…for type parameter" suggestions

We should demonstrate good behavior, just like rust-lang#99198 did for `alloc`.

…stion, r=fmease

Provide placeholder generics for traits in "no method found for type parameter" suggestions

In the diagnostics for the error ``no method named `method` found for type parameter `T` in the current scope [E0599]``, the compiler will suggest adding bounds on `T` for traits that define a method named `method`. However, these suggestions didn't include any generic arguments, so applying them would result in a `missing generics for trait` or `missing lifetime specifier` error. This PR adds placeholder arguments to the suggestion in such cases. Specifically, I tried to base the placeholders off of what's done in suggestions for when generics are missing or too few are provided:
- The placeholder for a parameter without a default is the name of the parameter.
- Placeholders are not provided for parameters with defaults.

Placeholder arguments are enclosed in `/*` and `*/`, and the applicability of the suggestion is downgraded to `Applicability::HasPlaceholders` if any placeholders are provided.

Fixes rust-lang#132407

…mpiler-errors

cleanup: Remove outdated comment of `thir_body`

When typeck fails, `thir_body` returns `ErrorGuaranteed` rather than empty body.

No other code follows this outdated description except `check_unsafety`, which is also cleaned up in this PR.

…=compiler-errors

Don't use `maybe_unwrap_block` when checking for macro calls in a block expr

Fixes rust-lang#131915

Using `maybe_unwrap_block` to determine if we are looking at a `{ mac_call!{} }` will fail sometimes as `mac_call!{}` could be a `StmtKind::MacCall` not a `StmtKind::Expr`. This caused the def collector to think that `{ mac_call!{} }` was a non-trivial const argument and create a definition for it even though it should not.

r? `@compiler-errors`  cc `@camelid`

…crum

Update mdbook to 0.4.42

This updates mdbook to 0.4.42
Changelog: https://github.com/rust-lang/mdBook/blob/master/CHANGELOG.md#mdbook-0441

There were some significant changes that I would like to get early testing on.

This also updates rust-by-example which was required due to an update to the theme file.

…Simulacrum

elem_offset / subslice_range: use addr() instead of 'as usize'

There's no reason to use ptr-to-int casts with their subtle semantics here.

…first_doc_paragraph, r=tgross35

split up the first paragraph of doc comments for better summaries

used `./x clippy -Aclippy::all '-Wclippy::too_long_first_doc_paragraph' library/core library/alloc` to find these issues.

…ss35

Check for null in the `alloc_zeroed` example

We should demonstrate good behavior, just like rust-lang#99198 did for `alloc`.

…, r=WaffleLapkin

Make sure that we suggest turbofishing the right type arg for never suggestion

I had a bug where rust would suggest the wrong arg to turbofish `()` if there were any early-bound lifetimes...

r? WaffleLapkin