From de620366d6a9e2d3d4397805750c00901c673e33 Mon Sep 17 00:00:00 2001
From: Wilfred Hughes <me@wilfred.me.uk>
Date: Sat, 29 Jun 2024 23:02:31 -0700
Subject: [PATCH] Use CanIgnore atom kind

---
 src/display/json.rs             |  1 +
 src/display/style.rs            |  2 +-
 src/parse/syntax.rs             | 15 +++++++++++++--
 src/parse/tree_sitter_parser.rs |  9 +++------
 4 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/src/display/json.rs b/src/display/json.rs
index 2dc867dee1..25dac1d715 100644
--- a/src/display/json.rs
+++ b/src/display/json.rs
@@ -267,6 +267,7 @@ impl Highlight {
                 AtomKind::Comment => Highlight::Comment,
                 AtomKind::Type => Highlight::Type,
                 AtomKind::Normal => Highlight::Normal,
+                AtomKind::CanIgnore => Highlight::Normal,
                 AtomKind::TreeSitterError => Highlight::TreeSitterError,
             },
         }
diff --git a/src/display/style.rs b/src/display/style.rs
index ff63c4da2b..ff55d0fde3 100644
--- a/src/display/style.rs
+++ b/src/display/style.rs
@@ -346,7 +346,7 @@ pub(crate) fn color_positions(
                                 style = style.bold();
                             }
                             AtomKind::TreeSitterError => style = style.purple(),
-                            AtomKind::Normal => {}
+                            AtomKind::Normal | AtomKind::CanIgnore => {}
                         }
                     }
                 }
diff --git a/src/parse/syntax.rs b/src/parse/syntax.rs
index bdde5934d5..901c10940c 100644
--- a/src/parse/syntax.rs
+++ b/src/parse/syntax.rs
@@ -391,8 +391,14 @@ fn set_content_id(nodes: &[&Syntax], existing: &mut DftHashMap<ContentKey, u32>)
                 // Recurse first, so children all have their content_id set.
                 set_content_id(children, existing);
 
-                let children_content_ids: Vec<_> =
-                    children.iter().map(|c| c.info().content_id.get()).collect();
+                let children_content_ids: Vec<_> = children
+                    .iter()
+                    .filter(|c| match c {
+                        List { .. } => true,
+                        Atom { kind, .. } => *kind != AtomKind::CanIgnore,
+                    })
+                    .map(|c| c.info().content_id.get())
+                    .collect();
 
                 (
                     Some(open_content.clone()),
@@ -579,6 +585,11 @@ pub(crate) enum AtomKind {
     Comment,
     Keyword,
     TreeSitterError,
+    /// Trailing commas can be ignored in some positions, such as the
+    /// last comma in `[1, 2,]` in JS. However, it's not obligatory,
+    /// and it's useful when diffing `[1,]` against `[1, 2]` to be
+    /// able to match up the commas.
+    CanIgnore,
 }
 
 /// Unlike atoms, tokens can be delimiters like `{`.
diff --git a/src/parse/tree_sitter_parser.rs b/src/parse/tree_sitter_parser.rs
index 5ae72535cd..6245338a7f 100644
--- a/src/parse/tree_sitter_parser.rs
+++ b/src/parse/tree_sitter_parser.rs
@@ -1875,15 +1875,12 @@ fn list_from_cursor<'a>(
     if should_ignore_last_child(config, &root_node, &between_delim) {
         if let Some(last_child) = between_delim.pop() {
             if let Syntax::Atom {
-                position,
-                content,
-                kind,
-                ..
+                position, content, ..
             } = last_child
             {
                 let position = position.clone();
-                // TODO: New unused kind for atoms.
-                let new_last_child = Syntax::new_atom(arena, position, content, *kind);
+                let new_last_child =
+                    Syntax::new_atom(arena, position, content, AtomKind::CanIgnore);
                 between_delim.push(new_last_child);
             }
         }