Make `MaybeUninit::assume_init()` a `const fn` #66579

slightlyoutofphase · 2019-11-20T17:51:37Z

It can be, because it simply calls an intrinsic and then another function which is already a const fn (ManuallyDrop::into_inner specifically.)

Example use case for this:

https://github.com/slightlyoutofphase/staticvec/blob/addf203c0ec11905c403d25faacfdd29f9191a28/src/lib.rs#L50

If assume_init were const fn, then the linked new function could be also.

It can be, because it simply calls an intrinsics and then another function which is already a `const fn` (`ManuallyDrop::into_inner` specifically.) Example use case for this: https://github.com/slightlyoutofphase/staticvec/blob/addf203c0ec11905c403d25faacfdd29f9191a28/src/lib.rs#L50 If `assume_init` were `const fn`, then the linked `new` function could be also.

rust-highfive · 2019-11-20T17:51:47Z

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @joshtriplett (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

rust-highfive · 2019-11-20T17:58:13Z

The job x86_64-gnu-llvm-6.0 of your PR failed (pretty log, raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

2019-11-20T17:52:17.8492984Z ##[command]git remote add origin https://github.com/rust-lang/rust
2019-11-20T17:52:17.8505957Z ##[command]git config gc.auto 0
2019-11-20T17:52:17.8510007Z ##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
2019-11-20T17:52:17.8513336Z ##[command]git config --get-all http.proxy
2019-11-20T17:52:17.8518363Z ##[command]git -c http.extraheader="AUTHORIZATION: basic ***" fetch --force --tags --prune --progress --no-recurse-submodules --depth=2 origin +refs/heads/*:refs/remotes/origin/* +refs/pull/66579/merge:refs/remotes/pull/66579/merge
---
2019-11-20T17:57:54.8265910Z    Compiling core v0.0.0 (/checkout/src/libcore)
2019-11-20T17:57:54.8789202Z error: expected one of `extern` or `fn`, found keyword `const`
2019-11-20T17:57:54.8790038Z    --> src/libcore/mem/maybe_uninit.rs:485:16
2019-11-20T17:57:54.8790264Z     |
2019-11-20T17:57:54.8790550Z 485 |     pub unsafe const fn assume_init(self) -> T {
2019-11-20T17:57:54.8791126Z     |                ^^^^^ expected one of `extern` or `fn` here
2019-11-20T17:57:57.7735322Z error: unused import: `crate::intrinsics`
2019-11-20T17:57:57.7735768Z  --> src/libcore/mem/maybe_uninit.rs:1:5
2019-11-20T17:57:57.7735989Z   |
2019-11-20T17:57:57.7736194Z 1 | use crate::intrinsics;
2019-11-20T17:57:57.7736194Z 1 | use crate::intrinsics;
2019-11-20T17:57:57.7736427Z   |     ^^^^^^^^^^^^^^^^^
2019-11-20T17:57:57.7736598Z   |
2019-11-20T17:57:57.7736822Z   = note: `-D unused-imports` implied by `-D warnings`
2019-11-20T17:57:57.7736883Z 
2019-11-20T17:58:00.2426154Z    Compiling build_helper v0.1.0 (/checkout/src/build_helper)
2019-11-20T17:58:01.2591143Z    Compiling libc v0.2.64
2019-11-20T17:58:01.3199592Z error[E0599]: no method named `assume_init` found for type `mem::maybe_uninit::MaybeUninit<[mem::maybe_uninit::MaybeUninit<T>; _]>` in the current scope
2019-11-20T17:58:01.3200222Z     |
2019-11-20T17:58:01.3200452Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:01.3200761Z     | ------------------------ method `assume_init` not found for this
2019-11-20T17:58:01.3201114Z ...
2019-11-20T17:58:01.3201114Z ...
2019-11-20T17:58:01.3201397Z 297 |             MaybeUninit::<[MaybeUninit<T>; LEN]>::uninit().assume_init()
2019-11-20T17:58:01.3202196Z     |                                                            ^^^^^^^^^^^ method not found in `mem::maybe_uninit::MaybeUninit<[mem::maybe_uninit::MaybeUninit<T>; _]>`
2019-11-20T17:58:01.3282655Z error[E0599]: no method named `get_mut` found for type `&mut mem::maybe_uninit::MaybeUninit<T>` in the current scope
2019-11-20T17:58:01.3282983Z    --> src/libcore/mem/maybe_uninit.rs:361:18
2019-11-20T17:58:01.3283190Z     |
2019-11-20T17:58:01.3283455Z 361 |             self.get_mut()
2019-11-20T17:58:01.3283455Z 361 |             self.get_mut()
2019-11-20T17:58:01.3283780Z     |                  ^^^^^^^ method not found in `&mut mem::maybe_uninit::MaybeUninit<T>`
2019-11-20T17:58:01.3283997Z     |
2019-11-20T17:58:01.3284289Z     = help: items from traits can only be used if the trait is implemented and in scope
2019-11-20T17:58:01.3284580Z     = note: the following trait defines an item `get_mut`, perhaps you need to implement it:
2019-11-20T17:58:01.3285363Z             candidate #1: `slice::SliceIndex`
2019-11-20T17:58:01.3296270Z error[E0599]: no method named `assume_init` found for type `mem::maybe_uninit::MaybeUninit<T>` in the current scope
2019-11-20T17:58:01.3296746Z    --> src/libcore/ptr/mod.rs:617:9
2019-11-20T17:58:01.3296932Z     |
2019-11-20T17:58:01.3297153Z 617 |     tmp.assume_init()
---
2019-11-20T17:58:01.3311169Z     |
2019-11-20T17:58:01.3311395Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:01.3311884Z     | ------------------------ method `assume_init` not found for this
2019-11-20T17:58:01.3316378Z 
2019-11-20T17:58:01.6068276Z error[E0599]: no method named `read` found for type `&mem::maybe_uninit::MaybeUninit<T>` in the current scope
2019-11-20T17:58:01.6069047Z    --> src/libcore/array/iter.rs:138:57
2019-11-20T17:58:01.6069531Z     |
2019-11-20T17:58:01.6069818Z 138 |         let out = unsafe { self.data.get_unchecked(idx).read() };
2019-11-20T17:58:01.6070222Z     |                                                         ^^^^ method not found in `&mem::maybe_uninit::MaybeUninit<T>`
2019-11-20T17:58:01.6070265Z 
2019-11-20T17:58:01.6104815Z error[E0599]: no method named `read` found for type `&mem::maybe_uninit::MaybeUninit<T>` in the current scope
2019-11-20T17:58:01.6105102Z    --> src/libcore/array/iter.rs:187:68
2019-11-20T17:58:01.6105304Z     |
2019-11-20T17:58:01.6105609Z 187 |         let out = unsafe { self.data.get_unchecked(self.alive.end).read() };
2019-11-20T17:58:01.6106222Z     |                                                                    ^^^^ method not found in `&mem::maybe_uninit::MaybeUninit<T>`
2019-11-20T17:58:01.6158247Z error[E0599]: no method named `assume_init` found for type `mem::maybe_uninit::MaybeUninit<_>` in the current scope
2019-11-20T17:58:01.6158515Z    --> src/libcore/array/iter.rs:252:75
2019-11-20T17:58:01.6158728Z     |
2019-11-20T17:58:01.6158728Z     |
2019-11-20T17:58:01.6159180Z 252 |             let mut new_data: [MaybeUninit<T>; N] = MaybeUninit::uninit().assume_init();
2019-11-20T17:58:01.6159538Z     |                                                                           ^^^^^^^^^^^ method not found in `mem::maybe_uninit::MaybeUninit<_>`
2019-11-20T17:58:01.6160154Z    ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:01.6160527Z     |
