From 06d16a18f632711de588ccd12a6a1ed6f2b9ad69 Mon Sep 17 00:00:00 2001
From: Marcus Klaas de Vries <mail@marcusklaas.nl>
Date: Thu, 17 Jan 2019 00:29:26 +0100
Subject: Implement match binding type inference and arm unification

---
 crates/ra_hir/src/ty.rs                         | 24 +++++++++++++++++-------
 crates/ra_hir/src/ty/tests/data/adt_pattern.txt |  9 ++++++++-
 2 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/crates/ra_hir/src/ty.rs b/crates/ra_hir/src/ty.rs
index 66940ec30..74996dda5 100644
--- a/crates/ra_hir/src/ty.rs
+++ b/crates/ra_hir/src/ty.rs
@@ -36,7 +36,7 @@ use crate::{
     db::HirDatabase,
     type_ref::{TypeRef, Mutability},
     name::KnownName,
-    expr::{Body, Expr, Literal, ExprId, Pat, PatId, UnaryOp, BinaryOp, Statement, FieldPat},
+    expr::{Body, Expr, MatchArm, Literal, ExprId, Pat, PatId, UnaryOp, BinaryOp, Statement, FieldPat},
 };
 
 /// The ID of a type variable.
@@ -1097,14 +1097,24 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 ret_ty
             }
             Expr::Match { expr, arms } => {
-                let _ty = self.infer_expr(*expr, &Expectation::none());
-                for arm in arms {
-                    // TODO type the bindings in pats
+                let mut expected = Expectation::none();
+                let input_ty = self.infer_expr(*expr, &Expectation::none());
+                let pat_expectation = Expectation::has_type(input_ty);
+
+                for MatchArm {
+                    pats,
+                    expr: arm_expr,
+                } in arms
+                {
+                    for &pat in pats {
+                        let _pat_ty = self.infer_pat(pat, &pat_expectation);
+                    }
                     // TODO type the guard
-                    let _ty = self.infer_expr(arm.expr, &Expectation::none());
+                    let ty = self.infer_expr(*arm_expr, &expected);
+                    expected = Expectation::has_type(ty);
                 }
-                // TODO unify all the match arm types
-                Ty::Unknown
+
+                expected.ty
             }
             Expr::Path(p) => self.infer_path_expr(expr, p).unwrap_or(Ty::Unknown),
             Expr::Continue => Ty::Never,
diff --git a/crates/ra_hir/src/ty/tests/data/adt_pattern.txt b/crates/ra_hir/src/ty/tests/data/adt_pattern.txt
index 41e9c9d34..3b9b9a078 100644
--- a/crates/ra_hir/src/ty/tests/data/adt_pattern.txt
+++ b/crates/ra_hir/src/ty/tests/data/adt_pattern.txt
@@ -1,4 +1,4 @@
-[68; 155) '{     ...= e; }': ()
+[68; 221) '{     ...  }; }': ()
 [78; 79) 'e': E
 [82; 95) 'E::A { x: 3 }': E
 [92; 93) '3': usize
@@ -9,3 +9,10 @@
 [129; 148) 'E::A {..._var }': E
 [139; 146) 'new_var': usize
 [151; 152) 'e': E
+[159; 218) 'match ...     }': usize
+[165; 166) 'e': E
+[177; 187) 'E::A { x }': E
+[184; 185) 'x': usize
+[191; 192) 'x': usize
+[202; 206) 'E::B': E
+[210; 211) '1': usize
-- 
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