the case, we would have to call
+            :meth:`databaseUrlFromOverride` and :meth:`databaseUrlFromExtract` manually.
+        """
+        url = self.dsnFromOverride(deployment)
+        if url:
+            return url
+        return self.dsnFromExtract(deployment)
+    def dsnFromOverride(self, deployment):
+        """
+        Extracts database URL from an explicit dsn override file.
+        """
+        try:
+            return sqlalchemy.engine.url.make_url(open(deployment.dsn_file).read().strip())
+        except IOError:
+            return None
+    def dsnFromExtract(self, deployment):
+        """
+        Extracts database URL from a deployment, and returns them as
+        a :class:`sqlalchemy.engine.url.URL`.  Returns ``None`` if we
+        can't figure it out: i.e. the conventional variables are not defined
+        for this application.
+        """
+        if not self.database:
+            return None
+        vars = self.extract(deployment)
+        names = ("WIZARD_DBSERVER", "WIZARD_DBUSER", "WIZARD_DBPASSWORD", "WIZARD_DBNAME")
+        host, user, password, database = (shlex.split(vars[x])[0] if vars[x] is not None else None for x in names)
+        # XXX: You'd have to put support for an explicit different database
+        # type here
+        return sqlalchemy.engine.url.URL(self.database, username=user, password=password, host=host, database=database)
+    def url(self, deployment):
+        """
+        Returns the deployment specific web URL.  Uses the override file
+        in :file:`.wizard` if it exists, and otherwise attempt to extract
+        the variables from the source files.
+
+        This function might return ``None``, which indicates we couldn't figure
+        it out.
+        """
+        url = self.urlFromOverride(deployment)
+        if url:
+            return url
+        return self.urlFromExtract(deployment)
+    def urlFromOverride(self, deployment):
+        """
+        Extracts URL from explicit url override file.
+        """
+        try:
+            return urlparse.urlparse(open(deployment.url_file).read().strip())
+        except IOError:
+            return None
+    def urlFromExtract(self, deployment):
+        """
+        Extracts URL from a deployment, and returns ``None`` if we can't
+        figure it out.  Default implementation is to fail; we might
+        do something clever with extractable variables in the future.
+        """
+        return None

     def parametrize(self, deployment, ref_deployment):
         """
         Takes a generic source checkout and parametrizes it according to the
         values of ``deployment``.  This function operates on the current
         working directory.  ``deployment`` should **not** be the same as the
     def parametrize(self, deployment, ref_deployment):
         """
         Takes a generic source checkout and parametrizes it according to the
         values of ``deployment``.  This function operates on the current
         working directory.  ``deployment`` should **not** be the same as the

-        current working directory.  Default implementation uses
-        :attr:`parametrized_files` and a simple search and replace on those
-        files.
+        current working directory.  See :meth:`parametrizeWithVars` for details
+        on the parametrization.

         """
         """

+        # deployment is not used in this implementation, but note that
+        # we do have the invariant the current directory matches
+        # deployment's directory

         variables = ref_deployment.extract()
         variables = ref_deployment.extract()

+        self.parametrizeWithVars(variables)
+    def parametrizeWithVars(self, variables):
+        """
+        Takes a generic source checkout and parametrizes it according to
+        the values of ``variables``.  Default implementation uses
+        :attr:`parametrized_files` and a simple search and replace on
+        those files.
+        """

         for file in self.parametrized_files:
         for file in self.parametrized_files:

+            logging.debug("Parametrizing file '%s'\n" % (file, ))

             try:
                 contents = open(file, "r").read()
             except IOError:
             try:
                 contents = open(file, "r").read()
             except IOError:

+                logging.debug("Failed to open file '%s'\n" % (file, ))

                 continue
             for key, value in variables.items():
                 if value is None: continue
                 continue
             for key, value in variables.items():
                 if value is None: continue


