Improve messages when helpers cannot be installed. Fixes #57

CHANGELOG.rst

@@ -10,6 +10,10 @@ This project adheres to `Semantic Versioning`_.
 
 - Support for Python 3.6
 
+**Fixed**
+
+- Improved messaging when COT is unable to install a helper program (`#57`_).
+
 `1.8.2`_ - 2017-01-18
 ---------------------
 
@@ -601,6 +605,7 @@ Initial public release.
 .. _#52: https://github.com/glennmatthews/cot/issues/52
 .. _#53: https://github.com/glennmatthews/cot/issues/53
 .. _#54: https://github.com/glennmatthews/cot/issues/54
+.. _#57: https://github.com/glennmatthews/cot/issues/57
 .. _#58: https://github.com/glennmatthews/cot/issues/58
 .. _#59: https://github.com/glennmatthews/cot/issues/59
 

COT/helpers/fatdisk.py

@@ -3,7 +3,7 @@
 # fatdisk.py - Helper for 'fatdisk'
 #
 # February 2015, Glenn F. Matthews
-# Copyright (c) 2013-2016 the COT project developers.
+# Copyright (c) 2013-2017 the COT project developers.
 # See the COPYRIGHT.txt file at the top-level directory of this distribution
 # and at https://github.com/glennmatthews/cot/blob/master/COPYRIGHT.txt.
 #
@@ -54,7 +54,7 @@ def _install(self):
             helpers['port'].install_package('fatdisk')
             return
         elif platform.system() != 'Linux':
-            self.unsure_how_to_install()
+            raise self.unsure_how_to_install()
 
         # Fatdisk installation requires make
         helpers['make'].install()

COT/helpers/helper.py

@@ -3,7 +3,7 @@
 # helper.py - Abstract provider of a non-Python helper program.
 #
 # February 2015, Glenn F. Matthews
-# Copyright (c) 2015-2016 the COT project developers.
+# Copyright (c) 2015-2017 the COT project developers.
 # See the COPYRIGHT.txt file at the top-level directory of this distribution
 # and at https://github.com/glennmatthews/cot/blob/master/COPYRIGHT.txt.
 #
@@ -51,6 +51,7 @@
 import os.path
 import contextlib
 import errno
+import platform
 import re
 import shutil
 import subprocess
@@ -324,7 +325,7 @@ def install(self):
         if self.installed:
             return
         if not self.installable:
-            self.unsure_how_to_install()
+            raise self.unsure_how_to_install()
         logger.info("Installing '%s'...", self.name)
         # Call the subclass implementation
         self._install()
@@ -338,11 +339,27 @@ def install(self):
         logger.info("Successfully installed '%s'", self.name)
 
     def unsure_how_to_install(self):
-        """Raise a NotImplementedError about missing install logic."""
+        """Return a RuntimeError or NotImplementedError for install trouble."""
         msg = "Unsure how to install {0}.".format(self.name)
         if self.info_uri:
             msg += "\nRefer to {0} for information".format(self.info_uri)
-        raise NotImplementedError(msg)
+
+        if platform.system() == 'Darwin' and (
+                'port' in self._provider_package and not helpers['port']):
+            msg += ("\nCOT can use MacPorts (https://www.macports.org/),"
+                    " if available on your system, to install {0} and other"
+                    " helpers for you.".format(self.name))
+            return RuntimeError(msg)
+        elif platform.system() == 'Linux' and (
+                ('apt-get' in self._provider_package or
+                 'yum' in self._provider_package) and
+                not (helpers['apt-get'] or helpers['yum'])):
+            msg += ("\nCOT can use package managers 'yum' or 'apt-get' to"
+                    " install helpers on your system, but it appears that"
+                    " you have neither of these package managers?")
+            return RuntimeError(msg)
+        else:
+            return NotImplementedError(msg)
 
     def _install(self):
         """Subclass-specific implementation of installation logic."""
@@ -352,7 +369,7 @@ def _install(self):
                 helpers[pm_name].install_package(package)
                 return
         # We shouldn't get here under normal call flow and logic.
-        self.unsure_how_to_install()
+        raise self.unsure_how_to_install()
 
     @staticmethod
     @contextlib.contextmanager
@@ -602,7 +619,7 @@ def helper_select(choices):
     Returns:
       Helper: The selected helper class instance.
     """
-    for choice in choices:
+    def _name_min_ver_from_choice(choice):
         if isinstance(choice, str):
             # Helper name only, no version constraints
             name = choice
@@ -611,21 +628,27 @@ def helper_select(choices):
             # Tuple of (name, version)
             (name, vers) = choice
             min_version = StrictVersion(vers)
+
+        return (name, min_version)
+
+    for choice in choices:
+        name, min_version = _name_min_ver_from_choice(choice)
         if helpers[name]:
             if min_version is None or helpers[name].version >= min_version:
                 return helpers[name]
 
     # OK, nothing yet installed. So what can we install?
     for choice in choices:
-        if isinstance(choice, str):
-            name = choice
-            min_version = None
-        else:
-            (name, vers) = choice
-            min_version = StrictVersion(vers)
+        name, min_version = _name_min_ver_from_choice(choice)
         if helpers[name].installable:
             helpers[name].install()
             if min_version is None or helpers[name].version >= min_version:
                 return helpers[name]
 
-    raise HelperNotFoundError("No helper available or installable!")
+    msg = "No helper in list {0} is available or installable!".format(choices)
+
+    for choice in choices:
+        name, _ = _name_min_ver_from_choice(choice)
+        msg += "\n" + str(helpers[name].unsure_how_to_install())
+
+    raise HelperNotFoundError(msg)

COT/helpers/ovftool.py

@@ -3,7 +3,7 @@
 # ovftool.py - Helper for 'ovftool'
 #
 # February 2015, Glenn F. Matthews
-# Copyright (c) 2013-2016 the COT project developers.
+# Copyright (c) 2013-2017 the COT project developers.
 # See the COPYRIGHT.txt file at the top-level directory of this distribution
 # and at https://github.com/glennmatthews/cot/blob/master/COPYRIGHT.txt.
 #
@@ -41,12 +41,12 @@ def installable(self):
         return False
 
     def unsure_how_to_install(self):
-        """Raise a NotImplementedError about missing install logic.
+        """Return a NotImplementedError about missing install logic.
 
         We override the default install implementation to raise a more
         detailed error message for ovftool.
         """
-        raise NotImplementedError(
+        return NotImplementedError(
             "No support for automated installation of ovftool, as VMware "
             "requires a site login to download it. See "
             "https://www.vmware.com/support/developer/ovf/"

COT/helpers/vmdktool.py

@@ -3,7 +3,7 @@
 # vmdktool.py - Helper for 'vmdktool'
 #
 # February 2015, Glenn F. Matthews
-# Copyright (c) 2013-2016 the COT project developers.
+# Copyright (c) 2013-2017 the COT project developers.
 # See the COPYRIGHT.txt file at the top-level directory of this distribution
 # and at https://github.com/glennmatthews/cot/blob/master/COPYRIGHT.txt.
 #
@@ -54,7 +54,7 @@ def _install(self):
             helpers['port'].install_package('vmdktool')
             return
         elif platform.system() != 'Linux':
-            self.unsure_how_to_install()
+            raise self.unsure_how_to_install()
 
         # We don't have vmdktool in apt or yum yet,
         # but we can build it manually: