resolve/expand: Improve attribute expansion on macro definitions and calls #80563
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
|
(rust-highfive has picked a reviewer for you, use r? to override) |
rust-highfive
added
the
S-waiting-on-review
This comment has been minimized.
This comment has been minimized.
jyn514
added
A-macros
|
r? @Aaron1011 |
|
r=me with the stderr files updated. |
petrochenkov
force-pushed
the
expattronmac
branch
from
a3fce4a to
d81c194
Compare
|
@bors r=Aaron1011 |
|
📌 Commit d81c194 has been approved by |
bors
added
S-waiting-on-bors
|
☀️ Test successful - checks-actions |
jyn514
added
the
F-extended_key_value_attributes
jyn514
added a commit
to jyn514/rust
that referenced
this pull request
May 18, 2021
# 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.
Dylan-DPC-zz
pushed a commit
to Dylan-DPC-zz/rust
that referenced
this pull request
May 18, 2021
…=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.
jackh726
added a commit
to jackh726/rust
that referenced
this pull request
May 19, 2021
…=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.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Fixes #80540