@@ -138,9 +287,24 @@ class Application(object):
         default implementation uses :attr:`resolutions`.
         """
         resolved = True
         default implementation uses :attr:`resolutions`.
         """
         resolved = True

-        sh = shell.Shell()
-        for status in sh.eval("git", "ls-files", "--unmerged").splitlines():
-            file = status.split()[-1]
+        files = set()
+        files = {}
+        for status in shell.eval("git", "ls-files", "--unmerged").splitlines():
+            mode, hash, role, name = status.split()
+            files.setdefault(name, set()).add(int(role))
+        for file, roles in files.items():
+            # some automatic resolutions
+            if 1 not in roles and 2 not in roles and 3 in roles:
+                # upstream added a file, but it conflicted for whatever reason
+                shell.call("git", "add", file)
+                continue
+            elif 1 in roles and 2 not in roles and 3 in roles:
+                # user deleted the file, but upstream changed it
+                shell.call("git", "rm", file)
+                continue
+            # manual resolutions
+            # XXX: this functionality is mostly subsumed by the rerere
+            # tricks we do

             if file in self.resolutions:
                 contents = open(file, "r").read()
                 for spec, result in self.resolutions[file]:
             if file in self.resolutions:
                 contents = open(file, "r").read()
                 for spec, result in self.resolutions[file]:


@@ -150,7 +314,7 @@ class Application(object):
                         logging.info("Did resolution with spec:\n" + spec)
                 open(file, "w").write(contents)
                 if not resolve.is_conflict(contents):
                         logging.info("Did resolution with spec:\n" + spec)
                 open(file, "w").write(contents)
                 if not resolve.is_conflict(contents):

-                    sh.call("git", "add", file)
+                    shell.call("git", "add", file)

                 else:
                     resolved = False
             else:
                 else:
                     resolved = False
             else:


@@ -175,7 +339,7 @@ class Application(object):
         """
         for key, subst in self.substitutions.items():
             subs = subst(deployment)
         """
         for key, subst in self.substitutions.items():
             subs = subst(deployment)

-            if not subs and key not in self.deprecated_keys:
+            if not subs and key not in self.deprecated_keys and key not in self.random_keys:

                 logging.warning("No substitutions for %s" % key)
     def install(self, version, options):
         """
                 logging.warning("No substitutions for %s" % key)
     def install(self, version, options):
         """


@@ -185,7 +349,7 @@ class Application(object):
         take a :class:`wizard.deploy.Deployment` as a parameter.)  Subclasses should
         provide an implementation.
         """
         take a :class:`wizard.deploy.Deployment` as a parameter.)  Subclasses should
         provide an implementation.
         """

-        raise NotImplemented
+        raise NotImplementedError

     def upgrade(self, deployment, version, options):
         """
         Run for 'wizard upgrade' to upgrade database schemas and other
     def upgrade(self, deployment, version, options):
         """
         Run for 'wizard upgrade' to upgrade database schemas and other


@@ -193,7 +357,7 @@ class Application(object):
         upgraded.  This assumes that the current working directory is the
         deployment.  Subclasses should provide an implementation.
         """
         upgraded.  This assumes that the current working directory is the
         deployment.  Subclasses should provide an implementation.
         """

-        raise NotImplemented
+        raise NotImplementedError

     def backup(self, deployment, outdir, options):
         """
         Run for 'wizard backup' and upgrades to backup database schemas
     def backup(self, deployment, outdir, options):
         """
         Run for 'wizard backup' and upgrades to backup database schemas


@@ -206,7 +370,7 @@ class Application(object):
             Static user files may not need to be backed up, since in
             many applications upgrades do not modify static files.
         """
             Static user files may not need to be backed up, since in
             many applications upgrades do not modify static files.
         """

-        raise NotImplemented
+        raise NotImplementedError

     def restore(self, deployment, backup_dir, options):
         """
         Run for 'wizard restore' and failed upgrades to restore database
     def restore(self, deployment, backup_dir, options):
         """
         Run for 'wizard restore' and failed upgrades to restore database


