Make impl Debug for rustdoc::clean::Item easier to read

[jyn514]

Before:

Item { name: Some("Send"), attrs: Attributes { doc_strings: [DocFragment { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:15:1: 15:60 (#0), parent_module: None, doc: " Types that can be transferred across thread boundaries.", kind: SugaredDoc, indent: 1 }, DocFragment { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:16:1: 16:4 (#0), parent_module: None, doc: "", kind: SugaredDoc, indent: 0 }, DocFragment { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:17:1: 17:78 (#0), parent_module: None, doc: " This trait is automatically implemented when the compiler determines it's", kind: SugaredDoc, indent: 1 }, DocFragment { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:18:1: 18:17 (#0), parent_module: None, doc: " appropriate.", kind: SugaredDoc, indent: 1 }, DocFragment { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:19:1: 19:4 (#0), parent_module: None, doc: "", kind: SugaredDoc, indent: 0 }, DocFragment { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:20:1: 20:70 (#0), parent_module: None, doc: " An example of a non-`Send` type is the reference-counting pointer", kind: SugaredDoc, indent: 1 }, DocFragment { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:21:1: 21:85 (#0), parent_module: None, doc: " [`rc::Rc`][`Rc`]. If two threads attempt to clone [`Rc`]s that point to the same", kind: SugaredDoc, indent: 1 }, DocFragment { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:22:1: 22:81 (#0), parent_module: None, doc: " reference-counted value, they might try to update the reference count at the", kind: SugaredDoc, indent: 1 }, DocFragment { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:23:1: 23:83 (#0), parent_module: None, doc: " same time, which is [undefined behavior][ub] because [`Rc`] doesn't use atomic", kind: SugaredDoc, indent: 1 }, DocFragment { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:24:1: 24:84 (#0), parent_module: None, doc: " operations. Its cousin [`sync::Arc`][arc] does use atomic operations (incurring", kind: SugaredDoc, indent: 1 }, DocFragment { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:25:1: 25:39 (#0), parent_module: None, doc: " some overhead) and thus is `Send`.", kind: SugaredDoc, indent: 1 }, DocFragment { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:26:1: 26:4 (#0), parent_module: None, doc: "", kind: SugaredDoc, indent: 0 }, DocFragment { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:27:1: 27:74 (#0), parent_module: None, doc: " See [the Nomicon](../../nomicon/send-and-sync.html) for more details.", kind: SugaredDoc, indent: 1 }, DocFragment { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:28:1: 28:4 (#0), parent_module: None, doc: "", kind: SugaredDoc, indent: 0 }, DocFragment { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:29:1: 29:40 (#0), parent_module: None, doc: " [`Rc`]: ../../std/rc/struct.Rc.html", kind: SugaredDoc, indent: 1 }, DocFragment { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:30:1: 30:42 (#0), parent_module: None, doc: " [arc]: ../../std/sync/struct.Arc.html", kind: SugaredDoc, indent: 1 }, DocFragment { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:31:1: 31:61 (#0), parent_module: None, doc: " [ub]: ../../reference/behavior-considered-undefined.html", kind: SugaredDoc, indent: 1 }], other_attrs: [Attribute { kind: Normal(AttrItem { path: Path { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:32:3: 32:9 (#0), segments: [PathSegment { ident: stable#0, id: NodeId(33577), args: None }], tokens: None }, args: Delimited(DelimSpan { open: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:32:9: 32:10 (#0), close: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:32:44: 32:45 (#0) }, Parenthesis, TokenStream([(Token(Token { kind: Ident("feature", false), span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:32:10: 32:17 (#0) }), Alone), (Token(Token { kind: Eq, span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:32:18: 32:19 (#0) }), Alone), (Token(Token { kind: Literal(Lit { kind: Str, symbol: "rust1", suffix: None }), span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:32:20: 32:27 (#0) }), Joint), (Token(Token { kind: Comma, span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:32:27: 32:28 (#0) }), Alone), (Token(Token { kind: Ident("since", false), span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:32:29: 32:34 (#0) }), Alone), (Token(Token { kind: Eq, span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:32:35: 32:36 (#0) }), Alone), (Token(Token { kind: Literal(Lit { kind: Str, symbol: "1.0.0", suffix: None }), span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:32:37: 32:44 (#0) }), Alone)])), tokens: None }, None), id: AttrId(48), style: Outer, span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:32:1: 32:46 (#0) }, Attribute { kind: Normal(AttrItem { path: Path { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:33:23: 33:44 (#0), segments: [PathSegment { ident: rustc_diagnostic_item#0, id: NodeId(33578), args: None }], tokens: None }, args: Eq(/rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:33:45: 33:46 (#0), Token { kind: Literal(Lit { kind: Str, symbol: "Send", suffix: None }), span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:33:47: 33:53 (#0) }), tokens: None }, None), id: AttrId(49), style: Outer, span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:33:23: 33:53 (#0) }, Attribute { kind: Normal(AttrItem { path: Path { span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:34:3: 34:25 (#0), segments: [PathSegment { ident: rustc_on_unimplemented#0, id: NodeId(33580), args: None }], tokens: None }, args: Delimited(DelimSpan { open: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:34:25: 34:26 (#0), close: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:37:1: 37:2 (#0) }, Parenthesis, TokenStream([(Token(Token { kind: Ident("message", false), span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:35:5: 35:12 (#0) }), Alone), (Token(Token { kind: Eq, span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:35:13: 35:14 (#0) }), Alone), (Token(Token { kind: Literal(Lit { kind: Str, symbol: "`{Self}` cannot be sent between threads safely", suffix: None }), span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:35:15: 35:63 (#0) }), Joint), (Token(Token { kind: Comma, span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:35:63: 35:64 (#0) }), Alone), (Token(Token { kind: Ident("label", false), span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:36:5: 36:10 (#0) }), Alone), (Token(Token { kind: Eq, span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:36:11: 36:12 (#0) }), Alone), (Token(Token { kind: Literal(Lit { kind: Str, symbol: "`{Self}` cannot be sent between threads safely", suffix: None }), span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:36:13: 36:61 (#0) }), Alone)])), tokens: None }, None), id: AttrId(50), style: Outer, span: /rustc/37b55c8a0cafdb60b9168da34f904acc70157df8/library/core/src/marker.rs:34:1: 37:3 (#0) }] }, visibility: Public, kind: TraitItem(Trait { unsafety: Unsafe, items: [], generics: Generics { params: [], where_predicates: [] }, bounds: [], is_auto: true }), def_id: DefId(DefId(2:3027 ~ core[7f4a]::marker::Send)), cfg: None }

