From e48b6b459974245efcfc9edda468b4c587cbf37c Mon Sep 17 00:00:00 2001 From: Joshua Nelson Date: Mon, 22 Mar 2021 01:10:10 -0400 Subject: [PATCH] Stabilize extended_key_value_attributes # Stabilization report ## Summary This stabilizes using macro expansion in key-value attributes, like so: ```rust #[doc = include_str!("my_doc.md")] struct S; #[path = concat!(env!("OUT_DIR"), "/generated.rs")] mod m; ``` See the changes to the reference for details on what macros are allowed; see Petrochenkov's excellent blog post [on internals](https://internals.rust-lang.org/t/macro-expansion-points-in-attributes/11455) for alternatives that were considered and rejected ("why accept no more and no less?") This has been available on nightly since 1.50 with no major issues. ## Notes ### Accepted syntax The parser accepts arbitrary Rust expressions in this position, but any expression other than a macro invocation will ultimately lead to an error because it is not expected by the built-in expression forms (e.g., `#[doc]`). Note that decorators and the like may be able to observe other expression forms. ### Expansion ordering Expansion of macro expressions in "inert" attributes occurs after decorators have executed, analogously to macro expressions appearing in the function body or other parts of decorator input. There is currently no way for decorators to accept macros in key-value position if macro expansion must be performed before the decorator executes (if the macro can simply be copied into the output for later expansion, that can work). ## Test cases - https://github.com/rust-lang/rust/blob/master/src/test/ui/attributes/key-value-expansion-on-mac.rs - https://github.com/rust-lang/rust/blob/master/src/test/rustdoc/external-doc.rs The feature has also been dogfooded extensively in the compiler and standard library: - https://github.com/rust-lang/rust/pull/83329 - https://github.com/rust-lang/rust/pull/83230 - https://github.com/rust-lang/rust/pull/82641 - https://github.com/rust-lang/rust/pull/80534 ## Implementation history - Initial proposal: https://github.com/rust-lang/rust/issues/55414#issuecomment-554005412 - Experiment to see how much code it would break: https://github.com/rust-lang/rust/pull/67121 - Preliminary work to restrict expansion that would conflict with this feature: https://github.com/rust-lang/rust/pull/77271 - Initial implementation: https://github.com/rust-lang/rust/pull/78837 - Fix for an ICE: https://github.com/rust-lang/rust/pull/80563 ## Unresolved Questions ~~https://github.com/rust-lang/rust/pull/83366#issuecomment-805180738 listed some concerns, but they have been resolved as of this final report.~~ ## Additional Information There are two workarounds that have a similar effect for `#[doc]` attributes on nightly. One is to emulate this behavior by using a limited version of this feature that was stabilized for historical reasons: ```rust macro_rules! forward_inner_docs { ($e:expr => $i:item) => { #[doc = $e] $i }; } forward_inner_docs!(include_str!("lib.rs") => struct S {}); ``` This also works for other attributes (like `#[path = concat!(...)]`). The other is to use `doc(include)`: ```rust #![feature(external_doc)] #[doc(include = "lib.rs")] struct S {} ``` The first works, but is non-trivial for people to discover, and difficult to read and maintain. The second is a strange special-case for a particular use of the macro. This generalizes it to work for any use case, not just including files. I plan to remove `doc(include)` when this is stabilized. The `forward_inner_docs` workaround will still compile without warnings, but I expect it to be used less once it's no longer necessary. --- compiler/rustc_ast_passes/src/feature_gate.rs | 4 -- compiler/rustc_codegen_llvm/src/lib.rs | 2 +- compiler/rustc_errors/src/lib.rs | 2 +- compiler/rustc_feature/src/accepted.rs | 2 + compiler/rustc_feature/src/active.rs | 3 -- compiler/rustc_hir/src/lib.rs | 2 +- compiler/rustc_parse/src/parser/mod.rs | 13 ------- library/core/src/lib.rs | 2 +- library/std/src/lib.rs | 2 +- src/doc/rustdoc/README.md | 5 +++ src/doc/rustdoc/src/the-doc-attribute.md | 7 ++++ src/test/rustdoc/external-doc.rs | 1 - .../attributes/key-value-expansion-on-mac.rs | 1 - .../key-value-expansion-on-mac.stderr | 2 +- ...ture-gate-extended_key_value_attributes.rs | 8 ---- ...