Use const generics in impl Default for arrays #71690

MikailBag · 2020-04-29T17:42:29Z

Names 'Bomb' and 'Wrapper' are not too clear
What about performance?

rust-highfive · 2020-04-29T17:42:32Z

(rust_highfive has picked a reviewer for you, use r? to override)

ecstatic-morse · 2020-04-29T18:08:12Z

This is a breaking change for arrays of length 0, which implement Default regardless of T.

rust-highfive · 2020-04-29T20:49:31Z

The job mingw-check 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.

========================== Starting Command Output ===========================
[command]/bin/bash --noprofile --norc /home/vsts/work/_temp/d5c307b1-ebd1-48fb-8fa6-7953d12cc3b2.sh

##[section]Finishing: Disable git automatic line ending conversion
##[section]Starting: Checkout rust-lang/rust@refs/pull/71690/merge to s
Task         : Get sources
Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.
Version      : 1.0.0
Author       : Microsoft
---
##[command]git remote add origin https://github.com/rust-lang/rust
##[command]git config gc.auto 0
##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
##[command]git config --get-all http.proxy
##[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/71690/merge:refs/remotes/pull/71690/merge
---
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Step 6/7 : ENV RUN_CHECK_WITH_PARALLEL_QUERIES 1
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Step 7/7 : ENV SCRIPT python3 ../x.py test src/tools/expand-yaml-anchors &&            python3 ../x.py check --target=i686-pc-windows-gnu --host=i686-pc-windows-gnu &&            python3 ../x.py build --stage 0 src/tools/build-manifest &&            python3 ../x.py test --stage 0 src/tools/compiletest &&            python3 ../x.py test src/tools/tidy &&            /scripts/validate-toolstate.sh
 ---> c5008ef7ae8e
Successfully built c5008ef7ae8e
Successfully tagged rust-ci:latest
Built container sha256:c5008ef7ae8e94d7ef502e3cef26e61208e14ebdb36913f3a8bb86291bd6430b
Built container sha256:c5008ef7ae8e94d7ef502e3cef26e61208e14ebdb36913f3a8bb86291bd6430b
Looks like docker image is the same as before, not uploading
[CI_JOB_NAME=mingw-check]
[CI_JOB_NAME=mingw-check]
== clock drift check ==
  local time: Wed Apr 29 19:30:35 UTC 2020
  network time: Wed, 29 Apr 2020 19:30:35 GMT
Starting sccache server...
configure: processing command line
configure: 
configure: rust.parallel-compiler := True
---
    Checking proc_macro v0.0.0 (/checkout/src/libproc_macro)
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    Checking getopts v0.2.21
    Checking test v0.0.0 (/checkout/src/libtest)
{"reason":"build-finished","success":true}
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    Checking cfg-if v0.1.10
   Compiling libc v0.2.69
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{"reason":"build-finished","success":true}
Checking rustdoc artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
    Checking cfg-if v0.1.10
   Compiling libc v0.2.69
   Compiling semver-parser v0.7.0
---
   Compiling serde_derive v1.0.81
    Checking serde_json v1.0.40
    Checking rustdoc v0.0.0 (/checkout/src/librustdoc)
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{"reason":"build-finished","success":true}
Build completed successfully in 0:05:25
configure: processing command line
configure: 
configure: rust.channel         := nightly
---
configure: rust.codegen-units-std := 1
configure: rust.verify-llvm-ir  := True
configure: build.cargo-native-static := True
configure: rust.dist-src        := False
configure: build.configure-args := ['--enable-sccache', '--disable-manage-submodu ...
configure: writing `config.toml` in current directory
configure: 
configure: run `python /checkout/x.py --help`
configure: 
---
Hugepagesize:       2048 kB
DirectMap4k:      157632 kB
DirectMap2M:     5085184 kB
DirectMap1G:     4194304 kB
+ python3 ../x.py test src/tools/expand-yaml-anchors
Ensuring the YAML anchors in the GitHub Actions config were expanded
Ensuring the YAML anchors in the GitHub Actions config were expanded
Building stage0 tool expand-yaml-anchors (x86_64-unknown-linux-gnu)
   Compiling unicode-xid v0.2.0
   Compiling syn v1.0.11
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    Finished release [optimized] target(s) in 26.64s
{"reason":"build-finished","success":true}
+ python3 ../x.py check --target=i686-pc-windows-gnu --host=i686-pc-windows-gnu
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    Checking cfg-if v0.1.10
   Compiling semver-parser v0.7.0
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---
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---
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    Finished release [optimized] target(s) in 2m 17s
{"reason":"build-finished","success":true}
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   Compiling semver-parser v0.7.0
   Compiling proc-macro2 v0.4.30
    Checking lazy_static v1.4.0
---
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    Checking rustdoc v0.0.0 (/checkout/src/librustdoc)
    Checking rustdoc-tool v0.0.0 (/checkout/src/tools/rustdoc)
    Finished release [optimized] target(s) in 58.97s
{"reason":"build-finished","success":true}
+ python3 ../x.py build --stage 0 src/tools/build-manifest
    Finished dev [unoptimized] target(s) in 0.17s
Building stage0 tool build-manifest (x86_64-unknown-linux-gnu)
   Compiling proc-macro2 v0.4.30
---
   Compiling toml v0.5.3
   Compiling serde_json v1.0.40
   Compiling build-manifest v0.1.0 (/checkout/src/tools/build-manifest)
    Finished release [optimized] target(s) in 50.49s
{"reason":"build-finished","success":true}
+ python3 ../x.py test --stage 0 src/tools/compiletest
    Finished dev [unoptimized] target(s) in 0.19s
   Compiling memchr v2.3.2
   Compiling log v0.4.8
---
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   Compiling tidy v0.1.0 (/checkout/src/tools/tidy)
    Finished release [optimized] target(s) in 23.51s
{"reason":"build-finished","success":true}
* 596 error codes
* highest error code: E0753
* 283 features
Checking which error codes lack tests...
---
skip untracked path cpu-usage.csv during rustfmt invocations
skip untracked path src/doc/book/ during rustfmt invocations
skip untracked path src/doc/rust-by-example/ during rustfmt invocations
skip untracked path src/llvm-project/ during rustfmt invocations
error: expected `;`, found ``assert_eq``
    |
272 |     }
272 |     }
    |      ^ help: add `;` here
273 |     assert_eq!(panic_msg, "bomb limit exceeded");
    |     --------- unexpected token

