Implement `#[cfg]` in `where` clauses #132388

frank-king · 2024-10-31T06:11:52Z

This PR implements #115590, which supports #[cfg] attributes in where clauses.

The biggest change is, that it adds AttrsVec and NodeId to the ast::WherePredicate and HirId to the hir::WherePredicate.

rustbot · 2024-10-31T06:12:01Z

r? @cjgillot

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rustbot · 2024-10-31T06:12:03Z

HIR ty lowering was modified

cc @fmease

Changes to the size of AST and/or HIR nodes.

cc @nnethercote

rustbot · 2024-10-31T09:17:11Z

Some changes occurred in src/tools/rustfmt

cc @rust-lang/rustfmt

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

src/tools/rustfmt/src/types.rs

cjgillot

Thanks @frank-king for the work. I haven't looked deeply into the parser code yet, I need to familiarize myself with it first.

compiler/rustc_ast/src/ast.rs

compiler/rustc_ast/src/mut_visit.rs

compiler/rustc_ast/src/visit.rs

compiler/rustc_ast_lowering/src/index.rs

compiler/rustc_expand/src/expand.rs

compiler/rustc_hir/src/hir.rs

compiler/rustc_hir/src/intravisit.rs

compiler/rustc_resolve/src/late.rs

compiler/rustc_expand/src/expand.rs

src/tools/rustfmt/tests/target/cfg_attribute_in_where.rs

compiler/rustc_expand/src/expand.rs

petrochenkov · 2024-11-16T18:42:17Z

I've opened #132894 for that refactoring.

Blocked on #132894.
@rustbot blocked

…=<try> Refactor `where` predicates, and reserve for attributes support Refactor `WherePredicate` to `WherePredicateKind`, and reserve for attributes support in `where` predicates. This is a part of rust-lang#115590 and is split from rust-lang#132388. r? petrochenkov

frank-king · 2024-11-26T12:29:46Z

@rustbot ready

compiler/rustc_parse/src/parser/generics.rs

petrochenkov · 2024-12-01T20:39:13Z

(I didn't finish the full review yet.)

tests/ui/feature-gates/feature-gate-cfg_attribute_in_where.rs

petrochenkov · 2025-02-20T16:27:36Z

compiler/rustc_expand/src/base.rs

@@ -52,6 +52,7 @@ pub enum Annotatable {
    FieldDef(ast::FieldDef),
    Variant(ast::Variant),
    Crate(ast::Crate),
+    WherePredicate(ast::WherePredicate),


Style nit: could you consistently put the logic for WherePredicate immediately after the logic for Variants (in annotatables, ast fragments, etc)?
The new fragment is most similar to Variant, and it's good to have things in the same order everywhere.

Still need to reorder a few things in expand.rs.

compiler/rustc_expand/src/expand.rs

petrochenkov · 2025-02-20T16:34:08Z

compiler/rustc_expand/src/placeholders.rs

+                span,
+                kind: ast::WherePredicateKind::BoundPredicate(ast::WhereBoundPredicate {
+                    bound_generic_params: Default::default(),
+                    bounded_ty: ty(),


So you put a macro here to recognize placeholders, instead of adding the is_placeholder flag like in variants.
This is a bit tricky and at least needs a documentation, but I'd probably recommend to just add the is_placeholder flag instead.

Note that you never check whether a where-predicate node is a placeholder, because this PR misses the attribute resolution/expansion logic in

compiler\rustc_resolve\src\def_collector.rs

compiler\rustc_resolve\src\build_reduced_graph.rs

compiler\rustc_expand\src\placeholders.rs

Search for the .is_placeholder there and you can also do the same things as Variants do.

After gaining more knowledge of placeholders, I started to realize that here we need is_placeholder because we don't have something like ast::ExprKind::MacCall or ast::ItemKind::ItemCall but we still need to repesent a macro call in the Variant and WherePredicate positions, is that correct?

