From 518f1d19d80a1ad1526054029cef7bcba7b3ff3a Mon Sep 17 00:00:00 2001
From: Bas Zalmstra <bas@abbeygames.com>
Date: Sun, 29 Dec 2019 16:22:57 +0100
Subject: [PATCH] feat: add simple binary operation type checking

---
 crates/mun_hir/src/expr.rs                    |  4 +--
 crates/mun_hir/src/ty/infer.rs                | 10 +++++-
 crates/mun_hir/src/ty/op.rs                   | 36 ++++++++++++++++---
 .../snapshots/tests__invalid_binary_ops.snap  | 13 +++++++
 crates/mun_hir/src/ty/tests.rs                | 13 +++++++
 5 files changed, 68 insertions(+), 8 deletions(-)
 create mode 100644 crates/mun_hir/src/ty/snapshots/tests__invalid_binary_ops.snap

diff --git a/crates/mun_hir/src/expr.rs b/crates/mun_hir/src/expr.rs
index 651665ecf..1dcaedd8d 100644
--- a/crates/mun_hir/src/expr.rs
+++ b/crates/mun_hir/src/expr.rs
@@ -326,9 +326,7 @@ pub enum Pat {
 }
 
 impl Pat {
-    pub fn walk_child_pats(&self, mut _f: impl FnMut(PatId)) {
-        unreachable!()
-    }
+    pub fn walk_child_pats(&self, mut _f: impl FnMut(PatId)) {}
 }
 
 // Queries
diff --git a/crates/mun_hir/src/ty/infer.rs b/crates/mun_hir/src/ty/infer.rs
index 0f0c8caec..06777a8a9 100644
--- a/crates/mun_hir/src/ty/infer.rs
+++ b/crates/mun_hir/src/ty/infer.rs
@@ -296,7 +296,15 @@ impl<'a, D: HirDatabase> InferenceResultBuilder<'a, D> {
                             })
                         }
                     };
-                    let rhs_expected = op::binary_op_rhs_expectation(*op, lhs_ty);
+                    let rhs_expected = op::binary_op_rhs_expectation(*op, lhs_ty.clone());
+                    if lhs_ty != Ty::Unknown && rhs_expected == Ty::Unknown {
+                        self.diagnostics
+                            .push(InferenceDiagnostic::CannotApplyBinaryOp {
+                                id: tgt_expr,
+                                lhs: lhs_ty,
+                                rhs: rhs_expected.clone(),
+                            })
+                    }
                     let rhs_ty = self.infer_expr(*rhs, &Expectation::has_type(rhs_expected));
                     op::binary_op_return_ty(*op, rhs_ty)
                 }
diff --git a/crates/mun_hir/src/ty/op.rs b/crates/mun_hir/src/ty/op.rs
index 1b0aa20b7..c7daef9aa 100644
--- a/crates/mun_hir/src/ty/op.rs
+++ b/crates/mun_hir/src/ty/op.rs
@@ -1,12 +1,40 @@
-use crate::{BinaryOp, Ty, TypeCtor};
+use crate::{ApplicationTy, BinaryOp, CmpOp, Ty, TypeCtor};
 
-pub(super) fn binary_op_rhs_expectation(_op: BinaryOp, lhs_ty: Ty) -> Ty {
-    lhs_ty
+/// Given a binary operation and the type on the left of that operation, returns the expected type
+/// for the right hand side of the operation or `Ty::Unknown` if such an operation is invalid.
+pub(super) fn binary_op_rhs_expectation(op: BinaryOp, lhs_ty: Ty) -> Ty {
+    match op {
+        BinaryOp::LogicOp(..) => Ty::simple(TypeCtor::Bool),
+        BinaryOp::Assignment { op: None } | BinaryOp::CmpOp(CmpOp::Eq { .. }) => match lhs_ty {
+            Ty::Apply(ApplicationTy { ctor, .. }) => match ctor {
+                TypeCtor::Int | TypeCtor::Float | TypeCtor::Bool => lhs_ty,
+                _ => Ty::Unknown,
+            },
+            _ => Ty::Unknown,
+        },
+        BinaryOp::CmpOp(CmpOp::Ord { .. })
+        | BinaryOp::Assignment { op: Some(_) }
+        | BinaryOp::ArithOp(_) => match lhs_ty {
+            Ty::Apply(ApplicationTy { ctor, .. }) => match ctor {
+                TypeCtor::Int | TypeCtor::Float => lhs_ty,
+                _ => Ty::Unknown,
+            },
+            _ => Ty::Unknown,
+        },
+    }
 }
 
+/// For a binary operation with the specified type on the right hand side of the operation, return
+/// the return type of that operation.
 pub(super) fn binary_op_return_ty(op: BinaryOp, rhs_ty: Ty) -> Ty {
     match op {
-        BinaryOp::ArithOp(_) => rhs_ty,
+        BinaryOp::ArithOp(_) => match rhs_ty {
+            Ty::Apply(ApplicationTy { ctor, .. }) => match ctor {
+                TypeCtor::Int | TypeCtor::Float => rhs_ty,
+                _ => Ty::Unknown,
+            },
+            _ => Ty::Unknown,
+        },
         BinaryOp::CmpOp(_) | BinaryOp::LogicOp(_) => Ty::simple(TypeCtor::Bool),
         BinaryOp::Assignment { .. } => Ty::Empty,
     }
diff --git a/crates/mun_hir/src/ty/snapshots/tests__invalid_binary_ops.snap b/crates/mun_hir/src/ty/snapshots/tests__invalid_binary_ops.snap
new file mode 100644
index 000000000..56c94066d
--- /dev/null
+++ b/crates/mun_hir/src/ty/snapshots/tests__invalid_binary_ops.snap
@@ -0,0 +1,13 @@
+---
+source: crates/mun_hir/src/ty/tests.rs
+expression: "fn foo() {\n    let b = false;\n    let n = 1;\n    let _ = b + n; // error: invalid binary operation\n}"
+---
+[57; 62): cannot apply binary operator
+[9; 100) '{     ...tion }': nothing
+[19; 20) 'b': bool
+[23; 28) 'false': bool
+[38; 39) 'n': int
+[42; 43) '1': int
+[57; 58) 'b': bool
+[57; 62) 'b + n': int
+[61; 62) 'n': int
diff --git a/crates/mun_hir/src/ty/tests.rs b/crates/mun_hir/src/ty/tests.rs
index 439f22907..df6ff1693 100644
--- a/crates/mun_hir/src/ty/tests.rs
+++ b/crates/mun_hir/src/ty/tests.rs
@@ -159,6 +159,19 @@ fn infer_while() {
     )
 }
 
+#[test]
+fn invalid_binary_ops() {
+    infer_snapshot(
+        r#"
+    fn foo() {
+        let b = false;
+        let n = 1;
+        let _ = b + n; // error: invalid binary operation
+    }
+    "#,
+    )
+}
+
 fn infer_snapshot(text: &str) {
     let text = text.trim().replace("\n    ", "\n");
     insta::assert_snapshot!(insta::_macro_support::AutoName, infer(&text), &text);