Preserve comments for Spack YAML objects (#11602)

This updates the configuration loading/dumping logic (now called
load_config/dump_config) in spack_yaml to preserve comments (by using
ruamel.yaml's RoundTripLoader). This has two effects:

* environment spack.yaml files expect to retain comments, which
  load_config now supports. By using load_config, users can now use the
  ':' override syntax that was previously unavailable for environment
  configs (but was available for other config files).

* config files now retain user comments by default (although in cases
  where Spack updates/overwrites config, the comments can still be
  removed).

Details:

* Subclasses `RoundTripLoader`/`RoundTripDumper` to parse yaml into
  ruamel's `CommentedMap` and analogous data structures

* Applies filename info directly to ruamel objects in cases where the
  updated loader returns those

* Copies management of sections in `SingleFileScope` from #10651 to allow
  overrides to occur

* Updates the loader/dumper to handle the processing of overrides by
  specifically checking for the `:` character
  * Possibly the most controversial aspect, but without that, the parsed
    objects have to be reconstructed (i.e. as was done in
    `mark_overrides`). It is possible that `mark_overrides` could remain
    and a deep copy will not cause problems, but IMO that's generally
    worth avoiding.
  * This is also possibly controversial because Spack YAML strings can
    include `:`. My reckoning is that this only occurs for version
    specifications, so it is safe to check for `endswith(':') and not
    ('@' in string)`
  * As a consequence, this PR ends up reserving spack yaml functions
    load_config/dump_config exclusively for the purpose of storing spack
    config

13 files changed, 171 insertions, 178 deletions

diff --git a/lib/spack/spack/binary_distribution.py b/lib/spack/spack/binary_distribution.py
index aab07b8a84..eafa1dcdb1 100644
--- a/lib/spack/spack/binary_distribution.py
+++ b/lib/spack/spack/binary_distribution.py
@@ -11,6 +11,7 @@ import shutil
 import tempfile
 import hashlib
 from contextlib import closing
+import ruamel.yaml as yaml
 
 import json
 
@@ -139,7 +140,7 @@ def read_buildinfo_file(prefix):
     filename = buildinfo_file_name(prefix)
     with open(filename, 'r') as inputfile:
         content = inputfile.read()
-        buildinfo = syaml.load(content)
+        buildinfo = yaml.load(content)
     return buildinfo
 
 
@@ -380,10 +381,9 @@ def build_tarball(spec, outdir, force=False, rel=False, unsigned=False,
     checksum = checksum_tarball(tarfile_path)
 
     # add sha256 checksum to spec.yaml
-    spec_dict = {}
     with open(spec_file, 'r') as inputfile:
         content = inputfile.read()
-        spec_dict = syaml.load(content)
+        spec_dict = yaml.load(content)
     bchecksum = {}
     bchecksum['hash_algorithm'] = 'sha256'
     bchecksum['hash'] = checksum
diff --git a/lib/spack/spack/cmd/release_jobs.py b/lib/spack/spack/cmd/release_jobs.py
index 65ba42053d..c5acc4ee2d 100644
--- a/lib/spack/spack/cmd/release_jobs.py
+++ b/lib/spack/spack/cmd/release_jobs.py
@@ -655,4 +655,4 @@ def release_jobs(parser, args):
     output_object['stages'] = stage_names
 
     with open(args.output_file, 'w') as outf:
-        outf.write(syaml.dump(output_object))
+        outf.write(syaml.dump_config(output_object, default_flow_style=True))
diff --git a/lib/spack/spack/config.py b/lib/spack/spack/config.py
index 1af8ad757b..3f536f3793 100644
--- a/lib/spack/spack/config.py
+++ b/lib/spack/spack/config.py
@@ -36,7 +36,6 @@ import re
 import sys
 import multiprocessing
 from contextlib import contextmanager
-from six import string_types
 from six import iteritems
 from ordereddict_backport import OrderedDict
 