2019-11-20T17:58:01.6160779Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:01.6161074Z     | ------------------------ method `assume_init` not found for this
2019-11-20T17:58:01.6161074Z     | ------------------------ method `assume_init` not found for this
2019-11-20T17:58:01.6165242Z 
2019-11-20T17:58:01.6188537Z error[E0599]: no method named `get_ref` found for type `&mem::maybe_uninit::MaybeUninit<T>` in the current scope
2019-11-20T17:58:01.6188975Z    --> src/libcore/array/iter.rs:259:58
2019-11-20T17:58:01.6189177Z     |
2019-11-20T17:58:01.6189679Z 259 |                 let clone = self.data.get_unchecked(idx).get_ref().clone();
2019-11-20T17:58:01.6190066Z     |                                                          ^^^^^^^ method not found in `&mem::maybe_uninit::MaybeUninit<T>`
2019-11-20T17:58:01.9014606Z    Compiling autocfg v0.1.6
2019-11-20T17:58:01.9014606Z    Compiling autocfg v0.1.6
2019-11-20T17:58:02.1032407Z error[E0599]: no method named `assume_init` found for type `mem::maybe_uninit::MaybeUninit<ffi::VaListImpl<'_>>` in the current scope
2019-11-20T17:58:02.1033019Z    --> src/libcore/ffi.rs:321:18
2019-11-20T17:58:02.1034271Z 321 |             dest.assume_init()
2019-11-20T17:58:02.1034271Z 321 |             dest.assume_init()
2019-11-20T17:58:02.1035322Z     |                  ^^^^^^^^^^^ method not found in `mem::maybe_uninit::MaybeUninit<ffi::VaListImpl<'_>>`
2019-11-20T17:58:02.1035933Z    ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:02.1036185Z     |
2019-11-20T17:58:02.1036465Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.1036812Z     | ------------------------ method `assume_init` not found for this
2019-11-20T17:58:02.1036812Z     | ------------------------ method `assume_init` not found for this
2019-11-20T17:58:02.1036875Z 
2019-11-20T17:58:02.3150771Z error[E0599]: no function or associated item named `first_ptr_mut` found for type `mem::maybe_uninit::MaybeUninit<_>` in the current scope
2019-11-20T17:58:02.3151102Z    --> src/libcore/slice/sort.rs:267:36
2019-11-20T17:58:02.3151324Z     |
2019-11-20T17:58:02.3151588Z 267 |             start_l = MaybeUninit::first_ptr_mut(&mut offsets_l);
2019-11-20T17:58:02.3152154Z     |                                    ^^^^^^^^^^^^^ function or associated item not found in `mem::maybe_uninit::MaybeUninit<_>`
2019-11-20T17:58:02.3152609Z    ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:02.3152811Z     |
2019-11-20T17:58:02.3153036Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.3153036Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.3153330Z     | ------------------------ function or associated item `first_ptr_mut` not found for this
2019-11-20T17:58:02.3153386Z 
2019-11-20T17:58:02.3181743Z error[E0599]: no function or associated item named `first_ptr_mut` found for type `mem::maybe_uninit::MaybeUninit<_>` in the current scope
2019-11-20T17:58:02.3182038Z    --> src/libcore/slice/sort.rs:268:34
2019-11-20T17:58:02.3182254Z     |
2019-11-20T17:58:02.3182506Z 268 |             end_l = MaybeUninit::first_ptr_mut(&mut offsets_l);
2019-11-20T17:58:02.3182841Z     |                                  ^^^^^^^^^^^^^ function or associated item not found in `mem::maybe_uninit::MaybeUninit<_>`
2019-11-20T17:58:02.3183258Z    ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:02.3183458Z     |
2019-11-20T17:58:02.3183671Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.3183671Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.3183951Z     | ------------------------ function or associated item `first_ptr_mut` not found for this
2019-11-20T17:58:02.3184016Z 
2019-11-20T17:58:02.3219427Z error[E0599]: no function or associated item named `first_ptr_mut` found for type `mem::maybe_uninit::MaybeUninit<_>` in the current scope
2019-11-20T17:58:02.3219749Z    --> src/libcore/slice/sort.rs:283:36
2019-11-20T17:58:02.3219961Z     |
2019-11-20T17:58:02.3220436Z 283 |             start_r = MaybeUninit::first_ptr_mut(&mut offsets_r);
2019-11-20T17:58:02.3221073Z     |                                    ^^^^^^^^^^^^^ function or associated item not found in `mem::maybe_uninit::MaybeUninit<_>`
2019-11-20T17:58:02.3221711Z    ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:02.3221908Z     |
2019-11-20T17:58:02.3222463Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.3222463Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.3222772Z     | ------------------------ function or associated item `first_ptr_mut` not found for this
2019-11-20T17:58:02.3226146Z 
2019-11-20T17:58:02.3252871Z error[E0599]: no function or associated item named `first_ptr_mut` found for type `mem::maybe_uninit::MaybeUninit<_>` in the current scope
2019-11-20T17:58:02.3253374Z    --> src/libcore/slice/sort.rs:284:34
2019-11-20T17:58:02.3253738Z     |
2019-11-20T17:58:02.3254163Z 284 |             end_r = MaybeUninit::first_ptr_mut(&mut offsets_r);
2019-11-20T17:58:02.3255304Z     |                                  ^^^^^^^^^^^^^ function or associated item not found in `mem::maybe_uninit::MaybeUninit<_>`
2019-11-20T17:58:02.3255780Z    ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:02.3255979Z     |
2019-11-20T17:58:02.3256219Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.3256219Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.3256563Z     | ------------------------ function or associated item `first_ptr_mut` not found for this
2019-11-20T17:58:02.6424887Z error[E0599]: no method named `get_mut` found for type `mem::maybe_uninit::MaybeUninit<[u8; 1024]>` in the current scope
2019-11-20T17:58:02.6425360Z    --> src/libcore/fmt/float.rs:24:64
2019-11-20T17:58:02.6425607Z     |
2019-11-20T17:58:02.6425607Z     |
2019-11-20T17:58:02.6425930Z 24  | ...                   false, buf.get_mut(), parts.get_mut());
2019-11-20T17:58:02.6426692Z     |                                  ^^^^^^^ method not found in `mem::maybe_uninit::MaybeUninit<[u8; 1024]>`
2019-11-20T17:58:02.6427444Z    ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:02.6427660Z     |
2019-11-20T17:58:02.6427915Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.6428251Z     | ------------------------ method `get_mut` not found for this
2019-11-20T17:58:02.6428251Z     | ------------------------ method `get_mut` not found for this
2019-11-20T17:58:02.6428477Z     |
2019-11-20T17:58:02.6428798Z     = help: items from traits can only be used if the trait is implemented and in scope
2019-11-20T17:58:02.6429280Z     = note: the following trait defines an item `get_mut`, perhaps you need to implement it:
2019-11-20T17:58:02.6429740Z             candidate #1: `slice::SliceIndex`
