chore: stricter control flow syntax validation in runes mode (#12342)

disallow characters between `{` and `#` / `:` / `@` in runes mode

closes #11975

.changeset/mighty-paws-smash.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: stricter control flow syntax validation in runes mode

packages/svelte/messages/compile-errors/template.md

@@ -88,6 +88,10 @@
 
 > Block was left open
 
+## block_unexpected_character
+
+> Expected a `%character%` character immediately following the opening bracket
+
 ## block_unexpected_close
 
 > Unexpected block closing tag

packages/svelte/src/compiler/errors.js

@@ -730,6 +730,16 @@ export function block_unclosed(node) {
 	e(node, "block_unclosed", "Block was left open");
 }
 
+/**
+ * Expected a `%character%` character immediately following the opening bracket
+ * @param {null | number | NodeLike} node
+ * @param {string} character
+ * @returns {never}
+ */
+export function block_unexpected_character(node, character) {
+	e(node, "block_unexpected_character", `Expected a \`${character}\` character immediately following the opening bracket`);
+}
+
 /**
  * Unexpected block closing tag
  * @param {null | number | NodeLike} node

packages/svelte/src/compiler/phases/1-parse/state/tag.js

@@ -39,7 +39,8 @@ export default function tag(parser) {
 
 /** @param {import('../index.js').Parser} parser */
 function open(parser) {
-	const start = parser.index - 2;
+	let start = parser.index - 2;
+	while (parser.template[start] !== '{') start -= 1;
 
 	if (parser.eat('if')) {
 		parser.require_whitespace();
@@ -343,9 +344,12 @@ function next(parser) {
 			parser.allow_whitespace();
 			parser.eat('}', true);
 
+			let elseif_start = start - 1;
+			while (parser.template[elseif_start] !== '{') elseif_start -= 1;
+
 			/** @type {ReturnType<typeof parser.append<import('#compiler').IfBlock>>} */
 			const child = parser.append({
-				start: start - 1,
+				start: elseif_start,
 				end: -1,
 				type: 'IfBlock',
 				elseif: true,

packages/svelte/src/compiler/phases/2-analyze/validation.js

@@ -1090,6 +1090,20 @@ function validate_no_const_assignment(node, argument, scope, is_binding) {
 	}
 }
 
+/**
+ * Validates that the opening of a control flow block is `{` immediately followed by the expected character.
+ * In legacy mode whitespace is allowed inbetween. TODO remove once legacy mode is gone and move this into parser instead.
+ * @param {{start: number; end: number}} node
+ * @param {import('./types.js').AnalysisState} state
+ * @param {string} expected
+ */
+function validate_opening_tag(node, state, expected) {
+	if (state.analysis.source[node.start + 1] !== expected) {
+		// avoid a sea of red and only mark the first few characters
+		e.block_unexpected_character({ start: node.start, end: node.start + 5 }, expected);
+	}
+}
+
 /**
  * @param {import('estree').AssignmentExpression | import('estree').UpdateExpression} node
  * @param {import('estree').Pattern | import('estree').Expression} argument
@@ -1217,6 +1231,8 @@ export const validation_runes = merge(validation, a11y_validators, {
 		validate_call_expression(node, state.scope, path);
 	},
 	EachBlock(node, { next, state }) {
+		validate_opening_tag(node, state, '#');
+
 		const context = node.context;
 		if (
 			context.type === 'Identifier' &&
@@ -1226,6 +1242,51 @@ export const validation_runes = merge(validation, a11y_validators, {
 		}
 		next({ ...state });
 	},
+	IfBlock(node, { state, path }) {
+		const parent = path.at(-1);
+		const expected =
+			path.at(-2)?.type === 'IfBlock' && parent?.type === 'Fragment' && parent.nodes.length === 1
+				? ':'
+				: '#';
+		validate_opening_tag(node, state, expected);
+	},
+	AwaitBlock(node, { state }) {
+		validate_opening_tag(node, state, '#');
+
+		if (node.value) {
+			const start = /** @type {number} */ (node.value.start);
+			const match = state.analysis.source.substring(start - 10, start).match(/{(\s*):then\s+$/);
+			if (match && match[1] !== '') {
+				e.block_unexpected_character({ start: start - 10, end: start }, ':');
+			}
+		}
+
+		if (node.error) {
+			const start = /** @type {number} */ (node.error.start);
+			const match = state.analysis.source.substring(start - 10, start).match(/{(\s*):catch\s+$/);
+			if (match && match[1] !== '') {
+				e.block_unexpected_character({ start: start - 10, end: start }, ':');
+			}
+		}
+	},
+	KeyBlock(node, { state }) {
+		validate_opening_tag(node, state, '#');
+	},
+	SnippetBlock(node, { state }) {
+		validate_opening_tag(node, state, '#');
+	},
+	ConstTag(node, { state }) {
+		validate_opening_tag(node, state, '@');
+	},
+	HtmlTag(node, { state }) {
+		validate_opening_tag(node, state, '@');
+	},
+	DebugTag(node, { state }) {
+		validate_opening_tag(node, state, '@');
+	},
+	RenderTag(node, { state }) {
+		validate_opening_tag(node, state, '@');
+	},
 	VariableDeclarator(node, { state }) {
 		ensure_no_module_import_conflict(node, state);
 

packages/svelte/tests/validator/samples/if-block-whitespace-legacy/errors.json

@@ -0,0 +1 @@
+[]

packages/svelte/tests/validator/samples/if-block-whitespace-legacy/input.svelte

@@ -0,0 +1,8 @@
+<svelte:options runes={false} />
+
+<!-- prettier-ignore -->
+<div>
+	{ #if true}
+		<p>hi</p>
+	{/if}
+</div>

packages/svelte/tests/validator/samples/if-block-whitespace-runes/errors.json

@@ -0,0 +1,14 @@
+[
+	{
+		"code": "block_unexpected_character",
+		"message": "Expected a `#` character immediately following the opening bracket",
+		"start": {
+			"line": 5,
+			"column": 1
+		},
+		"end": {
+			"line": 5,
+			"column": 6
+		}
+	}
+]

packages/svelte/tests/validator/samples/if-block-whitespace-runes/input.svelte

@@ -0,0 +1,8 @@
+<svelte:options runes={true} />
+
+<!-- prettier-ignore -->
+<div>
+	{ #if true}
+		<p>hi</p>
+	{/if}
+</div>