Accept arbitrary expressions in key-value attributes at parse time #78837
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r? @davidtwco (rust_highfive has picked a reviewer for you, use r? to override) |
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This was referenced Nov 7, 2020
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does this solve the translatable docs problem? |
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This should already work, I will add a test. |
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This change will allow for finally cleaning up the |
Before recommending this, someone should test how this interacts with |
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(but to be clear: I'm strongly in favor of this, I'm always +1 for having features in rustc instead of special-casing rustdoc.) |
@jyn514 Looks like that works just fine: #![feature(extended_key_value_attributes)]
const _: &[u8] = compile_time_run::run_command!("sh", "-c", "echo ' .second(\"hello\")' > somefile");
/// You are supposed to call it like this
///
/// # Example
///
/// ```
/// let example = Example::new()
/// .first("hello")
#[cfg_attr(not(feature = "one"), doc = include_str!("../somefile"))]
/// .third("hello")
/// .build();
/// ```
pub struct Example {}This results in:
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To lang team: this PR has lower priority than #79078. |
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We discussed this during the lang team meeting and felt that if this is just adding unstable surface area we can proceed here without a T-lang FCP. If there is something we're stabilizing then we'd like that called out more explicitly though and we can take another look :) We also had a question around the hygiene behavior of the passed tokens -- do we handle those equivalently to other macro input? If so then no concerns. |
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The change this PR makes in -macro foo($type_name: ident, $docs: expr) {
+macro foo($type_name:ident, $docs:expr) {Without the |
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Ah, apparently rustfmt doesn't format the macro parameters if it cannot format/parse the body. The full test case is: macro foo($type_name: ident, $docs: expr) {
#[allow(non_camel_case_types)]
#[doc=$docs]
#[derive(Debug, Clone, Copy)]
pub struct $type_name;
}The body contained a Mystery solved. |
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I passed over this issue the first time through the list, but…does this need |
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@pthariensflame |
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Understood! |
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ast: Remove some indirection layers from values in key-value attributes Trying to address some perf regressions from rust-lang#78837 (comment).
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# 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:
- rust-lang#83329
- rust-lang#83230
- rust-lang#82641
- rust-lang#80534
## Implementation history
- Initial proposal: rust-lang#55414 (comment)
- Experiment to see how much code it would break: rust-lang#67121
- Preliminary work to restrict expansion that would conflict with this
feature: rust-lang#77271
- Initial implementation: rust-lang#78837
- Fix for an ICE: rust-lang#80563
## Unresolved Questions
~~rust-lang#83366 (comment) 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.
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…=petrochenkov Stabilize extended_key_value_attributes Closes rust-lang#44732. Closes rust-lang#78835. Closes rust-lang#82768 (by making it irrelevant). # 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 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: - rust-lang#83329 - rust-lang#83230 - rust-lang#82641 - rust-lang#80534 ## Implementation history - Initial proposal: rust-lang#55414 (comment) - Experiment to see how much code it would break: rust-lang#67121 - Preliminary work to restrict expansion that would conflict with this feature: rust-lang#77271 - Initial implementation: rust-lang#78837 - Fix for an ICE: rust-lang#80563 ## Unresolved Questions ~~rust-lang#83366 (comment) 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 (rust-lang#82539). The `forward_inner_docs` workaround will still compile without warnings, but I expect it to be used less once it's no longer necessary.
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…=petrochenkov Stabilize extended_key_value_attributes Closes rust-lang#44732. Closes rust-lang#78835. Closes rust-lang#82768 (by making it irrelevant). # 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 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: - rust-lang#83329 - rust-lang#83230 - rust-lang#82641 - rust-lang#80534 ## Implementation history - Initial proposal: rust-lang#55414 (comment) - Experiment to see how much code it would break: rust-lang#67121 - Preliminary work to restrict expansion that would conflict with this feature: rust-lang#77271 - Initial implementation: rust-lang#78837 - Fix for an ICE: rust-lang#80563 ## Unresolved Questions ~~rust-lang#83366 (comment) 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 (rust-lang#82539). The `forward_inner_docs` workaround will still compile without warnings, but I expect it to be used less once it's no longer necessary.
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Continuation of #77271.
We now support arbitrary expressions in values of key-value attributes at parse time.
Previously only unsuffixed literals and interpolated expressions (
$expr) were accepted.There are two immediate motivational cases for this:
#[doc = include_str!("my_doc.md")], eliminating the need in Tracking issue: rfc 1990 - add external doc attribute to rustc #44732) and expanding macros in this position in general. Currently such macro expansions are supported in this position in interpolated$exprs (the#[doc = $doc]idiom).#[namespace = foo::bar] extern "C++" { ... }) like proposed in Allow path as value in name-value attribute #76734.If the attribute in question survives expansion, then the value is still restricted to unsuffixed literals by a semantic check.
This restriction doesn't prevent the use cases listed above, so this PR keeps it in place for now.
Closes #52607.
Previous attempt - #67121.
Some more detailed write up on internals - https://internals.rust-lang.org/t/macro-expansion-points-in-attributes/11455.
Tracking issue - #78835.