Forbid elided lifetimes within const generic parameter types #68143

BenLewis-Seequent · 2020-01-12T03:02:28Z

Disallows fn foo<const T: &u32>(), the lifetime must be explicitly given, i.e. fn foo<const T: &'static u32>().

rust-highfive · 2020-01-12T03:02:32Z

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

Centril · 2020-01-12T03:38:33Z

src/test/ui/const-generics/const-param-elided-lifetime.rs

@@ -0,0 +1,19 @@
+#![feature(const_generics)]


Could you give a brief comment at the top explaining why the behavior is how it is? (Contrast and compare with e.g. fn foo<T: Ord<&u8>>() {}.)

I have added that comment. Though I'm not sure what the behaviour should be in the long term, it was the easiest fix(for the ICE) to just disallow elided lifetimes.

I think the only lifetime const generic arguments can have is 'static, so maybe we should do ''static lifetime elision'(https://doc.rust-lang.org/reference/lifetime-elision.html#static-lifetime-elision), like what happens for const/static items.

It's better to make this an error for now.
Then we'll be able to introduce a 'static default more explicitly than in some bugfix PR, when const generics are stable and we have more experience with them.
(The 'static default for const items actually went through an RFC.)

rust-highfive · 2020-01-12T05:41:45Z

The job x86_64-gnu-llvm-7 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.

