From a72dd4a5b973a3d94876ebea66e428fabaff00b0 Mon Sep 17 00:00:00 2001
From: Hirochika Matsumoto <git@hkmatsumoto.com>
Date: Tue, 19 Oct 2021 01:31:23 +0900
Subject: [PATCH] Explain why `Self` is invalid in generic parameters
---
compiler/rustc_parse/src/parser/generics.rs | 13 +++++++++
.../ui/keyword/keyword-self-as-type-param.rs | 6 ++--
.../keyword/keyword-self-as-type-param.stderr | 29 ++++++++++++-------
3 files changed, 35 insertions(+), 13 deletions(-)
diff --git a/compiler/rustc_parse/src/parser/generics.rs b/compiler/rustc_parse/src/parser/generics.rs
index f175c5b50b397..ec7e376656618 100644
--- a/compiler/rustc_parse/src/parser/generics.rs
+++ b/compiler/rustc_parse/src/parser/generics.rs
@@ -89,6 +89,19 @@ impl<'a> Parser<'a> {
let attrs = self.parse_outer_attributes()?;
let param =
self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
+ if this.eat_keyword_noexpect(kw::SelfUpper) {
+ // `Self` as a generic param is invalid. Here we emit the diagnostic and continue parsing
+ // as if `Self` never existed.
+ this.struct_span_err(
+ this.prev_token.span,
+ "unexpected keyword `Self` in generic parameters",
+ )
+ .note("you cannot use `Self` as a generic parameter because it is reserved for associated items")
+ .emit();
+
+ this.eat(&token::Comma);
+ }
+
let param = if this.check_lifetime() {
let lifetime = this.expect_lifetime();
// Parse lifetime parameter.
diff --git a/src/test/ui/keyword/keyword-self-as-type-param.rs b/src/test/ui/keyword/keyword-self-as-type-param.rs
index 785d64ec8ea22..55c7ac128ffde 100644
--- a/src/test/ui/keyword/keyword-self-as-type-param.rs
+++ b/src/test/ui/keyword/keyword-self-as-type-param.rs
@@ -1,10 +1,10 @@
// Regression test of #36638.
struct Foo<Self>(Self);
-//~^ ERROR expected identifier, found keyword `Self`
-//~^^ ERROR E0392
+//~^ ERROR unexpected keyword `Self` in generic parameters
+//~| ERROR recursive type `Foo` has infinite size
trait Bar<Self> {}
-//~^ ERROR expected identifier, found keyword `Self`
+//~^ ERROR unexpected keyword `Self` in generic parameters
fn main() {}
diff --git a/src/test/ui/keyword/keyword-self-as-type-param.stderr b/src/test/ui/keyword/keyword-self-as-type-param.stderr
index cc3df2e36f7f5..fd101b32b4c9c 100644
--- a/src/test/ui/keyword/keyword-self-as-type-param.stderr
+++ b/src/test/ui/keyword/keyword-self-as-type-param.stderr
@@ -1,24 +1,33 @@
-error: expected identifier, found keyword `Self`
+error: unexpected keyword `Self` in generic parameters
--> $DIR/keyword-self-as-type-param.rs:3:12
|
LL | struct Foo<Self>(Self);
- | ^^^^ expected identifier, found keyword
+ | ^^^^
+ |
+ = note: you cannot use `Self` as a generic parameter because it is reserved for associated items
-error: expected identifier, found keyword `Self`
+error: unexpected keyword `Self` in generic parameters
--> $DIR/keyword-self-as-type-param.rs:7:11
|
LL | trait Bar<Self> {}
- | ^^^^ expected identifier, found keyword
+ | ^^^^
+ |
+ = note: you cannot use `Self` as a generic parameter because it is reserved for associated items
-error[E0392]: parameter `Self` is never used
- --> $DIR/keyword-self-as-type-param.rs:3:12
+error[E0072]: recursive type `Foo` has infinite size
+ --> $DIR/keyword-self-as-type-param.rs:3:1
|
LL | struct Foo<Self>(Self);
- | ^^^^ unused parameter
+ | ^^^^^^^^^^^^^^^^^----^^
+ | | |
+ | | recursive without indirection
+ | recursive type has infinite size
+ |
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `Foo` representable
|
- = help: consider removing `Self`, referring to it in a field, or using a marker such as `PhantomData`
- = help: if you intended `Self` to be a const parameter, use `const Self: usize` instead
+LL | struct Foo<Self>(Box<Self>);
+ | ++++ +
error: aborting due to 3 previous errors
-For more information about this error, try `rustc --explain E0392`.
+For more information about this error, try `rustc --explain E0072`.