2019-11-20T17:58:02.6435225Z 
2019-11-20T17:58:02.6478396Z error[E0599]: no method named `get_mut` found for type `mem::maybe_uninit::MaybeUninit<[num::flt2dec::Part<'_>; 4]>` in the current scope
2019-11-20T17:58:02.6478785Z    --> src/libcore/fmt/float.rs:24:81
2019-11-20T17:58:02.6479044Z     |
2019-11-20T17:58:02.6479597Z 24  | ...                   false, buf.get_mut(), parts.get_mut());
2019-11-20T17:58:02.6480172Z     |                                                   ^^^^^^^ method not found in `mem::maybe_uninit::MaybeUninit<[num::flt2dec::Part<'_>; 4]>`
2019-11-20T17:58:02.6480878Z    ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:02.6481101Z     |
2019-11-20T17:58:02.6481365Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.6481667Z     | ------------------------ method `get_mut` not found for this
2019-11-20T17:58:02.6481667Z     | ------------------------ method `get_mut` not found for this
2019-11-20T17:58:02.6481890Z     |
2019-11-20T17:58:02.6482333Z     = help: items from traits can only be used if the trait is implemented and in scope
2019-11-20T17:58:02.6482632Z     = note: the following trait defines an item `get_mut`, perhaps you need to implement it:
2019-11-20T17:58:02.6482916Z             candidate #1: `slice::SliceIndex`
2019-11-20T17:58:02.6541766Z error[E0599]: no method named `get_mut` found for type `mem::maybe_uninit::MaybeUninit<[u8; 17]>` in the current scope
2019-11-20T17:58:02.6542088Z    --> src/libcore/fmt/float.rs:42:78
2019-11-20T17:58:02.6542285Z     |
2019-11-20T17:58:02.6542285Z     |
2019-11-20T17:58:02.6542543Z 42  | ...                   sign, precision, false, buf.get_mut(),
2019-11-20T17:58:02.6542904Z     |                                                   ^^^^^^^ method not found in `mem::maybe_uninit::MaybeUninit<[u8; 17]>`
2019-11-20T17:58:02.6543358Z    ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:02.6543541Z     |
2019-11-20T17:58:02.6543764Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.6544065Z     | ------------------------ method `get_mut` not found for this
2019-11-20T17:58:02.6544065Z     | ------------------------ method `get_mut` not found for this
2019-11-20T17:58:02.6544429Z     |
2019-11-20T17:58:02.6544718Z     = help: items from traits can only be used if the trait is implemented and in scope
2019-11-20T17:58:02.6545003Z     = note: the following trait defines an item `get_mut`, perhaps you need to implement it:
2019-11-20T17:58:02.6545252Z             candidate #1: `slice::SliceIndex`
2019-11-20T17:58:02.6552215Z 
2019-11-20T17:58:02.6642211Z error[E0599]: no method named `get_mut` found for type `mem::maybe_uninit::MaybeUninit<[num::flt2dec::Part<'_>; 4]>` in the current scope
2019-11-20T17:58:02.6642518Z    --> src/libcore/fmt/float.rs:43:56
2019-11-20T17:58:02.6643220Z 43  | ...                   parts.get_mut());
2019-11-20T17:58:02.6643220Z 43  | ...                   parts.get_mut());
2019-11-20T17:58:02.6643655Z     |                             ^^^^^^^ method not found in `mem::maybe_uninit::MaybeUninit<[num::flt2dec::Part<'_>; 4]>`
2019-11-20T17:58:02.6644185Z    ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:02.6644532Z     |
2019-11-20T17:58:02.6644792Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.6645106Z     | ------------------------ method `get_mut` not found for this
2019-11-20T17:58:02.6645106Z     | ------------------------ method `get_mut` not found for this
2019-11-20T17:58:02.6645334Z     |
2019-11-20T17:58:02.6645645Z     = help: items from traits can only be used if the trait is implemented and in scope
2019-11-20T17:58:02.6645955Z     = note: the following trait defines an item `get_mut`, perhaps you need to implement it:
2019-11-20T17:58:02.6646244Z             candidate #1: `slice::SliceIndex`
2019-11-20T17:58:02.6654061Z error[E0599]: no method named `get_mut` found for type `mem::maybe_uninit::MaybeUninit<[u8; 1024]>` in the current scope
2019-11-20T17:58:02.6654387Z    --> src/libcore/fmt/float.rs:82:62
2019-11-20T17:58:02.6654604Z     |
2019-11-20T17:58:02.6654604Z     |
2019-11-20T17:58:02.6654905Z 82  | ...                   upper, buf.get_mut(), parts.get_mut());
2019-11-20T17:58:02.6655327Z     |                                  ^^^^^^^ method not found in `mem::maybe_uninit::MaybeUninit<[u8; 1024]>`
2019-11-20T17:58:02.6655839Z    ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:02.6656054Z     |
2019-11-20T17:58:02.6656316Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.6656672Z     | ------------------------ method `get_mut` not found for this
2019-11-20T17:58:02.6656672Z     | ------------------------ method `get_mut` not found for this
2019-11-20T17:58:02.6656888Z     |
2019-11-20T17:58:02.6657195Z     = help: items from traits can only be used if the trait is implemented and in scope
2019-11-20T17:58:02.6657538Z     = note: the following trait defines an item `get_mut`, perhaps you need to implement it:
2019-11-20T17:58:02.6657977Z             candidate #1: `slice::SliceIndex`
2019-11-20T17:58:02.6664379Z 
2019-11-20T17:58:02.6664918Z error[E0599]: no method named `get_mut` found for type `mem::maybe_uninit::MaybeUninit<[num::flt2dec::Part<'_>; 6]>` in the current scope
2019-11-20T17:58:02.6665178Z    --> src/libcore/fmt/float.rs:82:79
2019-11-20T17:58:02.6665426Z     |
2019-11-20T17:58:02.6665715Z 82  | ...                   upper, buf.get_mut(), parts.get_mut());
2019-11-20T17:58:02.6666113Z     |                                                   ^^^^^^^ method not found in `mem::maybe_uninit::MaybeUninit<[num::flt2dec::Part<'_>; 6]>`
2019-11-20T17:58:02.6666739Z    ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:02.6666999Z     |
2019-11-20T17:58:02.6667289Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.6667600Z     | ------------------------ method `get_mut` not found for this
2019-11-20T17:58:02.6667600Z     | ------------------------ method `get_mut` not found for this
2019-11-20T17:58:02.6667843Z     |
2019-11-20T17:58:02.6668145Z     = help: items from traits can only be used if the trait is implemented and in scope
2019-11-20T17:58:02.6668451Z     = note: the following trait defines an item `get_mut`, perhaps you need to implement it:
2019-11-20T17:58:02.6668726Z             candidate #1: `slice::SliceIndex`
2019-11-20T17:58:02.6703847Z error[E0599]: no method named `get_mut` found for type `mem::maybe_uninit::MaybeUninit<[u8; 17]>` in the current scope
2019-11-20T17:58:02.6704185Z    --> src/libcore/fmt/float.rs:102:58
2019-11-20T17:58:02.6704393Z     |
2019-11-20T17:58:02.6704393Z     |
2019-11-20T17:58:02.6704666Z 102 | ...                   buf.get_mut(), parts.get_mut());