@@ -155,7 +154,7 @@ class ConfigScope(object):
             mkdirp(self.path)
             with open(filename, 'w') as f:
                 validate(data, section_schemas[section])
-                syaml.dump(data, stream=f, default_flow_style=False)
+                syaml.dump_config(data, stream=f, default_flow_style=False)
         except (yaml.YAMLError, IOError) as e:
             raise ConfigFileError(
                 "Error writing to config file: '%s'" % str(e))
@@ -200,6 +199,22 @@ class SingleFileScope(ConfigScope):
         #      ... data ...
         #   },
         # }
+        #
+        # To preserve overrides up to the section level (e.g. to override
+        # the "packages" section with the "::" syntax), data in self.sections
+        # looks like this:
+        # {
+        #   'config': {
+        #      'config': {
+        #         ... data ...
+        #       }
+        #   },
+        #   'packages': {
+        #      'packages': {
+        #         ... data ...
+        #      }
+        #   }
+        # }
         if self._raw_data is None:
             self._raw_data = _read_config_file(self.path, self.schema)
             if self._raw_data is None:
@@ -215,29 +230,10 @@ class SingleFileScope(ConfigScope):
 
                 self._raw_data = self._raw_data[key]
 
-        # data in self.sections looks (awkwardly) like this:
-        # {
-        #   'config': {
-        #      'config': {
-        #         ... data ...
-        #       }
-        #   },
-        #   'packages': {
-        #      'packages': {
-        #         ... data ...
-        #      }
-        #   }
-        # }
-        #
-        # UNLESS there is no section, in which case it is stored as:
-        # {
-        #   'config': None,
-        #   ...
-        # }
-        value = self._raw_data.get(section)
-        self.sections.setdefault(
-            section, None if value is None else {section: value})
-        return self.sections[section]
+            for section_key, data in self._raw_data.items():
+                self.sections[section_key] = {section_key: data}
+
+        return self.sections.get(section, None)
 
     def write_section(self, section):
         validate(self.sections, self.schema)
@@ -247,7 +243,8 @@ class SingleFileScope(ConfigScope):
 
             tmp = os.path.join(parent, '.%s.tmp' % self.path)
             with open(tmp, 'w') as f:
-                syaml.dump(self.sections, stream=f, default_flow_style=False)
+                syaml.dump_config(self.sections, stream=f,
+                                  default_flow_style=False)
             os.path.move(tmp, self.path)
         except (yaml.YAMLError, IOError) as e:
             raise ConfigFileError(
@@ -533,7 +530,7 @@ class Configuration(object):
         try:
             data = syaml.syaml_dict()
             data[section] = self.get_config(section)
-            syaml.dump(
+            syaml.dump_config(
                 data, stream=sys.stdout, default_flow_style=False, blame=blame)
         except (yaml.YAMLError, IOError):
             raise ConfigError("Error reading configuration: %s" % section)
@@ -708,7 +705,7 @@ def _read_config_file(filename, schema):
     try:
         tty.debug("Reading config file %s" % filename)
         with open(filename) as f:
-            data = _mark_overrides(syaml.load(f))
+            data = syaml.load_config(f)
 
         if data:
             validate(data, schema)
@@ -734,23 +731,6 @@ def _override(string):
     return hasattr(string, 'override') and string.override
 
 
-def _mark_overrides(data):
-    if isinstance(data, list):
-        return syaml.syaml_list(_mark_overrides(elt) for elt in data)
-
-    elif isinstance(data, dict):
-        marked = syaml.syaml_dict()
-        for key, val in iteritems(data):
-            if isinstance(key, string_types) and key.endswith(':'):
-                key = syaml.syaml_str(key[:-1])
-                key.override = True
-            marked[key] = _mark_overrides(val)
-        return marked
-
-    else:
-        return data
-
-
 def _mark_internal(data, name):
     """Add a simple name mark to raw YAML/JSON data.
 
