Auto merge of #100456 - Dylan-DPC:rollup-fn17z9f, r=Dylan-DPC

Rollup of 9 pull requests

Successful merges:

 - #100022 (Optimize thread ID generation)
 - #100030 (cleanup code w/ pointers in std a little)
 - #100229 (add -Zextra-const-ub-checks to enable more UB checking in const-eval)
 - #100247 (Generalize trait object generic param check to aliases.)
 - #100255 (Adding more verbose documentation for `std::fmt::Write`)
 - #100366 (errors: don't fail on broken primary translations)
 - #100396 (Suggest const and static for global variable)
 - #100409 (rustdoc: don't generate DOM element for operator)
 - #100443 (Add two let else regression tests)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

25 files changed, 320 insertions, 63 deletions

diff --git a/src/test/run-make/translation/Makefile b/src/test/run-make/translation/Makefile
index bfff75e7acb..20e86c7f9a0 100644
--- a/src/test/run-make/translation/Makefile
+++ b/src/test/run-make/translation/Makefile
@@ -9,16 +9,29 @@ FAKEROOT=$(TMPDIR)/fakeroot
 
 all: normal custom sysroot
 
-normal: basic-translation.rs
+# Check that the test works normally, using the built-in fallback bundle.
+normal: test.rs
 	$(RUSTC) $< 2>&1 | grep "struct literal body without path"
 
-custom: basic-translation.rs basic-translation.ftl
-	$(RUSTC) $< -Ztranslate-additional-ftl=$(CURDIR)/basic-translation.ftl 2>&1 | grep "this is a test message"
+# Check that a primary bundle can be loaded and will be preferentially used
+# where possible.
+custom: test.rs working.ftl
+	$(RUSTC) $< -Ztranslate-additional-ftl=$(CURDIR)/working.ftl 2>&1 | grep "this is a test message"
+
+# Check that a primary bundle with a broken message (e.g. a interpolated
+# variable is missing) will use the fallback bundle.
+missing: test.rs missing.ftl
+	$(RUSTC) $< -Ztranslate-additional-ftl=$(CURDIR)/missing.ftl 2>&1 | grep "struct literal body without path"
+
+# Check that a primary bundle without the desired message will use the fallback
+# bundle.
+broken: test.rs broken.ftl
+	$(RUSTC) $< -Ztranslate-additional-ftl=$(CURDIR)/broken.ftl 2>&1 | grep "struct literal body without path"
 
 # Check that a locale can be loaded from the sysroot given a language
 # identifier by making a local copy of the sysroot and adding the custom locale
 # to it.
-sysroot: basic-translation.rs basic-translation.ftl
+sysroot: test.rs working.ftl
 	mkdir $(FAKEROOT)
 	ln -s $(SYSROOT)/* $(FAKEROOT)
 	rm -f $(FAKEROOT)/lib
@@ -31,7 +44,7 @@ sysroot: basic-translation.rs basic-translation.ftl
 	mkdir $(FAKEROOT)/lib/rustlib/src
 	ln -s $(SYSROOT)/lib/rustlib/src/* $(FAKEROOT)/lib/rustlib/src
 	mkdir -p $(FAKEROOT)/share/locale/zh-CN/
-	ln -s $(CURDIR)/basic-translation.ftl $(FAKEROOT)/share/locale/zh-CN/basic-translation.ftl
+	ln -s $(CURDIR)/working.ftl $(FAKEROOT)/share/locale/zh-CN/basic-translation.ftl
 	$(RUSTC) $< --sysroot $(FAKEROOT) -Ztranslate-lang=zh-CN 2>&1 | grep "this is a test message"
 