-gate-extended_key_value_attributes.stderr | 39 ------------------- src/test/ui/suffixed-literal-meta.rs | 2 +- 17 files changed, 21 insertions(+), 76 deletions(-) create mode 100644 src/doc/rustdoc/README.md delete mode 100644 src/test/ui/feature-gates/feature-gate-extended_key_value_attributes.rs delete mode 100644 src/test/ui/feature-gates/feature-gate-extended_key_value_attributes.stderr diff --git a/compiler/rustc_ast_passes/src/feature_gate.rs b/compiler/rustc_ast_passes/src/feature_gate.rs index 4215d5c55a049..4996c2195efdf 100644 --- a/compiler/rustc_ast_passes/src/feature_gate.rs +++ b/compiler/rustc_ast_passes/src/feature_gate.rs @@ -712,10 +712,6 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session) { gate_all!(const_trait_impl, "const trait impls are experimental"); gate_all!(half_open_range_patterns, "half-open range patterns are unstable"); gate_all!(inline_const, "inline-const is experimental"); - gate_all!( - extended_key_value_attributes, - "arbitrary expressions in key-value attributes are unstable" - ); gate_all!( const_generics_defaults, "default values for const generic parameters are experimental" diff --git a/compiler/rustc_codegen_llvm/src/lib.rs b/compiler/rustc_codegen_llvm/src/lib.rs index 329458773ffaf..8eef06f018f3a 100644 --- a/compiler/rustc_codegen_llvm/src/lib.rs +++ b/compiler/rustc_codegen_llvm/src/lib.rs @@ -8,7 +8,7 @@ #![feature(bool_to_option)] #![feature(const_cstr_unchecked)] #![feature(crate_visibility_modifier)] -#![feature(extended_key_value_attributes)] +#![cfg_attr(bootstrap, feature(extended_key_value_attributes))] #![feature(extern_types)] #![feature(in_band_lifetimes)] #![feature(iter_zip)] diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs index f53ce7ceace13..65352f0bc6e7b 100644 --- a/compiler/rustc_errors/src/lib.rs +++ b/compiler/rustc_errors/src/lib.rs @@ -5,7 +5,7 @@ #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")] #![feature(crate_visibility_modifier)] #![feature(backtrace)] -#![feature(extended_key_value_attributes)] +#![cfg_attr(bootstrap, feature(extended_key_value_attributes))] #![feature(format_args_capture)] #![feature(iter_zip)] #![feature(nll)] diff --git a/compiler/rustc_feature/src/accepted.rs b/compiler/rustc_feature/src/accepted.rs index e8642a52749c4..eef71e096a52e 100644 --- a/compiler/rustc_feature/src/accepted.rs +++ b/compiler/rustc_feature/src/accepted.rs @@ -281,6 +281,8 @@ declare_features! ( (accepted, or_patterns, "1.53.0", Some(54883), None), /// Allows defining identifiers beyond ASCII. (accepted, non_ascii_idents, "1.53.0", Some(55467), None), + /// Allows arbitrary expressions in key-value attributes at parse time. + (accepted, extended_key_value_attributes, "1.54.0", Some(78835), None), // ------------------------------------------------------------------------- // feature-group-end: accepted features diff --git a/compiler/rustc_feature/src/active.rs b/compiler/rustc_feature/src/active.rs index 80fe5bafc6ee6..763264476b341 100644 --- a/compiler/rustc_feature/src/active.rs +++ b/compiler/rustc_feature/src/active.rs @@ -601,9 +601,6 @@ declare_features! ( /// Allows capturing disjoint fields in a closure/generator (RFC 2229). (active, capture_disjoint_fields, "1.49.0", Some(53488), None), - /// Allows arbitrary expressions in key-value attributes at parse time. - (active, extended_key_value_attributes, "1.50.0", Some(78835), None), - /// Allows const generics to have default values (e.g. `struct Foo(...);`). (active, const_generics_defaults, "1.51.0", Some(44580), None), diff --git a/compiler/rustc_hir/src/lib.rs b/compiler/rustc_hir/src/lib.rs index 65c99535c4e34..71e997994deff 100644 --- a/compiler/rustc_hir/src/lib.rs +++ b/compiler/rustc_hir/src/lib.rs @@ -4,7 +4,7 @@ #![feature(crate_visibility_modifier)] #![feature(const_panic)] -#![feature(extended_key_value_attributes)] +#![cfg_attr(bootstrap, feature(extended_key_value_attributes))] #![feature(in_band_lifetimes)] #![feature(once_cell)] #![cfg_attr(bootstrap, feature(or_patterns))] diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs index 35cfaae13a4a0..4c2bc6ebf3143 100644 --- a/compiler/rustc_parse/src/parser/mod.rs +++ b/compiler/rustc_parse/src/parser/mod.rs @@ -1065,24 +1065,11 @@ impl<'a> Parser<'a> { } else if !delimited_only { if self.eat(&token::Eq) { let eq_span = self.prev_token.span; - let mut is_interpolated_expr = false; - if let token::Interpolated(nt) = &self.token.kind { - if let token::NtExpr(..) = **nt { - is_interpolated_expr = true; - } - } // Collect tokens because they are used during lowering to HIR. let expr = self.parse_expr_force_collect()?; let span = expr.span; - match &expr.kind { - // Not gated to support things like `doc = $expr` that work on stable. - _ if is_interpolated_expr => {} - ExprKind::Lit(lit) if lit.kind.is_unsuffixed() => {} - _ => self.sess.gated_spans.gate(sym::extended_key_value_attributes, span), - } - let token_kind = token::Interpolated(Lrc::new(token::NtExpr(expr))); MacArgs::Eq(eq_span, Token::new(token_kind, span)) } else { diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs index 6a4f2d5a544c1..f652c52db5301 100644 --- a/library/core/src/lib.rs +++ b/library/core/src/lib.rs @@ -113,7 +113,7 @@ #![cfg_attr(bootstrap, feature(doc_spotlight))] #![cfg_attr(not(bootstrap), feature(doc_notable_trait))] #![feature(duration_consts_2)] -#![feature(extended_key_value_attributes)] +#![cfg_attr(bootstrap, feature(extended_key_value_attributes))] #![feature(extern_types)] #![feature(fundamental)] #![feature(intra_doc_pointers)] diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs index 5f89ac059fd2d..6d11698d26822 100644 --- a/library/std/src/lib.rs +++ b/library/std/src/lib.rs @@ -268,7 +268,7 @@ #![feature(exact_size_is_empty)] #![feature(exhaustive_patterns)] #![feature(extend_one)] -#![feature(extended_key_value_attributes)] +#![cfg_attr(bootstrap, feature(extended_key_value_attributes))] #![feature(fn_traits)] #![feature(format_args_nl)] #![feature(gen_future)] diff --git a/src/doc/rustdoc/README.md b/src/doc/rustdoc/README.md new file mode 100644 index 0000000000000..7d97d5e4ab52f --- /dev/null +++ b/src/doc/rustdoc/README.md @@ -0,0 +1,5 @@ +# Rustdoc + +This is documentation for rustdoc itself, written in mdbook format. +To build the book, use `x.py doc src/doc/rustdoc`. +To run doctests, use `x.py test src/doc/rustdoc`. diff --git a/src/doc/rustdoc/src/the-doc-attribute.md b/src/doc/rustdoc/src/the-doc-attribute.md index 52f2a3728fabb..d192f7d5ce9e5 100644 --- a/src/doc/rustdoc/src/the-doc-attribute.md +++ b/src/doc/rustdoc/src/the-doc-attribute.md @@ -35,6 +35,13 @@ Which can feel more flexible. Note that this would generate this: but given that docs are rendered via Markdown, it will remove these newlines. +Another use case is for including external files as documentation: + +```rust,no_run +#[doc = include_str!("../README.md")] +# fn f() {} +``` + The `doc` attribute has more options though! These don't involve the text of the output, but instead, various aspects of the presentation of the output. We've split them into two kinds below: attributes that are useful at the diff --git a/src/test/rustdoc/external-doc.rs b/src/test/rustdoc/external-doc.rs index befd31a549290..0dadca551a9ff 100644 --- a/src/test/rustdoc/external-doc.rs +++ b/src/test/rustdoc/external-doc.rs @@ -1,5 +1,4 @@ #![feature(external_doc)] -#![feature(extended_key_value_attributes)] // @has external_doc/struct.CanHasDocs.html // @has - '//h1' 'External Docs' diff --git a/src/test/ui/attributes/key-value-expansion-on-mac.rs b/src/test/ui/attributes/key-value-expansion-on-mac.rs index 1247ff2b23075..95bc1c04961b0 100644 --- a/src/test/ui/attributes/key-value-expansion-on-mac.rs +++ b/src/test/ui/attributes/key-value-expansion-on-mac.rs @@ -1,4 +1,3 @@ -#![feature(extended_key_value_attributes)] #![feature(rustc_attrs)] #[rustc_dummy = stringify!