2020-01-12T04:33:40.2436360Z ##[command]git remote add origin https://github.com/rust-lang/rust
2020-01-12T04:33:40.2446337Z ##[command]git config gc.auto 0
2020-01-12T04:33:40.2448658Z ##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
2020-01-12T04:33:40.2450556Z ##[command]git config --get-all http.proxy
2020-01-12T04:33:40.2453353Z ##[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/68143/merge:refs/remotes/pull/68143/merge
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---
2020-01-12T05:41:38.9546662Z 1 error[E0637]: `&` without an explicit lifetime name cannot be used here
2020-01-12T05:41:38.9546929Z -   --> $DIR/const-param-elided-lifetime.rs:4:19
2020-01-12T05:41:38.9547186Z +   --> $DIR/const-param-elided-lifetime.rs:9:19
2020-01-12T05:41:38.9547232Z 3    |
2020-01-12T05:41:38.9547275Z 4 LL | struct A<const N: &u8>;
2020-01-12T05:41:38.9547371Z 
2020-01-12T05:41:38.9547410Z 6 
2020-01-12T05:41:38.9547471Z 7 error[E0637]: `&` without an explicit lifetime name cannot be used here
2020-01-12T05:41:38.9547715Z -   --> $DIR/const-param-elided-lifetime.rs:8:15
2020-01-12T05:41:38.9547715Z -   --> $DIR/const-param-elided-lifetime.rs:8:15
2020-01-12T05:41:38.9547936Z +   --> $DIR/const-param-elided-lifetime.rs:13:15
2020-01-12T05:41:38.9547983Z 9    |
2020-01-12T05:41:38.9548039Z 10 LL | impl<const N: &u8> A<N> {
2020-01-12T05:41:38.9548127Z 
2020-01-12T05:41:38.9548166Z 12 
2020-01-12T05:41:38.9548227Z 13 error[E0637]: `&` without an explicit lifetime name cannot be used here
2020-01-12T05:41:38.9548451Z -   --> $DIR/const-param-elided-lifetime.rs:9:21
2020-01-12T05:41:38.9548451Z -   --> $DIR/const-param-elided-lifetime.rs:9:21
2020-01-12T05:41:38.9548969Z +   --> $DIR/const-param-elided-lifetime.rs:14:21
2020-01-12T05:41:38.9549046Z 15    |
2020-01-12T05:41:38.9549089Z 16 LL |     fn foo<const M: &u8>(&self) {}
2020-01-12T05:41:38.9549183Z 
2020-01-12T05:41:38.9549222Z 18 
2020-01-12T05:41:38.9549477Z 19 error[E0637]: `&` without an explicit lifetime name cannot be used here
2020-01-12T05:41:38.9549759Z -   --> $DIR/const-param-elided-lifetime.rs:13:15
2020-01-12T05:41:38.9549759Z -   --> $DIR/const-param-elided-lifetime.rs:13:15
2020-01-12T05:41:38.9550004Z +   --> $DIR/const-param-elided-lifetime.rs:18:15
2020-01-12T05:41:38.9550049Z 21    |
2020-01-12T05:41:38.9550091Z 22 LL | impl<const N: &u8> B for A<N> {}
2020-01-12T05:41:38.9550290Z 
2020-01-12T05:41:38.9550336Z 24 
2020-01-12T05:41:38.9550383Z 25 error[E0637]: `&` without an explicit lifetime name cannot be used here
2020-01-12T05:41:38.9550661Z -   --> $DIR/const-param-elided-lifetime.rs:16:17
2020-01-12T05:41:38.9550661Z -   --> $DIR/const-param-elided-lifetime.rs:16:17
2020-01-12T05:41:38.9550880Z +   --> $DIR/const-param-elided-lifetime.rs:21:17
2020-01-12T05:41:38.9550924Z 27    |
2020-01-12T05:41:38.9550980Z 28 LL | fn bar<const N: &u8>() {}
2020-01-12T05:41:38.9551059Z 
2020-01-12T05:41:38.9551112Z 30 
2020-01-12T05:41:38.9551171Z 31 warning: the feature `const_generics` is incomplete and may cause the compiler to crash
2020-01-12T05:41:38.9551399Z -   --> $DIR/const-param-elided-lifetime.rs:1:12
2020-01-12T05:41:38.9551399Z -   --> $DIR/const-param-elided-lifetime.rs:1:12
2020-01-12T05:41:38.9551617Z +   --> $DIR/const-param-elided-lifetime.rs:6:12
2020-01-12T05:41:38.9551676Z 33    |
2020-01-12T05:41:38.9551718Z 34 LL | #![feature(const_generics)]
2020-01-12T05:41:38.9551762Z 35    |            ^^^^^^^^^^^^^^
2020-01-12T05:41:38.9551814Z 
2020-01-12T05:41:38.9551841Z 
2020-01-12T05:41:38.9551884Z The actual stderr differed from the expected stderr.
2020-01-12T05:41:38.9552215Z Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/const-generics/const-param-elided-lifetime/const-param-elided-lifetime.stderr
2020-01-12T05:41:38.9552476Z To update references, rerun the tests and pass the `--bless` flag
2020-01-12T05:41:38.9552756Z To only update this specific test, also pass `--test-args const-generics/const-param-elided-lifetime.rs`
2020-01-12T05:41:38.9552858Z error: 1 errors occurred comparing output.
2020-01-12T05:41:38.9552902Z status: exit code: 1
2020-01-12T05:41:38.9552902Z status: exit code: 1
2020-01-12T05:41:38.9553761Z command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/const-generics/const-param-elided-lifetime.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/const-generics/const-param-elided-lifetime" "-Crpath" "-O" "-Cdebuginfo=0" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/const-generics/const-param-elided-lifetime/auxiliary" "-A" "unused"
2020-01-12T05:41:38.9554083Z ------------------------------------------
2020-01-12T05:41:38.9554130Z 
2020-01-12T05:41:38.9554338Z ------------------------------------------
2020-01-12T05:41:38.9554393Z stderr:
2020-01-12T05:41:38.9554393Z stderr:
2020-01-12T05:41:38.9554611Z ------------------------------------------
2020-01-12T05:41:38.9554663Z error[E0637]: `&` without an explicit lifetime name cannot be used here
2020-01-12T05:41:38.9554915Z   --> /checkout/src/test/ui/const-generics/const-param-elided-lifetime.rs:9:19
2020-01-12T05:41:38.9555179Z    |
2020-01-12T05:41:38.9555229Z LL | struct A<const N: &u8>;
2020-01-12T05:41:38.9555321Z 
2020-01-12T05:41:38.9555379Z error[E0637]: `&` without an explicit lifetime name cannot be used here
2020-01-12T05:41:38.9555681Z   --> /checkout/src/test/ui/const-generics/const-param-elided-lifetime.rs:13:15
2020-01-12T05:41:38.9555729Z    |
2020-01-12T05:41:38.9555729Z    |
2020-01-12T05:41:38.9555794Z LL | impl<const N: &u8> A<N> { //~ ERROR `&` without an explicit lifetime name cannot be used here
2020-01-12T05:41:38.9556313Z 
2020-01-12T05:41:38.9556379Z error[E0637]: `&` without an explicit lifetime name cannot be used here
2020-01-12T05:41:38.9562063Z   --> /checkout/src/test/ui/const-generics/const-param-elided-lifetime.rs:14:21
2020-01-12T05:41:38.9562142Z    |
2020-01-12T05:41:38.9562142Z    |
2020-01-12T05:41:38.9563145Z LL |     fn foo<const M: &u8>(&self) {}
2020-01-12T05:41:38.9563258Z 
2020-01-12T05:41:38.9563438Z error[E0637]: `&` without an explicit lifetime name cannot be used here
2020-01-12T05:41:38.9563882Z   --> /checkout/src/test/ui/const-generics/const-param-elided-lifetime.rs:18:15
2020-01-12T05:41:38.9563934Z    |
2020-01-12T05:41:38.9563934Z    |
2020-01-12T05:41:38.9563978Z LL | impl<const N: &u8> B for A<N> {}
2020-01-12T05:41:38.9564071Z 
2020-01-12T05:41:38.9564116Z error[E0637]: `&` without an explicit lifetime name cannot be used here
2020-01-12T05:41:38.9564376Z   --> /checkout/src/test/ui/const-generics/const-param-elided-lifetime.rs:21:17
2020-01-12T05:41:38.9564450Z    |
2020-01-12T05:41:38.9564450Z    |
2020-01-12T05:41:38.9564490Z LL | fn bar<const N: &u8>() {}
2020-01-12T05:41:38.9564583Z 
2020-01-12T05:41:38.9564631Z warning: the feature `const_generics` is incomplete and may cause the compiler to crash
2020-01-12T05:41:38.9566877Z   --> /checkout/src/test/ui/const-generics/const-param-elided-lifetime.rs:6:12
2020-01-12T05:41:38.9566967Z    |
---
2020-01-12T05:41:38.9568814Z thread 'main' panicked at 'Some tests failed', src/tools/compiletest/src/main.rs:386:22
2020-01-12T05:41:38.9568882Z note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
2020-01-12T05:41:38.9568933Z 
2020-01-12T05:41:38.9568958Z 
2020-01-12T05:41:38.9570579Z command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/compiletest" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/compiletest" "--compile-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib" "--run-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "--rustc-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "--src-base" "/checkout/src/test/ui" "--build-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--mode" "ui" "--target" "x86_64-unknown-linux-gnu" "--host" "x86_64-unknown-linux-gnu" "--llvm-filecheck" "/usr/lib/llvm-7/bin/FileCheck" "--host-rustcflags" "-Crpath -O -Cdebuginfo=0 -Zunstable-options  -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--target-rustcflags" "-Crpath -O -Cdebuginfo=0 -Zunstable-options  -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--docck-python" "/usr/bin/python2.7" "--lldb-python" "/usr/bin/python2.7" "--gdb" "/usr/bin/gdb" "--quiet" "--llvm-version" "7.0.0\n" "--system-llvm" "--cc" "" "--cxx" "" "--cflags" "" "--llvm-components" "" "--llvm-cxxflags" "" "--adb-path" "adb" "--adb-test-dir" "/data/tmp/work" "--android-cross-path" "" "--color" "always"
2020-01-12T05:41:38.9570994Z 
2020-01-12T05:41:38.9571024Z 
2020-01-12T05:41:38.9627049Z failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
2020-01-12T05:41:38.9627366Z Build completed unsuccessfully in 1:02:08
2020-01-12T05:41:38.9627366Z Build completed unsuccessfully in 1:02:08
2020-01-12T05:41:38.9632690Z == clock drift check ==
2020-01-12T05:41:38.9653832Z   local time: Sun Jan 12 05:41:38 UTC 2020
2020-01-12T05:41:39.2509793Z   network time: Sun, 12 Jan 2020 05:41:39 GMT
2020-01-12T05:41:39.2509995Z == end clock drift check ==
2020-01-12T05:41:39.7459916Z 
2020-01-12T05:41:39.7556127Z ##[error]Bash exited with code '1'.
2020-01-12T05:41:39.7598868Z ##[section]Starting: Checkout
2020-01-12T05:41:39.7600978Z ==============================================================================
2020-01-12T05:41:39.7601046Z Task         : Get sources
2020-01-12T05:41:39.7601093Z 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)

