perf: cache element interactivity and source line splitting (#17839)

## Summary

Two small compiler optimizations that reduce redundant work:

- **Cache `element_interactivity` per element in a11y checks**:
`check_element` was calling `element_interactivity()` up to 10 times per
element (via `is_interactive_element`, `is_non_interactive_element`,
`is_static_element` wrappers), each time re-iterating schema arrays. Now
computed once after building the attribute map and reused. The
now-unused wrapper functions are removed.

- **Split source lines once in `state.set_source`**: Every compiler
warning called `get_code_frame` which split the entire source string
with `source.split('\n')`. Now the split happens once in `set_source()`
and is exported as `state.source_lines`, naturally cleared by `reset()`.

## Benchmark

Synthetic component (80 state vars, 30 each blocks, ~1300 lines):

```
                    Min      Best3     Median
Before           66.55ms    67.03ms    73.44ms
After            61.14ms    61.90ms    70.63ms
Improvement        8.1%      7.7%      3.8%
```

Realistic component (~80 lines, ~25 elements, few warnings): **~1-4%**
improvement. The a11y cache scales with element count, the source.split
saving scales with warning count.

## Test plan

- [x] All 326 validator tests pass (includes all a11y tests)
- [x] All 5671 runtime tests pass
- [x] 145 compiler-error tests pass


🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

.changeset/calm-clouds-wave.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+perf: cache element interactivity and source line splitting in compiler

packages/svelte/src/compiler/phases/2-analyze/visitors/shared/a11y/index.js

@@ -100,6 +100,11 @@ export function check_element(node, context) {
 		}
 	}
 
+	const interactivity = element_interactivity(node.name, attribute_map);
+	const is_interactive = interactivity === ElementInteractivity.Interactive;
+	const is_non_interactive = interactivity === ElementInteractivity.NonInteractive;
+	const is_static = interactivity === ElementInteractivity.Static;
+
 	for (const attribute of node.attributes) {
 		if (attribute.type !== 'Attribute') continue;
 
@@ -133,7 +138,7 @@ export function check_element(node, context) {
 			if (
 				name === 'aria-activedescendant' &&
 				!is_dynamic_element &&
-				!is_interactive_element(node.name, attribute_map) &&
+				!is_interactive &&
 				!attribute_map.has('tabindex') &&
 				!has_spread
 			) {
@@ -215,7 +220,7 @@ export function check_element(node, context) {
 						!is_hidden_from_screen_reader(node.name, attribute_map) &&
 						!is_presentation_role(current_role) &&
 						is_interactive_roles(current_role) &&
-						is_static_element(node.name, attribute_map) &&
+						is_static &&
 						!attribute_map.get('tabindex')
 					) {
 						const has_interactive_handlers = [...handlers].some((handler) =>
@@ -229,7 +234,7 @@ export function check_element(node, context) {
 					// no-interactive-element-to-noninteractive-role
 					if (
 						!has_spread &&
-						is_interactive_element(node.name, attribute_map) &&
+						is_interactive &&
 						(is_non_interactive_roles(current_role) || is_presentation_role(current_role))
 					) {
 						w.a11y_no_interactive_element_to_noninteractive_role(node, node.name, current_role);
@@ -238,7 +243,7 @@ export function check_element(node, context) {
 					// no-noninteractive-element-to-interactive-role
 					if (
 						!has_spread &&
-						is_non_interactive_element(node.name, attribute_map) &&
+						is_non_interactive &&
 						is_interactive_roles(current_role) &&
 						!a11y_non_interactive_element_to_interactive_role_exceptions[node.name]?.includes(
 							current_role
@@ -291,7 +296,7 @@ export function check_element(node, context) {
 			!is_dynamic_element &&
 			!is_hidden_from_screen_reader(node.name, attribute_map) &&
 			(!role || is_non_presentation_role) &&
-			!is_interactive_element(node.name, attribute_map) &&
+			!is_interactive &&
 			!has_spread
 		) {
 			const has_key_event =
@@ -307,11 +312,7 @@ export function check_element(node, context) {
 	);
 