@@ -820,9 +800,14 @@ def _merge_yaml(dest, source):
 
         # ensure that keys are marked in the destination.  the key_marks dict
         # ensures we can get the actual source key objects from dest keys
-        for dk in dest.keys():
-            if dk in key_marks:
+        for dk in list(dest.keys()):
+            if dk in key_marks and syaml.markable(dk):
                 syaml.mark(dk, key_marks[dk])
+            elif dk in key_marks:
+                # The destination key may not be markable if it was derived
+                # from a schema default. In this case replace the key.
+                val = dest.pop(dk)
+                dest[key_marks[dk]] = val
 
         return dest
 
diff --git a/lib/spack/spack/environment.py b/lib/spack/spack/environment.py
index 5204f7d288..b6b1814819 100644
--- a/lib/spack/spack/environment.py
+++ b/lib/spack/spack/environment.py
@@ -11,7 +11,6 @@ import shutil
 import copy
 import socket
 
-import ruamel.yaml
 import six
 
 from ordereddict_backport import OrderedDict
@@ -27,6 +26,7 @@ import spack.repo
 import spack.schema.env
 import spack.spec
 import spack.util.spack_json as sjson
+import spack.util.spack_yaml as syaml
 import spack.config
 import spack.build_environment as build_env
 
@@ -401,7 +401,7 @@ def validate(data, filename=None):
 
 def _read_yaml(str_or_file):
     """Read YAML from a file for round-trip parsing."""
-    data = ruamel.yaml.load(str_or_file, ruamel.yaml.RoundTripLoader)
+    data = syaml.load_config(str_or_file)
     filename = getattr(str_or_file, 'name', None)
     validate(data, filename)
     return data
@@ -411,8 +411,7 @@ def _write_yaml(data, str_or_file):
     """Write YAML to a file preserving comments and dict order."""
     filename = getattr(str_or_file, 'name', None)
     validate(data, filename)
-    ruamel.yaml.dump(data, str_or_file, Dumper=ruamel.yaml.RoundTripDumper,
-                     default_flow_style=False)
+    syaml.dump_config(data, str_or_file, default_flow_style=False)
 
 
 def _eval_conditional(string):
diff --git a/lib/spack/spack/filesystem_view.py b/lib/spack/spack/filesystem_view.py
index 417466cd83..448254f26b 100644
--- a/lib/spack/spack/filesystem_view.py
+++ b/lib/spack/spack/filesystem_view.py
@@ -211,7 +211,7 @@ class YamlFilesystemView(FilesystemView):
         if self.projections:
             mkdirp(os.path.dirname(self.projections_path))
             with open(self.projections_path, 'w') as f:
-                f.write(s_yaml.dump({'projections': self.projections}))
+                f.write(s_yaml.dump_config({'projections': self.projections}))
 
     def read_projections(self):
         if os.path.exists(self.projections_path):
diff --git a/lib/spack/spack/hooks/yaml_version_check.py b/lib/spack/spack/hooks/yaml_version_check.py
index 76ebceab79..ff8be58481 100644
--- a/lib/spack/spack/hooks/yaml_version_check.py
+++ b/lib/spack/spack/hooks/yaml_version_check.py
@@ -24,7 +24,7 @@ def check_compiler_yaml_version():
         data = None
         if os.path.isfile(file_name):
             with open(file_name) as f:
-                data = syaml.load(f)
+                data = syaml.load_config(f)
 
         if data:
             compilers = data.get('compilers')
diff --git a/lib/spack/spack/modules/common.py b/lib/spack/spack/modules/common.py
index d38ede1385..434d09c125 100644
--- a/lib/spack/spack/modules/common.py
+++ b/lib/spack/spack/modules/common.py
@@ -235,7 +235,7 @@ def generate_module_index(root, modules):
     index_path = os.path.join(root, 'module-index.yaml')
     llnl.util.filesystem.mkdirp(root)
     with open(index_path, 'w') as index_file:
-        syaml.dump(index, index_file, default_flow_style=False)
+        syaml.dump(index, default_flow_style=False, stream=index_file)
 
 
 def _generate_upstream_module_index():
diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index 1a6cc5f6bd..cb4942b157 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -79,7 +79,6 @@ expansion when it is the first character in an id typed on the command line.
 import base64
 import sys
 import collections
-import ctypes
 import hashlib
 import itertools
 import os
@@ -88,6 +87,7 @@ import re
 import six
 
 from operator import attrgetter
+import ruamel.yaml as yaml
 
 from llnl.util.filesystem import find_headers, find_libraries, is_exe
 from llnl.util.lang import key_ordering, HashableMap, ObjectWrapper, dedupe
@@ -185,9 +185,6 @@ _separators = '[\\%s]' % '\\'.join(color_formats.keys())
 #: every time we call str()
 _any_version = VersionList([':'])
 
