This commit adds fuzzing for the (expr) formatter, with the same invariants that we use for fmt tests:
* We start with text, which we parse
* We format the AST, which must succeed
* We parse back the AST and make sure it's identical igoring whitespace+comments
* We format the new AST and assert it's equal to the first formatted version ("idempotency")
Interestingly, while a lot of bugs this found were in the formatter, it also found some parsing bugs.
It then fixes a bunch of bugs that fell out:
* Some small oversights in RemoveSpaces
* Make sure `_a` doesn't parse as an inferred type (`_`) followed by an identifier (parsing bug!)
* Call `extract_spaces` on a parsed expr before matching on it, lest it be Expr::SpaceBefore - when parsing aliases
* A few cases where the formatter generated invalid/different code
* Numerous formatting bugs that caused the formatting to not be idempotent
The last point there is worth talking further about. There were several cases where the old code was trying to enforce strong
opinions about how to insert newlines in function types and defs. In both of those cases, it looked like the goals of
(1) idempotency, (2) giving the user some say in the output, and (3) these strong opinions - were often in conflict.
For these cases, I erred on the side of following the user's existing choices about where to put newlines.
We can go back and re-add this strong opinionation later - but this seemed the right approach for now.
Both of these cases do not tie to a platform. The roc app can be built without considering the platform.
It is often the case that the platform is using one of these options because roc cannot build the platform.
This allows for more flexibility and avoids wasting time compiling the platform.
And provide expectation subs when expectations should be compiled. This
will be useful for getting the specialized type of an expect lookup when
it's available.
Now that mono does not store expect lookup layouts, the layout cache
should be primed only when specializing the condition of an expect, and
so #4749 is resolved.
Closes#4749
