Add info about `!` and `impl Trait` #76099

camelid · 2020-08-30T02:54:15Z

Fixes #76094.

@rustbot modify labels: T-doc C-enhancement

rust-highfive · 2020-08-30T02:54:18Z

r? @sfackler

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camelid · 2020-08-30T02:55:24Z

Note that this is still very work-in-progress, I just wanted to write something down to see if it's roughly correct.

camelid · 2020-08-30T03:01:30Z

Cc @jyn514

library/std/src/primitive_docs.rs

jyn514 · 2020-08-30T03:10:20Z

library/std/src/primitive_docs.rs

+///
+/// [#36375]: https://github.com/rust-lang/rust/issues/36375
+///
+/// As it turns out, though, most traits can have an `impl` for `!`. Take [`Debug`]


Most -> all? Not sure if that's true but it seems like it should be.

That's what I thought too; I would think you would be able to impl any trait for ! since it can never :) exist. The body of it could just be panic!("This shouldn't happen!").

Or even simpler, *self, yeah.

You mean because it can be coerced to any concrete type, so it can just return itself?

-> impl Trait is not allowed in trait methods. So any trait it implemented would require returning some concrete type. Since ! can be coerced to any type, it would be coerced to the required type.

library/std/src/primitive_docs.rs

camelid · 2020-08-30T03:44:51Z

library/std/src/primitive_docs.rs

 /// # trait Debug {
-/// # fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result;
+/// #     fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result;
 /// # }


Why is Debug defined here instead of imported?

I'm going to delete this redefinition and import it instead.

Looks like it's because of the orphan rule or something, so I had to revert my change :(

I no longer say "polymorphic" since it's a bit ambiguous here.

library/std/src/primitive_docs.rs

This reverts commit 7e2548f. Now I know why it was redefined: it seems like it's potentially because of the orphan rule. Here are the error messages: error[E0119]: conflicting implementations of trait `std::fmt::Debug` for type `!`: --> src/primitive_docs.rs:236:1 | 6 | impl Debug for ! { | ^^^^^^^^^^^^^^^^ | = note: conflicting implementation in crate `core`: - impl std::fmt::Debug for !; error[E0117]: only traits defined in the current crate can be implemented for arbitrary types --> src/primitive_docs.rs:236:1 | 6 | impl Debug for ! { | ^^^^^^^^^^^^^^^- | | | | | `!` is not defined in the current crate | impl doesn't use only types from inside the current crate | = note: define and implement a trait or new type instead

Co-authored-by: Joshua Nelson <[email protected]>

jyn514 · 2020-09-01T02:43:49Z

@bors r+ rollup

Thanks for the PR!

bors · 2020-09-01T02:43:50Z

📌 Commit 913354b has been approved by jyn514

camelid · 2020-09-01T02:45:44Z

Oh well, it looks like the line break commit didn't get through in time ;)

jyn514 · 2020-09-01T02:47:33Z

@bors r+ rollup

bors · 2020-09-01T02:47:35Z

📌 Commit 55637f5 has been approved by jyn514

jyn514 · 2020-09-01T02:48:16Z

Oh well, it looks like the line break commit didn't get through in time ;)

Bors will automatically abort the merge if you push new commits. It will not however remove the S-waiting-on-bors tag :(

bors · 2020-09-01T07:41:15Z

⌛ Testing commit 55637f5 with merge c79747195683ac4842eaacf65e8e4cddac6f7e69...

bors · 2020-09-01T07:44:27Z

💔 Test failed - checks-azure

rust-log-analyzer · 2020-09-01T07:53:51Z

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.

##[group]Run exit 1
exit 1
shell: /bin/bash --noprofile --norc -e -o pipefail {0}
##[endgroup]
##[error]Process completed with exit code 1.

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 @rust-lang/infra. (Feature Requests)

jyn514 · 2020-09-01T12:12:06Z

curl: (56) SSLRead() return error -9806
clang+llvm-10.0.0-x86_64-apple-darwin/lib/clang/10.0.0/lib/darwin/libclang_rt.tsan_ios_dynamic.dylib: Lzma library error:  No progress is possible
tar: Error exit delayed from previous errors.

##[error]Bash exited with code '1'.
Finishing: Install clang

What a strange error ... Looks network related?