@@ -214,21 +378,55 @@ class Application(object):
         that the current working directory is the deployment.  Subclasses
         should provide an implementation.
         """
         that the current working directory is the deployment.  Subclasses
         should provide an implementation.
         """

-        raise NotImplemented
+        raise NotImplementedError
+    def remove(self, deployment, options):
+        """
+        Run for 'wizard remove' to delete all database and non-local
+        file data.  This assumes that the current working directory is
+        the deployment.  Subclasses should provide an implementation.
+        """
+        raise NotImplementedError

     def detectVersion(self, deployment):
         """
         Checks source files to determine the version manually.  This assumes
         that the current working directory is the deployment.  Subclasses
         should provide an implementation.
         """
     def detectVersion(self, deployment):
         """
         Checks source files to determine the version manually.  This assumes
         that the current working directory is the deployment.  Subclasses
         should provide an implementation.
         """

-        raise NotImplemented
-    def checkWeb(self, deployment, output=None):
+        raise NotImplementedError
+    def detectVersionFromFile(self, filename, regex):

         """
         """

-        Checks if the autoinstall is viewable from the web.  To get
-        the HTML source that was retrieved, pass a variable containing
-        an empty list to ``output``; it will be mutated to have its
-        first element be the output.  Subclasses should provide an
-        implementation.
+        Helper method that detects a version by using a regular expression
+        from a file.  The regexed value is passed through :mod:`shlex`.
+        This assumes that the current working directory is the deployment.
+        """
+        contents = open(filename).read()
+        match = regex.search(contents)
+        if not match: return None
+        return distutils.version.LooseVersion(shlex.split(match.group(2))[0])
+    # XXX: This signature doesn't really make too much sense...
+    def detectVersionFromGit(self, tagPattern, preStrip = ''):
+        """
+        Helper method that detects a version by using the most recent tag
+        in git that matches the specified pattern.
+        This assumes that the current working directory is the deployment.
+        """
+        sh = wizard.shell.Shell()
+        cmd = ['git', 'describe', '--tags', '--match', tagPattern, ]
+        tag = sh.call(*cmd, strip=True)
+        if tag and len(tag) > len(preStrip) and tag[:len(preStrip)] == preStrip:
+            tag = tag[len(preStrip):]
+        if not tag: return None
+        return distutils.version.LooseVersion(tag)
+    def download(self, version):
+        """
+        Returns a URL that can be used to download a tarball of ``version`` of
+        this application.
+        """
+        raise NotImplementedError
+    def checkWeb(self, deployment):
+        """
+        Checks if the autoinstall is viewable from the web.  Subclasses should
+        provide an implementation.

 
         .. note::
             Finding a reasonable heuristic that works across skinning
 
         .. note::
             Finding a reasonable heuristic that works across skinning


@@ -237,7 +435,34 @@ class Application(object):
             page does not contain the features you search for.  Try
             not to depend on pages that are not the main page.
         """
             page does not contain the features you search for.  Try
             not to depend on pages that are not the main page.
         """

-        raise NotImplemented
+        raise NotImplementedError
+    def checkDatabase(self, deployment):
+        """
+        Checks if the database is accessible.
+        """
+        try:
+            sql.connect(deployment.dsn)
+            return True
+        except sqlalchemy.exc.DBAPIError:
+            return False
+    def checkWebPage(self, deployment, page, outputs=[], exclude=[]):
+        """
+        Checks if a given page of an autoinstall contains a particular string.
+        """
+        page = deployment.fetch(page)
+        for x in exclude:
+            if page.find(x) != -1:
+                logging.info("checkWebPage (failed due to %s):\n\n%s", x, page)
+                return False
+        votes = 0
+        for output in outputs:
+            votes += page.find(output) != -1
+        if votes > len(outputs) / 2:
+            logging.debug("checkWebPage (passed):\n\n" + page)
+            return True
+        else:
+            logging.info("checkWebPage (failed):\n\n" + page)
+            return False

     def checkConfig(self, deployment):
         """
         Checks whether or not an autoinstall has been configured/installed
     def checkConfig(self, deployment):
         """
         Checks whether or not an autoinstall has been configured/installed