2019-11-20T17:58:02.6705244Z     |                           ^^^^^^^ method not found in `mem::maybe_uninit::MaybeUninit<[u8; 17]>`
2019-11-20T17:58:02.6705719Z    ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:02.6705924Z     |
2019-11-20T17:58:02.6706171Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.6706502Z     | ------------------------ method `get_mut` not found for this
2019-11-20T17:58:02.6706502Z     | ------------------------ method `get_mut` not found for this
2019-11-20T17:58:02.6706709Z     |
2019-11-20T17:58:02.6706999Z     = help: items from traits can only be used if the trait is implemented and in scope
2019-11-20T17:58:02.6707336Z     = note: the following trait defines an item `get_mut`, perhaps you need to implement it:
2019-11-20T17:58:02.6707600Z             candidate #1: `slice::SliceIndex`
2019-11-20T17:58:02.6712110Z 
2019-11-20T17:58:02.6752010Z error[E0599]: no method named `get_mut` found for type `mem::maybe_uninit::MaybeUninit<[num::flt2dec::Part<'_>; 6]>` in the current scope
2019-11-20T17:58:02.6752291Z    --> src/libcore/fmt/float.rs:102:75
2019-11-20T17:58:02.6752506Z     |
2019-11-20T17:58:02.6752781Z 102 | ...                   buf.get_mut(), parts.get_mut());
2019-11-20T17:58:02.6753139Z     |                                            ^^^^^^^ method not found in `mem::maybe_uninit::MaybeUninit<[num::flt2dec::Part<'_>; 6]>`
2019-11-20T17:58:02.6753601Z    ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:02.6753790Z     |
2019-11-20T17:58:02.6754048Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.6754333Z     | ------------------------ method `get_mut` not found for this
2019-11-20T17:58:02.6754333Z     | ------------------------ method `get_mut` not found for this
2019-11-20T17:58:02.6754540Z     |
2019-11-20T17:58:02.6755318Z     = help: items from traits can only be used if the trait is implemented and in scope
2019-11-20T17:58:02.6755686Z     = note: the following trait defines an item `get_mut`, perhaps you need to implement it:
2019-11-20T17:58:02.6755971Z             candidate #1: `slice::SliceIndex`
2019-11-20T17:58:02.6760390Z 
2019-11-20T17:58:02.6885253Z error[E0599]: no function or associated item named `first_ptr` found for type `mem::maybe_uninit::MaybeUninit<_>` in the current scope
2019-11-20T17:58:02.6885589Z    --> src/libcore/fmt/num.rs:87:26
2019-11-20T17:58:02.6886068Z 87  |             MaybeUninit::first_ptr(buf),
2019-11-20T17:58:02.6886068Z 87  |             MaybeUninit::first_ptr(buf),
2019-11-20T17:58:02.6886544Z     |                          ^^^^^^^^^ function or associated item not found in `mem::maybe_uninit::MaybeUninit<_>`
2019-11-20T17:58:02.6887314Z    ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:02.6887756Z     |
2019-11-20T17:58:02.6888464Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.6888464Z 221 | pub union MaybeUninit<T> {
2019-11-20T17:58:02.6888978Z     | ------------------------ function or associated item `first_ptr` not found for this
2019-11-20T17:58:02.6893834Z 
2019-11-20T17:58:02.7179970Z error[E0599]: no function or associated item named `first_ptr_mut` found for type `mem::maybe_uninit::MaybeUninit<_>` in the current scope
2019-11-20T17:58:02.7180266Z    --> src/libcore/fmt/num.rs:196:40
2019-11-20T17:58:02.7180732Z 191 | / macro_rules! impl_Display {
2019-11-20T17:58:02.7180732Z 191 | / macro_rules! impl_Display {
2019-11-20T17:58:02.7181024Z 192 | |     ($($t:ident),* as $u:ident via $conv_fn:ident named $name:ident) => {
2019-11-20T17:58:02.7181355Z 193 | |         fn $name(mut n: $u, is_nonnegative: bool, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2019-11-20T17:58:02.7181665Z 194 | |             let mut buf = [MaybeUninit::<u8>::uninit(); 39];
2019-11-20T17:58:02.7181934Z 195 | |             let mut curr = buf.len() as isize;
2019-11-20T17:58:02.7182247Z 196 | |             let buf_ptr = MaybeUninit::first_ptr_mut(&mut buf);
2019-11-20T17:58:02.7182606Z     | |                                        ^^^^^^^^^^^^^ function or associated item not found in `mem::maybe_uninit::MaybeUninit<_>`
2019-11-20T17:58:02.7183093Z 259 | |     };
2019-11-20T17:58:02.7183327Z 260 | | }
2019-11-20T17:58:02.7183327Z 260 | | }
2019-11-20T17:58:02.7183608Z     | |_- in this expansion of `impl_Display!`
2019-11-20T17:58:02.7184157Z 267 | /     impl_Display!(
2019-11-20T17:58:02.7184157Z 267 | /     impl_Display!(
2019-11-20T17:58:02.7184701Z 268 | |         i8, u8, i16, u16, i32, u32, i64, u64, usize, isize
2019-11-20T17:58:02.7185223Z 269 | |             as u64 via to_u64 named fmt_u64
2019-11-20T17:58:02.7185766Z     | |______- in this macro invocation
2019-11-20T17:58:02.7185952Z     | 
2019-11-20T17:58:02.7186195Z    ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:02.7186380Z     |
2019-11-20T17:58:02.7186380Z     |
2019-11-20T17:58:02.7186632Z 221 |   pub union MaybeUninit<T> {
2019-11-20T17:58:02.7186970Z     |   ------------------------ function or associated item `first_ptr_mut` not found for this
2019-11-20T17:58:02.7191488Z 
2019-11-20T17:58:02.7356284Z error[E0599]: no function or associated item named `first_ptr_mut` found for type `mem::maybe_uninit::MaybeUninit<_>` in the current scope
2019-11-20T17:58:02.7356577Z    --> src/libcore/fmt/num.rs:196:40
2019-11-20T17:58:02.7357001Z 191 | / macro_rules! impl_Display {
2019-11-20T17:58:02.7357001Z 191 | / macro_rules! impl_Display {
2019-11-20T17:58:02.7357326Z 192 | |     ($($t:ident),* as $u:ident via $conv_fn:ident named $name:ident) => {
2019-11-20T17:58:02.7357638Z 193 | |         fn $name(mut n: $u, is_nonnegative: bool, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2019-11-20T17:58:02.7357947Z 194 | |             let mut buf = [MaybeUninit::<u8>::uninit(); 39];
2019-11-20T17:58:02.7358215Z 195 | |             let mut curr = buf.len() as isize;
2019-11-20T17:58:02.7358493Z 196 | |             let buf_ptr = MaybeUninit::first_ptr_mut(&mut buf);
2019-11-20T17:58:02.7358869Z     | |                                        ^^^^^^^^^^^^^ function or associated item not found in `mem::maybe_uninit::MaybeUninit<_>`
2019-11-20T17:58:02.7359339Z 259 | |     };
2019-11-20T17:58:02.7359581Z 260 | | }
2019-11-20T17:58:02.7359581Z 260 | | }
2019-11-20T17:58:02.7359833Z     | |_- in this expansion of `impl_Display!`
2019-11-20T17:58:02.7360024Z ...
2019-11-20T17:58:02.7360282Z 280 |   impl_Display!(i128, u128 as u128 via to_u128 named fmt_u128);
2019-11-20T17:58:02.7360991Z     | 
2019-11-20T17:58:02.7361206Z    ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:02.7361409Z     |
2019-11-20T17:58:02.7361639Z 221 |   pub union MaybeUninit<T> {
