New Lint: ambiguous closures like `return || true`

The proposal is to implement a new lint to capture closures that are appear ambiguous to the reader. Such closures have no args, which makes the leading || look like a logical OR, and have an expression body without surrounding block. It may also only be ambiguous if the closure's body expression returns a boolean.

the classic example is return || true which at first glance looks like nonsense but actually returns a closure that always returns true.

Clippy should warn that this closure is potentially ambiguous to the reader and may be misinterpreted as boolean logic. It would also be nice if it suggests a machine applicable solution so that rustfix can benefit from the lint.

Possible suggestions include

return || { true }

return { || true }

return { || { true } }

Though I think the former is still ambiguous

The issue names no implementation files, tests, or entry points. Start by locating the existing Clippy lint and UI-test conventions for closure syntax, then resolve which zero-argument expression closures should be diagnosed and which machine-applicable suggestion is acceptable. Done means the new lint and its selected fix are covered by tests.