@@ -245,17 +470,26 @@ class Application(object):
         Subclasses should provide an implementation.
         """
         # XXX: Unfortunately, this doesn't quite work because we package
         Subclasses should provide an implementation.
         """
         # XXX: Unfortunately, this doesn't quite work because we package

-        # bogus config files in the -scripts versions of installs.  Maybe
-        # we should check a hash or something?
-        raise NotImplemented
-    @staticmethod
-    def make(name):
-        """Makes an application, but uses the correct subtype if available."""
-        try:
-            __import__("wizard.app." + name)
-            return getattr(wizard.app, name).Application(name)
-        except ImportError:
-            return Application(name)
+        # bogus config files.  Maybe we should check a hash or
+        # something?
+        raise NotImplementedError
+    def researchFilter(self, filename, added, deleted):
+        """
+        Allows an application to selectively ignore certain diffstat signatures
+        during research; for example, configuration files will have a very
+        specific set of changes, so ignore them; certain installation files
+        may be removed, etc.  Return ``True`` if a diffstat signature should be
+        ignored,
+        """
+        return False
+    def researchVerbose(self, filename):
+        """
+        Allows an application to exclude certain dirty files from the output
+        report; usually this will just be parametrized files, since those are
+        guaranteed to have changes.  Return ``True`` if a file should only
+        be displayed in verbose mode.
+        """
+        return filename in self.parametrized_files

 
 class ApplicationVersion(object):
     """Represents an abstract notion of a version for an application, where
 
 class ApplicationVersion(object):
     """Represents an abstract notion of a version for an application, where


@@ -276,10 +510,11 @@ class ApplicationVersion(object):
         """
         return "%s-%s" % (self.application, self.version)
     @property
         """
         return "%s-%s" % (self.application, self.version)
     @property

-    def scripts_tag(self):
+    def wizard_tag(self):

         """
         Returns the name of the Git tag for this version.
         """
         """
         Returns the name of the Git tag for this version.
         """

+        # XXX: Scripts specific

         end = str(self.version).partition('-scripts')[2].partition('-')[0]
         return "%s-scripts%s" % (self.pristine_tag, end)
     @property
         end = str(self.version).partition('-scripts')[2].partition('-')[0]
         return "%s-scripts%s" % (self.pristine_tag, end)
     @property


@@ -329,12 +564,9 @@ class ApplicationVersion(object):
         Makes/retrieves a singleton :class:`ApplicationVersion` from
         a``app`` and ``version`` string.
         """
         Makes/retrieves a singleton :class:`ApplicationVersion` from
         a``app`` and ``version`` string.
         """

-        try:
-            # defer to the application for version creation to enforce
-            # singletons
-            return applications()[app].makeVersion(version)
-        except KeyError:
-            raise NoSuchApplication(app)
+        # defer to the application for version creation to enforce
+        # singletons
+        return getApplication(app).makeVersion(version)

 
 def expand_re(val):
     """
 
 def expand_re(val):
     """


@@ -355,7 +587,7 @@ def expand_re(val):
 
 def make_extractors(seed):
     """
 
 def make_extractors(seed):
     """

-    Take a dictionary of ``key``s to ``(file, regex)`` tuples and convert them into
+    Take a dictionary of ``key`` to ``(file, regex)`` tuples and convert them into

     extractor functions (which take a :class:`wizard.deploy.Deployment`
     and return the value of the second subpattern of ``regex`` when matched
     with the contents of ``file``).
     extractor functions (which take a :class:`wizard.deploy.Deployment`
     and return the value of the second subpattern of ``regex`` when matched
     with the contents of ``file``).


