fix(format/html): format a Svelte array pattern that skips a position (#11194)

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
Co-authored-by: Emanuele Stoppa <my.burning@gmail.com>

Author: 3 people

.changeset/fix-svelte-array-pattern-hole.md

@@ -0,0 +1,12 @@
+---
+"@biomejs/biome": patch
+---
+
+Fixed the HTML formatter refusing to format a Svelte file containing an array pattern that skips a position:
+
+```svelte
+{#each animals as [, value]}
+	<p>{value}</p>
+{/each}
+```
+

crates/biome_html_formatter/src/svelte/lists/binding_assignment_binding_list.rs

@@ -15,21 +15,27 @@ impl FormatRule<SvelteBindingAssignmentBindingList> for FormatSvelteBindingAssig
         let mut join = f.join_nodes_with_space();
 
         for binding_assignment in node.elements() {
-            let node = binding_assignment.node()?;
             let separator = binding_assignment.trailing_separator()?;
 
-            join.entry(
-                node.syntax(),
-                &format_with(|f| {
-                    write!(f, [node.format()])?;
+            match binding_assignment.node() {
+                Ok(node) => join.entry(
+                    node.syntax(),
+                    &format_with(|f| {
+                        write!(f, [node.format()])?;
 
-                    if let Some(separator) = separator {
-                        write!(f, [separator.format()])?;
-                    }
+                        if let Some(separator) = separator {
+                            write!(f, [separator.format()])?;
+                        }
 
-                    Ok(())
-                }),
-            )
+                        Ok(())
+                    }),
+                ),
+                Err(error) => {
+                    let separator = separator.ok_or(error)?;
+                    let parent = separator.parent().ok_or(error)?;
+                    join.entry(&parent, &separator.format());
+                }
+            }
         }
 
         join.finish()

crates/biome_html_formatter/tests/specs/html/svelte/each_array_hole.svelte

@@ -0,0 +1,11 @@
+{#each animals as [, value]}
+	<p>{value}</p>
+{/each}
+
+{#each animals as [key, , value]}
+	<p>{key}: {value}</p>
+{/each}
+
+{#each animals as [key, value]}
+	<p>{key}: {value}</p>
+{/each}

crates/biome_html_formatter/tests/specs/html/svelte/each_array_hole.svelte.snap

@@ -0,0 +1,39 @@
+---
+source: crates/biome_formatter_test/src/snapshot_builder.rs
+info: svelte/each_array_hole.svelte
+---
+
+# Input
+
+```svelte
+{#each animals as [, value]}
+	<p>{value}</p>
+{/each}
+
+{#each animals as [key, , value]}
+	<p>{key}: {value}</p>
+{/each}
+
+{#each animals as [key, value]}
+	<p>{key}: {value}</p>
+{/each}
+
+```
+
+
+# Formatted
+
+```svelte
+{#each animals as [, value]}
+	<p>{value}</p>
+{/each}
+
+{#each animals as [key, , value]}
+	<p>{key}: {value}</p>
+{/each}
+
+{#each animals as [key, value]}
+	<p>{key}: {value}</p>
+{/each}
+
+```