(a)] // OK diff --git a/src/test/ui/attributes/key-value-expansion-on-mac.stderr b/src/test/ui/attributes/key-value-expansion-on-mac.stderr index b74f3518a7e97..fa9ea543765f7 100644 --- a/src/test/ui/attributes/key-value-expansion-on-mac.stderr +++ b/src/test/ui/attributes/key-value-expansion-on-mac.stderr @@ -1,5 +1,5 @@ error: unexpected token: `stringify!(b)` - --> $DIR/key-value-expansion-on-mac.rs:12:17 + --> $DIR/key-value-expansion-on-mac.rs:11:17 | LL | #[rustc_dummy = stringify!(b)] | ^^^^^^^^^^^^^ diff --git a/src/test/ui/feature-gates/feature-gate-extended_key_value_attributes.rs b/src/test/ui/feature-gates/feature-gate-extended_key_value_attributes.rs deleted file mode 100644 index f19fdb45f1f1e..0000000000000 --- a/src/test/ui/feature-gates/feature-gate-extended_key_value_attributes.rs +++ /dev/null @@ -1,8 +0,0 @@ -#[cfg(FALSE)] -#[attr = multi::segment::path] //~ ERROR arbitrary expressions in key-value attributes are unstable -#[attr = macro_call!()] //~ ERROR arbitrary expressions in key-value attributes are unstable -#[attr = 1 + 2] //~ ERROR arbitrary expressions in key-value attributes are unstable -#[attr = what?] //~ ERROR arbitrary expressions in key-value attributes are unstable -struct S; - -fn main() {} diff --git a/src/test/ui/feature-gates/feature-gate-extended_key_value_attributes.stderr b/src/test/ui/feature-gates/feature-gate-extended_key_value_attributes.stderr deleted file mode 100644 index 9887814b90762..0000000000000 --- a/src/test/ui/feature-gates/feature-gate-extended_key_value_attributes.stderr +++ /dev/null @@ -1,39 +0,0 @@ -error[E0658]: arbitrary expressions in key-value attributes are unstable - --> $DIR/feature-gate-extended_key_value_attributes.rs:2:10 - | -LL | #[attr = multi::segment::path] - | ^^^^^^^^^^^^^^^^^^^^ - | - = note: see issue #78835 for more information - = help: add `#![feature(extended_key_value_attributes)]` to the crate attributes to enable - -error[E0658]: arbitrary expressions in key-value attributes are unstable - --> $DIR/feature-gate-extended_key_value_attributes.rs:3:10 - | -LL | #[attr = macro_call!()] - | ^^^^^^^^^^^^^ - | - = note: see issue #78835 for more information - = help: add `#![feature(extended_key_value_attributes)]` to the crate attributes to enable - -error[E0658]: arbitrary expressions in key-value attributes are unstable - --> $DIR/feature-gate-extended_key_value_attributes.rs:4:10 - | -LL | #[attr = 1 + 2] - | ^^^^^ - | - = note: see issue #78835 for more information - = help: add `#![feature(extended_key_value_attributes)]` to the crate attributes to enable - -error[E0658]: arbitrary expressions in key-value attributes are unstable - --> $DIR/feature-gate-extended_key_value_attributes.rs:5:10 - | -LL | #[attr = what?] - | ^^^^^ - | - = note: see issue #78835 for more information - = help: add `#![feature(extended_key_value_attributes)]` to the crate attributes to enable - -error: aborting due to 4 previous errors - -For more information about this error, try `rustc --explain E0658`. diff --git a/src/test/ui/suffixed-literal-meta.rs b/src/test/ui/suffixed-literal-meta.rs index 319264aec9cd6..a6531490c0159 100644 --- a/src/test/ui/suffixed-literal-meta.rs +++ b/src/test/ui/suffixed-literal-meta.rs @@ -1,4 +1,4 @@ -#![feature(rustc_attrs, extended_key_value_attributes)] +#![feature(rustc_attrs)] #[rustc_dummy = 1usize] //~ ERROR: suffixed literals are not allowed in attributes #[rustc_dummy = 1u8] //~ ERROR: suffixed literals are not allowed in attributes