Auto merge of #86502 - JohnTitor:rollup-wge0f3x, r=JohnTitor

Rollup of 8 pull requests

Successful merges:

 - #83739 (Account for bad placeholder errors on consts/statics with trait objects)
 - #85637 (document PartialEq, PartialOrd, Ord requirements more explicitly)
 - #86152 (Lazify is_really_default condition in the RustdocGUI bootstrap step)
 - #86156 (Fix a bug in the linkchecker)
 - #86427 (Updated release note)
 - #86452 (fix panic-safety in specialized Zip::next_back)
 - #86484 (Do not set depth to 0 in fully_expand_fragment)
 - #86491 (expand: Move some more derive logic to rustc_builtin_macros)

Failed merges:

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

src/test/ui/error-codes/E0121.rs

@@ -2,5 +2,4 @@ fn foo() -> _ { 5 } //~ ERROR E0121
 
 static BAR: _ = "test"; //~ ERROR E0121
 
-fn main() {
-}
+fn main() {}

src/test/ui/macros/issue-84632-eager-expansion-recursion-limit.rs

@@ -0,0 +1,16 @@
+// Regression test for #84632: Recursion limit is ignored
+// for builtin macros that eagerly expands.
+
+#![recursion_limit = "15"]
+macro_rules! a {
+    () => ("");
+    (A) => (concat!("", a!()));
+    (A, $($A:ident),*) => (concat!("", a!($($A),*)))
+    //~^ ERROR recursion limit reached
+    //~| HELP consider adding
+}
+
+fn main() {
+    a!(A, A, A, A, A);
+    a!(A, A, A, A, A, A, A, A, A, A, A);
+}

src/test/ui/macros/issue-84632-eager-expansion-recursion-limit.stderr

@@ -0,0 +1,14 @@
+error: recursion limit reached while expanding `concat!`
+  --> $DIR/issue-84632-eager-expansion-recursion-limit.rs:8:28
+   |
+LL |     (A, $($A:ident),*) => (concat!("", a!($($A),*)))
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL |     a!(A, A, A, A, A, A, A, A, A, A, A);
+   |     ------------------------------------ in this macro invocation
+   |
+   = help: consider adding a `#![recursion_limit="30"]` attribute to your crate (`issue_84632_eager_expansion_recursion_limit`)
+   = note: this error originates in the macro `a` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to previous error
+

src/test/ui/typeck/issue-75889.rs

@@ -0,0 +1,6 @@
+// Regression test for #75889.
+
+const FOO: dyn Fn() -> _ = ""; //~ ERROR E0121
+static BOO: dyn Fn() -> _ = ""; //~ ERROR E0121
+
+fn main() {}

src/test/ui/typeck/issue-75889.stderr

@@ -0,0 +1,15 @@
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/issue-75889.rs:3:24
+   |
+LL | const FOO: dyn Fn() -> _ = "";
+   |                        ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/issue-75889.rs:4:25
+   |
+LL | static BOO: dyn Fn() -> _ = "";
+   |                         ^ not allowed in type signatures
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0121`.