better error for unclosed curly brace in props

src/compiler/parse/errors.ts

@@ -169,6 +169,10 @@ export default {
 		code: 'unclosed-comment',
 		message: 'comment was left open, expected -->'
 	},
+	unclosed_attribute_value: (token: string) => ({
+		code: 'unclosed-attribute-value',
+		message: `Expected to close the attribute value with ${token}`
+	}),
 	unexpected_block_close: {
 		code: 'unexpected-block-close',
 		message: 'Unexpected block closing tag'

src/compiler/parse/state/tag.ts

@@ -438,7 +438,21 @@ function read_attribute_value(parser: Parser) {
 				/(\/>|[\s"'=<>`])/
 	);
 
-	const value = read_sequence(parser, () => !!parser.match_regex(regex));
+	let value;
+	try {
+		value = read_sequence(parser, () => !!parser.match_regex(regex));
+	} catch (error) {
+		if (error.code === 'parse-error') {
+			// if the attribute value didn't close + self-closing tag
+			// eg: `<Component test={{a:1} />`
+			// acorn may throw a `Unterminated regular expression` because of `/>`
+			if (parser.template.slice(error.pos - 1, error.pos + 1) === '/>') {
+				parser.index = error.pos;
+				parser.error(parser_errors.unclosed_attribute_value(quote_mark || '}'));
+			}
+		}
+		throw error;
+	}
 
 	if (quote_mark) parser.index += 1;
 	return value;

test/parser/samples/error-unclosed-attribute-self-close-tag/error.json

@@ -0,0 +1,10 @@
+{
+	"code": "unclosed-attribute-value",
+	"message": "Expected to close the attribute value with }",
+	"pos": 25,
+	"start": {
+		"character": 25,
+		"column": 25,
+		"line": 1
+	}
+}

test/parser/samples/error-unclosed-attribute-self-close-tag/input.svelte

@@ -0,0 +1 @@
+<Component test={{a: 1} />