 # Check that the compiler errors out when the sysroot requested cannot be
@@ -43,7 +56,7 @@ sysroot-missing:
 # Check that the compiler errors out when the sysroot requested cannot be
 # found. This test might start failing if there actually exists a Klingon
 # translation of rustc's error messages.
-sysroot-invalid: basic-translation.rs basic-translation.ftl
+sysroot-invalid: test.rs working.ftl
 	mkdir $(FAKEROOT)
 	ln -s $(SYSROOT)/* $(FAKEROOT)
 	rm -f $(FAKEROOT)/lib
diff --git a/src/test/run-make/translation/broken.ftl b/src/test/run-make/translation/broken.ftl
new file mode 100644
index 00000000000..1482dd2824a
--- /dev/null
+++ b/src/test/run-make/translation/broken.ftl
@@ -0,0 +1,3 @@
+# `foo` isn't provided by this diagnostic so it is expected that the fallback message is used.
+parser-struct-literal-body-without-path = this is a {$foo} message
+    .suggestion = this is a test suggestion
diff --git a/src/test/run-make/translation/missing.ftl b/src/test/run-make/translation/missing.ftl
new file mode 100644
index 00000000000..43076b1d6ae
--- /dev/null
+++ b/src/test/run-make/translation/missing.ftl
@@ -0,0 +1,3 @@
+# `parser-struct-literal-body-without-path` isn't provided by this resource at all, so the
+# fallback should be used.
+foo = bar
diff --git a/src/test/run-make/translation/basic-translation.rs b/src/test/run-make/translation/test.rs
index b8f5bff3153..b8f5bff3153 100644
--- a/src/test/run-make/translation/basic-translation.rs
+++ b/src/test/run-make/translation/test.rs
diff --git a/src/test/run-make/translation/basic-translation.ftl b/src/test/run-make/translation/working.ftl
index 4681b879cda..4681b879cda 100644
--- a/src/test/run-make/translation/basic-translation.ftl
+++ b/src/test/run-make/translation/working.ftl
diff --git a/src/test/rustdoc-ui/z-help.stdout b/src/test/rustdoc-ui/z-help.stdout
index 6dc41231559..236469ce979 100644
--- a/src/test/rustdoc-ui/z-help.stdout
+++ b/src/test/rustdoc-ui/z-help.stdout
@@ -38,6 +38,7 @@
     -Z                        emit-stack-sizes=val -- emit a section containing stack size metadata (default: no)
     -Z                           emit-thin-lto=val -- emit the bc module with thin LTO info (default: yes)
     -Z               export-executable-symbols=val -- export symbols from executables, as if they were dynamic libraries
+    -Z                   extra-const-ub-checks=val -- turns on more checks to detect const UB, which can be slow (default: no)
     -Z                             fewer-names=val -- reduce memory use by retaining fewer names within compilation artifacts (LLVM-IR) (default: no)
     -Z              force-unstable-if-unmarked=val -- force all crates to be `rustc_private` unstable (default: no)
     -Z                                    fuel=val -- set the optimization fuel quota for a crate
diff --git a/src/test/rustdoc/macro_rules-matchers.rs b/src/test/rustdoc/macro_rules-matchers.rs
index efc3b21e6da..131c53ec24b 100644
--- a/src/test/rustdoc/macro_rules-matchers.rs
+++ b/src/test/rustdoc/macro_rules-matchers.rs
@@ -6,16 +6,13 @@
 // @has 'foo/macro.todo.html'
 // @has - '//span[@class="macro"]' 'macro_rules!'
 // @has - '//span[@class="ident"]' 'todo'
-// Note: the only op is the `+`
-// @count - '//pre[@class="rust macro"]//span[@class="op"]' 1
 
 // @has - '{ () =&gt; { ... }; ($('
 // @has - '//span[@class="macro-nonterminal"]' '$'
 // @has - '//span[@class="macro-nonterminal"]' 'arg'
 // @has - ':'
 // @has - '//span[@class="ident"]' 'tt'
-// @has - '),'
-// @has - '//span[@class="op"]' '+'
+// @has - ')+'
 // @has - ') =&gt; { ... }; }'
 pub use std::todo;
 
