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diff --git a/src/data/sources/defaults.rs b/src/data/sources/defaults.rs
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+// This file is part of GAnarchy - decentralized development hub
+// Copyright (C) 2021  Soni L.
+// 
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+// 
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+//! Data source for compile-time defaults.
+
+use std::collections::BTreeSet;
+use std::error;
+use std::time::Duration;
+
+use impl_trait::impl_trait;
+
+use super::super::DataSource;
+use super::super::DataSourceBase;
+use super::super::effective::EffectiveKind;
+use super::super::kinds::{
+    InstanceBaseUrl,
+    InstanceTitle,
+    ProjectFork,
+    RepoListUrl,
+};
+
+/// Data source that provides compile-time defaults.
+///
+/// # Examples
+///
+/// Constructing a `DefaultsDataSource`:
+///
+/// ```rust
+/// use ganarchy::data::sources::DefaultsDataSource;
+///
+/// let x = DefaultsDataSource;
+/// # let _ = x;
+/// ```
+#[derive(Copy, Clone, Debug, Default)]
+pub struct DefaultsDataSource;
+
+impl_trait! {
+    impl DefaultsDataSource {
+        /// Always updates successfully, with an unknown refresh interval.
+        impl trait DataSourceBase {
+            fn update(&mut self) -> (
+                Option<Duration>,
+                Result<(), Box<dyn error::Error + Send + Sync + 'static>>,
+            ) {
+                (None, Ok(()))
+            }
+
+            fn exists(&self) -> bool {
+                true
+            }
+        }
+
+        impl trait std::fmt::Display {
+            fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+                write!(f, "compile-time defaults")
+            }
+        }
+
+        /// Default [`InstanceTitle`] source. Always `None`.
+        impl trait DataSource<InstanceTitle> {
+            fn get_values(&self) -> Option<InstanceTitle> {
+                None
+            }
+        }
+
+        /// Default [`InstanceBaseUrl`] source. Always `None`.
+        impl trait DataSource<InstanceBaseUrl> {
+            fn get_values(&self) -> Option<InstanceBaseUrl> {
+                None
+            }
+        }
+
+        /// Default [`RepoListUrl`] source.
+        impl trait DataSource<RepoListUrl> {
+            fn get_values(&self) -> Vec<RepoListUrl> {
+                // Forks may wish to add stuff here.
+                vec![
+                ]
+            }
+        }
+
+        /// Default [`ProjectFork`] source.
+        impl trait DataSource<EffectiveKind<ProjectFork>> {
+            fn get_values(&self) -> BTreeSet<EffectiveKind<ProjectFork>> {
+                // Forks may wish to add stuff here.
+                // In particular, as this DataSource is a kind of config,
+                // these override external repo lists (but not local config),
+                // including for setting certain repos to off.
+                vec![
+                ].into_iter().collect()
+            }
+        }
+    }
+}