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Implement slow-path for FirstSets::first
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When 2 or more sequences share the same span, we can't use the precomputed map
for their first set. So we compute it recursively.

Fixes #62831.
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ia0 committed Jul 25, 2019
1 parent eedf6ce commit df4b23e
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Showing 4 changed files with 119 additions and 27 deletions.
53 changes: 26 additions & 27 deletions src/libsyntax/ext/tt/macro_rules.rs
Original file line number Diff line number Diff line change
Expand Up @@ -625,38 +625,37 @@ impl FirstSets {
return first;
}
TokenTree::Sequence(sp, ref seq_rep) => {
match self.first.get(&sp.entire()) {
Some(&Some(ref subfirst)) => {
// If the sequence contents can be empty, then the first
// token could be the separator token itself.

if let (Some(sep), true) = (&seq_rep.separator, subfirst.maybe_empty) {
first.add_one_maybe(TokenTree::Token(sep.clone()));
}

assert!(first.maybe_empty);
first.add_all(subfirst);
if subfirst.maybe_empty
|| seq_rep.kleene.op == quoted::KleeneOp::ZeroOrMore
|| seq_rep.kleene.op == quoted::KleeneOp::ZeroOrOne
{
// continue scanning for more first
// tokens, but also make sure we
// restore empty-tracking state
first.maybe_empty = true;
continue;
} else {
return first;
}
}

let subfirst_owned;
let subfirst = match self.first.get(&sp.entire()) {
Some(&Some(ref subfirst)) => subfirst,
Some(&None) => {
panic!("assume all sequences have (unique) spans for now");
subfirst_owned = self.first(&seq_rep.tts[..]);
&subfirst_owned
}

None => {
panic!("We missed a sequence during FirstSets construction");
}
};

// If the sequence contents can be empty, then the first
// token could be the separator token itself.
if let (Some(sep), true) = (&seq_rep.separator, subfirst.maybe_empty) {
first.add_one_maybe(TokenTree::Token(sep.clone()));
}

assert!(first.maybe_empty);
first.add_all(subfirst);
if subfirst.maybe_empty
|| seq_rep.kleene.op == quoted::KleeneOp::ZeroOrMore
|| seq_rep.kleene.op == quoted::KleeneOp::ZeroOrOne
{
// Continue scanning for more first
// tokens, but also make sure we
// restore empty-tracking state.
first.maybe_empty = true;
continue;
} else {
return first;
}
}
}
Expand Down
36 changes: 36 additions & 0 deletions src/test/ui/macros/auxiliary/proc_macro_sequence.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,36 @@
// force-host
// no-prefer-dynamic

#![crate_type = "proc-macro"]
#![feature(proc_macro_span, proc_macro_hygiene, proc_macro_quote)]

extern crate proc_macro;

use proc_macro::{quote, Span, TokenStream};

fn assert_same_span(a: Span, b: Span) {
assert_eq!(a.start(), b.start());
assert_eq!(a.end(), b.end());
}

// This macro generates a macro with the same macro definition as `manual_foo` in
// `same-sequence-span.rs` but with the same span for all sequences.
#[proc_macro]
pub fn make_foo(_: TokenStream) -> TokenStream {
let result = quote! {
macro_rules! generated_foo {
(1 $$x:expr $$($$y:tt,)* $$(= $$z:tt)*) => {};
}
};

// Check that all spans are equal.
let mut span = None;
for tt in result.clone() {
match span {
None => span = Some(tt.span()),
Some(span) => assert_same_span(tt.span(), span),
}
}

result
}
23 changes: 23 additions & 0 deletions src/test/ui/macros/same-sequence-span.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,23 @@
// aux-build:proc_macro_sequence.rs

// Regression test for issue #62831: Check that multiple sequences with the same span in the
// left-hand side of a macro definition behave as if they had unique spans, and in particular that
// they don't crash the compiler.

#![feature(proc_macro_hygiene)]
#![allow(unused_macros)]

extern crate proc_macro_sequence;

// When ignoring spans, this macro has the same macro definition as `generated_foo` in
// `proc_macro_sequence.rs`.
macro_rules! manual_foo {
(1 $x:expr $($y:tt,)* //~ERROR `$x:expr` may be followed by `$y:tt`
$(= $z:tt)* //~ERROR `$x:expr` may be followed by `=`
) => {};
}

proc_macro_sequence::make_foo!(); //~ERROR `$x:expr` may be followed by `$y:tt`
//~^ERROR `$x:expr` may be followed by `=`

fn main() {}
34 changes: 34 additions & 0 deletions src/test/ui/macros/same-sequence-span.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,34 @@
error: `$x:expr` may be followed by `$y:tt`, which is not allowed for `expr` fragments
--> $DIR/same-sequence-span.rs:15:18
|
LL | (1 $x:expr $($y:tt,)*
| ^^^^^ not allowed after `expr` fragments
|
= note: allowed there are: `=>`, `,` or `;`

error: `$x:expr` may be followed by `=`, which is not allowed for `expr` fragments
--> $DIR/same-sequence-span.rs:16:18
|
LL | $(= $z:tt)*
| ^ not allowed after `expr` fragments
|
= note: allowed there are: `=>`, `,` or `;`

error: `$x:expr` may be followed by `$y:tt`, which is not allowed for `expr` fragments
--> $DIR/same-sequence-span.rs:20:1
|
LL | proc_macro_sequence::make_foo!();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not allowed after `expr` fragments
|
= note: allowed there are: `=>`, `,` or `;`

error: `$x:expr` may be followed by `=`, which is not allowed for `expr` fragments
--> $DIR/same-sequence-span.rs:20:1
|
LL | proc_macro_sequence::make_foo!();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not allowed after `expr` fragments
|
= note: allowed there are: `=>`, `,` or `;`

error: aborting due to 4 previous errors

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