 	// no-noninteractive-tabindex
-	if (
-		!is_dynamic_element &&
-		!is_interactive_element(node.name, attribute_map) &&
-		!is_interactive_roles(role_static_value)
-	) {
+	if (!is_dynamic_element && !is_interactive && !is_interactive_roles(role_static_value)) {
 		const tab_index = attribute_map.get('tabindex');
 		const tab_index_value = get_static_text_value(tab_index);
 		if (tab_index && (tab_index_value === null || Number(tab_index_value) >= 0)) {
@@ -341,9 +342,8 @@ export function check_element(node, context) {
 		!has_contenteditable_attr &&
 		!is_hidden_from_screen_reader(node.name, attribute_map) &&
 		!is_presentation_role(role_static_value) &&
-		((!is_interactive_element(node.name, attribute_map) &&
-			is_non_interactive_roles(role_static_value)) ||
-			(is_non_interactive_element(node.name, attribute_map) && !role))
+		((!is_interactive && is_non_interactive_roles(role_static_value)) ||
+			(is_non_interactive && !role))
 	) {
 		const has_interactive_handlers = [...handlers].some((handler) =>
 			a11y_recommended_interactive_handlers.includes(handler)
@@ -359,9 +359,9 @@ export function check_element(node, context) {
 		(!role || role_static_value !== null) &&
 		!is_hidden_from_screen_reader(node.name, attribute_map) &&
 		!is_presentation_role(role_static_value) &&
-		!is_interactive_element(node.name, attribute_map) &&
+		!is_interactive &&
 		!is_interactive_roles(role_static_value) &&
-		!is_non_interactive_element(node.name, attribute_map) &&
+		!is_non_interactive &&
 		!is_non_interactive_roles(role_static_value) &&
 		!is_abstract_role(role_static_value)
 	) {
@@ -643,33 +643,6 @@ function element_interactivity(tag_name, attribute_map) {
 	return ElementInteractivity.Static;
 }
 
-/**
- * @param {string} tag_name
- * @param {Map<string, AST.Attribute>} attribute_map
- * @returns {boolean}
- */
-function is_interactive_element(tag_name, attribute_map) {
-	return element_interactivity(tag_name, attribute_map) === ElementInteractivity.Interactive;
-}
-
-/**
- * @param {string} tag_name
- * @param {Map<string, AST.Attribute>} attribute_map
- * @returns {boolean}
- */
-function is_non_interactive_element(tag_name, attribute_map) {
-	return element_interactivity(tag_name, attribute_map) === ElementInteractivity.NonInteractive;
-}
-
-/**
- * @param {string} tag_name
- * @param {Map<string, AST.Attribute>} attribute_map
- * @returns {boolean}
- */
-function is_static_element(tag_name, attribute_map) {
-	return element_interactivity(tag_name, attribute_map) === ElementInteractivity.Static;
-}
-
 /**
  * @param {ARIARoleDefinitionKey} role
  * @param {string} tag_name

packages/svelte/src/compiler/state.js

@@ -32,6 +32,12 @@ export let component_name = '<unknown>';
  */
 export let source;
 
+/**
+ * The source code split into lines (set by `set_source`)
+ * @type {string[]}
+ */
+export let source_lines = [];
+
 /**
  * True if compiling with `dev: true`
  * @type {boolean}
@@ -46,6 +52,7 @@ export let locator;
 /** @param {string} value */
 export function set_source(value) {
 	source = value;
+	source_lines = source.split('\n');
 
 	const l = getLocator(source, { offsetLine: 1 });
 
@@ -134,6 +141,7 @@ export function reset(state) {
 	runes = false;
 	component_name = UNKNOWN_FILENAME;
 	source = '';
+	source_lines = [];
 	filename = (state.filename ?? UNKNOWN_FILENAME).replace(/\\/g, '/');
 	warning_filter = state.warning ?? (() => true);
 	warnings = [];

packages/svelte/src/compiler/utils/compile_diagnostic.js

@@ -11,12 +11,11 @@ function tabs_to_spaces(str) {
 }
 
 /**
- * @param {string} source
  * @param {number} line
  * @param {number} column
  */
-function get_code_frame(source, line, column) {
-	const lines = source.split('\n');
+function get_code_frame(line, column) {
+	const lines = state.source_lines;
 	const frame_start = Math.max(0, line - 2);
 	const frame_end = Math.min(line + 3, lines.length);
 	const digits = String(frame_end + 1).length;
@@ -70,7 +69,7 @@ export class CompileDiagnostic {
 			this.start = state.locator(position[0]);
 			this.end = state.locator(position[1]);
 			if (this.start && this.end) {
-				this.frame = get_code_frame(state.source, this.start.line - 1, this.end.column);
+				this.frame = get_code_frame(this.start.line - 1, this.end.column);
 			}
 		}
 	}