2019-11-20T17:58:02.7361639Z 221 |   pub union MaybeUninit<T> {
2019-11-20T17:58:02.7361969Z     |   ------------------------ function or associated item `first_ptr_mut` not found for this
2019-11-20T17:58:02.9867856Z    Compiling std v0.0.0 (/checkout/src/libstd)
2019-11-20T17:58:02.9867856Z    Compiling std v0.0.0 (/checkout/src/libstd)
2019-11-20T17:58:03.1318639Z error[E0599]: no method named `assume_init` found for type `mem::maybe_uninit::MaybeUninit<core_arch::x86::__m128>` in the current scope
2019-11-20T17:58:03.1319046Z     --> src/libcore/../stdarch/crates/core_arch/src/x86/sse.rs:1867:42
2019-11-20T17:58:03.1319275Z      |
2019-11-20T17:58:03.1319746Z 1867 |     mem::MaybeUninit::<__m128>::uninit().assume_init()
2019-11-20T17:58:03.1320115Z      |                                          ^^^^^^^^^^^ method not found in `mem::maybe_uninit::MaybeUninit<core_arch::x86::__m128>`
2019-11-20T17:58:03.1320839Z     ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:03.1321214Z      |
2019-11-20T17:58:03.1321479Z 221  | pub union MaybeUninit<T> {
2019-11-20T17:58:03.1321801Z      | ------------------------ method `assume_init` not found for this
2019-11-20T17:58:03.1321801Z      | ------------------------ method `assume_init` not found for this
2019-11-20T17:58:03.1321841Z 
2019-11-20T17:58:03.3638890Z error[E0599]: no method named `assume_init` found for type `mem::maybe_uninit::MaybeUninit<core_arch::x86::__m128d>` in the current scope
2019-11-20T17:58:03.3639249Z     --> src/libcore/../stdarch/crates/core_arch/src/x86/sse2.rs:2862:43
2019-11-20T17:58:03.3639537Z      |
2019-11-20T17:58:03.3639981Z 2862 |     mem::MaybeUninit::<__m128d>::uninit().assume_init()
2019-11-20T17:58:03.3640318Z      |                                           ^^^^^^^^^^^ method not found in `mem::maybe_uninit::MaybeUninit<core_arch::x86::__m128d>`
2019-11-20T17:58:03.3640767Z     ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:03.3640976Z      |
2019-11-20T17:58:03.3641197Z 221  | pub union MaybeUninit<T> {
2019-11-20T17:58:03.3641474Z      | ------------------------ method `assume_init` not found for this
2019-11-20T17:58:03.3641474Z      | ------------------------ method `assume_init` not found for this
2019-11-20T17:58:03.3645521Z 
2019-11-20T17:58:03.3667094Z error[E0599]: no method named `assume_init` found for type `mem::maybe_uninit::MaybeUninit<core_arch::x86::__m128i>` in the current scope
2019-11-20T17:58:03.3667380Z     --> src/libcore/../stdarch/crates/core_arch/src/x86/sse2.rs:2873:43
2019-11-20T17:58:03.3667601Z      |
2019-11-20T17:58:03.3667845Z 2873 |     mem::MaybeUninit::<__m128i>::uninit().assume_init()
2019-11-20T17:58:03.3668356Z      |                                           ^^^^^^^^^^^ method not found in `mem::maybe_uninit::MaybeUninit<core_arch::x86::__m128i>`
2019-11-20T17:58:03.3668835Z     ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:03.3669034Z      |
2019-11-20T17:58:03.3669246Z 221  | pub union MaybeUninit<T> {
2019-11-20T17:58:03.3669513Z      | ------------------------ method `assume_init` not found for this
2019-11-20T17:58:03.3669513Z      | ------------------------ method `assume_init` not found for this
2019-11-20T17:58:03.3673219Z 
2019-11-20T17:58:03.3832643Z    Compiling cmake v0.1.38
2019-11-20T17:58:03.7474498Z error[E0599]: no method named `assume_init` found for type `mem::maybe_uninit::MaybeUninit<core_arch::x86::__m256>` in the current scope
2019-11-20T17:58:03.7475011Z     --> src/libcore/../stdarch/crates/core_arch/src/x86/avx.rs:2960:42
2019-11-20T17:58:03.7475467Z      |
2019-11-20T17:58:03.7475778Z 2960 |     mem::MaybeUninit::<__m256>::uninit().assume_init()
2019-11-20T17:58:03.7476559Z      |                                          ^^^^^^^^^^^ method not found in `mem::maybe_uninit::MaybeUninit<core_arch::x86::__m256>`
2019-11-20T17:58:03.7477041Z     ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:03.7477239Z      |
2019-11-20T17:58:03.7477504Z 221  | pub union MaybeUninit<T> {
2019-11-20T17:58:03.7478206Z      | ------------------------ method `assume_init` not found for this
2019-11-20T17:58:03.7478206Z      | ------------------------ method `assume_init` not found for this
2019-11-20T17:58:03.7482857Z 
2019-11-20T17:58:03.7511211Z error[E0599]: no method named `assume_init` found for type `mem::maybe_uninit::MaybeUninit<core_arch::x86::__m256d>` in the current scope
2019-11-20T17:58:03.7511730Z     --> src/libcore/../stdarch/crates/core_arch/src/x86/avx.rs:2972:43
2019-11-20T17:58:03.7511970Z      |
2019-11-20T17:58:03.7512254Z 2972 |     mem::MaybeUninit::<__m256d>::uninit().assume_init()
2019-11-20T17:58:03.7512646Z      |                                           ^^^^^^^^^^^ method not found in `mem::maybe_uninit::MaybeUninit<core_arch::x86::__m256d>`
2019-11-20T17:58:03.7513132Z     ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:03.7513333Z      |
2019-11-20T17:58:03.7513605Z 221  | pub union MaybeUninit<T> {
2019-11-20T17:58:03.7513925Z      | ------------------------ method `assume_init` not found for this
2019-11-20T17:58:03.7513925Z      | ------------------------ method `assume_init` not found for this
2019-11-20T17:58:03.7513964Z 
2019-11-20T17:58:03.7550070Z error[E0599]: no method named `assume_init` found for type `mem::maybe_uninit::MaybeUninit<core_arch::x86::__m256i>` in the current scope
2019-11-20T17:58:03.7550378Z     --> src/libcore/../stdarch/crates/core_arch/src/x86/avx.rs:2984:43
2019-11-20T17:58:03.7550600Z      |
2019-11-20T17:58:03.7551457Z 2984 |     mem::MaybeUninit::<__m256i>::uninit().assume_init()
2019-11-20T17:58:03.7551889Z      |                                           ^^^^^^^^^^^ method not found in `mem::maybe_uninit::MaybeUninit<core_arch::x86::__m256i>`
2019-11-20T17:58:03.7552392Z     ::: src/libcore/mem/maybe_uninit.rs:221:1
2019-11-20T17:58:03.7552616Z      |
2019-11-20T17:58:03.7552866Z 221  | pub union MaybeUninit<T> {
2019-11-20T17:58:03.7553171Z      | ------------------------ method `assume_init` not found for this
---
2019-11-20T17:58:05.3393938Z   local time: Wed Nov 20 17:58:05 UTC 2019
2019-11-20T17:58:05.6412901Z   network time: Wed, 20 Nov 2019 17:58:05 GMT
2019-11-20T17:58:05.6417696Z == end clock drift check ==
2019-11-20T17:58:07.2387168Z 
2019-11-20T17:58:07.2521577Z ##[error]Bash exited with code '1'.
2019-11-20T17:58:07.2544653Z ##[section]Starting: Checkout
2019-11-20T17:58:07.2546058Z ==============================================================================
2019-11-20T17:58:07.2546120Z Task         : Get sources
2019-11-20T17:58:07.2546156Z Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

