delegation: Implement glob delegation #124135

petrochenkov · 2024-04-18T20:20:20Z

Support delegating to all trait methods in one go.
Overriding globs with explicit definitions is also supported.

The implementation is generally based on the design from rust-lang/rfcs#3530 (comment), but unlike with list delegation in #123413 we cannot expand glob delegation eagerly.
We have to enqueue it into the queue of unexpanded macros (most other macros are processed this way too), and then a glob delegation waits in that queue until its trait path is resolved, and enough code expands to generate the identifier list produced from the glob.

Glob delegation is only allowed in impls, and can only point to traits.
Supporting it in other places gives very little practical benefit, but significantly raises the implementation complexity.

Part of #118212.

rustbot · 2024-04-18T20:20:29Z

r? @estebank

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rustbot · 2024-04-19T18:54:32Z

Some changes occurred in src/tools/rustfmt

cc @rust-lang/rustfmt

fmease · 2024-04-23T20:52:18Z

I guess it makes the most sense if I review this one, too.

r? fmease

petrochenkov · 2024-04-23T22:04:17Z

This is basically blocked on #123413 now.
@rustbot blocked

delegation: Implement list delegation ```rust reuse prefix::{a, b, c}; ``` Using design described in rust-lang/rfcs#3530 (comment) (the lists are desugared at macro expansion time). List delegations are expanded eagerly when encountered, similarly to `#[cfg]`s, and not enqueued for later resolution/expansion like regular macros or glob delegation (rust-lang#124135). Part of rust-lang#118212.

petrochenkov · 2024-05-31T16:54:51Z

@rustbot ready

fmease

(partial review)

fmease · 2024-06-07T13:30:45Z

compiler/rustc_ast/src/ast.rs

@@ -3149,13 +3149,16 @@ pub struct Delegation {
    pub path: Path,
    pub rename: Option<Ident>,
    pub body: Option<P<Block>>,
+    /// The item was expanded from a glob delegation item.
+    pub from_glob: bool,


(not blocking) maybe even with enum FromGlob { Yes, No }

fmease · 2024-06-07T13:32:16Z

compiler/rustc_ast/src/ast.rs

 }

 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct DelegationMac {
    pub qself: Option<P<QSelf>>,
    pub prefix: Path,
-    pub suffixes: ThinVec<(Ident, Option<Ident>)>,
+    // Some for list delegation, and None for glob delegation.
+    pub suffixes: Option<ThinVec<(Ident, Option<Ident>)>>,


(not blocking) maybe even enum DelegationMacKind { List(/*...*/), Glob }

compiler/rustc_expand/src/base.rs

compiler/rustc_expand/src/expand.rs

compiler/rustc_resolve/src/macros.rs

compiler/rustc_expand/src/expand.rs

fmease · 2024-06-07T14:25:00Z

compiler/rustc_parse/src/parser/item.rs

Overriding globs with explicit definitions is also supported.

With that, I thought you meant sth. like reuse prefix::{*, src as dest}; which is obviously not the case. Do you plan on supporting that eventually?

Overriding typically means the function body is different, or at least the "target expression" is different.

reuse prefix::* { self.field } fn override1() { overridden_body() } reuse prefix::override2 { self.other_field }

In your example the body and the target expr are the same, only the name is different, which doesn't seem too useful.
But it can be supported, I guess, it should be pretty simple to do it as a part of list delegation expansion.

Nested lists could also be supported, but that's a significant complication for very little gain.
I sort of regret supporting them in use items.

compiler/rustc_expand/src/expand.rs

fmease

23/28 viewed (continuing in a sec)

fmease · 2024-06-13T03:32:34Z

tests/ui/delegation/empty-glob.rs

+
+struct S;
+impl S {
+    reuse Trait::*; //~ ERROR empty glob delegation is not supported


(non-blocking) we probably want to permit that at some point. might be useful for macro authors generating reuse (similar how we permit struct S<T:>(T);, struct S where String:,;, fn f<T: Copy +>(){} and the like for flexibility)

In this case it's annoying to support because Trait (and possible generic arguments in it), still needs to be checked for stability, privacy, etc.
So we'll have to keep an otherwise unnecessary dummy item after expansion, and even in HIR, to perform these checks.

tests/ui/delegation/glob-glob-conflict.rs

fmease · 2024-06-13T04:02:42Z

tests/ui/delegation/glob-non-fn.rs

+
+struct Bad(u8);
+impl Trait for Bad { //~ ERROR not all trait items implemented, missing: `CONST`, `Type`, `method`
+    reuse Trait::* { &self.0 }


(non-blocking) What do you think about skipping any non-fns? Not sure if that'd be less or more confusing for users. The diagnostics right now are certainly not helping the uninitiated ^^

The plan is to eventually support delegating non-function associated items too.
For now they are just supposed to report some kind of error (which they do).
I agree that the current error is suboptimal, but that's not very critical.

tests/ui/delegation/glob-non-impl.stderr

fmease · 2024-06-13T04:13:55Z

tests/ui/delegation/macro-inside-glob.rs

+macro_rules! u8 { () => { u8 } }
+macro_rules! self_0 { () => { &self.0 } }
+impl Trait for S {
+    reuse <u8!() as Trait>::* { self_0!() }


I'm surprised to see self_0 having access to the local binding self. Isn't this breaking hygiene rules? For comparison with normal functions, see this playground.

