implement distinct attribute

distinct can return error

facet distinct on numbers

return distinct error

review fixes

make get_facet_value more generic

fixes

milli/src/search/distinct/mod.rs

@@ -0,0 +1,21 @@
+mod facet_distinct;
+mod map_distinct;
+mod noop_distinct;
+
+use roaring::RoaringBitmap;
+
+pub use facet_distinct::FacetDistinct;
+pub use map_distinct::MapDistinct;
+pub use noop_distinct::NoopDistinct;
+use crate::DocumentId;
+
+pub trait DocIter: Iterator<Item=anyhow::Result<DocumentId>> {
+    /// Returns ownership on the internal RoaringBitmaps: (candidates, excluded)
+    fn into_excluded(self) -> RoaringBitmap;
+}
+
+pub trait Distinct<'a> {
+    type Iter: DocIter;
+
+    fn distinct(&'a mut self, candidates: RoaringBitmap, excluded: RoaringBitmap) -> Self::Iter;
+}