-#: Max integer helps avoid passing too large a value to cyaml.
-maxint = 2 ** (ctypes.sizeof(ctypes.c_int) * 8 - 1) - 1
-
 default_format = '{name}{@version}'
 default_format += '{%compiler.name}{@compiler.version}{compiler_flags}'
 default_format += '{variants}{arch=architecture}'
@@ -1366,8 +1363,8 @@ class Spec(object):
         """
         # TODO: curently we strip build dependencies by default.  Rethink
         # this when we move to using package hashing on all specs.
-        yaml_text = syaml.dump(self.to_node_dict(hash=hash),
-                               default_flow_style=True, width=maxint)
+        yaml_text = syaml.dump(
+            self.to_node_dict(hash=hash), default_flow_style=True)
         sha = hashlib.sha1(yaml_text.encode('utf-8'))
         b32_hash = base64.b32encode(sha.digest()).lower()
 
@@ -1937,7 +1934,7 @@ class Spec(object):
         stream -- string or file object to read from.
         """
         try:
-            data = syaml.load(stream)
+            data = yaml.load(stream)
             return Spec.from_dict(data)
         except MarkedYAMLError as e:
             raise syaml.SpackYAMLError("error parsing YAML spec:", str(e))
diff --git a/lib/spack/spack/test/cmd/release_jobs.py b/lib/spack/spack/test/cmd/release_jobs.py
index c4f44308d9..0dbe8c5d5c 100644
--- a/lib/spack/spack/test/cmd/release_jobs.py
+++ b/lib/spack/spack/test/cmd/release_jobs.py
@@ -5,6 +5,7 @@
 
 import os
 import pytest
+import re
 
 import spack
 import spack.environment as ev
@@ -122,6 +123,6 @@ spack:
             release_jobs('--output-file', outputfile)
 
         with open(outputfile) as f:
-            contents = f.read()
+            contents = f.read().replace(os.linesep, '')
             assert('archive-files' in contents)
-            assert('stages: [stage-0' in contents)
+            assert(re.search(r'stages:\s*\[\s*stage-0', contents))
diff --git a/lib/spack/spack/test/concretize_preferences.py b/lib/spack/spack/test/concretize_preferences.py
index 5563bad75b..e5fa4a851d 100644
--- a/lib/spack/spack/test/concretize_preferences.py
+++ b/lib/spack/spack/test/concretize_preferences.py
@@ -29,7 +29,7 @@ def concretize_scope(config, tmpdir):
 
 @pytest.fixture()
 def configure_permissions():
-    conf = syaml.load("""\
+    conf = syaml.load_config("""\
 all:
   permissions:
     read: group
@@ -182,9 +182,9 @@ class TestConcretizePreferences(object):
         """Verify that virtuals are not allowed in packages.yaml."""
 
         # set up a packages.yaml file with a vdep as a key.  We use
-        # syaml.load here to make sure source lines in the config are
+        # syaml.load_config here to make sure source lines in the config are
         # attached to parsed strings, as the error message uses them.
-        conf = syaml.load("""\
+        conf = syaml.load_config("""\
 mpi:
     paths:
       mpi-with-lapack@2.1: /path/to/lapack
@@ -197,7 +197,7 @@ mpi:
 
     def test_all_is_not_a_virtual(self):
         """Verify that `all` is allowed in packages.yaml."""
-        conf = syaml.load("""\
+        conf = syaml.load_config("""\
 all:
         variants: [+mpi]
 """)
@@ -214,7 +214,7 @@ all:
         assert not spec['mpi'].external
 
         # load config
-        conf = syaml.load("""\
+        conf = syaml.load_config("""\
 all:
     providers:
         mpi: [mpich]
diff --git a/lib/spack/spack/test/config.py b/lib/spack/spack/test/config.py
index 3b85bb2a23..605c37d468 100644
--- a/lib/spack/spack/test/config.py
+++ b/lib/spack/spack/test/config.py
@@ -12,7 +12,6 @@ from six import StringIO
 from llnl.util.filesystem import touch, mkdirp
 
 import pytest
-import ruamel.yaml as yaml
 
 import spack.paths
 import spack.config
@@ -57,7 +56,7 @@ def write_config_file(tmpdir):
         config_yaml = tmpdir.join(scope, config + '.yaml')
         config_yaml.ensure()
         with config_yaml.open('w') as f:
-            yaml.dump(data, f)
+            syaml.dump_config(data, f)
     return _write
 
