Problems with the syntax of lifetimes and labels

The FLS's grammar defines a lifetime as follows:

§4.14.1 (fls_yqcygq3y6m5j):

Lifetime ::=
    ' (NonKeywordIdentifier | RawIdentifierKeyword)

and a label as follows:

§6.15.5 (fls_uusi0zej55is)

   LabelIndication ::=
       ' NonKeywordIdentifier

Problem 1

In Rust, whitespace is not permitted here between the ' and the identifier, but nothing in the grammar indicates that the usual rule about whitespace is suspended here.

Problem 2

The LexicalElement production in §2.2 (fls_fgnllgz5k3e6) doesn't allow '.

The only LexicalElement that can begin with ' is CharacterLiteral.

That means that

• TokenTree* doesn't accept 'a
• so MacroInvocation doesn't accept m!('a)

But Rust accepts that macro invocation.

(Perhaps the intent was to include ' in the Punctuation production, but it isn't there.)

Problem 3

Possibly more seriously, I don't think a grammar that tries to treat 'a as made up of two separate lexical elements can be made to work.

Consider the following macro invocation: m!('r"a").

In Rust the macro will see two tokens: 'r and "a".

A model which allows ' to stand alone at lexing time is going to end up analysing this as
' followed by a raw string literal r"a".

Note this is a place where the FLS has diverged from the Reference, which defines a LIFETIME_TOKEN and includes it in its equivalent of LexicalElement.

Start with the FLS grammar sections §2.2 (LexicalElement), §4.14.1 (Lifetime), and §6.15.5 (LabelIndication), then compare their treatment with the Rust Reference's LIFETIME_TOKEN. Verify the grammar against m!('a) and m!('r"a"); done means lifetime and label syntax, whitespace, and macro tokenization are specified consistently.