Yeah, looks like a hygiene bug.
We'll need to decide what the "expected" context for self should be inherited from (since there's no explicit definition for it, like in regular methods).
Perhaps from *, but we don't keep the *'s precise span right now.

This is a pre-existing issue with the way in which the self binding is created, not related to glob delegation, I'll fix this separately.
(Upd: I've pushed the fix into this PR, but I'll move it to a new PR with a test.)

PR - #126497

…rrors delegation: Fix hygiene for `self` And fix diagnostics for `self` from a macro. The missing rib caused `self` to be treated as a generic parameter and ignore `macro_rules` hygiene. Addresses this comment rust-lang#124135 (comment).

Rollup merge of rust-lang#126497 - petrochenkov:delehyg, r=compiler-errors delegation: Fix hygiene for `self` And fix diagnostics for `self` from a macro. The missing rib caused `self` to be treated as a generic parameter and ignore `macro_rules` hygiene. Addresses this comment rust-lang#124135 (comment).

fmease

Thanks a lot! Sorry for the long review times

fmease · 2024-06-18T19:37:09Z

compiler/rustc_expand/src/expand.rs

+) -> impl Iterator<Item = ast::Item<Node::ItemKind>> + 'a {
+    if suffixes.is_empty() {
+        // Report an error for now, to avoid keeping stem for resolution and
+        // stability checks.


fmease · 2024-06-18T20:16:44Z

I guess this doesn't require a rebase (despite #126497) 🤔
@bors r+

bors · 2024-06-18T20:16:47Z

📌 Commit 22d0b1e has been approved by fmease

It is now in the queue for this repository.

delegation: Implement glob delegation Support delegating to all trait methods in one go. Overriding globs with explicit definitions is also supported. The implementation is generally based on the design from rust-lang/rfcs#3530 (comment), but unlike with list delegation in rust-lang#123413 we cannot expand glob delegation eagerly. We have to enqueue it into the queue of unexpanded macros (most other macros are processed this way too), and then a glob delegation waits in that queue until its trait path is resolved, and enough code expands to generate the identifier list produced from the glob. Glob delegation is only allowed in impls, and can only point to traits. Supporting it in other places gives very little practical benefit, but significantly raises the implementation complexity. Part of rust-lang#118212.

Rollup of 10 pull requests Successful merges: - rust-lang#124135 (delegation: Implement glob delegation) - rust-lang#125078 (fix: break inside async closure has incorrect span for enclosing closure) - rust-lang#125293 (Place tail expression behind terminating scope) - rust-lang#126422 (Suggest using a standalone doctest for non-local impl defs) - rust-lang#126493 (safe transmute: support non-ZST, variantful, uninhabited enums) - rust-lang#126504 (Sync fuchsia test runner with clang test runner) - rust-lang#126558 (hir_typeck: be more conservative in making "note caller chooses ty param" note) - rust-lang#126586 (Add `@badboy` and `@BlackHoleFox` as Mac Catalyst maintainers) - rust-lang#126615 (Add `rustc-ice*` to `.gitignore`) - rust-lang#126632 (Replace `move||` with `move ||`) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#124135 - petrochenkov:deleglob, r=fmease delegation: Implement glob delegation Support delegating to all trait methods in one go. Overriding globs with explicit definitions is also supported. The implementation is generally based on the design from rust-lang/rfcs#3530 (comment), but unlike with list delegation in rust-lang#123413 we cannot expand glob delegation eagerly. We have to enqueue it into the queue of unexpanded macros (most other macros are processed this way too), and then a glob delegation waits in that queue until its trait path is resolved, and enough code expands to generate the identifier list produced from the glob. Glob delegation is only allowed in impls, and can only point to traits. Supporting it in other places gives very little practical benefit, but significantly raises the implementation complexity. Part of rust-lang#118212.

rustbot assigned estebank Apr 18, 2024

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petrochenkov mentioned this pull request Apr 19, 2024

delegation: Implement list delegation #123413

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rustbot added S-blocked Status: Marked as blocked ❌ on something else such as an RFC or other implementation work. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Apr 23, 2024

petrochenkov force-pushed the deleglob branch from 2737bcf to 4e6c21f Compare May 15, 2024 14:06

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fmease reviewed Jun 7, 2024

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delegation: Implement glob delegation

22d0b1e

petrochenkov force-pushed the deleglob branch from c2af71a to 22d0b1e Compare June 14, 2024 16:31

petrochenkov mentioned this pull request Jun 14, 2024

delegation: Fix hygiene for self #126497

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bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 18, 2024

This was referenced Jun 19, 2024

Rollup of 20 pull requests #126653

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Rollup of 10 pull requests #126655

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bors merged commit f8ce1cf into rust-lang:master Jun 19, 2024
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matthiaskrgr mentioned this pull request Jun 20, 2024

ICE: macros: entered unreachable code' #126742

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petrochenkov mentioned this pull request Jun 24, 2024

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