petrochenkov · 2020-01-12T09:07:01Z

@bors r+

bors · 2020-01-12T09:07:03Z

📌 Commit 82b90bd has been approved by petrochenkov

…ifetime, r=petrochenkov Forbid elided lifetimes within const generic parameter types Disallows `fn foo<const T: &u32>()`, the lifetime must be explicitly given, i.e. `fn foo<const T: &'static u32>()`. Fixes rust-lang#67883

@ghost

Rollup of 10 pull requests Successful merges: - #67854 (Use `report_in_external_macro` for internal lints) - #67989 (rustdoc: Don't allow `#![feature(...)]` on stable or beta) - #68036 (libterm: parse extended terminfo format) - #68127 (Clarify the relationship between `extended` and `tools` in `config.toml`) - #68143 (Forbid elided lifetimes within const generic parameter types) - #68150 (Document behavior of set_nonblocking on UnixListener) - #68166 (rustdoc: HTML escape arrows on help popup) - #68176 (Clean up err codes) - #68179 (Remove unneeded scope) - #68188 (Tweak assertion note in format check) Failed merges: r? @ghost

Forbid elided lifetimes within const generic parameter types.

b4fddf0

rust-highfive assigned petrochenkov Jan 12, 2020

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jan 12, 2020

Centril reviewed Jan 12, 2020

View reviewed changes

Centril added the F-const_generics `#![feature(const_generics)]` label Jan 12, 2020

Added comment about behaviour.

9e46ddc

Update test benchmark file

82b90bd

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 Jan 12, 2020

Dylan-DPC-zz mentioned this pull request Jan 13, 2020

Rollup of 5 pull requests #68181

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JohnTitor mentioned this pull request Jan 14, 2020

Rollup of 10 pull requests #68201

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bors merged commit 82b90bd into rust-lang:master Jan 14, 2020

varkor mentioned this pull request Jul 22, 2020

Tracking issue for const generics (RFC 2000) #44580

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Forbid elided lifetimes within const generic parameter types #68143

Forbid elided lifetimes within const generic parameter types #68143

BenLewis-Seequent commented Jan 12, 2020 •

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Forbid elided lifetimes within const generic parameter types #68143

Forbid elided lifetimes within const generic parameter types #68143

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