Did not know it mattered TBH!

rust-highfive · 2019-11-20T18:07:41Z

The job x86_64-gnu-llvm-6.0 of your PR failed (pretty log, raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

2019-11-20T18:00:06.2030858Z ##[command]git remote add origin https://github.com/rust-lang/rust
2019-11-20T18:00:06.8007333Z ##[command]git config gc.auto 0
2019-11-20T18:00:06.8015273Z ##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
2019-11-20T18:00:06.8017016Z ##[command]git config --get-all http.proxy
2019-11-20T18:00:06.8020441Z ##[command]git -c http.extraheader="AUTHORIZATION: basic ***" fetch --force --tags --prune --progress --no-recurse-submodules --depth=2 origin +refs/heads/*:refs/remotes/origin/* +refs/pull/66579/merge:refs/remotes/pull/66579/merge
---
2019-11-20T18:07:30.9287062Z    Compiling compiler_builtins v0.1.18
2019-11-20T18:07:30.9288361Z error[E0723]: can only call a curated list of intrinsics in `min_const_fn`
2019-11-20T18:07:30.9288847Z    --> src/libcore/mem/maybe_uninit.rs:486:9
2019-11-20T18:07:30.9289091Z     |
2019-11-20T18:07:30.9289389Z 486 |         intrinsics::panic_if_uninhabited::<T>();
2019-11-20T18:07:30.9289879Z     |
2019-11-20T18:07:30.9289879Z     |
2019-11-20T18:07:30.9290271Z     = note: for more information, see issue ***/issues/57563
2019-11-20T18:07:30.9290569Z     = help: add `#![feature(const_fn)]` to the crate attributes to enable
2019-11-20T18:07:32.1727612Z    Compiling backtrace-sys v0.1.32
2019-11-20T18:07:33.1253742Z    Compiling unwind v0.0.0 (/checkout/src/libunwind)
2019-11-20T18:07:33.8961161Z error: aborting due to previous error
2019-11-20T18:07:33.8961300Z 
---
2019-11-20T18:07:34.0670723Z   local time: Wed Nov 20 18:07:34 UTC 2019
2019-11-20T18:07:34.3510655Z   network time: Wed, 20 Nov 2019 18:07:34 GMT
2019-11-20T18:07:34.3510772Z == end clock drift check ==
2019-11-20T18:07:35.7477276Z 
2019-11-20T18:07:35.7539256Z ##[error]Bash exited with code '1'.
2019-11-20T18:07:35.7567545Z ##[section]Starting: Checkout
2019-11-20T18:07:35.7569150Z ==============================================================================
2019-11-20T18:07:35.7569204Z Task         : Get sources
2019-11-20T18:07:35.7569266Z Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

Hopefully this works. Based on the following playground link, panic_if_uninhabited *is* already valid in `const fn`, to be clear: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=8cbb9b4778e8f93ee1863c64995d15a7

rust-highfive · 2019-11-20T19:39:55Z

The job x86_64-gnu-llvm-6.0 of your PR failed (pretty log, raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

2019-11-20T19:33:30.0604629Z ##[command]git remote add origin https://github.com/rust-lang/rust
2019-11-20T19:33:30.0801818Z ##[command]git config gc.auto 0
2019-11-20T19:33:30.0881227Z ##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
2019-11-20T19:33:30.0944126Z ##[command]git config --get-all http.proxy
2019-11-20T19:33:30.1105196Z ##[command]git -c http.extraheader="AUTHORIZATION: basic ***" fetch --force --tags --prune --progress --no-recurse-submodules --depth=2 origin +refs/heads/*:refs/remotes/origin/* +refs/pull/66579/merge:refs/remotes/pull/66579/merge
---
2019-11-20T19:39:40.6556214Z    Compiling compiler_builtins v0.1.18
2019-11-20T19:39:41.1987352Z error[E0723]: can only call a curated list of intrinsics in `min_const_fn`
2019-11-20T19:39:41.1988566Z    --> src/libcore/mem/maybe_uninit.rs:486:9
2019-11-20T19:39:41.1989148Z     |
2019-11-20T19:39:41.1990287Z 486 |         crate::intrinsics::panic_if_uninhabited::<T>();
2019-11-20T19:39:41.1991212Z     |
2019-11-20T19:39:41.1991212Z     |
2019-11-20T19:39:41.1991691Z     = note: for more information, see issue ***/issues/57563
2019-11-20T19:39:41.1992039Z     = help: add `#![feature(const_fn)]` to the crate attributes to enable
2019-11-20T19:39:42.4719690Z    Compiling backtrace-sys v0.1.32
2019-11-20T19:39:43.3982407Z    Compiling unwind v0.0.0 (/checkout/src/libunwind)
2019-11-20T19:39:44.2896352Z error: aborting due to previous error
2019-11-20T19:39:44.2900284Z 
---
2019-11-20T19:39:44.5990524Z   local time: Wed Nov 20 19:39:44 UTC 2019
2019-11-20T19:39:44.8821771Z   network time: Wed, 20 Nov 2019 19:39:44 GMT
2019-11-20T19:39:44.8821907Z == end clock drift check ==
2019-11-20T19:39:46.3444051Z 
2019-11-20T19:39:46.3553655Z ##[error]Bash exited with code '1'.
2019-11-20T19:39:46.3584559Z ##[section]Starting: Checkout
2019-11-20T19:39:46.3586365Z ==============================================================================
2019-11-20T19:39:46.3586448Z Task         : Get sources
2019-11-20T19:39:46.3586503Z Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

