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Attributes are reordered before they are passed to a proc-macro #67839
Description
I am working on a proc-macro, where I would like to give the user the option, to decide, which attributes (and doc comments) should be forwarded.
For example
use shorthand::ShortHand;
#[derive(ShortHand)]
#[shorthand(enable(forward(doc)))]
/// This should be in the output
#[shorthand(disable(forward(doc)))]
/// This line should not.
#[shorthand(enable(forward(doc)))]
/// This should be in the output
struct Example {
value: String,
}as you can see in the above case, the order of the attributes is very important.
Sadly the rust compiler (or the proc_macro crate) does reorder the attributes, before passing them to the function as a TokenStream.
#![feature(prelude_import)]
#[prelude_import]
use std::prelude::v1::*;
#[macro_use]
extern crate std;
use shorthand::ShortHand;
/// This should be in the output
/// This line should not.
/// This should be in the output
#[shorthand(enable(forward(doc)))]
#[shorthand(disable(forward(doc)))]
#[shorthand(enable(forward(doc)))]
struct Example {
value: String,
}
#[allow(dead_code)]
impl Example {
#[inline(always)]
pub fn value(&self) -> &String {
&self.value
}
#[inline(always)]
pub fn set_value(&mut self, value: String) -> &mut Self {
self.value = value;
self
}
}
#[allow(dead_code)]
fn main() {}
#[main]
pub fn main() -> () {
extern crate test;
test::test_main_static(&[])
}(this is the output of cargo expand, the proc-macro gets a similar TokenStream, where the order is not preserved either)
I think this should not happen and the order should be preserved! Are there any good reasons for reordering them?
related to #36211
Activity
[-]Struct attributes are reordered before they are passed to a proc-macro[/-][+]Attributes are reordered before they are passed to a proc-macro[/+]petrochenkov commentedon Jan 3, 2020
I agree that the relative order of inert attributes should be kept.
The reordering happens because built-in attributes (like doc comments) and non-builtin attributes are treated differently by macro expansion infrastructure.
I plan to fix this during the upcoming macro invocation collector rewrite (#54727 (comment)), unless someone gets to it earlier (this should be doable without rewriting the invocation collector entirely).
cc #63221
Luro02 commentedon Jan 3, 2020
I think this change can wait, until the new macro system is implemented, becuse this would be a breaking change either way. (for example the code given above would have different output, if a macro relies on the current order of attributes)
pksunkara commentedon Nov 5, 2020
Would this issue also include the proposal of ordering from rust-lang/reference#565 (comment)? If I currently write,
As far as I observed:
fooproc macro doesn't seem to getderiveattribute because it looks likederiveis expanded before it.petrochenkov commentedon Feb 22, 2021
Fixed in #82419.
@pksunkara
I think your case is different, but it was recently addressed by #79078.
pksunkara commentedon Feb 22, 2021
@petrochenkov Really appreciate your hard work in fixing both the issues. I have reworked some of my APIs to not run into this, but I am happy that I can now pick the best ergonomics for my proc-macro libraries instead of trying to navigate these issues.
Rollup merge of rust-lang#82419 - petrochenkov:inertord, r=Aaron1011
Rollup merge of rust-lang#82419 - petrochenkov:inertord, r=Aaron1011
Rollup merge of rust-lang#82419 - petrochenkov:inertord, r=Aaron1011
Rollup merge of rust-lang#82419 - petrochenkov:inertord, r=Aaron1011
Rollup merge of rust-lang#82419 - petrochenkov:inertord, r=Aaron1011
Append generated test macro so next test macros are aware of it
Append generated test macro so next test macros are aware of it
Append generated test macro so next test macros are aware of it
Append generated test macro so next test macros are aware of it
Append generated test macro so next test macros are aware of it
Append generated test macro so next test macros are aware of it
Append generated test macro so next test macros are aware of it
Append generated test macro so next test macros are aware of it