Is it better to add a new variant ast::WherePredicateKind::MacCall? Then the size of ast::WherePredicate can be smaller that adding an is_placeholder: bool field. That also makes the codes more readable, and reserves the posibility that we can support macro calls in where clauses in the future.

Is it better to add a new variant ast::WherePredicateKind::MacCall?

Nah, MacCall is only for function-like macro calls, if they are not currently supported in some position, then it's better to not introduce it, and just use is_placeholder.

tests/ui/where-clauses/cfg_attribute.rs

compiler/rustc_feature/src/unstable.rs

compiler/rustc_passes/src/check_attr.rs

petrochenkov · 2025-02-20T16:56:45Z

compiler/rustc_passes/messages.ftl

@@ -784,6 +784,10 @@ passes_unstable_attr_for_already_stable_feature =
    .item = the stability attribute annotates this item
    .help = consider removing the attribute

+passes_unsupported_attributes_in_where =
+    attributes in `where` clauses are not supported


Suggested change

attributes in `where` clauses are not supported

most attributes are not supported in `where` clauses

"in where clauses" in the end is a bit better grammatically.

compiler/rustc_passes/messages.ftl

petrochenkov · 2025-02-20T17:03:57Z

Sorry for the long delay, I've finished the review now.
@rustbot author

rustbot · 2025-02-24T11:47:05Z

Some changes occurred in compiler/rustc_passes/src/check_attr.rs

cc @jdonszelmann

rust-log-analyzer · 2025-02-24T12:02:01Z

The job mingw-check failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

    Checking walkdir v2.5.0
    Checking filetime v0.2.25
    Checking if_chain v1.0.2
    Checking rinja v0.3.5
error[E0004]: non-exhaustive patterns: `&rustc_ast::WherePredicateKind::MacCall(_)` not covered
    |
    |
54  |                 match &clause.kind {
    |                       ^^^^^^^^^^^^ pattern `&rustc_ast::WherePredicateKind::MacCall(_)` not covered
note: `rustc_ast::WherePredicateKind` defined here
   --> /checkout/compiler/rustc_ast/src/ast.rs:428:1
    |
428 | pub enum WherePredicateKind {
428 | pub enum WherePredicateKind {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
...
436 |     MacCall(P<MacCall>),
    = note: the matched value is of type `&rustc_ast::WherePredicateKind`
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |
    |
72  ~                     WherePredicateKind::EqPredicate(_) => {},
73  ~                     &rustc_ast::WherePredicateKind::MacCall(_) => todo!(),

For more information about this error, try `rustc --explain E0004`.
error: could not compile `clippy_lints` (lib) due to 1 previous error
Build completed unsuccessfully in 0:03:23

petrochenkov · 2025-02-24T15:25:08Z

tests/ui/where-clauses/cfg_attribute.rs

+        #[derive_const(Clone)] ():,
+        //~^ ERROR most attributes in `where` clauses are not supported
+        //~| ERROR expected non-macro attribute, found attribute macro `derive_const`
+        #[test_case] ():,


No need to test all the macros exhaustively, it makes the tests harder to read, just one macro would be enough.

bors · 2025-02-25T02:50:07Z

☔ The latest upstream changes (presumably #135726) made this pull request unmergeable. Please resolve the merge conflicts.

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tgross35 changed the title ~~Implment #[cfg] in where clauses~~ Implement #[cfg] in where clauses Oct 31, 2024

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frank-king mentioned this pull request Nov 11, 2024

Refactor where predicates, and reserve for attributes support #132894

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Implment #[cfg] and #[cfg_attr] in where clauses

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Implement `#[cfg]` in `where` clauses #132388

Implement `#[cfg]` in `where` clauses #132388

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bors commented Feb 25, 2025

	attributes in `where` clauses are not supported
	most attributes are not supported in `where` clauses

Implement #[cfg] in where clauses #132388

Are you sure you want to change the base?

Implement #[cfg] in where clauses #132388

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bors commented Feb 25, 2025

Implement `#[cfg]` in `where` clauses #132388

Implement `#[cfg]` in `where` clauses #132388