Merge #701

701: Minor type inference tweaks r=flodiebold a=marcusklaas

Pass down expectation for reference expressions and type the guard in match expressions.

I wasn't able to add a test for the former addition because the type variable previously introduced would always resolve to the right type in the things I tried!

Co-authored-by: Marcus Klaas de Vries <mail@marcusklaas.nl>

crates/ra_hir/src/expr.rs

@@ -219,7 +219,7 @@ pub use ra_syntax::ast::BinOp as BinaryOp;
 #[derive(Debug, Clone, Eq, PartialEq)]
 pub struct MatchArm {
     pub pats: Vec<PatId>,
-    // guard: Option<ExprId>, // TODO
+    pub guard: Option<ExprId>,
     pub expr: ExprId,
 }
 
@@ -515,10 +515,12 @@ impl ExprCollector {
                         MatchArm {
                             pats: vec![pat],
                             expr: then_branch,
+                            guard: None,
                         },
                         MatchArm {
                             pats: vec![placeholder_pat],
                             expr: else_branch,
+                            guard: None,
                         },
                     ];
                     self.alloc_expr(
@@ -617,6 +619,10 @@ impl ExprCollector {
                         .map(|arm| MatchArm {
                             pats: arm.pats().map(|p| self.collect_pat(p)).collect(),
                             expr: self.collect_expr_opt(arm.expr()),
+                            guard: arm
+                                .guard()
+                                .and_then(|guard| guard.expr())
+                                .map(|e| self.collect_expr(e)),
                         })
                         .collect()
                 } else {