… pretty-printing mechanism.

…ation event.

Before this commit, we had an event that would only track the compression step
for proc-macros and Rust dylibs. After the commit we measure the time for
acutally generating the crate metadata bytes.

…nikomatsakis

Custom lifetime error for `impl` item doesn't conform to `trait`

Partly addresses rust-lang#42706, rust-lang#41343, fix rust-lang#40900.

Improve the "try using a variant of the expected type" hint.

Fix rust-lang#65494.

- Change type-printing output.
- Use `span_to_snippet` when possible.
- Change the message to `try using a variant of the expected enum`

…-E0587, r=Dylan-DPC

Add long error explanation for E0587

Part of rust-lang#61137.

r? @kinnison

…st-placeholder, r=eddyb

Correct handling of type flags with `ConstValue::Placeholder`

This fixes a mistake, but not rust-lang#65623.

r? @eddyb

rustc: use IndexVec<DefIndex, T> instead of Vec<T>.

Now that `DefIndex` is a proper index type, we can do that.
There was also an unnecessary `Option` I removed, I wonder if that has perf implications.

doc: mention `get(_mut)` in Vec

… r=wesleywiser

self-profiling: Record something more useful for crate metadata generation event.

Before this commit, we had an event that would only track the compression step
for proc-macros and Rust dylibs. After the commit we measure the time for
acutally generating the crate metadata bytes.

r? @wesleywiser