static lifetime being required too often

[carllerche]

Repro:
https://gist.github.com/carllerche/c426ece39be0705ba6c2

I am not really sure what is going on. Maybe this is a dup of #8874? Unsure.

[alexcrichton]

cc @nikomatsakis

Replacing equal_to("zomg") with equal_to("zomg".as_slice()) makes the error go away, which makes me think that this should not be a compiler error.

[carllerche]

Woops, I guess I forgot to add the .as_slice() fix in the Gist... sorry.

[huonw]

This now works fine (only changes were updating to make it compile):

struct StrWrap {
  s: String
}

impl StrWrap {
  fn new(s: &str) -> StrWrap {
    StrWrap { s: s.into_string() }
  }

  fn get_s<'a>(&'a self) -> &'a str {
    self.s.as_slice()
  }
}

struct MyStruct {
  s: StrWrap
}

impl MyStruct {
  fn new(s: &str) -> MyStruct {
    MyStruct { s: StrWrap::new(s) }
  }

  fn get_str_wrap<'a>(&'a self) -> &'a StrWrap {
    &self.s
  }
}

trait Matcher<T> {
  fn matches(&self, actual: T) -> bool;
}

fn assert_that<T, U: Matcher<T>>(actual: T, matcher: &U) {
  assert!(matcher.matches(actual));
}

struct EqualTo<T> {
  expected: T
}

impl<T: Eq> Matcher<T> for EqualTo<T> {
  fn matches(&self, actual: T) -> bool {
    self.expected.eq(&actual)
  }
}

fn equal_to<T: Eq>(expected: T) -> Box<EqualTo<T>> {
  box EqualTo { expected: expected }
}

pub fn main() {
  let my_struct = MyStruct::new("zomg");
  let s = my_struct.get_str_wrap();

  assert_that(s.get_s(), &*equal_to("zomg"));
}

Changing the second last line to

  assert_that(s.get_s(), &*equal_to::<&'static str>("zomg"));

causes the same compilation error as in the original code, suggesting that this is actually rustc being more intelligent, and is not just being disguised by the language changes since this was filed; yay!

Flagging as needstest.

[tamird]

This should have been closed by #19780! See https://github.com/rust-lang/rust/blob/master/src/test/run-pass/issue-13323.rs

cc @jakub-

[alexcrichton]

Thanks @tamird!