editor: Fix SelectionsCollection::disjoint not being ordered correctly (#40249)

We've been seeing the occasional `cannot seek backwards` panic within
`SelectionsCollection` without means to reproduce.

I believe the cause is one of the callers of
`MutableSelectionsCollection::select` not passing a well formed
`Selection` where `start > end`, so this PR enforces the invariant in
`select` by swapping the fields and setting `reversed` as required as
the other mutator functions already do that as well.

We could also just assert this instead, but it callers usually won't
care about this so its the less user facing annoyance to just fix this
invariant up internally.

Fixes ZED-253
Fixes ZED-ZJ
Fixes ZED-23S
Fixes ZED-222
Fixes ZED-1ZV
Fixes ZED-1SN
Fixes ZED-1Z0
Fixes ZED-10E
Fixes ZED-1X0
Fixes ZED-12M
Fixes ZED-1GR
Fixes ZED-1VE
Fixes ZED-13X
Fixes ZED-1G4

Release Notes:

- Fixed occasional panics when querying selections

Author: Veykril

crates/editor/src/selections_collection.rs

@@ -610,21 +610,32 @@ impl<'a> MutableSelectionsCollection<'a> {
         self.select(selections);
     }
 
-    pub fn select<T>(&mut self, mut selections: Vec<Selection<T>>)
+    pub fn select<T>(&mut self, selections: Vec<Selection<T>>)
     where
-        T: ToOffset + ToPoint + Ord + std::marker::Copy + std::fmt::Debug,
+        T: ToOffset + std::marker::Copy + std::fmt::Debug,
     {
         let buffer = self.buffer.read(self.cx).snapshot(self.cx);
+        let mut selections = selections
+            .into_iter()
+            .map(|selection| selection.map(|it| it.to_offset(&buffer)))
+            .map(|mut selection| {
+                if selection.start > selection.end {
+                    mem::swap(&mut selection.start, &mut selection.end);
+                    selection.reversed = true
+                }
+                selection
+            })
+            .collect::<Vec<_>>();
         selections.sort_unstable_by_key(|s| s.start);
         // Merge overlapping selections.
         let mut i = 1;
         while i < selections.len() {
-            if selections[i - 1].end >= selections[i].start {
+            if selections[i].start <= selections[i - 1].end {
                 let removed = selections.remove(i);
                 if removed.start < selections[i - 1].start {
                     selections[i - 1].start = removed.start;
                 }
-                if removed.end > selections[i - 1].end {
+                if selections[i - 1].end < removed.end {
                     selections[i - 1].end = removed.end;
                 }
             } else {
@@ -968,13 +979,10 @@ impl DerefMut for MutableSelectionsCollection<'_> {
     }
 }
 
-fn selection_to_anchor_selection<T>(
-    selection: Selection<T>,
+fn selection_to_anchor_selection(
+    selection: Selection<usize>,
     buffer: &MultiBufferSnapshot,
-) -> Selection<Anchor>
-where
-    T: ToOffset + Ord,
-{
+) -> Selection<Anchor> {
     let end_bias = if selection.start == selection.end {
         Bias::Right
     } else {
@@ -1012,7 +1020,7 @@ fn resolve_selections_point<'a>(
     })
 }
 
-// Panics if passed selections are not in order
+/// Panics if passed selections are not in order
 fn resolve_selections_display<'a>(
     selections: impl 'a + IntoIterator<Item = &'a Selection<Anchor>>,
     map: &'a DisplaySnapshot,
@@ -1044,7 +1052,7 @@ fn resolve_selections_display<'a>(
     coalesce_selections(selections)
 }
 
-// Panics if passed selections are not in order
+/// Panics if passed selections are not in order
 pub(crate) fn resolve_selections<'a, D, I>(
     selections: I,
     map: &'a DisplaySnapshot,