feat: allow generics on snippets

.changeset/ten-colts-grab.md

@@ -0,0 +1,5 @@
+---
+'svelte': minor
+---
+
+feat: allow generics on snippets

packages/svelte/src/compiler/phases/1-parse/read/context.js

@@ -1,7 +1,7 @@
 /** @import { Location } from 'locate-character' */
 /** @import { Pattern } from 'estree' */
 /** @import { Parser } from '../index.js' */
-import { is_bracket_open, is_bracket_close, get_bracket_close } from '../utils/bracket.js';
+import { match_bracket } from '../utils/bracket.js';
 import { parse_expression_at } from '../acorn.js';
 import { regex_not_newline_characters } from '../../patterns.js';
 import * as e from '../../../errors.js';
@@ -33,7 +33,9 @@ export default function read_pattern(parser) {
 		};
 	}
 
-	if (!is_bracket_open(parser.template[i])) {
+	const char = parser.template[i];
+
+	if (char !== '{' && char !== '[') {
 		e.expected_pattern(i);
 	}
 
@@ -71,75 +73,6 @@ export default function read_pattern(parser) {
 	}
 }
 
-/**
- * @param {Parser} parser
- * @param {number} start
- */
-function match_bracket(parser, start) {
-	const bracket_stack = [];
-
-	let i = start;
-
-	while (i < parser.template.length) {
-		let char = parser.template[i++];
-
-		if (char === "'" || char === '"' || char === '`') {
-			i = match_quote(parser, i, char);
-			continue;
-		}
-
-		if (is_bracket_open(char)) {
-			bracket_stack.push(char);
-		} else if (is_bracket_close(char)) {
-			const popped = /** @type {string} */ (bracket_stack.pop());
-			const expected = /** @type {string} */ (get_bracket_close(popped));
-
-			if (char !== expected) {
-				e.expected_token(i - 1, expected);
-			}
-
-			if (bracket_stack.length === 0) {
-				return i;
-			}
-		}
-	}
-
-	e.unexpected_eof(parser.template.length);
-}
-
-/**
- * @param {Parser} parser
- * @param {number} start
- * @param {string} quote
- */
-function match_quote(parser, start, quote) {
-	let is_escaped = false;
-	let i = start;
-
-	while (i < parser.template.length) {
-		const char = parser.template[i++];
-
-		if (is_escaped) {
-			is_escaped = false;
-			continue;
-		}
-
-		if (char === quote) {
-			return i;
-		}
-
-		if (char === '\\') {
-			is_escaped = true;
-		}
-
-		if (quote === '`' && char === '$' && parser.template[i] === '{') {
-			i = match_bracket(parser, i);
-		}
-	}
-
-	e.unterminated_string_constant(start);
-}
-
 /**
  * @param {Parser} parser
  * @returns {any}

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

@@ -8,9 +8,12 @@ import { parse_expression_at } from '../acorn.js';
 import read_pattern from '../read/context.js';
 import read_expression, { get_loose_identifier } from '../read/expression.js';
 import { create_fragment } from '../utils/create.js';
+import { match_bracket } from '../utils/bracket.js';
 
 const regex_whitespace_with_closing_curly_brace = /^\s*}/;
 
+const pointy_bois = { '<': '>' };
+
 /** @param {Parser} parser */
 export default function tag(parser) {
 	const start = parser.index;
@@ -351,6 +354,22 @@ function open(parser) {
 
 		const params_start = parser.index;
 
+		// snippets could have a generic signature, e.g. `#snippet foo<T>(...)`
+		/** @type {string | undefined} */
+		let type_params;
+
+		// if we match a generic opening
+		if (parser.ts && parser.match('<')) {
+			const start = parser.index;
+			const end = match_bracket(parser, start, pointy_bois);
+
+			type_params = parser.template.slice(start + 1, end - 1);
+
+			parser.index = end;
+		}
+
+		parser.allow_whitespace();
+
 		const matched = parser.eat('(', true, false);
 
 		if (matched) {
@@ -388,6 +407,7 @@ function open(parser) {
 				end: name_end,
 				name
 			},
+			typeParams: type_params,
 			parameters: function_expression.params,
 			body: create_fragment(),
 			metadata: {