diff --git a/src/test/ui/associated-types/issue-22560.stderr b/src/test/ui/associated-types/issue-22560.stderr
index 700923c1b3f..2b88cf0b441 100644
--- a/src/test/ui/associated-types/issue-22560.stderr
+++ b/src/test/ui/associated-types/issue-22560.stderr
@@ -1,25 +1,3 @@
-error[E0393]: the type parameter `Rhs` must be explicitly specified
-  --> $DIR/issue-22560.rs:9:23
-   |
-LL | trait Sub<Rhs=Self> {
-   | ------------------- type parameter `Rhs` must be specified for this
-...
-LL | type Test = dyn Add + Sub;
-   |                       ^^^ help: set the type parameter to the desired type: `Sub<Rhs>`
-   |
-   = note: because of the default `Self` reference, type parameters must be specified on object types
-
-error[E0393]: the type parameter `Rhs` must be explicitly specified
-  --> $DIR/issue-22560.rs:9:17
-   |
-LL | trait Add<Rhs=Self> {
-   | ------------------- type parameter `Rhs` must be specified for this
-...
-LL | type Test = dyn Add + Sub;
-   |                 ^^^ help: set the type parameter to the desired type: `Add<Rhs>`
-   |
-   = note: because of the default `Self` reference, type parameters must be specified on object types
-
 error[E0225]: only auto traits can be used as additional traits in a trait object
   --> $DIR/issue-22560.rs:9:23
    |
@@ -28,7 +6,7 @@ LL | type Test = dyn Add + Sub;
    |                 |
    |                 first non-auto trait
    |
-   = help: consider creating a new trait with all of these as supertraits and using that trait here instead: `trait NewTrait: Add<[type error]> + Sub<[type error]> {}`
+   = help: consider creating a new trait with all of these as supertraits and using that trait here instead: `trait NewTrait: Add + Sub {}`
    = note: auto-traits like `Send` and `Sync` are traits that have special properties; for more information on them, visit <https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits>
 
 error[E0191]: the value of the associated types `Output` (from trait `Add`), `Output` (from trait `Sub`) must be specified
@@ -50,6 +28,28 @@ help: specify the associated types
 LL | type Test = dyn Add<Output = Type> + Sub<Output = Type>;
    |                 ~~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~~~~~~
 
+error[E0393]: the type parameter `Rhs` must be explicitly specified
+  --> $DIR/issue-22560.rs:9:17
+   |
+LL | trait Add<Rhs=Self> {
+   | ------------------- type parameter `Rhs` must be specified for this
+...
+LL | type Test = dyn Add + Sub;
+   |                 ^^^ help: set the type parameter to the desired type: `Add<Rhs>`
+   |
+   = note: because of the default `Self` reference, type parameters must be specified on object types
+
+error[E0393]: the type parameter `Rhs` must be explicitly specified
+  --> $DIR/issue-22560.rs:9:23
+   |
+LL | trait Sub<Rhs=Self> {
+   | ------------------- type parameter `Rhs` must be specified for this
+...
+LL | type Test = dyn Add + Sub;
+   |                       ^^^ help: set the type parameter to the desired type: `Sub<Rhs>`
+   |
+   = note: because of the default `Self` reference, type parameters must be specified on object types
+
 error: aborting due to 4 previous errors
 