@@ -364,7 +596,7 @@ def make_extractors(seed):
 
 def make_substitutions(seed):
     """
 
 def make_substitutions(seed):
     """

-    Take a dictionary of ``key``s to ``(file, regex)`` tuples and convert them into substitution
+    Take a dictionary of ``key`` to ``(file, regex)`` tuples and convert them into substitution

     functions (which take a :class:`wizard.deploy.Deployment`, replace the second subpattern
     of ``regex`` with ``key`` in ``file``, and returns the number of substitutions made.)
     """
     functions (which take a :class:`wizard.deploy.Deployment`, replace the second subpattern
     of ``regex`` with ``key`` in ``file``, and returns the number of substitutions made.)
     """


@@ -464,53 +696,24 @@ def filename_regex_substitution(key, files, regex):
         return subs
     return h
 
         return subs
     return h
 

-# XXX: rename to show that it's mysql specific
-def backup_database(outdir, deployment):
+@decorator.decorator
+def throws_database_errors(f, self, *args, **kwargs):

     """
     """

-    Generic database backup function for MySQL.  Assumes that ``WIZARD_DBNAME``
-    is extractable, and that :func:`wizard.scripts.get_sql_credentials`
-    works.
+    Decorator that takes database errors from :mod:`wizard.sql` and
+    converts them into application script failures from
+    :mod:`wizard.app`.  We can't throw application errors directly from
+    :mod:`wizard.sql` because that would result in a cyclic import;
+    also, it's cleaner to distinguish between a database error and an
+    application script failure.

     """
     """

-    sh = shell.Shell()
-    outfile = os.path.join(outdir, "db.sql")

     try:
     try:

-        sh.call("mysqldump", "--compress", "-r", outfile, *get_mysql_args(deployment))
-        sh.call("gzip", "--best", outfile)
-    except shell.CallError as e:
-        shutil.rmtree(outdir)
-        raise BackupFailure(e.stderr)
-
-def restore_database(backup_dir, deployment):
-    """
-    Generic database restoration function for MySQL.  See :func:`backup_database`
-    for the assumptions that we make.
-    """
-    sh = shell.Shell()
-    if not os.path.exists(backup_dir):
-        raise RestoreFailure("Backup %s doesn't exist", backup_dir.rpartition("/")[2])
-    sql = open(os.path.join(backup_dir, "db.sql"), 'w+')
-    sh.call("gunzip", "-c", os.path.join(backup_dir, "db.sql.gz"), stdout=sql)
-    sql.seek(0)
-    sh.call("mysql", *get_mysql_args(deployment), stdin=sql)
-    sql.close()
-
-def get_mysql_args(d):
-    """
-    Extracts arguments that would be passed to the command line mysql utility
-    from a deployment.
-    """
-    # XXX: add support for getting these out of options
-    vars = d.extract()
-    if 'WIZARD_DBNAME' not in vars:
-        raise app.BackupFailure("Could not determine database name")
-    triplet = scripts.get_sql_credentials(vars)
-    args = []
-    if triplet is not None:
-        server, user, password = triplet
-        args += ["-h", server, "-u", user, "-p" + password]
-    name = shlex.split(vars['WIZARD_DBNAME'])[0]
-    args.append(name)
-    return args
+        return f(self, *args, **kwargs)
+    except sql.BackupDatabaseError:
+        raise BackupFailure(traceback.format_exc())
+    except sql.RestoreDatabaseError:
+        raise RestoreFailure(traceback.format_exc())
+    except sql.RemoveDatabaseError:
+        raise RemoveFailure(traceback.format_exc())

 
 class Error(wizard.Error):
     """Generic error class for this module."""
 
 class Error(wizard.Error):
     """Generic error class for this module."""