Running `"/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/rustfmt" "--config-path" "/checkout" "--edition" "2018" "--unstable-features" "--skip-children" "--check" "/checkout/src/libcore/tests/array.rs"` failed.
If you're running `tidy`, try again with `--bless` flag. Or, you just want to format code, run `./x.py fmt` instead.
Build completed unsuccessfully in 0:00:38
== clock drift check ==
  local time: Wed Apr 29 19:43:48 UTC 2020
  local time: Wed Apr 29 19:43:48 UTC 2020
  network time: Wed, 29 Apr 2020 19:43:48 GMT


##[error]Bash exited with code '1'.
##[section]Finishing: Run build
##[section]Starting: Checkout rust-lang/rust@refs/pull/71690/merge to s
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Version      : 1.0.0
Author       : Microsoft
Author       : Microsoft
Help         : [More Information](https://go.microsoft.com/fwlink/?LinkId=798199)
==============================================================================
Cleaning any cached credential from repository: rust-lang/rust (GitHub)
##[section]Finishing: Checkout rust-lang/rust@refs/pull/71690/merge to s
Cleaning up task key
Start cleaning up orphan processes.
Terminate orphan process: pid (3858) (python)
##[section]Finishing: Finalize Job

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rust-highfive · 2020-04-29T22:08:49Z

The job mingw-check 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.