 Some errors have detailed explanations: E0191, E0225, E0393.
diff --git a/src/test/ui/consts/extra-const-ub/detect-extra-ub.rs b/src/test/ui/consts/extra-const-ub/detect-extra-ub.rs
new file mode 100644
index 00000000000..97c9e150519
--- /dev/null
+++ b/src/test/ui/consts/extra-const-ub/detect-extra-ub.rs
@@ -0,0 +1,45 @@
+// revisions: no_flag with_flag
+// [no_flag] check-pass
+// [with_flag] compile-flags: -Zextra-const-ub-checks
+#![feature(const_ptr_read)]
+
+use std::mem::transmute;
+
+const INVALID_BOOL: () = unsafe {
+    let _x: bool = transmute(3u8);
+    //[with_flag]~^ ERROR: evaluation of constant value failed
+    //[with_flag]~| invalid value
+};
+
+const INVALID_PTR_IN_INT: () = unsafe {
+    let _x: usize = transmute(&3u8);
+    //[with_flag]~^ ERROR: evaluation of constant value failed
+    //[with_flag]~| invalid value
+};
+
+const INVALID_SLICE_TO_USIZE_TRANSMUTE: () = unsafe {
+    let x: &[u8] = &[0; 32];
+    let _x: (usize, usize) = transmute(x);
+    //[with_flag]~^ ERROR: evaluation of constant value failed
+    //[with_flag]~| invalid value
+};
+
+const UNALIGNED_PTR: () = unsafe {
+    let _x: &u32 = transmute(&[0u8; 4]);
+    //[with_flag]~^ ERROR: evaluation of constant value failed
+    //[with_flag]~| invalid value
+};
+
+const UNALIGNED_READ: () = {
+    INNER; //[with_flag]~ERROR any use of this value will cause an error
+    //[with_flag]~| previously accepted
+    // There is an error here but its span is in the standard library so we cannot match it...
+    // so we have this in a *nested* const, such that the *outer* const fails to use it.
+    const INNER: () = unsafe {
+        let x = &[0u8; 4];
+        let ptr = x.as_ptr().cast::<u32>();
+        ptr.read();
+    };
+};
+
+fn main() {}
diff --git a/src/test/ui/consts/extra-const-ub/detect-extra-ub.with_flag.stderr b/src/test/ui/consts/extra-const-ub/detect-extra-ub.with_flag.stderr
new file mode 100644
index 00000000000..1706db7ac43
--- /dev/null
+++ b/src/test/ui/consts/extra-const-ub/detect-extra-ub.with_flag.stderr
@@ -0,0 +1,71 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/detect-extra-ub.rs:9:20
+   |
+LL |     let _x: bool = transmute(3u8);
+   |                    ^^^^^^^^^^^^^^ constructing invalid value: encountered 0x03, but expected a boolean
+
+error[E0080]: evaluation of constant value failed
+  --> $DIR/detect-extra-ub.rs:15:21
+   |
+LL |     let _x: usize = transmute(&3u8);
+   |                     ^^^^^^^^^^^^^^^ constructing invalid value: encountered (potentially part of) a pointer, but expected plain (non-pointer) bytes
+
+error[E0080]: evaluation of constant value failed
+  --> $DIR/detect-extra-ub.rs:22:30
+   |
+LL |     let _x: (usize, usize) = transmute(x);
+   |                              ^^^^^^^^^^^^ constructing invalid value at .0: encountered (potentially part of) a pointer, but expected plain (non-pointer) bytes
+
+error[E0080]: evaluation of constant value failed
+  --> $DIR/detect-extra-ub.rs:28:20
+   |
+LL |     let _x: &u32 = transmute(&[0u8; 4]);
+   |                    ^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered an unaligned reference (required 4 byte alignment but found 1)
+
+error[E0080]: evaluation of constant value failed
+  --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL
+   |
+LL |         copy_nonoverlapping(src, tmp.as_mut_ptr(), 1);
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |         |
+   |         accessing memory with alignment 1, but alignment 4 is required
+   |         inside `std::ptr::read::<u32>` at $SRC_DIR/core/src/ptr/mod.rs:LL:COL
+   |
+  ::: $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL
+   |
+LL |         unsafe { read(self) }
+   |                  ---------- inside `ptr::const_ptr::<impl *const u32>::read` at $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL
+   |
+  ::: $DIR/detect-extra-ub.rs:41:9
+   |
+LL |         ptr.read();
+   |         ---------- inside `INNER` at $DIR/detect-extra-ub.rs:41:9
+
+error: any use of this value will cause an error
+  --> $DIR/detect-extra-ub.rs:34:5
+   |
+LL | const UNALIGNED_READ: () = {
+   | ------------------------
+LL |     INNER;
+   |     ^^^^^ referenced constant has errors
+   |
+   = note: `#[deny(const_err)]` on by default
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
+
+error: aborting due to 6 previous errors
+
+For more information about this error, try `rustc --explain E0080`.
+Future incompatibility report: Future breakage diagnostic:
+error: any use of this value will cause an error
+  --> $DIR/detect-extra-ub.rs:34:5
+   |
+LL | const UNALIGNED_READ: () = {
+   | ------------------------
+LL |     INNER;
+   |     ^^^^^ referenced constant has errors
+   |
+   = note: `#[deny(const_err)]` on by default
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
+
diff --git a/src/test/ui/cycle-trait/cycle-trait-default-type-trait.rs b/src/test/ui/cycle-trait/cycle-trait-default-type-trait.rs
index b2edc1a1f66..6175b7df110 100644
--- a/src/test/ui/cycle-trait/cycle-trait-default-type-trait.rs
+++ b/src/test/ui/cycle-trait/cycle-trait-default-type-trait.rs
@@ -3,7 +3,6 @@
 
