Some cleanup changes and commenting

[nox]

r? @nikomatsakis
Cc @eddyb

[nox]

@eddyb

Seems like we forgot about nonsensical bounds in nonsensical code.

---- [ui] ui/trivial-bounds/trivial-bounds-inconsistent-well-formed.rs stdout ----

error: test compilation failed although it shouldn't!
status: exit code: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/trivial-bounds/trivial-bounds-inconsistent-well-formed.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/trivial-bounds/trivial-bounds-inconsistent-well-formed/a" "-Crpath" "-O" "-Cdebuginfo=0" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/trivial-bounds/trivial-bounds-inconsistent-well-formed/auxiliary"
stdout:
------------------------------------------

------------------------------------------
stderr:
------------------------------------------
error[E0161]: cannot move a value of type str: the size of str cannot be statically determined
  --> /checkout/src/test/ui/trivial-bounds/trivial-bounds-inconsistent-well-formed.rs:10:18
   |
LL |     let x = vec![*"1"];
   |                  ^^^^

error: aborting due to previous error

That test does str: Copy hah.

[nox]

I'll change that commit to be adding a comment explaining why we can't fast-path types that are trivially !Sized.

[nox]

I added a comment on is_trivially_sized. This PR does pretty much nothing now, so you may just want to close it and spare the CI cycles.

[eddyb]

I want @nikomatsakis to see this (I forgot about trivial bounds too!), but also, we can:

@bors rollup

[jyn514]

@bors r=eddyb rollup

[bors]

📌 Commit caf6c92 has been approved by eddyb