1 files changed, 21 insertions, 11 deletions
diff --git a/rprt-engine/src/state.rs b/rprt-engine/src/state.rs
index 80b5e86..7ef5a19 100644
--- a/rprt-engine/src/state.rs
+++ b/rprt-engine/src/state.rs
@@ -4,6 +4,7 @@ use crate::{
 };
 use std::collections::{HashMap, HashSet};
 use std::path::PathBuf;
+use thiserror::Error;
 
 #[derive(Debug, Clone)]
 pub enum StateChange {
@@ -23,19 +24,19 @@ pub enum StateChange {
     },
 }
 
-#[derive(Debug, Clone)]
+#[derive(Error, Debug, Clone)]
 pub enum GroupedChangeError {
+    #[error("Changes for buffer ID {buffer} overlap in regions {first:#?} and {second:#?}")]
     OverlappingChanges {
         buffer: BufferID,
         first: (usize, usize),
         second: (usize, usize),
     },
-    BufferNotLive {
-        buffer: BufferID,
-    },
-    BufferAlreadyExists {
-        buffer: BufferID,
-    },
+    #[error("Buffer ID {buffer} does not exist at time of processing")]
+    BufferNotLive { buffer: BufferID },
+    #[error("Buffer ID {buffer} already exists at time of processing")]
+    BufferAlreadyExists { buffer: BufferID },
+    #[error("Inconsistent final buffer set")]
     InconsistentFinalBufferSet,
 }
 
@@ -154,14 +155,14 @@ impl EditorState {
         }
     }
 
-    pub fn commit_changes_grouped(
-        &mut self,
-        arms: Vec<Vec<StateChange>>,
+    pub fn validate_grouped_changes(
+        &self,
+        arms: &Vec<Vec<StateChange>>,
     ) -> Result<(), GroupedChangeError> {
         let initial_buffers: std::collections::HashSet<BufferID> =
             self.buffers.keys().copied().collect();
 
-        self.validate_arms_buffer_liveness(&arms, &initial_buffers)?;
+        self.validate_arms_buffer_liveness(arms, &initial_buffers)?;
 
         let all_modifications: Vec<&StateChange> = arms
             .iter()
@@ -171,6 +172,15 @@ impl EditorState {
 
         Self::validate_modifications(&all_modifications)?;
 
+        Ok(())
+    }
+
+    pub fn commit_changes_grouped(
+        &mut self,
+        arms: Vec<Vec<StateChange>>,
+    ) -> Result<(), GroupedChangeError> {
+        self.validate_grouped_changes(&arms)?;
+
         let all_changes: Vec<StateChange> = arms.into_iter().flatten().collect();
 
         let mut creates = Vec::new();