 trait Foo<X = Box<dyn Foo>> {
     //~^ ERROR cycle detected
-    //~| ERROR cycle detected
 }
 
 fn main() { }
diff --git a/src/test/ui/cycle-trait/cycle-trait-default-type-trait.stderr b/src/test/ui/cycle-trait/cycle-trait-default-type-trait.stderr
index d4976a0f9c9..9d715f49471 100644
--- a/src/test/ui/cycle-trait/cycle-trait-default-type-trait.stderr
+++ b/src/test/ui/cycle-trait/cycle-trait-default-type-trait.stderr
@@ -10,30 +10,11 @@ note: cycle used when collecting item types in top-level module
    |
 LL | / trait Foo<X = Box<dyn Foo>> {
 LL | |
-LL | |
-LL | | }
-LL | |
-LL | | fn main() { }
-   | |_____________^
-
-error[E0391]: cycle detected when computing type of `Foo::X`
-  --> $DIR/cycle-trait-default-type-trait.rs:4:23
-   |
-LL | trait Foo<X = Box<dyn Foo>> {
-   |                       ^^^
-   |
-   = note: ...which immediately requires computing type of `Foo::X` again
-note: cycle used when collecting item types in top-level module
-  --> $DIR/cycle-trait-default-type-trait.rs:4:1
-   |
-LL | / trait Foo<X = Box<dyn Foo>> {
-LL | |
-LL | |
 LL | | }
 LL | |
 LL | | fn main() { }
    | |_____________^
 
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
 For more information about this error, try `rustc --explain E0391`.
diff --git a/src/test/ui/issues/issue-21950.stderr b/src/test/ui/issues/issue-21950.stderr
index 4909398bb84..731615a6bd8 100644
--- a/src/test/ui/issues/issue-21950.stderr
+++ b/src/test/ui/issues/issue-21950.stderr
@@ -1,3 +1,12 @@
+error[E0191]: the value of the associated type `Output` (from trait `Add`) must be specified
+  --> $DIR/issue-21950.rs:10:25
+   |
+LL |     type Output;
+   |     ----------- `Output` defined here
+...
+LL |     let x = &10 as &dyn Add;
+   |                         ^^^ help: specify the associated type: `Add<Output = Type>`
+
 error[E0393]: the type parameter `Rhs` must be explicitly specified
   --> $DIR/issue-21950.rs:10:25
    |
@@ -9,15 +18,6 @@ LL |     let x = &10 as &dyn Add;
    |
    = note: because of the default `Self` reference, type parameters must be specified on object types
 
-error[E0191]: the value of the associated type `Output` (from trait `Add`) must be specified
-  --> $DIR/issue-21950.rs:10:25
-   |
-LL |     type Output;
-   |     ----------- `Output` defined here
-...
-LL |     let x = &10 as &dyn Add;
-   |                         ^^^ help: specify the associated type: `Add<Output = Type>`
-
 error: aborting due to 2 previous errors
 
