Merge #3706

3706: missing match arms diagnostic r=flodiebold a=JoshMcguigan

Following up on https://github.com/rust-analyzer/rust-analyzer/pull/3689#issuecomment-602718222, this PR creates a missing match arms diagnostic.

At the moment this is a very early draft, but I wanted to open it just to get some initial feedback.

Initial questions:

* Have I roughly created the correct boilerplate? 
* Inside the new `validate_match` function:
  * Am I correct in thinking I want to do validation by comparing the match arms against `match_expr`? And when analyzing `match_expr` I should be looking at it as a `hir_def::expr::Expr`?
  * I mostly copied the chained if-let statements from the struct validation. Shouldn't there be a non-failable way to get an AstPtr from the hir data structures? 

Thanks for all the guidance.

Co-authored-by: Josh Mcguigan <[email protected]>

1 files changed, 1 insertions, 0 deletions

diff --git a/crates/ra_hir_ty/Cargo.toml b/crates/ra_hir_ty/Cargo.toml
index 45be08430..9a4a7aa6f 100644
--- a/crates/ra_hir_ty/Cargo.toml
+++ b/crates/ra_hir_ty/Cargo.toml
@@ -9,6 +9,7 @@ doctest = false
 
 [dependencies]
 arrayvec = "0.5.1"
+smallvec = "1.2.0"
 ena = "0.13.1"
 log = "0.4.8"
 rustc-hash = "1.1.0"