rust-analyzer

diff --git a/crates/hir-ty/src/lower/diagnostics.rs b/crates/hir-ty/src/lower/diagnostics.rs
index 009f047109..2565fb46ce 100644
--- a/crates/hir-ty/src/lower/diagnostics.rs
+++ b/crates/hir-ty/src/lower/diagnostics.rs

@@ -81,6 +81,11 @@ pub enum PathLoweringDiagnostic {

def: GenericDefId,

expected_count: u32,

+ /// Generic defaults are not allowed to refer to `Self`.

+ GenericDefaultRefersToSelf {

+ /// Index of the `Self` segment.

+ segment: u32,

+ },

}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]

diff --git a/crates/hir-ty/src/lower/path.rs b/crates/hir-ty/src/lower/path.rs
index 4f70732178..a364894539 100644
--- a/crates/hir-ty/src/lower/path.rs
+++ b/crates/hir-ty/src/lower/path.rs

@@ -300,8 +300,10 @@ impl<'a, 'b, 'db> PathLoweringContext<'a, 'b, 'db> {

prohibit_generics_on_resolved(GenericArgsProhibitedReason::SelfTy);

if self.ctx.lowering_param_default.is_some() {

- // Generic defaults are not allowed to refer to `Self`.

- // FIXME: Emit an error.

+ let segment = self.current_segment_u32();

+ self.on_diagnostic(PathLoweringDiagnostic::GenericDefaultRefersToSelf {

+ segment,

+ });

return false;

}

diff --git a/crates/hir-ty/src/tests.rs b/crates/hir-ty/src/tests.rs
index 430a570444..83767c42ea 100644
--- a/crates/hir-ty/src/tests.rs
+++ b/crates/hir-ty/src/tests.rs

@@ -88,15 +88,12 @@ fn check_impl(

let file_range = FileRange { file_id, range };

if only_types {

types.insert(file_range, expected);

- } else if expected.starts_with("type: ") {

- types.insert(file_range, expected.trim_start_matches("type: ").to_owned());

+ } else if let Some(ty) = expected.strip_prefix("type: ") {

+ types.insert(file_range, ty.to_owned());

} else if expected.starts_with("expected") {

mismatches.insert(file_range, expected);

- } else if expected.starts_with("adjustments:") {

- adjustments.insert(

- file_range,

- expected.trim_start_matches("adjustments:").trim().to_owned(),

- );

+ } else if let Some(adjs) = expected.strip_prefix("adjustments:") {

+ adjustments.insert(file_range, adjs.trim().to_owned());

} else {

panic!("unexpected annotation: {expected} @ {range:?}");

}

diff --git a/crates/hir-ty/src/tests/diagnostics.rs b/crates/hir-ty/src/tests/diagnostics.rs
index f257aa1b6e..94ca88088d 100644
--- a/crates/hir-ty/src/tests/diagnostics.rs
+++ b/crates/hir-ty/src/tests/diagnostics.rs

@@ -1,6 +1,4 @@

-use crate::tests::check_no_mismatches;

-use super::check;

+use super::{check, check_no_mismatches};

#[test]

fn function_return_type_mismatch_1() {

diff --git a/crates/hir/src/diagnostics.rs b/crates/hir/src/diagnostics.rs
index b14bf64266..110cc19cf1 100644
--- a/crates/hir/src/diagnostics.rs
+++ b/crates/hir/src/diagnostics.rs

@@ -57,6 +57,7 @@ diagnostics![AnyDiagnostic<'db> ->

BreakOutsideOfLoop,

CastToUnsized<'db>,

ExpectedFunction<'db>,

+ GenericDefaultRefersToSelf,

InactiveCode,

IncoherentImpl,

IncorrectCase,

@@ -465,6 +466,12 @@ pub struct IncorrectGenericsOrder {

pub expected_kind: GenericArgKind,

}

+#[derive(Debug)]

+pub struct GenericDefaultRefersToSelf {

+ /// The `Self` segment.

+ pub segment: InFile<AstPtr<ast::PathSegment>>,

impl<'db> AnyDiagnostic<'db> {

pub(crate) fn body_validation_diagnostic(

db: &'db dyn HirDatabase,

@@ -888,6 +895,11 @@ impl<'db> AnyDiagnostic<'db> {

}

.into()

}

+ PathLoweringDiagnostic::GenericDefaultRefersToSelf { segment } => {

+ let segment = hir_segment_to_ast_segment(&path.value, segment)?;

+ let segment = path.with_value(AstPtr::new(&segment));

+ GenericDefaultRefersToSelf { segment }.into()

+ }

})

}

diff --git a/crates/ide-diagnostics/src/handlers/generic_default_refers_to_self.rs b/crates/ide-diagnostics/src/handlers/generic_default_refers_to_self.rs
new file mode 100644
index 0000000000..3d38159c4f
--- /dev/null
+++ b/crates/ide-diagnostics/src/handlers/generic_default_refers_to_self.rs

@@ -0,0 +1,43 @@

+use crate::{Diagnostic, DiagnosticCode, DiagnosticsContext};

+// Diagnostic: generic-default-refers-to-self

+//

+// This diagnostic is shown when a generic default refers to `Self`

+pub(crate) fn generic_default_refers_to_self(

+ ctx: &DiagnosticsContext<'_>,

+ d: &hir::GenericDefaultRefersToSelf,

+) -> Diagnostic {

+ Diagnostic::new_with_syntax_node_ptr(

+ ctx,

+ DiagnosticCode::RustcHardError("E0735"),

+ "generic parameters cannot use `Self` in their defaults",

+ d.segment.map(Into::into),

+ )

+ .stable()

+#[cfg(test)]

+mod tests {

+ use crate::tests::check_diagnostics;

+ #[test]

+ fn plain_self() {

+ check_diagnostics(

+ r#"

+struct Foo<T = Self>(T);

+ // ^^^^ error: generic parameters cannot use `Self` in their defaults

+"#,

+ );

+ }

+ #[test]

+ fn self_as_generic() {

+ check_diagnostics(

+ r#"

+struct Wrapper<T>(T);

+struct Foo<T = Wrapper<Self>>(T);

+ // ^^^^ error: generic parameters cannot use `Self` in their defaults

+"#,

+ );

+ }

diff --git a/crates/ide-diagnostics/src/lib.rs b/crates/ide-diagnostics/src/lib.rs
index 09c9f8eab0..54af3a35f4 100644
--- a/crates/ide-diagnostics/src/lib.rs
+++ b/crates/ide-diagnostics/src/lib.rs

@@ -35,6 +35,7 @@ mod handlers {

pub(crate) mod elided_lifetimes_in_path;

pub(crate) mod expected_function;

pub(crate) mod generic_args_prohibited;

+ pub(crate) mod generic_default_refers_to_self;

pub(crate) mod inactive_code;

pub(crate) mod incoherent_impl;

pub(crate) mod incorrect_case;

@@ -477,6 +478,7 @@ pub fn semantic_diagnostics(

AnyDiagnostic::IncorrectGenericsOrder(d) => handlers::incorrect_generics_order::incorrect_generics_order(&ctx, &d),

AnyDiagnostic::MissingLifetime(d) => handlers::missing_lifetime::missing_lifetime(&ctx, &d),

AnyDiagnostic::ElidedLifetimesInPath(d) => handlers::elided_lifetimes_in_path::elided_lifetimes_in_path(&ctx, &d),

+ AnyDiagnostic::GenericDefaultRefersToSelf(d) => handlers::generic_default_refers_to_self::generic_default_refers_to_self(&ctx, &d),

};

res.push(d)

}