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fix various const eval errors #33339

Merged
merged 5 commits into from
May 5, 2016
Merged

fix various const eval errors #33339

merged 5 commits into from
May 5, 2016

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oli-obk
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@oli-obk oli-obk commented May 2, 2016 •
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These were found after const_evaluating arbitrary expressions and linting if the const evaluator failed

fixes #33275 (int -> float casts for negative ints)
fixes #33291 (int -> char casts (new! wasn't allowed in constants until this PR))

r? @eddyb

cc @bluss @japaric

eddyb
eddyb reviewed May 2, 2016
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src/librustc_const_eval/eval.rs
Ok(Float(val as f64))
ty::TyFloat(ast::FloatTy::F32) => match val.erase_type() {
Infer(u) => Ok(Float(u as f32 as f64)),
InferSigned(i) => Ok(Float(i as f32 as f64)),
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This reminds me, we need 2 variants, one for f32 and one for f64.

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japaric commented May 2, 2016

hmm... where's bors? or is @japaric not a reviewer?

I have r+ rights, but I think I'm not be registered with the highfive bot.

fixes #33291 (int -> float casts for negative ints)
fixes #33275 (int -> char casts (new! wasn't allowed in constants until this PR))

the descriptions seem to be backward.

@oli-obk r=me with added tests cases 😄.

@oli-obk
* as char assumes * to be of type u8
10737a5
@oli-obk
tests
f080b13
@oli-obk
refactor infer function
ce6ea47 
There was no span available in the cast function, but we need to infer the `x` in `x as char` to `u8`.
The spans are now removed from all functions using `infer` and instead added in `eval_const_expr_partial`
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oli-obk commented May 2, 2016 •
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the descriptions seem to be backward.

whoops :) fixed

added tests cases

hmm... when I tried to create a cfail test for the error message I found out that it's the wrong message and the wrong logic. It's not possible to cast anything but a u8 to a char. And the regular rustc error message even says so. So I made sure that the value is either a u8 or at least can be inferred into a u8. But that caused some fallout in the infer function, because the cast-function doesn't have a span, but the infer function expects a span to report any errors. I changed this to only return an ErrKind and to attach the span in eval_const_expr_partial.

Note that typeck catches this issue, so we can only test for the const_eval error message by evaluating a pattern or array length

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japaric commented May 2, 2016

It's not possible to cast anything but a u8 to a char. And the regular rustc error message even says so.

Oh, right. I didn't remember that was the case.

Note that typeck catches this issue, so we can only test for the const_eval error message by evaluating a pattern or array length

So typeck doesn't reject this cast when it's in an array length. That's ... interesting.

japaric
japaric reviewed May 2, 2016
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src/test/compile-fail/const-eval-overflow-4b.rs
println!("{:?}", x);
}
const A_CHAR_USIZE
: [u32; 5u8 as char as usize]
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Yay, more const casting possibilities.

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japaric commented May 2, 2016

@bors r+

Thanks @oli-obk!

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bors commented May 2, 2016

📌 Commit ce6ea47 has been approved by japaric

@Manishearth Manishearth mentioned this pull request May 3, 2016
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Manishearth added a commit to Manishearth/rust that referenced this pull request May 3, 2016
@Manishearth
Rollup merge of rust-lang#33339 - oli-obk:fix/const_eval, r=japaric
041a269 
fix various const eval errors

These were found after const_evaluating arbitrary expressions and linting if the const evaluator failed

fixes rust-lang#33275 (int -> float casts for negative ints)
fixes rust-lang#33291 (int -> char casts (new! wasn't allowed in constants until this PR))

r? @eddyb

cc @bluss @japaric
bors added a commit that referenced this pull request May 3, 2016
@bors
Auto merge of #33376 - Manishearth:rollup, r=Manishearth
1fb4b5b 
Rollup of 14 pull requests

- Successful merges: #33277, #33294, #33314, #33322, #33333, #33338, #33339, #33340, #33343, #33357, #33363, #33365, #33371, #33372
- Failed merges:
bors added a commit that referenced this pull request May 3, 2016
@bors
Auto merge of #33376 - Manishearth:rollup, r=Manishearth
f7125fc 
Rollup of 14 pull requests

- Successful merges: #33277, #33294, #33314, #33322, #33333, #33338, #33339, #33340, #33343, #33357, #33363, #33365, #33371, #33372
- Failed merges:
bors added a commit that referenced this pull request May 4, 2016
@bors
Auto merge of #33376 - Manishearth:rollup, r=Manishearth
1895d08 
Rollup of 14 pull requests

- Successful merges: #33277, #33294, #33314, #33322, #33333, #33338, #33339, #33340, #33343, #33357, #33363, #33365, #33371, #33372
- Failed merges:
bors added a commit that referenced this pull request May 4, 2016
@bors
Auto merge of #33376 - Manishearth:rollup, r=Manishearth
7a0ccc4 
Rollup of 14 pull requests

- Successful merges: #33277, #33294, #33314, #33322, #33333, #33338, #33339, #33340, #33343, #33357, #33363, #33365, #33371, #33372
- Failed merges:
@bors bors merged commit ce6ea47 into rust-lang:master May 5, 2016
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durka commented Jun 18, 2016

another one: b"x" as &[u8]

@oli-obk oli-obk deleted the fix/const_eval branch June 18, 2016 07:45
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oli-obk commented Jun 20, 2016

@durka I can fix this easily. This is a mis-use of as, so we should probably start warning on it anyway

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durka commented Jun 20, 2016

How is it a misuse? It's unsizing the &[u8; 1] to a &[u8]. But more than that, the message is bad -- it says "cannot cast this type" while the code compiles, so it certainly does cast the type, and it doesn't give the user any information about why the cast might be invalid.

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oli-obk commented Jun 21, 2016

shouldn't a simple as_ref suffice?

#![feature(type_ascription)]

fn main() {
    let x = b"foo".as_ref();
    let y = x : &[u8];
}

I was under the impression that as should only be used for casting when there's no other way.

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eddyb commented Jun 21, 2016

@oli-obk Calling as_ref in non-generic code is an anti-pattern. Also, it doesn't matter if as is bad style, sometimes it's the simplest option (given that ascription doesn't coerce).
&b"foo"[..] works but it's a bit uglier.
The problem is that the warning is wrong: the coercion/cast works fine, even if it's not implemented in const_eval.

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