Add a 'sources' field to project.conf to override defaults

Equivalent to the 'elements' field, but slightly different because
sources don't have accompanying yaml.

3 files changed, 56 insertions, 3 deletions

diff --git a/buildstream/_project.py b/buildstream/_project.py
index 6ff44b0a2..cb19b55e3 100644
--- a/buildstream/_project.py
+++ b/buildstream/_project.py
@@ -66,6 +66,7 @@ class Project():
         self._variables = {}     # The default variables overridden with project wide overrides
         self._environment = {}   # The base sandbox environment
         self._elements = {}      # Element specific configurations
+        self._sources = {}       # Source specific configurations
         self._aliases = {}       # Aliases dictionary
         self._workspaces = {}    # Workspaces
         self._plugin_source_origins = []   # Origins of custom sources
@@ -123,10 +124,13 @@ class Project():
         project_conf = _yaml.load(projectfile)
         _yaml.composite(config, project_conf)
 
-        # Element type configurations will be composited later onto element types,
-        # so we delete it from here and run our final assertion after.
+        # Element and Source  type configurations will be composited later onto
+        # element/source types, so we delete it from here and run our final
+        # assertion after.
         self._elements = _yaml.node_get(config, Mapping, 'elements', default_value={})
+        self._sources = _yaml.node_get(config, Mapping, 'sources', default_value={})
         config.pop('elements', None)
+        config.pop('sources', None)
         _yaml.node_final_assertions(config)
         _yaml.node_validate(config, [
             'format-version',
diff --git a/buildstream/source.py b/buildstream/source.py
index 590d0e262..d8c36ba99 100644
--- a/buildstream/source.py
+++ b/buildstream/source.py
@@ -23,6 +23,7 @@ Source
 """
 
 import os
+from collections import Mapping
 from contextlib import contextmanager
 
 from . import Plugin
@@ -74,6 +75,9 @@ class Source(Plugin):
     All Sources derive from this class, this interface defines how
     the core will be interacting with Sources.
     """
+    __defaults = {}          # The defaults from the project
+    __defaults_set = False   # Flag, in case there are not defaults at all
+
     def __init__(self, context, project, meta):
         provenance = _yaml.node_get_provenance(meta.config)
         super().__init__(meta.name, context, project, provenance, "source")
@@ -88,7 +92,11 @@ class Source(Plugin):
         self.__workspace = None                         # Directory of the currently active workspace
         self.__workspace_key = None                     # Cached directory content hashes for workspaced source
 
-        self.configure(meta.config)
+        # Collect the composited element configuration and
+        # ask the element to configure itself.
+        self.__init_defaults()
+        self.__config = self.__extract_config(meta)
+        self.configure(self.__config)
 
     COMMON_CONFIG_KEYS = ['kind', 'directory']
     """Common source config keys
@@ -97,6 +105,25 @@ class Source(Plugin):
     should be checked for using node_validate().
     """
 
+    def __init_defaults(self):
+        if not self.__defaults_set:
+            project = self._get_project()
+            sources = project._sources
+            type(self).__defaults = sources.get(self.get_kind(), {})
+            type(self).__defaults_set = True
+
+    # This will resolve the final configuration to be handed
+    # off to source.configure()
+    #
+    def __extract_config(self, meta):
+        config = _yaml.node_get(self.__defaults, Mapping, 'config', default_value={})
+        config = _yaml.node_chain_copy(config)
+
+        _yaml.composite(config, meta.config)
+        _yaml.node_final_assertions(config)
+
+        return config
+
     def get_mirror_directory(self):
         """Fetches the directory where this source should store things
 
diff --git a/doc/source/projectconf.rst b/doc/source/projectconf.rst
index ead949c6c..de19c9e84 100644
--- a/doc/source/projectconf.rst
+++ b/doc/source/projectconf.rst
@@ -503,6 +503,8 @@ be specified here.
        %{libdir}/lib*.la
 
 
+.. _project_element_overrides:
+
 Element Overrides
 ~~~~~~~~~~~~~~~~~
 Base attributes declared by element default yaml files can be overridden
@@ -527,6 +529,26 @@ variables, environments or plugin specific configuration data as shown below.
          PKG_CONFIG_PATH=%{libdir}/pkgconfig
 
 
+.. _project_source_overrides:
+
+Source Overrides
+~~~~~~~~~~~~~~~~
+Default values (overriding built-in defaults) can be set on a project
+wide basis. The sources dictionary can be used to override plugin specific
+configuration data as shown below.
+
+
+.. code:: yaml
+
+   sources:
+
+     # Override default values for all git sources
+     git:
+
+       config:
+         checkout-submodules: False
+
+
 .. _project_builtin_defaults:
 
 Builtin Defaults