packages/svelte/src/compiler/phases/1-parse/utils/bracket.js

@@ -1,34 +1,5 @@
-const SQUARE_BRACKET_OPEN = '[';
-const SQUARE_BRACKET_CLOSE = ']';
-const CURLY_BRACKET_OPEN = '{';
-const CURLY_BRACKET_CLOSE = '}';
-const PARENTHESES_OPEN = '(';
-const PARENTHESES_CLOSE = ')';
-
-/** @param {string} char */
-export function is_bracket_open(char) {
-	return char === SQUARE_BRACKET_OPEN || char === CURLY_BRACKET_OPEN;
-}
-
-/** @param {string} char */
-export function is_bracket_close(char) {
-	return char === SQUARE_BRACKET_CLOSE || char === CURLY_BRACKET_CLOSE;
-}
-
-/** @param {string} open */
-export function get_bracket_close(open) {
-	if (open === SQUARE_BRACKET_OPEN) {
-		return SQUARE_BRACKET_CLOSE;
-	}
-
-	if (open === CURLY_BRACKET_OPEN) {
-		return CURLY_BRACKET_CLOSE;
-	}
-
-	if (open === PARENTHESES_OPEN) {
-		return PARENTHESES_CLOSE;
-	}
-}
+/** @import { Parser } from '../index.js' */
+import * as e from '../../../errors.js';
 
 /**
  * @param {number} num
@@ -121,7 +92,7 @@ function count_leading_backslashes(string, search_start_index) {
  * @returns {number | undefined} The index of the closing bracket, or undefined if not found.
  */
 export function find_matching_bracket(template, index, open) {
-	const close = get_bracket_close(open);
+	const close = default_brackets[open];
 	let brackets = 1;
 	let i = index;
 	while (brackets > 0 && i < template.length) {
@@ -162,3 +133,81 @@ export function find_matching_bracket(template, index, open) {
 	}
 	return undefined;
 }
+
+/** @type {Record<string, string>} */
+const default_brackets = {
+	'{': '}',
+	'(': ')',
+	'[': ']'
+};
+
+/**
+ * @param {Parser} parser
+ * @param {number} start
+ * @param {Record<string, string>} brackets
+ */
+export function match_bracket(parser, start, brackets = default_brackets) {
+	const close = Object.values(brackets);
+	const bracket_stack = [];
+
+	let i = start;
+
+	while (i < parser.template.length) {
+		let char = parser.template[i++];
+
+		if (char === "'" || char === '"' || char === '`') {
+			i = match_quote(parser, i, char);
+			continue;
+		}
+
+		if (char in brackets) {
+			bracket_stack.push(char);
+		} else if (close.includes(char)) {
+			const popped = /** @type {string} */ (bracket_stack.pop());
+			const expected = /** @type {string} */ (brackets[popped]);
+
+			if (char !== expected) {
+				e.expected_token(i - 1, expected);
+			}
+
+			if (bracket_stack.length === 0) {
+				return i;
+			}
+		}
+	}
+
+	e.unexpected_eof(parser.template.length);
+}
+
+/**
+ * @param {Parser} parser
+ * @param {number} start
+ * @param {string} quote
+ */
+function match_quote(parser, start, quote) {
+	let is_escaped = false;
+	let i = start;
+
+	while (i < parser.template.length) {
+		const char = parser.template[i++];
+
+		if (is_escaped) {
+			is_escaped = false;
+			continue;
+		}
+
+		if (char === quote) {
+			return i;
+		}
+
+		if (char === '\\') {
+			is_escaped = true;
+		}
+
+		if (quote === '`' && char === '$' && parser.template[i] === '{') {
+			i = match_bracket(parser, i);
+		}
+	}
+
+	e.unterminated_string_constant(start);
+}

packages/svelte/src/compiler/types/template.d.ts

@@ -468,6 +468,7 @@ export namespace AST {
 		type: 'SnippetBlock';
 		expression: Identifier;
 		parameters: Pattern[];
+		typeParams?: string;
 		body: Fragment;
 		/** @internal */
 		metadata: {

packages/svelte/tests/parser-modern/samples/generic-snippets/input.svelte

@@ -0,0 +1,10 @@
+<script lang="ts">
+</script>
+
+{#snippet generic<T extends string>(val: T)}
+	{val}
+{/snippet}
+
+{#snippet complex_generic<T extends { bracket: "<" } | "<" | Set<"<>">>(val: T)}
+	{val}
+{/snippet}