@bors retry

@ghost

Rollup of 14 pull requests Successful merges: - rust-lang#74880 (Add trailing comma support to matches macro) - rust-lang#76074 (Add new `-Z dump-mir-spanview` option) - rust-lang#76088 (Add more examples to lexicographic cmp on Iterators.) - rust-lang#76099 (Add info about `!` and `impl Trait`) - rust-lang#76126 (Use "Fira Sans" for crate list font) - rust-lang#76132 (Factor out StmtKind::MacCall fields into `MacCallStmt` struct) - rust-lang#76143 (Give a better error message for duplicate built-in macros) - rust-lang#76158 (Stabilise link-self-contained option) - rust-lang#76201 (Move to intra-doc links for library/core/src/panic.rs) - rust-lang#76206 (Make all methods of `std::net::Ipv6Addr` const) - rust-lang#76207 (# Move to intra-doc links for library/core/src/clone.rs) - rust-lang#76212 (Document lint missing_doc_code_examples is nightly-only) - rust-lang#76218 (lexer: Tiny improvement to shebang detection) - rust-lang#76221 (Clean up header in `iter` docs for `for` loops) Failed merges: r? @ghost

rust-highfive assigned sfackler Aug 30, 2020

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 30, 2020

rustbot added C-enhancement Category: An issue proposing an enhancement or a PR with one. A-docs Area: documentation for any part of the project, including the compiler, standard library, and tools labels Aug 30, 2020

camelid force-pushed the patch-8 branch from 2c141d8 to 5fc252a Compare August 30, 2020 02:59

Add info about ! and impl Trait

4aae781

camelid force-pushed the patch-8 branch from 5fc252a to 4aae781 Compare August 30, 2020 02:59

jyn514 reviewed Aug 30, 2020

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cannot have divergence -> cannot diverge

fd985e2

jyn514 reviewed Aug 30, 2020

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library/std/src/primitive_docs.rs Outdated Show resolved Hide resolved

It's only an issue without an impl Trait for !

0d9a2ab

camelid commented Aug 30, 2020

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camelid added 3 commits August 29, 2020 20:48

Specify 0 of type u32

26eab6a

Be more specific about polymorphic return types

80dcad9

I no longer say "polymorphic" since it's a bit ambiguous here.

other branch -> else branch

bd31962

camelid commented Aug 30, 2020

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library/std/src/primitive_docs.rs Outdated Show resolved Hide resolved

camelid added 2 commits August 30, 2020 11:39

Import Debug instead of redefining it

7e2548f

Explain why the 0 is a u32

37ea97c

camelid commented Aug 30, 2020

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camelid marked this pull request as ready for review August 31, 2020 23:35

jyn514 reviewed Sep 1, 2020

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jyn514 reviewed Sep 1, 2020

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library/std/src/primitive_docs.rs Outdated Show resolved Hide resolved

camelid and others added 3 commits August 31, 2020 19:33

Remove empty comment

cdd6f11

Improve wording

c4c058c

Co-authored-by: Joshua Nelson <[email protected]>

camelid force-pushed the patch-8 branch from 0db9209 to c4c058c Compare September 1, 2020 02:33

Improve assert! section in bool docs

913354b

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 1, 2020

Break line at 100 characters

55637f5

bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Sep 1, 2020

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 1, 2020

tmandry mentioned this pull request Sep 2, 2020

Rollup of 14 pull requests #76231

Merged

bors merged commit 34c8b7a into rust-lang:master Sep 2, 2020

camelid deleted the patch-8 branch September 2, 2020 03:33

cuviper added this to the 1.48.0 milestone Nov 17, 2023

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Add info about `!` and `impl Trait` #76099

Add info about `!` and `impl Trait` #76099

camelid commented Aug 30, 2020 •

edited

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Add info about ! and impl Trait #76099

Add info about ! and impl Trait #76099

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jyn514 commented Sep 1, 2020

bors commented Sep 1, 2020

camelid commented Sep 1, 2020

jyn514 commented Sep 1, 2020

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jyn514 commented Sep 1, 2020

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jyn514 commented Sep 1, 2020

Add info about `!` and `impl Trait` #76099

Add info about `!` and `impl Trait` #76099

camelid commented Aug 30, 2020 •

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