Structs

FirstSets 🔒
A noop tracker that is used in the hot path of the expansion, has zero overhead thanks to monomorphization.
TokenSet 🔒

Enums

CanRetry 🔒
IsInFollow 🔒
TtHandle 🔒

Constants

TOKENS 🔒
TOKENS 🔒
TOKENS 🔒
TOKENS 🔒
TOKENS 🔒

Statics

CALLSITE 🔒
CALLSITE 🔒
CALLSITE 🔒
CALLSITE 🔒
CALLSITE 🔒
CALLSITE 🔒
CALLSITE 🔒
CALLSITE 🔒
CALLSITE 🔒
META 🔒
META 🔒
META 🔒
META 🔒
META 🔒
META 🔒
META 🔒
META 🔒
META 🔒

Traits

Tracker 🔒

Functions

Checks that the lhs contains no repetition which could match an empty token tree, because then the matcher would hang indefinitely.
check_rhs 🔒
Converts a macro item into a syntax extension.
Expands the rules based macro defined by lhses and rhses for a given input arg.
Returns true if a fragment of type frag can be followed by any sort of token. We use this (among other things) as a useful approximation for when frag can be followed by a repetition like $(...)* or $(...)+. In general, these can be a bit tricky to reason about, so we adopt a conservative position that says that any fragment specifier which consumes at most one token tree can be followed by a fragment specifier (indeed, these fragments can be followed by ANYTHING without fear of future compatibility hazards).
Returns true if frag can legally be followed by the token tok. For fragments that can consume an unbounded number of tokens, tok must be within a well-defined follow set. This is intended to guarantee future compatibility: for example, without this rule, if we expanded expr to include a new binary operator, we might break macros that were relying on that binary operator as a separator.
Try expanding the macro. Returns the index of the successful arm and its named_matches if it was successful, and nothing if it failed. On failure, it’s the callers job to use track accordingly to record all errors correctly.