Handle broken resource mapping files (by throwing exceptions).

Testing Done:
Ran new tests locally.

CI is green: https://travis-ci.org/pantsbuild/pants/builds/57559852

Reviewed at https://rbcommons.com/s/twitter/r/2038/

src/python/pants/backend/jvm/tasks/jvm_compile/resource_mapping.py

@@ -14,6 +14,21 @@
 class ResourceMapping(object):
   RESOURCES_BY_CLASS_NAME_RE = re.compile(r'^(?P<classname>[\w+.\$]+) -> (?P<path>.+)$')
 
+  class ResourceMappingFormatException(Exception):
+    pass
+
+  class MissingItemsLineException(ResourceMappingFormatException):
+    pass
+
+  class TooLongFileException(ResourceMappingFormatException):
+    pass
+
+  class TruncatedFileException(ResourceMappingFormatException):
+    pass
+
+  class UnparseableLineException(ResourceMappingFormatException):
+    pass
+
   def __init__(self, classes_dir):
     self._classes_dir = classes_dir
     self._resource_mappings = None
@@ -24,7 +39,7 @@ def parse_items(line):
         n, items = line.split(" ")
         return int(n)
       except ValueError as error:
-        raise ValueError(dedent('''
+        raise self.MissingItemsLineException(dedent('''
           Unable to parse resource mappings.
           Expected "N items", got "{line}: {error}"'''.format(line=line, error=error)))
 
@@ -52,11 +67,19 @@ def parse_items(line):
         items_left -= 1
         match = ResourceMapping.RESOURCES_BY_CLASS_NAME_RE.match(line)
         if not match:
-          raise ValueError(dedent('''
+          raise self.UnparseableLineException(dedent('''
             Unable to parse resource mappings.
             Expected classname -> path, got "{line}"'''.format(line=line)))
         classname, path = match.group('classname'), match.group('path')
         mappings[classname].append(path)
+      else:
+        raise self.TooLongFileException('Unexpected line "{line}" in section {section}.'.format(
+          line=line, section=section))
+
+    if items_left:
+      raise self.TruncatedFileException(dedent('''
+        Unable to parse resource mappings.
+        Found EOF while still missing {items_left} lines'''.format(items_left=items_left)))
 
   @property
   def mappings(self):

tests/python/pants_test/backend/jvm/tasks/jvm_compile/BUILD

@@ -5,6 +5,7 @@ target(
   name='jvm_compile',
   dependencies=[
     ':jvm_fingerprint_strategy',
+    ':resource_mapping',
     ':zinc_utils',
     'tests/python/pants_test/backend/jvm/tasks/jvm_compile/java',
     'tests/python/pants_test/backend/jvm/tasks/jvm_compile/scala',
@@ -21,6 +22,16 @@ python_tests(
   ]
 )
 
+python_tests(
+  name = 'resource_mapping',
+  sources = ['test_resource_mapping.py'],
+  dependencies = [
+    'src/python/pants/backend/jvm/tasks/jvm_compile:resource_mapping',
+    'tests/python/pants_test:base_test',
+  ],
+  resources=rglobs('test-data/*'),
+)
+
 python_tests(
   name = 'zinc_utils',
   sources = ['test_zinc_utils.py'],

tests/python/pants_test/backend/jvm/tasks/jvm_compile/test-data/resource_mapping-broken-long/META-INF/compiler/resource-mappings/org.pantsbuild.example.ExampleProcessor

@@ -0,0 +1,6 @@
+resources by class name:
+1 items
+org.pantsbuild.example.Morx -> /home/user/project/.pants.d/compile/jvm/java/classes/org/pantsbuild/example/resource1.txt
+#comment
+org.pantsbuild.example.Fleem -> /home/user/project/.pants.d/compile/jvm/java/classes/org/pantsbuild/example/resource1.txt
+#comment

tests/python/pants_test/backend/jvm/tasks/jvm_compile/test-data/resource_mapping-broken-mangled/META-INF/compiler/resource-mappings/org.pantsbuild.example.ExampleProcessor

