3700: fill match arms with empty block rather than unit tuple r=matklad a=JoshMcguigan
As requested by @Veetaha in #3689 and #3687, this modifies the fill match arms assist to create match arms as an empty block `{}` rather than a unit tuple `()`.
In one test I left one of the pre-existing match arms as a unit tuple, and added a body to another match arm, to demonstrate that the contents of existing match arms persist.
Co-authored-by: Josh Mcguigan <joshmcg88@gmail.com>
Addresses #3039
This essentially adds missing match arms. The algorithm for this
can get complicated rather quickly so bail in certain conditions
and rely on a PlaceholderPat.
The algorighm works as such:
- Iterate through the Enum Def Variants
- Attempt to see if the variant already exists as a match arm
- If yes, skip the enum variant. If no, include it.
- If it becomes complicated, rather than exhaustively deal with every
branch, mark it as a "partial match" and simply include the
placeholder.
Conditions for "complication":
- The match arm contains a match guard
- Any kind of nested destrucuring
Order the resulting merged match branches as such:
1. Provided match arms
2. Missing enum variant branch arms
3. End with Placeholder if required
- Add extra tests
This introduces the new type -- Semantics.
Semantics maps SyntaxNodes to various semantic info, such as type,
name resolution or macro expansions.
To do so, Semantics maintains a HashMap which maps every node it saw
to the file from which the node originated. This is enough to get all
the necessary hir bits just from syntax.
