Lambda as UDA is valid but spec requires brackets

[dlangBugzillaToGithub]

Richard (Rikki) Andrew Cattermole reported this on 2024-01-20T01:25:08Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=24346

CC List

Description

From: https://forum.dlang.org/post/[email protected]

The lambda here is valid, even though it is not in a brackets.

```d
@a=>7 int b;
pragma(msg, __traits(getAttributes, b)); // AliasSeq!((a) => 7)
```

Should only be supported (according to specification):

```d
@(a=>7) int b;
pragma(msg, __traits(getAttributes, b)); // AliasSeq!((a) => 7)
```

Clarification or a compiler bug fix is needed.

[dlangBugzillaToGithub]

hsteoh commented on 2024-01-20T01:34:51Z

I'm inclined to say that parentheses should be required, for consistency with the single-token requirement on unparenthesized UDAs. (Cf also binary `!` syntax, where the unparenthesized version also requires exactly 1 token, and in all other cases parentheses are required.)