Pretty-printer incorrectly outputs type items with where clauses

[jooert]

So I wrote a regression test for a certain error and it held up the rollup PR (see #24979) because while my test passed the run-pass it failed during the pretty pass. The problem is that the prettifier (compiling with -Z unstable-options --pretty=expanded) transforms the original code example from #22471

type Foo<T> where T: Copy = Box<T>;

into

type Foo<T> = Box<T> where T: Copy;

which upon compilation leads to the following error:

error: expected one of `+`, `::`, or `;`, found `where`
type Foo<T> = Box<T> where T: Copy;

This seems to indicate a bug in the prettifier as (seemingly) valid code is transformed into non-compiling one.

[bluss]

basically the PR that added the syntax type Foo<T> where T: Copy = Box<T>; should have updated the pretty code to handle that too. That's what the pretty tests are trying to enforce.

[jooert]

It still may, as it isn't merged yet, but I have no idea how to do that. 😃

[jooert]

Sorry, I misread your comment, you weren't talking about my PR.