allow class/function expressions in tags (#18324)

We shouldn't error on encountering `class` and `function`, because they
are treated as expressions rather than declarations

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

@@ -14,8 +14,7 @@ const regex_whitespace_with_closing_curly_brace = /\s*}/y;
 const regex_supported_declaration = /(?:let|const)\b/y;
 // All except `type` are reserved keywords and cannot be used as variable names.
 // For type we check if it's not something like `type .x` / `type ()` / `type % 2` / ...
-const regex_unsupported_declaration =
+const regex_unsupported_declaration = /(?:(?:var|interface|enum)\b)|(?:type\s+[^?.(`<[&|%^}])/y;
-	/(?:(?:var|function|class|interface|enum)\b)|(?:type\s+[^?.(`<[&|%^}])/y;
 
 const pointy_bois = { '<': '>' };
 

packages/svelte/tests/validator/samples/declaration-tag-invalid-function/errors.json

@@ -1,14 +1 @@
-[
+[]
-	{
-		"code": "declaration_tag_invalid_type",
-		"message": "Declaration tags must be `let` or `const` declarations",
-		"start": {
-			"line": 2,
-			"column": 2
-		},
-		"end": {
-			"line": 2,
-			"column": 10
-		}
-	}
-]