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Change `indirect_structural_match` lint to allow-by-default.

This is a way to address the regression aspect of #62614 in the
short term without actually fixing the bug. (My thinking is that the bug that
this lint detects has gone undetected for this long, it can wait a bit longer
until I or someone else has a chance to put in a proper fix that accounts for
#62614.)
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pnkfelix committed Jul 12, 2019
1 parent 00e0d87 commit 44d27ba28df30f80d039f0486cac46d7fb265fa3
Showing with 62 additions and 1 deletion.
  1. +3 −1 src/librustc/lint/builtin.rs
  2. +59 −0 src/test/ui/rfc1445/allow-use-behind-cousin-variant.rs
@@ -350,7 +350,8 @@ declare_lint! {

declare_lint! {
pub INDIRECT_STRUCTURAL_MATCH,
Warn,
// defaulting to allow until rust-lang/rust#62614 is fixed.
Allow,
"pattern with const indirectly referencing non-`#[structural_match]` type"
}

@@ -451,6 +452,7 @@ declare_lint_pass! {
AMBIGUOUS_ASSOCIATED_ITEMS,
NESTED_IMPL_TRAIT,
MUTABLE_BORROW_RESERVATION_CONFLICT,
INDIRECT_STRUCTURAL_MATCH,
]
}

@@ -0,0 +1,59 @@
// rust-lang/rust#62614: we want to allow matching on constants of types that
// have non-structural-match variants, *if* the constant itself does not use
// any such variant.

// NOTE: for now, deliberately leaving the lint `indirect_structural_match` set
// to its default, so that we will not issue a diangostic even if
// rust-lang/rust#62614 remains an open issue.

// run-pass

struct Sum(u32, u32);

impl PartialEq for Sum {
fn eq(&self, other: &Self) -> bool { self.0 + self.1 == other.0 + other.1 }
}

impl Eq for Sum { }

#[derive(PartialEq, Eq)]
enum Eek {
TheConst,
UnusedByTheConst(Sum)
}

const THE_CONST: Eek = Eek::TheConst;
const SUM_THREE: Eek = Eek::UnusedByTheConst(Sum(3,0));

const EEK_ZERO: &[Eek] = &[];
const EEK_ONE: &[Eek] = &[THE_CONST];

pub fn main() {
match Eek::UnusedByTheConst(Sum(1,2)) {
ref sum if sum == &SUM_THREE => { println!("Hello 0"); }
_ => { println!("Gbye"); }
}

match Eek::TheConst {
THE_CONST => { println!("Hello 1"); }
_ => { println!("Gbye"); }
}


match & &Eek::TheConst {
& & THE_CONST => { println!("Hello 2"); }
_ => { println!("Gbye"); }
}

match & & &[][..] {
& & EEK_ZERO => { println!("Hello 3"); }
& & EEK_ONE => { println!("Gbye"); }
_ => { println!("Gbye"); }
}

match & & &[Eek::TheConst][..] {
& & EEK_ZERO => { println!("Gby"); }
& & EEK_ONE => { println!("Hello 4"); }
_ => { println!("Gbye"); }
}
}

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