1 files changed, 85 insertions, 0 deletions
diff --git a/src/tools/rust-analyzer/crates/base-db/src/change.rs b/src/tools/rust-analyzer/crates/base-db/src/change.rs
new file mode 100644
index 000000000..b57f23457
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/base-db/src/change.rs
@@ -0,0 +1,85 @@
+//! Defines a unit of change that can applied to the database to get the next
+//! state. Changes are transactional.
+
+use std::{fmt, sync::Arc};
+
+use salsa::Durability;
+use vfs::FileId;
+
+use crate::{CrateGraph, SourceDatabaseExt, SourceRoot, SourceRootId};
+
+/// Encapsulate a bunch of raw `.set` calls on the database.
+#[derive(Default)]
+pub struct Change {
+    pub roots: Option<Vec<SourceRoot>>,
+    pub files_changed: Vec<(FileId, Option<Arc<String>>)>,
+    pub crate_graph: Option<CrateGraph>,
+}
+
+impl fmt::Debug for Change {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut d = fmt.debug_struct("Change");
+        if let Some(roots) = &self.roots {
+            d.field("roots", roots);
+        }
+        if !self.files_changed.is_empty() {
+            d.field("files_changed", &self.files_changed.len());
+        }
+        if self.crate_graph.is_some() {
+            d.field("crate_graph", &self.crate_graph);
+        }
+        d.finish()
+    }
+}
+
+impl Change {
+    pub fn new() -> Change {
+        Change::default()
+    }
+
+    pub fn set_roots(&mut self, roots: Vec<SourceRoot>) {
+        self.roots = Some(roots);
+    }
+
+    pub fn change_file(&mut self, file_id: FileId, new_text: Option<Arc<String>>) {
+        self.files_changed.push((file_id, new_text))
+    }
+
+    pub fn set_crate_graph(&mut self, graph: CrateGraph) {
+        self.crate_graph = Some(graph);
+    }
+
+    pub fn apply(self, db: &mut dyn SourceDatabaseExt) {
+        let _p = profile::span("RootDatabase::apply_change");
+        if let Some(roots) = self.roots {
+            for (idx, root) in roots.into_iter().enumerate() {
+                let root_id = SourceRootId(idx as u32);
+                let durability = durability(&root);
+                for file_id in root.iter() {
+                    db.set_file_source_root_with_durability(file_id, root_id, durability);
+                }
+                db.set_source_root_with_durability(root_id, Arc::new(root), durability);
+            }
+        }
+
+        for (file_id, text) in self.files_changed {
+            let source_root_id = db.file_source_root(file_id);
+            let source_root = db.source_root(source_root_id);
+            let durability = durability(&source_root);
+            // XXX: can't actually remove the file, just reset the text
+            let text = text.unwrap_or_default();
+            db.set_file_text_with_durability(file_id, text, durability)
+        }
+        if let Some(crate_graph) = self.crate_graph {
+            db.set_crate_graph_with_durability(Arc::new(crate_graph), Durability::HIGH)
+        }
+    }
+}
+
+fn durability(source_root: &SourceRoot) -> Durability {
+    if source_root.is_library {
+        Durability::HIGH
+    } else {
+        Durability::LOW
+    }
+}