Definitely confused about why `libcore` can't already use fully itself though.

rust-highfive · 2019-11-20T19:51:08Z

The job x86_64-gnu-llvm-6.0 of your PR failed (pretty log, raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

2019-11-20T19:44:40.4053842Z ##[command]git remote add origin https://github.com/rust-lang/rust
2019-11-20T19:44:40.4264116Z ##[command]git config gc.auto 0
2019-11-20T19:44:40.4331259Z ##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
2019-11-20T19:44:40.4392000Z ##[command]git config --get-all http.proxy
2019-11-20T19:44:40.4539917Z ##[command]git -c http.extraheader="AUTHORIZATION: basic ***" fetch --force --tags --prune --progress --no-recurse-submodules --depth=2 origin +refs/heads/*:refs/remotes/origin/* +refs/pull/66579/merge:refs/remotes/pull/66579/merge
---
2019-11-20T19:50:57.8110344Z    Compiling compiler_builtins v0.1.18
2019-11-20T19:50:58.1249053Z error[E0723]: can only call a curated list of intrinsics in `min_const_fn`
2019-11-20T19:50:58.1249507Z    --> src/libcore/mem/maybe_uninit.rs:486:9
2019-11-20T19:50:58.1249771Z     |
2019-11-20T19:50:58.1250071Z 486 |         crate::intrinsics::panic_if_uninhabited::<T>();
2019-11-20T19:50:58.1250641Z     |
2019-11-20T19:50:58.1250641Z     |
2019-11-20T19:50:58.1251048Z     = note: for more information, see issue ***/issues/57563
2019-11-20T19:50:58.1251389Z     = help: add `#![feature(const_fn)]` to the crate attributes to enable
2019-11-20T19:50:59.7159671Z    Compiling unwind v0.0.0 (/checkout/src/libunwind)
2019-11-20T19:51:00.5870125Z    Compiling backtrace-sys v0.1.32
2019-11-20T19:51:01.2403933Z error: aborting due to previous error
2019-11-20T19:51:01.2404086Z 
---
2019-11-20T19:51:01.5259532Z   local time: Wed Nov 20 19:51:01 UTC 2019
2019-11-20T19:51:01.8036378Z   network time: Wed, 20 Nov 2019 19:51:01 GMT
2019-11-20T19:51:01.8036470Z == end clock drift check ==
2019-11-20T19:51:03.1556403Z 
2019-11-20T19:51:03.1655305Z ##[error]Bash exited with code '1'.
2019-11-20T19:51:03.1684043Z ##[section]Starting: Checkout
2019-11-20T19:51:03.1685566Z ==============================================================================
2019-11-20T19:51:03.1685617Z Task         : Get sources
2019-11-20T19:51:03.1685676Z Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

slightlyoutofphase · 2019-11-20T19:58:41Z

Alright, I don't get it. Am I seeing some kind of weird attribute bug here?

#![feature(const_fn)] is of course already set in lib.rs for libcore, as it pretty obviously has to be.

slightlyoutofphase · 2019-11-20T20:15:24Z

For reference, here is the entirety of maybe_uninit.rs extracted into a playground crate, with no changes but to comment out the stability attributes so that the compiler doesn't raise E0734, as well as to add the necessary attributes directly at the top, and change a couple of instances of crate:: to core:::

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=7e7a906d30454899603e91555eb2e95c

In this form, assume_init compiles without issues as a const fn (which is to say, it's something anyone using nightly could write themselves at any time.)

rust-highfive · 2019-11-20T21:03:51Z

The job x86_64-gnu-llvm-6.0 of your PR failed (pretty log, raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

2019-11-20T20:57:03.0407851Z ##[command]git remote add origin https://github.com/rust-lang/rust
2019-11-20T20:57:03.0619174Z ##[command]git config gc.auto 0
2019-11-20T20:57:03.0691009Z ##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
2019-11-20T20:57:03.0740827Z ##[command]git config --get-all http.proxy
2019-11-20T20:57:03.0890514Z ##[command]git -c http.extraheader="AUTHORIZATION: basic ***" fetch --force --tags --prune --progress --no-recurse-submodules --depth=2 origin +refs/heads/*:refs/remotes/origin/* +refs/pull/66579/merge:refs/remotes/pull/66579/merge
---
2019-11-20T21:03:31.1934477Z    Compiling compiler_builtins v0.1.18
2019-11-20T21:03:31.7347702Z error[E0723]: can only call a curated list of intrinsics in `min_const_fn`
2019-11-20T21:03:31.7348123Z    --> src/libcore/mem/maybe_uninit.rs:486:9
2019-11-20T21:03:31.7348362Z     |
2019-11-20T21:03:31.7348844Z 486 |         intrinsics::panic_if_uninhabited::<T>();
2019-11-20T21:03:31.7349526Z     |
2019-11-20T21:03:31.7349526Z     |
2019-11-20T21:03:31.7349927Z     = note: for more information, see issue ***/issues/57563
2019-11-20T21:03:31.7350231Z     = help: add `#![feature(const_fn)]` to the crate attributes to enable
2019-11-20T21:03:33.1160414Z    Compiling backtrace-sys v0.1.32
2019-11-20T21:03:34.0397143Z    Compiling unwind v0.0.0 (/checkout/src/libunwind)
2019-11-20T21:03:34.8493342Z error: aborting due to previous error
2019-11-20T21:03:34.8493452Z 
---
2019-11-20T21:03:35.2145066Z   local time: Wed Nov 20 21:03:35 UTC 2019
2019-11-20T21:03:35.2992865Z   network time: Wed, 20 Nov 2019 21:03:35 GMT
2019-11-20T21:03:35.2997157Z == end clock drift check ==
2019-11-20T21:03:36.7609417Z 
2019-11-20T21:03:36.7715121Z ##[error]Bash exited with code '1'.
2019-11-20T21:03:36.7745012Z ##[section]Starting: Checkout
2019-11-20T21:03:36.7747055Z ==============================================================================
2019-11-20T21:03:36.7747113Z Task         : Get sources
2019-11-20T21:03:36.7747194Z Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

slightlyoutofphase · 2019-11-20T21:07:21Z

Alright, not gonna clog up the build queue anymore.