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========================== Starting Command Output ===========================
[command]/bin/bash --noprofile --norc /home/vsts/work/_temp/db8262a7-f6e6-49c9-a51b-92f892e47149.sh

##[section]Finishing: Disable git automatic line ending conversion
##[section]Starting: Checkout rust-lang/rust@refs/pull/71690/merge to s
Task         : Get sources
Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.
Version      : 1.0.0
Author       : Microsoft
---
##[command]git remote add origin https://github.com/rust-lang/rust
##[command]git config gc.auto 0
##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
##[command]git config --get-all http.proxy
##[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/71690/merge:refs/remotes/pull/71690/merge
---
 ---> f7353ccad5b1
Step 6/7 : ENV RUN_CHECK_WITH_PARALLEL_QUERIES 1
 ---> Using cache
 ---> ed38efbaa060
Step 7/7 : ENV SCRIPT python3 ../x.py test src/tools/expand-yaml-anchors &&            python3 ../x.py check --target=i686-pc-windows-gnu --host=i686-pc-windows-gnu &&            python3 ../x.py build --stage 0 src/tools/build-manifest &&            python3 ../x.py test --stage 0 src/tools/compiletest &&            python3 ../x.py test src/tools/tidy &&            /scripts/validate-toolstate.sh
 ---> c5008ef7ae8e
Successfully built c5008ef7ae8e
Successfully tagged rust-ci:latest
Built container sha256:c5008ef7ae8e94d7ef502e3cef26e61208e14ebdb36913f3a8bb86291bd6430b
Built container sha256:c5008ef7ae8e94d7ef502e3cef26e61208e14ebdb36913f3a8bb86291bd6430b
Looks like docker image is the same as before, not uploading
[CI_JOB_NAME=mingw-check]
[CI_JOB_NAME=mingw-check]
== clock drift check ==
  local time: Wed Apr 29 20:55:51 UTC 2020
  network time: Wed, 29 Apr 2020 20:55:51 GMT
Starting sccache server...
configure: processing command line
configure: 
configure: rust.parallel-compiler := True
---
    Checking unicode-width v0.1.6
    Checking getopts v0.2.21
    Checking test v0.0.0 (/checkout/src/libtest)
    Finished release [optimized] target(s) in 30.36s
{"reason":"build-finished","success":true}
    Checking cfg-if v0.1.10
   Compiling libc v0.2.69
   Compiling semver-parser v0.7.0
   Compiling byteorder v1.3.2
---
    Checking rustc_feature v0.0.0 (/checkout/src/librustc_feature)
    Checking fmt_macros v0.0.0 (/checkout/src/libfmt_macros)
    Checking rustc_ast_pretty v0.0.0 (/checkout/src/librustc_ast_pretty)
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    Finished release [optimized] target(s) in 2m 42s
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   Compiling proc-macro2 v0.4.30
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{"reason":"build-finished","success":true}
configure: processing command line
configure: 
configure: llvm.assertions      := True
configure: rust.channel         := nightly
---
configure: rust.codegen-units-std := 1
configure: rust.verify-llvm-ir  := True
configure: build.cargo-native-static := True
configure: build.locked-deps    := True
configure: build.configure-args := ['--enable-sccache', '--disable-manage-submodu ...
configure: writing `config.toml` in current directory
configure: 
configure: run `python /checkout/x.py --help`
configure: 
---
Hugepagesize:       2048 kB
DirectMap4k:      147392 kB
DirectMap2M:     5095424 kB
DirectMap1G:     4194304 kB
+ python3 ../x.py test src/tools/expand-yaml-anchors
Ensuring the YAML anchors in the GitHub Actions config were expanded
Ensuring the YAML anchors in the GitHub Actions config were expanded
Building stage0 tool expand-yaml-anchors (x86_64-unknown-linux-gnu)
   Compiling unicode-xid v0.2.0
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    Finished dev [unoptimized] target(s) in 0.20s
Building stage0 tool build-manifest (x86_64-unknown-linux-gnu)
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---
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{"reason":"build-finished","success":true}
tidy check
* 596 error codes
* highest error code: E0753
* 283 features
---
skip untracked path cpu-usage.csv during rustfmt invocations
skip untracked path src/doc/book/ during rustfmt invocations
skip untracked path src/doc/rust-by-example/ during rustfmt invocations
skip untracked path src/llvm-project/ during rustfmt invocations
error: expected `;`, found ``assert_eq``
    |
272 |     }
272 |     }
    |      ^ help: add `;` here
273 |     assert_eq!(panic_msg, "bomb limit exceeded");
    |     --------- unexpected token

