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Stabilize the #[diagnostic] namespace and `#[diagnostic::on_unimple…
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…mented]` attribute

This PR stabilizes the `#[diagnostic]` attribute namespace and a minimal
option of the `#[diagnostic::on_unimplemented]` attribute.

The `#[diagnostic]` attribute namespace is meant to provide a home for
attributes that allow users to influence error messages emitted by the
compiler. The compiler is not guaranteed to use any of this hints,
however it should accept any (non-)existing attribute in this namespace
and potentially emit lint-warnings for unused attributes and options.
This is meant to allow discarding certain attributes/options in the
future to allow fundamental changes to the compiler without the need to
keep then non-meaningful options working.

The `#[diagnostic::on_unimplemented]` attribute is allowed to appear
on a trait definition. This allows crate authors to hint the compiler
to emit a specific error message if a certain trait is not implemented.
For the `#[diagnostic::on_unimplemented]` attribute the following
options are implemented:

* `message` which provides the text for the top level error message
* `label` which provides the text for the label shown inline in the
broken code in the error message
* `note` which provides additional notes.

The `note` option can appear several times, which results in several
note messages being emitted. If any of the other options appears several
times the first occurrence of the relevant option specifies the actually
used value. Any other occurrence generates an lint warning. For any
other non-existing option a lint-warning is generated.

All three options accept a text as argument. This text is allowed to
contain format parameters referring to generic argument or `Self` by
name via the `{Self}` or `{NameOfGenericArgument}` syntax. For any
non-existing argument a lint warning is generated.

Tracking issue: #111996
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weiznich committed Jan 25, 2024
1 parent 039d887 commit d906c0c
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Showing 27 changed files with 93 additions and 272 deletions.
8 changes: 0 additions & 8 deletions compiler/rustc_ast_passes/src/feature_gate.rs
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Expand Up @@ -200,14 +200,6 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
);
}
}
if !attr.is_doc_comment()
&& let [seg, _] = attr.get_normal_item().path.segments.as_slice()
&& seg.ident.name == sym::diagnostic
&& !self.features.diagnostic_namespace
{
let msg = "`#[diagnostic]` attribute name space is experimental";
gate!(self, diagnostic_namespace, seg.ident.span, msg);
}

// Emit errors for non-staged-api crates.
if !self.features.staged_api {
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2 changes: 2 additions & 0 deletions compiler/rustc_feature/src/accepted.rs
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Expand Up @@ -144,6 +144,8 @@ declare_features! (
(accepted, derive_default_enum, "1.62.0", Some(86985)),
/// Allows the use of destructuring assignments.
(accepted, destructuring_assignment, "1.59.0", Some(71126)),
/// Allows using the `#[diagnostic]` attribute tool namespace
(accepted, diagnostic_namespace, "CURRENT_RUSTC_VERSION", Some(111996)),
/// Allows `#[doc(alias = "...")]`.
(accepted, doc_alias, "1.48.0", Some(50146)),
/// Allows `..` in tuple (struct) patterns.
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2 changes: 0 additions & 2 deletions compiler/rustc_feature/src/unstable.rs
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Expand Up @@ -436,8 +436,6 @@ declare_features! (
(unstable, deprecated_safe, "1.61.0", Some(94978)),
/// Allows having using `suggestion` in the `#[deprecated]` attribute.
(unstable, deprecated_suggestion, "1.61.0", Some(94785)),
/// Allows using the `#[diagnostic]` attribute tool namespace
(unstable, diagnostic_namespace, "1.73.0", Some(111996)),
/// Controls errors in trait implementations.
(unstable, do_not_recommend, "1.67.0", Some(51992)),
/// Tells rustdoc to automatically generate `#[doc(cfg(...))]`.
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1 change: 1 addition & 0 deletions library/core/src/lib.rs
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Expand Up @@ -200,6 +200,7 @@
//
// Language features:
// tidy-alphabetical-start
#![cfg_attr(bootstrap, feature(diagnostic_namespace))]
#![cfg_attr(not(bootstrap), feature(is_val_statically_known))]
#![feature(abi_unadjusted)]
#![feature(adt_const_params)]
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1 change: 0 additions & 1 deletion tests/ui/diagnostic_namespace/existing_proc_macros.rs
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@@ -1,4 +1,3 @@
#![feature(diagnostic_namespace)]
// check-pass
// aux-build:proc-macro-helper.rs

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13 changes: 0 additions & 13 deletions tests/ui/diagnostic_namespace/feature-gate-diagnostic_namespace.rs

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Original file line number Diff line number Diff line change
@@ -1,4 +1,3 @@
#![feature(diagnostic_namespace)]
// check-pass
#[diagnostic::non_existing_attribute]
//~^WARN unknown diagnostic attribute
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Original file line number Diff line number Diff line change
@@ -1,13 +1,13 @@
warning: unknown diagnostic attribute
--> $DIR/non_existing_attributes_accepted.rs:3:15
--> $DIR/non_existing_attributes_accepted.rs:2:15
|
LL | #[diagnostic::non_existing_attribute]
| ^^^^^^^^^^^^^^^^^^^^^^
|
= note: `#[warn(unknown_or_malformed_diagnostic_attributes)]` on by default

warning: unknown diagnostic attribute
--> $DIR/non_existing_attributes_accepted.rs:8:15
--> $DIR/non_existing_attributes_accepted.rs:7:15
|
LL | #[diagnostic::non_existing_attribute(with_option = "foo")]
| ^^^^^^^^^^^^^^^^^^^^^^
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Original file line number Diff line number Diff line change
@@ -1,5 +1,3 @@
#![feature(diagnostic_namespace)]

#[diagnostic::on_unimplemented(
message = "Message",
note = "Note",
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Original file line number Diff line number Diff line change
@@ -1,5 +1,3 @@
#![feature(diagnostic_namespace)]

#[diagnostic::on_unimplemented(
on(_Self = "&str"),
//~^WARN malformed `on_unimplemented` attribute
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