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Allow multiple allow_internal_unstable attributes#77183

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bors merged 1 commit intorust-lang:masterfrom
bugadani:issue-77088
Sep 25, 2020
Merged

Allow multiple allow_internal_unstable attributes#77183
bors merged 1 commit intorust-lang:masterfrom
bugadani:issue-77088

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@bugadani bugadani commented Sep 25, 2020

Fixes #77088

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rust-highfive commented Sep 25, 2020

r? @varkor

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@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Sep 25, 2020
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r=me after adjusting the error text.

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Allow multiple allow_internal_unstable attributes
54c9c94 
Co-authored-by: varkor <github@varkor.com>
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bugadani commented Sep 25, 2020

@varkor it should be good now, I've also squashed the changes

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varkor commented Sep 25, 2020

Thanks!

@bors r+ rollup

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bors commented Sep 25, 2020

📌 Commit 54c9c94 has been approved by varkor

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Sep 25, 2020
@jonas-schievink jonas-schievink mentioned this pull request Sep 25, 2020
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bors added a commit to rust-lang-ci/rust that referenced this pull request Sep 25, 2020
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Auto merge of rust-lang#77198 - jonas-schievink:rollup-i59i41h, r=jon…
c6e4db6 
…as-schievink

Rollup of 15 pull requests

Successful merges:

 - rust-lang#76932 (Relax promises about condition variable.)
 - rust-lang#76973 (Unstably allow assume intrinsic in const contexts)
 - rust-lang#77005 (BtreeMap: refactoring around edges)
 - rust-lang#77066 (Fix dest prop miscompilation around references)
 - rust-lang#77073 (dead_code: look at trait impls even if they don't contain items)
 - rust-lang#77086 (Include libunwind in the rust-src component.)
 - rust-lang#77097 (Make [].as_[mut_]ptr_range() (unstably) const.)
 - rust-lang#77106 (clarify that `changelog-seen = 1` goes to the beginning of config.toml)
 - rust-lang#77120 (Add `--keep-stage-std` to `x.py` for keeping only standard library artifacts)
 - rust-lang#77126 (Invalidate local LLVM cache less often)
 - rust-lang#77146 (Install std for non-host targets)
 - rust-lang#77155 (remove enum name from ImplSource variants)
 - rust-lang#77176 (Removing erroneous semicolon in transmute documentation)
 - rust-lang#77183 (Allow multiple allow_internal_unstable attributes)
 - rust-lang#77189 (Remove extra space from vec drawing)

Failed merges:

r? `@ghost`
@bors bors merged commit 12b8d89 into rust-lang:master Sep 25, 2020
@rustbot rustbot added this to the 1.48.0 milestone Sep 25, 2020
@bugadani bugadani deleted the issue-77088 branch September 25, 2020 21:46
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RalfJung commented Sep 26, 2020

Cc @rust-lang/wg-const-eval

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compiler/rustc_attr/src/builtin.rs
.span_err(attr.span, "allow_internal_unstable expects list of feature names");
None
})?;
let attrs = sess.filter_by_name(attrs, sym::allow_internal_unstable);
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I don't see how this PR fixes anything. All you've done is replace a ? operator with a filter map. But find_by_name will still only return a single attribute.

Please revert the PR. I'll reopen the issue, then we can discuss an actual fix.

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It's not find_by_name, but filter_by_name which returns an iterator with all matching attributes, instead of the first one.

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🤦 I apologize. I should not review half asleep

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It's fine. I'll check locally if the test case I added actually fails without

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bugadani commented Sep 26, 2020

@oli-obk

Without the changes, the added test case fails with the following (diff of stderr):

-       error: aborting due to 5 previous errors
+       error[E0658]: use of unstable library feature 'struct2_field'
+         --> $DIR/internal-unstable.rs:31:35
+          |
+       LL |     |x: internal_unstable::Bar| { access_field_allow2!(x) }; // regression test for #77088
+          |                                   ^^^^^^^^^^^^^^^^^^^^^^^
+          |
+          = help: add `#![feature(struct2_field)]` to the crate attributes to enable
+          = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+       error: aborting due to 6 previous errors

Yesterday, I had some trouble with this, the changes didn't seem to apply and the test case failed regardless. It seemed for a long time that even getting the list of attributes returned only 1. After wasting an hour and a half, I realized that I added struct_field2 to the macro, instead of struct2_field. 🤷‍♀️ I guess this piece of code is cursed.

Thanks for raising concerns, it's always good to double check.

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oli-obk commented Sep 26, 2020

Thanks for double checking!

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RalfJung commented Sep 26, 2020

Does this change fix both macros and stable const fn using #[allow_internal_unstable]?

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bugadani commented Sep 26, 2020

Does this change fix both macros and stable const fn using #[allow_internal_unstable]?

I'm not sure about const fn because I don't know which features would apply there and I had trouble with allowing the unchecked_unreachable hint. As far as I can see, the feature gates are checked through this piece of code, but I'm not sure if const fn actually accepts the features enabled this way.

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allow_internal_unstable attr only allowed once per function

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