Running `"/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/rustfmt" "--config-path" "/checkout" "--edition" "2018" "--unstable-features" "--skip-children" "--check" "/checkout/src/libcore/tests/array.rs"` failed.
If you're running `tidy`, try again with `--bless` flag. Or, you just want to format code, run `./x.py fmt` instead.
Build completed unsuccessfully in 0:00:45
== clock drift check ==
  local time: Wed Apr 29 21:11:06 UTC 2020
  local time: Wed Apr 29 21:11:06 UTC 2020
  network time: Wed, 29 Apr 2020 21:11:06 GMT


##[error]Bash exited with code '1'.
##[section]Finishing: Run build
##[section]Starting: Checkout rust-lang/rust@refs/pull/71690/merge to s
Task         : Get sources
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Version      : 1.0.0
Author       : Microsoft
Author       : Microsoft
Help         : [More Information](https://go.microsoft.com/fwlink/?LinkId=798199)
==============================================================================
Cleaning any cached credential from repository: rust-lang/rust (GitHub)
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Cleaning up task key
Start cleaning up orphan processes.
Terminate orphan process: pid (3659) (python)
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MikailBag · 2020-04-30T05:49:50Z

@ecstatic-morse thanks, this definitely must be fixed. Unfortunately, I don't know how.
Maybe, I have to wait until const generics become more powerful.

It there is no way to fix my new code, I will extract test into separate PR (and also I will add test for [T; 0] special behavior).

Mark-Simulacrum · 2020-05-05T12:25:18Z

I don't believe there's a good fix for the Default impl on arrays of length zero today with const generics, so I'm going to go head and close this -- please do file a separate PR, though!

leonardo-m · 2020-05-27T08:12:19Z

This is a breaking change for arrays of length 0, which implement Default regardless of T.

How much bad is this breaking change in practice? Can't the compiler special-case empty arrays?

…epmaster Add tests for 'impl Default for [T; N]' Related: rust-lang#71690. This pull request adds two tests: - Even it T::default() panics, no leaks occur. - [T; 0] is Default even if T is not. I believe at some moment `Default` impl for arrays will be rewritten to use const generics instead of macros, and these tests will help to prevent behavior changes.

MikailBag · 2020-07-11T19:22:12Z

@ecstatic-morse @Mark-Simulacrum
Can you take a look at https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=a411abb525023fbea17a1eafc1914974, please?
It seems that auto traits + negative impls do the trick.

UPD: I filed new pull request #74254.

rust-highfive assigned dtolnay Apr 29, 2020

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Apr 29, 2020

MikailBag marked this pull request as ready for review April 29, 2020 17:43

dtolnay added the T-libs Relevant to the library team, which will review and decide on the PR/issue. label Apr 29, 2020

dtolnay assigned Mark-Simulacrum and unassigned dtolnay Apr 29, 2020

MikailBag force-pushed the master branch 3 times, most recently from c370b37 to fb80cbc Compare April 29, 2020 19:26

Use const generics in impl Default for arrays

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MikailBag force-pushed the master branch from fb80cbc to fab4409 Compare April 29, 2020 20:52

Mark-Simulacrum closed this May 5, 2020

MikailBag mentioned this pull request May 26, 2020

Add tests for 'impl Default for [T; N]' #72628

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Use const generics in impl Default for arrays #71690

Use const generics in impl Default for arrays #71690

MikailBag commented Apr 29, 2020

rust-highfive commented Apr 29, 2020

ecstatic-morse commented Apr 29, 2020

rust-highfive commented Apr 29, 2020

rust-highfive commented Apr 29, 2020

MikailBag commented Apr 30, 2020

Mark-Simulacrum commented May 5, 2020

leonardo-m commented May 27, 2020

MikailBag commented Jul 11, 2020 •

edited

Use const generics in impl Default for arrays #71690

Use const generics in impl Default for arrays #71690

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MikailBag commented Apr 29, 2020

rust-highfive commented Apr 29, 2020

ecstatic-morse commented Apr 29, 2020

rust-highfive commented Apr 29, 2020

rust-highfive commented Apr 29, 2020

MikailBag commented Apr 30, 2020

Mark-Simulacrum commented May 5, 2020

leonardo-m commented May 27, 2020

MikailBag commented Jul 11, 2020 • edited

MikailBag commented Jul 11, 2020 •

edited