 Some errors have detailed explanations: E0191, E0393.
diff --git a/src/test/ui/let-else/issue-94176.rs b/src/test/ui/let-else/issue-94176.rs
new file mode 100644
index 00000000000..e35bbd88830
--- /dev/null
+++ b/src/test/ui/let-else/issue-94176.rs
@@ -0,0 +1,10 @@
+// Issue #94176: wrong span for the error message of a mismatched type error,
+// if the function uses a `let else` construct.
+#![feature(let_else)]
+
+pub fn test(a: Option<u32>) -> Option<u32> { //~ ERROR mismatched types
+    let Some(_) = a else { return None; };
+    println!("Foo");
+}
+
+fn main() {}
diff --git a/src/test/ui/let-else/issue-94176.stderr b/src/test/ui/let-else/issue-94176.stderr
new file mode 100644
index 00000000000..0cb97aceebf
--- /dev/null
+++ b/src/test/ui/let-else/issue-94176.stderr
@@ -0,0 +1,19 @@
+error[E0308]: mismatched types
+  --> $DIR/issue-94176.rs:5:32
+   |
+LL | pub fn test(a: Option<u32>) -> Option<u32> {
+   |        ----                    ^^^^^^^^^^^ expected enum `Option`, found `()`
+   |        |
+   |        implicitly returns `()` as its body has no tail or `return` expression
+   |
+   = note:   expected enum `Option<u32>`
+           found unit type `()`
+help: consider returning the local binding `a`
+   |
+LL ~     println!("Foo");
+LL +     a
+   |
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.
diff --git a/src/test/ui/let-else/let-else-then-diverge.rs b/src/test/ui/let-else/let-else-then-diverge.rs
new file mode 100644
index 00000000000..49633d943be
--- /dev/null
+++ b/src/test/ui/let-else/let-else-then-diverge.rs
@@ -0,0 +1,19 @@
+//
+// popped up in in #94012, where an alternative desugaring was
+// causing unreachable code errors
+
+#![feature(let_else)]
+#![deny(unused_variables)]
+#![deny(unreachable_code)]
+
+fn let_else_diverge() -> bool {
+    let Some(_) = Some("test") else {
+        let x = 5; //~ ERROR unused variable: `x`
+        return false;
+    };
+    return true;
+}
+
+fn main() {
+    let_else_diverge();
+}
diff --git a/src/test/ui/let-else/let-else-then-diverge.stderr b/src/test/ui/let-else/let-else-then-diverge.stderr
new file mode 100644
index 00000000000..ceb61029d38
--- /dev/null
+++ b/src/test/ui/let-else/let-else-then-diverge.stderr
@@ -0,0 +1,14 @@
+error: unused variable: `x`
+  --> $DIR/let-else-then-diverge.rs:11:13
+   |
+LL |         let x = 5;
+   |             ^ help: if this is intentional, prefix it with an underscore: `_x`
+   |
+note: the lint level is defined here
+  --> $DIR/let-else-then-diverge.rs:6:9
+   |
+LL | #![deny(unused_variables)]
+   |         ^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/parser/suggest-const-for-global-var.rs b/src/test/ui/parser/suggest-const-for-global-var.rs
new file mode 100644
index 00000000000..d6216cb7ac2
--- /dev/null
+++ b/src/test/ui/parser/suggest-const-for-global-var.rs
@@ -0,0 +1,6 @@
+let X: i32 = 12;
+//~^ ERROR expected item, found keyword `let`
+
+fn main() {
+    println!("{}", X);
+}
diff --git a/src/test/ui/parser/suggest-const-for-global-var.stderr b/src/test/ui/parser/suggest-const-for-global-var.stderr
new file mode 100644
index 00000000000..94e44ec7f6c
--- /dev/null
+++ b/src/test/ui/parser/suggest-const-for-global-var.stderr
@@ -0,0 +1,8 @@
+error: expected item, found keyword `let`
+  --> $DIR/suggest-const-for-global-var.rs:1:1
+   |
+LL | let X: i32 = 12;
+   | ^^^ consider using `const` or `static` instead of `let` for global variables
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/traits/alias/generic-default-in-dyn.rs b/src/test/ui/traits/alias/generic-default-in-dyn.rs
new file mode 100644
index 00000000000..d44e1c2a975
--- /dev/null
+++ b/src/test/ui/traits/alias/generic-default-in-dyn.rs