 
@@ -721,10 +720,44 @@ env:
             '/x/y/z', '$spack/var/spack/repos/builtin']
 
 
+def test_single_file_scope_section_override(tmpdir, config):
+    """Check that individual config sections can be overridden in an
+    environment config. The config here primarily differs in that the
+    ``packages`` section is intended to override all other scopes (using the
+    "::" syntax).
+    """
+    env_yaml = str(tmpdir.join("env.yaml"))
+    with open(env_yaml, 'w') as f:
+        f.write("""\
+env:
+    config:
+        verify_ssl: False
+    packages::
+        libelf:
+            compiler: [ 'gcc@4.5.3' ]
+    repos:
+        - /x/y/z
+""")
+
+    scope = spack.config.SingleFileScope(
+        'env', env_yaml, spack.schema.env.schema, ['env'])
+
+    with spack.config.override(scope):
+        # from the single-file config
+        assert spack.config.get('config:verify_ssl') is False
+        assert spack.config.get('packages:libelf:compiler') == ['gcc@4.5.3']
+
+        # from the lower config scopes
+        assert spack.config.get('config:checksum') is True
+        assert not spack.config.get('packages:externalmodule')
+        assert spack.config.get('repos') == [
+            '/x/y/z', '$spack/var/spack/repos/builtin']
+
+
 def check_schema(name, file_contents):
     """Check a Spack YAML schema against some data"""
     f = StringIO(file_contents)
-    data = syaml.load(f)
+    data = syaml.load_config(f)
     spack.config.validate(data, name)
 
 
diff --git a/lib/spack/spack/test/spack_yaml.py b/lib/spack/spack/test/spack_yaml.py
index 41a7c0e015..2166d294e9 100644
--- a/lib/spack/spack/test/spack_yaml.py
+++ b/lib/spack/spack/test/spack_yaml.py
@@ -27,7 +27,7 @@ config_file:
     [ 1, 2, 3 ]
   some_key: some_string
 """
-    return syaml.load(test_file)
+    return syaml.load_config(test_file)
 
 
 def test_parse(data):
diff --git a/lib/spack/spack/util/spack_yaml.py b/lib/spack/spack/util/spack_yaml.py
index f08be5fdb5..c4910be8bd 100644
--- a/lib/spack/spack/util/spack_yaml.py
+++ b/lib/spack/spack/util/spack_yaml.py
@@ -12,13 +12,14 @@
   default unorderd dict.
 
 """
+import ctypes
+
+
 from ordereddict_backport import OrderedDict
 from six import string_types, StringIO
 
 import ruamel.yaml as yaml
-from ruamel.yaml import Loader, Dumper
-from ruamel.yaml.nodes import MappingNode, SequenceNode, ScalarNode
-from ruamel.yaml.constructor import ConstructorError
+from ruamel.yaml import RoundTripLoader, RoundTripDumper
 
 from llnl.util.tty.color import colorize, clen, cextra
 
@@ -58,6 +59,11 @@ syaml_types = {
 }
 
 
+markable_types = set(syaml_types) | set([
+    yaml.comments.CommentedSeq,
+    yaml.comments.CommentedMap])
+
+
 def syaml_type(obj):
     """Get the corresponding syaml wrapper type for a primitive type.
 
@@ -72,19 +78,15 @@ def syaml_type(obj):
 
 def markable(obj):
     """Whether an object can be marked."""
-    return type(obj) in syaml_types
+    return type(obj) in markable_types
 
 
 def mark(obj, node):
     """Add start and end markers to an object."""
-    if not markable(obj):
-        return
-
     if hasattr(node, 'start_mark'):
         obj._start_mark = node.start_mark
     elif hasattr(node, '_start_mark'):
         obj._start_mark = node._start_mark
-
     if hasattr(node, 'end_mark'):
         obj._end_mark = node.end_mark
     elif hasattr(node, '_end_mark'):
@@ -97,8 +99,11 @@ def marked(obj):
             hasattr(obj, '_end_mark') and obj._end_mark)
 
 
-class OrderedLineLoader(Loader):
-    """YAML loader that preserves order and line numbers.
+class OrderedLineLoader(RoundTripLoader):
+    """YAML loader specifically intended for reading Spack configuration
+       files. It preserves order and line numbers. It also has special-purpose
+       logic for handling dictionary keys that indicate a Spack config
+       override: namely any key that contains an "extra" ':' character.
 
