Do not fire unhandled attribute assertion on multi-segment AttributeType::Normal attributes with builtin attribute as first segment

[jieyouxu]

The Problem

In #128581 I introduced an assertion to check that all builtin attributes are actually checked via
CheckAttrVisitor and aren't accidentally usable on completely unrelated HIR nodes.
Unfortunately, the assertion had correctness problems as revealed in #128622.

The match on attribute path segments looked like

// Normal handler
[sym::should_panic] => /* check is implemented */
// Fallback handler
[name, ..] => match BUILTIN_ATTRIBUTE_MAP.get(name) {
    // checked below
    Some(BuiltinAttribute { type_: AttributeType::CrateLevel, .. }) => {}
    Some(_) => {
        if !name.as_str().starts_with("rustc_") {
            span_bug!(
                attr.span,
                "builtin attribute {name:?} not handled by `CheckAttrVisitor`"
            )
        }
    }
    None => (),
}

However, it failed to account for edge cases such as an attribute whose:

1. path segments starts with a segment matching the name of a builtin attribute such as should_panic, and
2. the first segment's symbol does not start with rustc_, and
3. the matched builtin attribute is also of AttributeType::Normal attribute type upon registration with the builtin attribute map.

These conditions when all satisfied cause the span bug to be issued for e.g.
#[should_panic::skip] because the [sym::should_panic] arm is not matched (since it's
[sym::should_panic, sym::skip]).

Proposed Solution

This PR tries to remedy that by adjusting all normal/specific handlers to not match exactly on a single segment, but instead match a prefix segment.

i.e.

// Normal handler, notice the `, ..` rest pattern
[sym::should_panic, ..] => /* check is implemented */
// Fallback handler
[name, ..] => match BUILTIN_ATTRIBUTE_MAP.get(name) {
    // checked below
    Some(BuiltinAttribute { type_: AttributeType::CrateLevel, .. }) => {}
    Some(_) => {
        if !name.as_str().starts_with("rustc_") {
            span_bug!(
                attr.span,
                "builtin attribute {name:?} not handled by `CheckAttrVisitor`"
            )
        }
    }
    None => (),
}

Review Remarks

This PR contains 2 commits:

1. The first commit adds a regression test. This will ICE without the CheckAttrVisitor changes.
2. The second commit adjusts CheckAttrVisitor assertion logic. Once this commit is applied, the test should no longer ICE and produce the expected bless stderr.

Fixes #128622.

r? @nnethercote (since you reviewed #128581)

[nnethercote]

@bors r+

[bors]

📌 Commit 9d0eaa2 has been approved by nnethercote

It is now in the queue for this repository.