After:

Item { name: Some("Send"), visibility: Public, def_id: DefId(DefId(2:3027 ~ core[7f4a]::marker::Send)), kind: Trait, docs: "Types that can be transferred across thread boundaries.\n\nThis trait is automatically implemented when the compiler determines it's\nappropriate.\n\nAn example of a non-`Send` type is the reference-counting pointer\n[`rc::Rc`][`Rc`]. If two threads attempt to clone [`Rc`]s that point to the same\nreference-counted value, they might try to update the reference count at the\nsame time, which is [undefined behavior][ub] because [`Rc`] doesn't use atomic\noperations. Its cousin [`sync::Arc`][arc] does use atomic operations (incurring\nsome overhead) and thus is `Send`.\n\nSee [the Nomicon](../../nomicon/send-and-sync.html) for more details.\n\n[`Rc`]: ../../std/rc/struct.Rc.html\n[arc]: ../../std/sync/struct.Arc.html\n[ub]: ../../reference/behavior-considered-undefined.html" }

The previous output is still present if you really want it for some reason by using {:#?} instead of {:?}.

r? @camelid

[rust-highfive]

Some changes occurred in clean/types.rs.

cc @camelid

[camelid]

I think this is an interesting idea, although I'm a bit concerned that it could be confusing to new contributors or make existing log statements less useful (though they could of course be changed to use {:#?} if it were an issue).

I'm okay with landing this and seeing how it goes though. Could you post on rustdoc's Zulip to let people know about this change so they aren't confused when {:?} works differently?

cc @GuillaumeGomez to see what they think

[GuillaumeGomez]

I have to admit it's a bit strange for me to rely on #? vs ? to have one display or another. Usually I think we use Display vs Debug but in this case it seems wrong too... I appreciate the new debug formatting though. Maybe document the Debug impl so we can keep a trace of it? And maybe mention it in the rustc dev book (not sure if it's worth it, I'll let it up to you)?

[camelid]

Maybe document the Debug impl so we can keep a trace of it? And maybe mention it in the rustc dev book (not sure if it's worth it, I'll let it up to you)?

I think it's best to document it on the Item type itself since I believe contributors are more likely to see it there than among all the other docs in the dev guide.

[GuillaumeGomez]

That's a good point. As long as it's mentioned in the docs, it's good for me.

[jyn514]

I have to admit it's a bit strange for me to rely on #? vs ? to have one display or another. Usually I think we use Display vs Debug but in this case it seems wrong too...

Is "we" here "rust users" or "rustdoc"? because rustdoc definitely uses #? :P See

rust/src/librustdoc/html/format.rs

Line 203 in 05d2221

if f.alternate() {

and about 20 other occurrences in that file.

I think I addressed all the review comments :)

[jyn514]

I'm okay with landing this and seeing how it goes though. Could you post on rustdoc's Zulip to let people know about this change so they aren't confused when {:?} works differently?

https://rust-lang.zulipchat.com/#narrow/stream/266220-rustdoc/topic/debug.20output.20for.20Items.20is.20changing

@rustbot ready

[GuillaumeGomez]

Is "we" here "rust users" or "rustdoc"? because rustdoc definitely uses #? :P See

It does for HTML rendering, not sure if it's used for debugging. But in any case, as long as it's documented somewhere, it's fine for me.

[camelid]

Thanks again!

[camelid]

@bors r+ rollup

[bors]

📌 Commit 4fc23a1 has been approved by camelid