        Mappings read in by this loader behave like an ordered dict.
        Sequences, mappings, and strings also have new attributes,
@@ -107,74 +112,46 @@ class OrderedLineLoader(Loader):
 
     """
     #
-    # Override construct_yaml_* so that they build our derived types,
-    # which allows us to add new attributes to them.
+    # Override construct_yaml_* so that we can apply _start_mark/_end_mark to
+    # them. The superclass returns CommentedMap/CommentedSeq objects that we
+    # can add attributes to (and we depend on their behavior to preserve
+    # comments).
     #
-    # The standard YAML constructors return empty instances and fill
-    # in with mappings later.  We preserve this behavior.
+    # The inherited sequence/dictionary constructors return empty instances
+    # and fill in with mappings later.  We preserve this behavior.
     #
 
     def construct_yaml_str(self, node):
-        value = self.construct_scalar(node)
-        value = syaml_str(value)
+        value = super(OrderedLineLoader, self).construct_yaml_str(node)
+        # There is no specific marker to indicate that we are parsing a key,
+        # so this assumes we are talking about a Spack config override key if
+        # it ends with a ':' and does not contain a '@' (which can appear
+        # in config values that refer to Spack specs)
+        if value and value.endswith(':') and '@' not in value:
+            value = syaml_str(value[:-1])
+            value.override = True
+        else:
+            value = syaml_str(value)
         mark(value, node)
         return value
 
     def construct_yaml_seq(self, node):
-        data = syaml_list()
-        mark(data, node)
+        gen = super(OrderedLineLoader, self).construct_yaml_seq(node)
+        data = next(gen)
+        if markable(data):
+            mark(data, node)
         yield data
-        data.extend(self.construct_sequence(node))
+        for x in gen:
+            pass
 
     def construct_yaml_map(self, node):
-        data = syaml_dict()
-        mark(data, node)
+        gen = super(OrderedLineLoader, self).construct_yaml_map(node)
+        data = next(gen)
+        if markable(data):
+            mark(data, node)
         yield data
-        value = self.construct_mapping(node)
-        data.update(value)
-
-    #
-    # Override the ``construct_*`` routines. These fill in empty
-    # objects after yielded by the above ``construct_yaml_*`` methods.
-    #
-    def construct_sequence(self, node, deep=False):
-        if not isinstance(node, SequenceNode):
-            raise ConstructorError(
-                None, None,
-                "expected a sequence node, but found %s" % node.id,
-                node.start_mark)
-        value = syaml_list(self.construct_object(child, deep=deep)
-                           for child in node.value)
-        mark(value, node)
-        return value
-
-    def construct_mapping(self, node, deep=False):
-        """Store mappings as OrderedDicts instead of as regular python
-           dictionaries to preserve file ordering."""
-        if not isinstance(node, MappingNode):
-            raise ConstructorError(
-                None, None,
-                "expected a mapping node, but found %s" % node.id,
-                node.start_mark)
-
-        mapping = syaml_dict()
-        for key_node, value_node in node.value:
-            key = self.construct_object(key_node, deep=deep)
-            try:
-                hash(key)
-            except TypeError as exc:
-                raise ConstructorError(
-                    "while constructing a mapping", node.start_mark,
-                    "found unacceptable key (%s)" % exc, key_node.start_mark)
-            value = self.construct_object(value_node, deep=deep)
-            if key in mapping:
-                raise ConstructorError(
-                    "while constructing a mapping", node.start_mark,
-                    "found already in-use key (%s)" % key, key_node.start_mark)
-            mapping[key] = value
-
-        mark(mapping, node)
-        return mapping
+        for x in gen:
+            pass
 
 
 # register above new constructors
@@ -186,7 +163,7 @@ OrderedLineLoader.add_constructor(
     'tag:yaml.org,2002:str', OrderedLineLoader.construct_yaml_str)
 
 
-class OrderedLineDumper(Dumper):
+class OrderedLineDumper(RoundTripDumper):
     """Dumper that preserves ordering and formats ``syaml_*`` objects.
 
