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macros: simplify tt matchers #39403

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jseyfried opened this issue Jan 30, 2017 · 2 comments · Fixed by #39419
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macros: simplify tt matchers #39403

jseyfried opened this issue Jan 30, 2017 · 2 comments · Fixed by #39419
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@jseyfried
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A-macros Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..)

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@jseyfried
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jseyfried commented Jan 30, 2017 •
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Ideally, tt matches either a single token or delimited sequence (e.g. { arbitrary tokens }).
However, the following compiles today:

macro_rules! m { ($t:tt) => {} }
m!($x);
m!($(x)*);
m!($x:ident);

We want to avoid leaking details of macro_rules! syntax into the semantics of tt, at least for macros 2.0.
@jseyfried jseyfried self-assigned this Jan 30, 2017
@jseyfried jseyfried added the A-macros Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..) label Jan 30, 2017
@jseyfried jseyfried mentioned this issue Jan 31, 2017
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@durka
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durka commented Jan 31, 2017

What does "fixing" this entail? Which examples still work?

@jseyfried
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@durka
None of those examples will work with macros 2.0, but then macros 2.0 will allow escaping $.

I think fixing this means that at least the second and third examples don't work. However, we might need to continue allowing the first example for back-compat and since there isn't a good workaround without being able to escape $.

Also, we could enable escaping $ in macro_rules! and then forbid the first example.

frewsxcv added a commit to frewsxcv/rust that referenced this issue Mar 1, 2017
@frewsxcv
Rollup merge of rust-lang#39419 - jseyfried:simplify_tokentree, r=nrc
4ba49ab 
Simplify `TokenTree` and fix `macro_rules!` bugs

This PR
 - fixes rust-lang#39390, fixes rust-lang#39403, and fixes rust-lang#39404 (each is a [breaking-change], see issues for examples),
 - fixes rust-lang#39889,
 - simplifies and optimizes macro invocation parsing,
 - cleans up `ext::tt::transcribe`,
 - removes `tokenstream::TokenTree::Sequence` and `Token::MatchNt`,
   - instead, adds a new type `ext::tt::quoted::TokenTree` for use by `macro_rules!` (`ext::tt`)
 - removes `parser.quote_depth` and `parser.parsing_token_tree`, and
 - removes `quote_matcher!`.
   - Instead, use `quote_tokens!` and `ext::tt::quoted::parse` the result with `expect_matchers=true`.
   - I found no outside uses of `quote_matcher!` when searching Rust code on Github.

r? @nrc
bors added a commit that referenced this issue Mar 1, 2017
@bors
Auto merge of #39419 - jseyfried:simplify_tokentree, r=nrc
7ce1fbe 
Simplify `TokenTree` and fix `macro_rules!` bugs

This PR
 - fixes #39390, fixes #39403, and fixes #39404 (each is a [breaking-change], see issues for examples),
 - fixes #39889,
 - simplifies and optimizes macro invocation parsing,
 - cleans up `ext::tt::transcribe`,
 - removes `tokenstream::TokenTree::Sequence` and `Token::MatchNt`,
   - instead, adds a new type `ext::tt::quoted::TokenTree` for use by `macro_rules!` (`ext::tt`)
 - removes `parser.quote_depth` and `parser.parsing_token_tree`, and
 - removes `quote_matcher!`.
   - Instead, use `quote_tokens!` and `ext::tt::quoted::parse` the result with `expect_matchers=true`.
   - I found no outside uses of `quote_matcher!` when searching Rust code on Github.

r? @nrc
@jseyfried jseyfried mentioned this issue May 8, 2017
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Simplify TokenTree and fix macro_rules! bugs jseyfried/rust
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@durka @jseyfried