Warn on @available(*, message: "abc")

[jrose-signal]

Motivation

Today, there are three sets of arguments for (the long form of) @available:

• The "platforms" (*, swift, or an actual platform name)
• The "conditions": version ranges, as well as the plain deprecated and unavailable
• Optional additional diagnostic context, message and renamed

The compiler enforces that the first is present and that it's not the only attribute, but it allows a platform and a diagnostic argument with no conditions, which can mislead people into thinking @available(*, message: "abc") or @available(*, renamed: "abc") will do something.

Proposed solution

Warn if @available has no conditions listed, as it does if there are neither conditions nor context arguments. It doesn't have to be an error, there's still a reasonable interpretation, but it is an easy mistake to make, especially if you're new to the attribute.

Alternatives considered

No response

Additional information

No response