@@ -539,6 +742,8 @@ class DeploymentParseError(Error):
     location = None
     def __init__(self, value):
         self.value = value
     location = None
     def __init__(self, value):
         self.value = value

+    def __str__(self):
+        return "Could not parse '%s' from versions store in '%s'" % (self.value, self.location)

 
 class NoSuchApplication(Error):
     """
 
 class NoSuchApplication(Error):
     """


@@ -552,8 +757,45 @@ class NoSuchApplication(Error):
     location = None
     def __init__(self, app):
         self.app = app
     location = None
     def __init__(self, app):
         self.app = app

+    def __str__(self):
+        return "Wizard doesn't know about an application named '%s'." % self.app
+
+class Failure(Error):
+    """
+    Represents a failure when performing some double-dispatched operation
+    such as an installation or an upgrade.  Failure classes are postfixed
+    with Failure, not Error.
+    """
+    pass
+
+class InstallFailure(Error):
+    """Installation failed for unknown reason."""
+    def __str__(self):
+        return """

 
 

-class UpgradeFailure(Error):
+ERROR: Installation failed for unknown reason.  You can
+retry the installation by appending --retry to the installation
+command."""
+
+class RecoverableInstallFailure(InstallFailure):
+    """
+    Installation failed, but we were able to determine what the
+    error was, and should give the user a second chance if we were
+    running interactively.
+    """
+    #: List of the errors that were found.
+    errors = None
+    def __init__(self, errors):
+        self.errors = errors
+    def __str__(self):
+        return """
+
+ERROR: Installation failed due to the following errors:  %s
+
+You can retry the installation by appending --retry to the
+installation command.""" % ", ".join(self.errors)
+
+class UpgradeFailure(Failure):

     """Upgrade script failed."""
     #: String details of failure (possibly stdout or stderr output)
     details = None
     """Upgrade script failed."""
     #: String details of failure (possibly stdout or stderr output)
     details = None


@@ -566,21 +808,29 @@ ERROR: Upgrade script failed, details:
 
 %s""" % self.details
 
 
 %s""" % self.details
 

-class UpgradeVerificationFailure(Error):
+class UpgradeVerificationFailure(Failure):

     """Upgrade script passed, but website wasn't accessible afterwards"""
     """Upgrade script passed, but website wasn't accessible afterwards"""

-    #: String details of failure (possibly stdout or stderr output)
+    def __str__(self):
+        return """
+
+ERROR: Upgrade script passed, but website wasn't accessible afterwards.  Check
+the debug logs for the contents of the page."""
+
+class BackupFailure(Failure):
+    """Backup script failed."""
+    #: String details of failure

     details = None
     def __init__(self, details):
         self.details = details
     def __str__(self):
         return """
 
     details = None
     def __init__(self, details):
         self.details = details
     def __str__(self):
         return """
 

-ERROR: Upgrade script passed, but website wasn't accessible afterwards. Details:
+ERROR: Backup script failed, details:

 
 %s""" % self.details
 
 
 %s""" % self.details
 

-class BackupFailure(Error):
-    """Backup script failed."""
+class RestoreFailure(Failure):
+    """Restore script failed."""

     #: String details of failure
     details = None
     def __init__(self, details):
     #: String details of failure
     details = None
     def __init__(self, details):


@@ -588,12 +838,12 @@ class BackupFailure(Error):
     def __str__(self):
         return """
 
     def __str__(self):
         return """
 

-ERROR: Backup script failed, details:
+ERROR: Restore script failed, details:

 
 %s""" % self.details
 
 
 %s""" % self.details
 

-class RestoreFailure(Error):
-    """Restore script failed."""
+class RemoveFailure(Failure):
+    """Remove script failed."""

     #: String details of failure
     details = None
     def __init__(self, details):
     #: String details of failure
     details = None
     def __init__(self, details):


@@ -601,6 +851,6 @@ class RestoreFailure(Error):
     def __str__(self):
         return """
 
     def __str__(self):
         return """
 

-ERROR: Restore script failed, details:
+ERROR: Remove script failed, details:

 
 %s""" % self.details
 
 %s""" % self.details