Should I open a bug for this, though, or is there something else I'm missing here?

Does it maybe have something to do with the fact that libcore is of course no_core, whereas the working playground example I linked to was not?

Centril · 2019-11-20T21:34:39Z

The behavior you are seeing is here is by design and not a bug. The difference between the playground example and the actual libcore is that you've omitted #![feature(staged_api)]. As part of the static analysis the compiler performs, we ensure that crates with #![feature(staged_api)] are not allowed to use unstable const-features in stable const fns (so called min_const_fns) irrespective of whether #![feature(const_fn)] or that feature is enabled. More specifically, there are two features here that you need but cannot use in stable const fns:

The ability to call panic_if_uninhabited in stable const fns.
The ability to access union fields (which effectively amount to mem::transmutes).

For the time being, you can use rustc_const_unstable instead to make the function const fn on nightly-only.

slightlyoutofphase · 2019-11-20T22:31:05Z

The behavior you are seeing is here is by design and not a bug. The difference between the playground example and the actual libcore is that you've omitted #![feature(staged_api)]. As part of the static analysis the compiler performs, we ensure that crates with #![feature(staged_api)] are not allowed to use unstable const-features in stable const fns (so called min_const_fns) irrespective of whether #![feature(const_fn)] or that feature is enabled. More specifically, there are two features here that you need but cannot use in stable const fns:

The ability to call panic_if_uninhabited in stable const fns.

The ability to access union fields (which effectively amount to mem::transmutes).

For the time being, you can use rustc_const_unstable instead to make the function const fn on nightly-only.

Ah, yeah, it would have to be that way wouldn't it? Sorry for my clumsy attempts so far. Pretty sure libcore compiled fine on the in-progress builds though so I think I got it right this time.

I can add a test for it a bit later also, if that's something that would generally be wanted.

Centril · 2019-11-20T22:37:09Z

Yeah I do think you got it right. It would be good to squash the commits. Tests would also be neat; somewhere in src/test/ui/consts/ would be ideal.

cc @oli-obk @RalfJung

slightlyoutofphase · 2019-11-21T01:08:01Z

Hmm, I'm not sure this will work as-is. Trying to actually use it while writing a test I get "calling intrinsic panic_if_uninhabited needs an rfc before being allowed inside constants".

It's unclear if that's meant literally though, because looking into it further, it seems like that message is just a catch-all for anything not present in librustc_mir/interpret/intrinsics.rs in the emulate_intrinsic function.

Miri seems to have a version of it that looks compatible (or at least that it could be made compatible) with the code in librustc_mir, though:
https://github.com/rust-lang/miri/blob/35e92d942093fad264ff010957d2eecb13a68315/src/shims/intrinsics.rs#L400

RalfJung · 2019-11-21T08:18:58Z

I am not a big fan of letting const code do the equivalent of mem::uninitialized() before it can do mem::zeroed().

RalfJung · 2019-11-21T08:20:05Z

Hmm, I'm not sure this will work as-is. Trying to actually use it while writing a test I get "calling intrinsic panic_if_uninhabited needs an rfc before being allowed inside constants".

See #66275: intrinsics need to be specifically support in const fn, and this one is not yet. Moreover, there is a bug in const-checking (fixed by said PR) that leads to a bad error message.

RalfJung · 2019-11-21T09:07:17Z

To elaborate on my earlier post: at the current state, I don't view "because we can" as sufficient motivation for making tricky operations like assume_init CTFE-compatible.

The one use-case given is already a hack. MaybeUninit::uninit().assume_init() should basically never be used, currently it is used because we don't have stable const-array-initializers yet. Now this PR proposes to home in on that hack and adjust even more things around it. That does not seem like a great road to go down.

This is just an unstable experiment, so not a terribly big deal, but I'd rather we block stabilizing assume_init in CTFE on first having const-array-initializers stable. Then we don't drive people even more towards using MaybeUninit::uninit().assume_init(), which really is like the dreaded mem::uninitialized() but worse.

For StaticVec, couldn't that become const-compatible by making things a bit more hacky and using a type like this?

pub struct StaticVec<T, const N: usize> {
  data: MaybeUninit<[MaybeUninit<T>; N]>,
  length: usize,
}

slightlyoutofphase · 2019-11-21T14:08:18Z

For StaticVec, couldn't that become const-compatible by making things a bit more hacky and using a type like this?
pub struct StaticVec<T, const N: usize> {
  data: MaybeUninit<[MaybeUninit<T>; N]>,
  length: usize,
}

Possibly. I'm not sure how much that would complicate the rest of the crate though. Might not be worth it just to support const new right away.

Anyways, seems like there's generally more complexity to this overall issue than I thought. Should I just close the PR for now, then? It's not that important to me anyways, I can definitely just wait for a better way of doing it that's what you think is a better way to go.

I might ask though if there's any aspect of the situation that does need specific work in some area that no one is really working on at the moment? Would be happy to try to help that way if so.

RalfJung · 2019-11-21T14:15:40Z

For array repeat expressions, the tracking issue is #49147. @ecstatic-morse would know the details, but I don't think it's implementation work blocking this right now.

For const mem::zeroed, the issue is #62061. AFAIK the blocker is &mut in const, which last I heard @christianpoveda is working on.

slightlyoutofphase · 2019-11-21T19:24:37Z

Ok, well I'll close this for now then I guess, and keep an eye on the PRs / issues for anything I think I'd be capable of helping with.

rust-highfive assigned joshtriplett Nov 20, 2019

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Nov 20, 2019

Fix order of unsafe and const

bc764fd

Did not know it mattered TBH!

I guess it's a different "intrinsics"?

04e1681

Hopefully this works. Based on the following playground link, panic_if_uninhabited *is* already valid in `const fn`, to be clear: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=8cbb9b4778e8f93ee1863c64995d15a7

Try something else...

ad9fc61

Definitely confused about why `libcore` can't already use fully itself though.

slightlyoutofphase added 2 commits November 20, 2019 15:53

Move #![feature(const_fn)] down the list, to see if it helps

6b28ffe

Remove crate:: prefix again as it can't possibly be necessary

70fde32

slightlyoutofphase added 3 commits November 20, 2019 17:17

Put #![feature(const_fn)] back where it goes first

44f99a0

Actually put it back properly.

68e1e77

Add rustc_const_unstable, properly I hope.

726a957

slightlyoutofphase closed this Nov 21, 2019

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Make `MaybeUninit::assume_init()` a `const fn` #66579

Make `MaybeUninit::assume_init()` a `const fn` #66579

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Make MaybeUninit::assume_init() a const fn #66579

Make MaybeUninit::assume_init() a const fn #66579

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Make `MaybeUninit::assume_init()` a `const fn` #66579

Make `MaybeUninit::assume_init()` a `const fn` #66579

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