Touch up type inference for boolean operators

Also try to infer its subexpressions and set type expectations
whenever possible.

crates/ra_hir/src/ty.rs

@@ -526,6 +526,20 @@ struct InferenceContext<'a, D: HirDatabase> {
     return_ty: Ty,
 }
 
+// helper function that determines whether a binary operator
+// always returns a boolean
+fn is_boolean_operator(op: BinOp) -> bool {
+    match op {
+        BinOp::BooleanOr
+        | BinOp::BooleanAnd
+        | BinOp::EqualityTest
+        | BinOp::LesserEqualTest
+        | BinOp::GreaterEqualTest
+        | BinOp::LesserTest
+        | BinOp::GreaterTest => true,
+    }
+}
+
 impl<'a, D: HirDatabase> InferenceContext<'a, D> {
     fn new(
         db: &'a D,
@@ -907,13 +921,21 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             }
             ast::Expr::RangeExpr(_e) => Ty::Unknown,
             ast::Expr::BinExpr(e) => match e.op() {
-                Some(BinOp::BooleanOr)
-                | Some(BinOp::BooleanAnd)
-                | Some(BinOp::EqualityTest)
-                | Some(BinOp::LesserEqualTest)
-                | Some(BinOp::GreaterEqualTest)
-                | Some(BinOp::LesserTest)
-                | Some(BinOp::GreaterTest) => Ty::Bool,
+                Some(op) => {
+                    let subtype_expectation = match op {
+                        BinOp::BooleanAnd | BinOp::BooleanOr => Expectation::has_type(Ty::Bool),
+                        _ => Expectation::none(),
+                    };
+                    let (lhs, rhs) = e.sub_exprs();
+                    let _lhs_ty = self.infer_expr_opt(lhs, &subtype_expectation)?;
+                    let _rhs_ty = self.infer_expr_opt(rhs, &subtype_expectation)?;
+
+                    if is_boolean_operator(op) {
+                        Ty::Bool
+                    } else {
+                        Ty::Unknown
+                    }
+                }
                 _ => Ty::Unknown,
             },
             ast::Expr::Literal(_e) => Ty::Unknown,

crates/ra_hir/src/ty/tests.rs

@@ -157,11 +157,18 @@ impl S {
 fn infer_boolean_op() {
     check_inference(
         r#"
+fn f(x: bool) -> i32 {
+    0i32
+}
+
 fn test() {
     let x = a && b;
     let y = true || false;
     let z = x == y;
     let h = CONST_1 <= CONST_2;
+    let c = f(z || y) + 5;
+    let d = b;
+    let e = 3i32 && "hello world";
 
     10 < 3
 }

crates/ra_hir/src/ty/tests/data/0008_boolean_op.txt

@@ -1,10 +1,31 @@
-[21; 22) 'x': bool
-[68; 69) 'z': bool
-[72; 78) 'x == y': bool
-[45; 58) 'true || false': bool
-[11; 125) '{     ... < 3 }': bool
-[117; 123) '10 < 3': bool
-[88; 89) 'h': bool
-[41; 42) 'y': bool
-[92; 110) 'CONST_...ONST_2': bool
-[25; 31) 'a && b': bool
+[28; 32) '0i32': i32
+[22; 34) '{     0i32 }': i32
+[6; 7) 'x': [unknown]
+[127; 134) 'CONST_1': [unknown]
+[201; 205) '3i32': bool
+[76; 77) 'y': bool
+[65; 66) 'b': bool
+[60; 66) 'a && b': bool
+[127; 145) 'CONST_...ONST_2': bool
+[182; 183) 'd': [unknown]
+[229; 231) '10': [unknown]
+[209; 222) '"hello world"': bool
+[229; 235) '10 < 3': bool
+[186; 187) 'b': [unknown]
+[159; 172) 'f(z || y) + 5': [unknown]
+[56; 57) 'x': bool
+[112; 113) 'y': bool
+[201; 222) '3i32 &...world"': bool
+[234; 235) '3': [unknown]
+[138; 145) 'CONST_2': [unknown]
+[80; 93) 'true || false': bool
+[46; 237) '{     ... < 3 }': bool
+[197; 198) 'e': bool
+[107; 113) 'x == y': bool
+[88; 93) 'false': bool
+[80; 84) 'true': bool
+[123; 124) 'h': bool
+[155; 156) 'c': [unknown]
+[103; 104) 'z': bool
+[60; 61) 'a': bool
+[107; 108) 'x': bool

crates/ra_syntax/src/ast.rs

@@ -511,20 +511,33 @@ impl<'a> BinExpr<'a> {
     pub fn op(&self) -> Option<BinOp> {
         self.syntax()
             .children()
-            .filter_map(|c| {
-                match c.kind() {
-                    PIPEPIPE => Some(BinOp::BooleanOr),
-                    AMPAMP => Some(BinOp::BooleanAnd),
-                    EQEQ => Some(BinOp::EqualityTest),
-                    LTEQ => Some(BinOp::LesserEqualTest),
-                    GTEQ => Some(BinOp::GreaterEqualTest),
-                    L_ANGLE => Some(BinOp::LesserTest),
-                    R_ANGLE => Some(BinOp::GreaterTest),
-                    _ => None,
-                }
+            .filter_map(|c| match c.kind() {
+                PIPEPIPE => Some(BinOp::BooleanOr),
+                AMPAMP => Some(BinOp::BooleanAnd),
+                EQEQ => Some(BinOp::EqualityTest),
+                LTEQ => Some(BinOp::LesserEqualTest),
+                GTEQ => Some(BinOp::GreaterEqualTest),
+                L_ANGLE => Some(BinOp::LesserTest),
+                R_ANGLE => Some(BinOp::GreaterTest),
+                _ => None,
             })
             .next()
     }
+
+    pub fn lhs(self) -> Option<Expr<'a>> {
+        children(self).nth(0)
+    }
+
+    pub fn rhs(self) -> Option<Expr<'a>> {
+        children(self).nth(1)
+    }
+
+    pub fn sub_exprs(self) -> (Option<Expr<'a>>, Option<Expr<'a>>) {
+        let mut children = children(self);
+        let first = children.next();
+        let second = children.next();
+        (first, second)
+    }
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]

crates/ra_syntax/src/ast/generated.rs

@@ -217,15 +217,7 @@ impl<R: TreeRoot<RaTypes>> BinExprNode<R> {
 }
 
 
-impl<'a> BinExpr<'a> {
-    pub fn lhs(self) -> Option<Expr<'a>> {
-        super::child_opt(self)
-    }
-
-    pub fn rhs(self) -> Option<Expr<'a>> {
-        super::child_opt(self)
-    }
-}
+impl<'a> BinExpr<'a> {}
 
 // BindPat
 #[derive(Debug, Clone, Copy,)]

crates/ra_syntax/src/grammar.ron

@@ -422,12 +422,7 @@ Grammar(
         "RefExpr": (options: ["Expr"]),
         "PrefixExpr": (options: ["Expr"]),
         "RangeExpr": (),
-        "BinExpr": (
-            options: [
-                ["lhs", "Expr"],
-                ["rhs", "Expr"]
-            ]
-        ),
+        "BinExpr": (),
         "String": (),
         "Byte": (),
         "ByteString": (),