@@ -0,0 +1,10 @@
+trait SendEqAlias<T> = PartialEq;
+//~^ ERROR trait aliases are experimental
+
+struct Foo<T>(dyn SendEqAlias<T>);
+//~^ ERROR the type parameter `Rhs` must be explicitly specified [E0393]
+
+struct Bar<T>(dyn SendEqAlias<T>, T);
+//~^ ERROR the type parameter `Rhs` must be explicitly specified [E0393]
+
+fn main() {}
diff --git a/src/test/ui/traits/alias/generic-default-in-dyn.stderr b/src/test/ui/traits/alias/generic-default-in-dyn.stderr
new file mode 100644
index 00000000000..76a068e864a
--- /dev/null
+++ b/src/test/ui/traits/alias/generic-default-in-dyn.stderr
@@ -0,0 +1,39 @@
+error[E0658]: trait aliases are experimental
+  --> $DIR/generic-default-in-dyn.rs:1:1
+   |
+LL | trait SendEqAlias<T> = PartialEq;
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #41517 <https://github.com/rust-lang/rust/issues/41517> for more information
+   = help: add `#![feature(trait_alias)]` to the crate attributes to enable
+
+error[E0393]: the type parameter `Rhs` must be explicitly specified
+  --> $DIR/generic-default-in-dyn.rs:4:19
+   |
+LL | struct Foo<T>(dyn SendEqAlias<T>);
+   |                   ^^^^^^^^^^^^^^ missing reference to `Rhs`
+   |
+  ::: $SRC_DIR/core/src/cmp.rs:LL:COL
+   |
+LL | pub trait PartialEq<Rhs: ?Sized = Self> {
+   | --------------------------------------- type parameter `Rhs` must be specified for this
+   |
+   = note: because of the default `Self` reference, type parameters must be specified on object types
+
+error[E0393]: the type parameter `Rhs` must be explicitly specified
+  --> $DIR/generic-default-in-dyn.rs:7:19
+   |
+LL | struct Bar<T>(dyn SendEqAlias<T>, T);
+   |                   ^^^^^^^^^^^^^^ missing reference to `Rhs`
+   |
+  ::: $SRC_DIR/core/src/cmp.rs:LL:COL
+   |
+LL | pub trait PartialEq<Rhs: ?Sized = Self> {
+   | --------------------------------------- type parameter `Rhs` must be specified for this
+   |
+   = note: because of the default `Self` reference, type parameters must be specified on object types
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0393, E0658.
+For more information about an error, try `rustc --explain E0393`.
diff --git a/src/test/ui/traits/alias/self-in-generics.rs b/src/test/ui/traits/alias/self-in-generics.rs
new file mode 100644
index 00000000000..6b99431f5bb
--- /dev/null
+++ b/src/test/ui/traits/alias/self-in-generics.rs
@@ -0,0 +1,8 @@
+#![feature(trait_alias)]
+
+pub trait SelfInput = Fn(&mut Self);
+
+pub fn f(_f: &dyn SelfInput) {}
+//~^ ERROR the trait alias `SelfInput` cannot be made into an object [E0038]
+
+fn main() {}
diff --git a/src/test/ui/traits/alias/self-in-generics.stderr b/src/test/ui/traits/alias/self-in-generics.stderr
new file mode 100644
index 00000000000..a1056872ea6
--- /dev/null
+++ b/src/test/ui/traits/alias/self-in-generics.stderr
@@ -0,0 +1,11 @@
+error[E0038]: the trait alias `SelfInput` cannot be made into an object
+  --> $DIR/self-in-generics.rs:5:19
+   |
+LL | pub fn f(_f: &dyn SelfInput) {}
+   |                   ^^^^^^^^^
+   |
+   = note: it cannot use `Self` as a type parameter in a supertrait or `where`-clause
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0038`.
diff --git a/src/test/ui/unspecified-self-in-trait-ref.rs b/src/test/ui/traits/unspecified-self-in-trait-ref.rs
index 158b5a98557..158b5a98557 100644
--- a/src/test/ui/unspecified-self-in-trait-ref.rs
+++ b/src/test/ui/traits/unspecified-self-in-trait-ref.rs
diff --git a/src/test/ui/unspecified-self-in-trait-ref.stderr b/src/test/ui/traits/unspecified-self-in-trait-ref.stderr
index 7869176bb3a..7869176bb3a 100644
--- a/src/test/ui/unspecified-self-in-trait-ref.stderr
+++ b/src/test/ui/traits/unspecified-self-in-trait-ref.stderr