@@ -0,0 +1,4 @@
+resources by class name:
+2 items
+org.pantsbuild.example.Morx -> /home/user/project/.pants.d/compile/jvm/java/classes/org/pantsbuild/example/resource1.txt
+org.pantsbuild.example.Fleem NO CARRIER

tests/python/pants_test/backend/jvm/tasks/jvm_compile/test-data/resource_mapping-broken-missing-items/META-INF/compiler/resource-mappings/org.pantsbuild.example.ExampleProcessor

@@ -0,0 +1,6 @@
+resources by class name:
+nonsense
+org.pantsbuild.example.Morx -> /home/user/project/.pants.d/compile/jvm/java/classes/org/pantsbuild/example/resource1.txt
+#comment
+org.pantsbuild.example.Fleem -> /home/user/project/.pants.d/compile/jvm/java/classes/org/pantsbuild/example/resource1.txt
+#comment

tests/python/pants_test/backend/jvm/tasks/jvm_compile/test-data/resource_mapping-broken-short/META-INF/compiler/resource-mappings/org.pantsbuild.example.ExampleProcessor

@@ -0,0 +1,4 @@
+resources by class name:
+2 items
+org.pantsbuild.example.Morx -> /home/user/project/.pants.d/compile/jvm/java/classes/org/pantsbuild/example/resource1.txt
+#comment

tests/python/pants_test/backend/jvm/tasks/jvm_compile/test-data/resource_mapping/META-INF/compiler/resource-mappings/org.pantsbuild.example.ExampleProcessor

@@ -0,0 +1,6 @@
+resources by class name:
+2 items
+org.pantsbuild.example.Morx -> /home/user/project/.pants.d/compile/jvm/java/classes/org/pantsbuild/example/resource1.txt
+#comment
+org.pantsbuild.example.Fleem -> /home/user/project/.pants.d/compile/jvm/java/classes/org/pantsbuild/example/resource1.txt
+#comment

tests/python/pants_test/backend/jvm/tasks/jvm_compile/test_resource_mapping.py

@@ -0,0 +1,48 @@
+# coding=utf-8
+# Copyright 2014 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+from __future__ import (absolute_import, division, generators, nested_scopes, print_function,
+                        unicode_literals, with_statement)
+
+import os
+
+from pants.backend.jvm.tasks.jvm_compile.resource_mapping import ResourceMapping
+from pants_test.base_test import BaseTest
+
+
+class ResourceMappingTest(BaseTest):
+  def test_resource_mapping_ok(self):
+    rel_dir = 'tests/python/pants_test/backend/jvm/tasks/jvm_compile/test-data/resource_mapping'
+    resource_mapping = ResourceMapping(rel_dir)
+
+    self.assertEquals(2, len(resource_mapping.mappings))
+
+  def test_resource_mapping_short(self):
+    rel_dir = 'tests/python/pants_test/backend/jvm/tasks/jvm_compile/test-data/resource_mapping-broken-short'
+    resource_mapping = ResourceMapping(rel_dir)
+
+    with self.assertRaises(ResourceMapping.TruncatedFileException):
+      resource_mapping.mappings
+
+  def test_resource_mapping_long(self):
+    rel_dir = 'tests/python/pants_test/backend/jvm/tasks/jvm_compile/test-data/resource_mapping-broken-long'
+    resource_mapping = ResourceMapping(rel_dir)
+
+    with self.assertRaises(ResourceMapping.TooLongFileException):
+      resource_mapping.mappings
+
+  def test_resource_mapping_mangled(self):
+    rel_dir = 'tests/python/pants_test/backend/jvm/tasks/jvm_compile/test-data/resource_mapping-broken-mangled'
+    resource_mapping = ResourceMapping(rel_dir)
+
+    with self.assertRaises(ResourceMapping.UnparseableLineException):
+      resource_mapping.mappings
+
+
+  def test_resource_mapping_noitems(self):
+    rel_dir = 'tests/python/pants_test/backend/jvm/tasks/jvm_compile/test-data/resource_mapping-broken-missing-items'
+    resource_mapping = ResourceMapping(rel_dir)
+
+    with self.assertRaises(ResourceMapping.MissingItemsLineException):
+      resource_mapping.mappings