       This dumper preserves insertion ordering ``syaml_dict`` objects
@@ -196,41 +173,15 @@ class OrderedLineDumper(Dumper):
 
     """
 
-    def represent_mapping(self, tag, mapping, flow_style=None):
-        value = []
-        node = MappingNode(tag, value, flow_style=flow_style)
-        if self.alias_key is not None:
-            self.represented_objects[self.alias_key] = node
-        best_style = True
-        if hasattr(mapping, 'items'):
-            # if it's a syaml_dict, preserve OrderedDict order.
-            # Otherwise do the default thing.
-            sort = not isinstance(mapping, syaml_dict)
-            mapping = list(mapping.items())
-            if sort:
-                mapping.sort()
-
-        for item_key, item_value in mapping:
-            node_key = self.represent_data(item_key)
-            node_value = self.represent_data(item_value)
-            if not (isinstance(node_key, ScalarNode) and not node_key.style):
-                best_style = False
-            if not (isinstance(node_value, ScalarNode) and
-                    not node_value.style):
-                best_style = False
-            value.append((node_key, node_value))
-        if flow_style is None:
-            if self.default_flow_style is not None:
-                node.flow_style = self.default_flow_style
-            else:
-                node.flow_style = best_style
-
-        return node
-
     def ignore_aliases(self, _data):
         """Make the dumper NEVER print YAML aliases."""
         return True
 
+    def represent_str(self, data):
+        if hasattr(data, 'override') and data.override:
+            data = data + ':'
+        return super(OrderedLineDumper, self).represent_str(data)
+
 
 # Make our special objects look like normal YAML ones.
 OrderedLineDumper.add_representer(syaml_dict, OrderedLineDumper.represent_dict)
@@ -239,6 +190,28 @@ OrderedLineDumper.add_representer(syaml_str, OrderedLineDumper.represent_str)
 OrderedLineDumper.add_representer(syaml_int, OrderedLineDumper.represent_int)
 
 
+class SafeDumper(RoundTripDumper):
+
+    def ignore_aliases(self, _data):
+        """Make the dumper NEVER print YAML aliases."""
+        return True
+
+
+# Allow syaml_dict objects to be represented by ruamel.yaml.dump. With this,
+# syaml_dict allows a user to provide an ordered dictionary to yaml.dump when
+# the RoundTripDumper is used.
+RoundTripDumper.add_representer(syaml_dict, RoundTripDumper.represent_dict)
+
+
+#: Max integer helps avoid passing too large a value to cyaml.
+maxint = 2 ** (ctypes.sizeof(ctypes.c_int) * 8 - 1) - 1
+
+
+def dump(obj, default_flow_style=False, stream=None):
+    return yaml.dump(obj, default_flow_style=default_flow_style, width=maxint,
+                     Dumper=SafeDumper, stream=stream)
+
+
 def file_line(mark):
     """Format a mark as <file>:<line> information."""
     result = mark.name
@@ -288,7 +261,8 @@ class LineAnnotationDumper(OrderedLineDumper):
         result = super(LineAnnotationDumper, self).represent_data(data)
         if isinstance(result.value, string_types):
             result.value = syaml_str(data)
-        mark(result.value, data)
+        if markable(result.value):
+            mark(result.value, data)
         return result
 
     def write_stream_start(self):
@@ -319,14 +293,18 @@ class LineAnnotationDumper(OrderedLineDumper):
             _annotations.append('')
 
 
-def load(*args, **kwargs):
+def load_config(*args, **kwargs):
     """Load but modify the loader instance so that it will add __line__
-       atrributes to the returned object."""
+       attributes to the returned object."""
     kwargs['Loader'] = OrderedLineLoader
     return yaml.load(*args, **kwargs)
 
 
-def dump(*args, **kwargs):
+def load(*args, **kwargs):
+    return yaml.load(*args, **kwargs)
+
+
+def dump_config(*args, **kwargs):
     blame = kwargs.pop('blame', False)
 
     if blame: