Module rustc_expand::mbe::macro_rules
source · Structs
Enums
Constants
Functions
Checks that the lhs contains no repetition which could match an empty token
tree, because then the matcher would hang indefinitely.
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.Generates an appropriate parsing failure message. For EOF, this is “unexpected end…”. For
other tokens, this is “unexpected token…”.