From 252eb78dc3852707969b27b8a30f8844289aa985 Mon Sep 17 00:00:00 2001
From: Lukas Wirth <lukastw97@gmail.com>
Date: Sat, 10 Apr 2021 16:56:32 +0200
Subject: Implement more precise binary op return type prediction

---
 crates/hir_ty/src/op.rs | 58 +++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 46 insertions(+), 12 deletions(-)

(limited to 'crates/hir_ty/src/op.rs')

diff --git a/crates/hir_ty/src/op.rs b/crates/hir_ty/src/op.rs
index 0491c5cb4..0222de2bc 100644
--- a/crates/hir_ty/src/op.rs
+++ b/crates/hir_ty/src/op.rs
@@ -9,21 +9,55 @@ pub(super) fn binary_op_return_ty(op: BinaryOp, lhs_ty: Ty, rhs_ty: Ty) -> Ty {
         BinaryOp::LogicOp(_) | BinaryOp::CmpOp(_) => TyKind::Scalar(Scalar::Bool).intern(&Interner),
         BinaryOp::Assignment { .. } => TyBuilder::unit(),
         BinaryOp::ArithOp(ArithOp::Shl) | BinaryOp::ArithOp(ArithOp::Shr) => {
-            match lhs_ty.kind(&Interner) {
+            // all integer combinations are valid here
+            if matches!(
+                lhs_ty.kind(&Interner),
                 TyKind::Scalar(Scalar::Int(_))
-                | TyKind::Scalar(Scalar::Uint(_))
-                | TyKind::Scalar(Scalar::Float(_)) => lhs_ty,
-                TyKind::InferenceVar(_, TyVariableKind::Integer)
-                | TyKind::InferenceVar(_, TyVariableKind::Float) => lhs_ty,
-                _ => TyKind::Error.intern(&Interner),
+                    | TyKind::Scalar(Scalar::Uint(_))
+                    | TyKind::InferenceVar(_, TyVariableKind::Integer)
+            ) && matches!(
+                rhs_ty.kind(&Interner),
+                TyKind::Scalar(Scalar::Int(_))
+                    | TyKind::Scalar(Scalar::Uint(_))
+                    | TyKind::InferenceVar(_, TyVariableKind::Integer)
+            ) {
+                lhs_ty
+            } else {
+                TyKind::Error.intern(&Interner)
             }
         }
-        BinaryOp::ArithOp(_) => match rhs_ty.kind(&Interner) {
-            TyKind::Scalar(Scalar::Int(_))
-            | TyKind::Scalar(Scalar::Uint(_))
-            | TyKind::Scalar(Scalar::Float(_)) => rhs_ty,
-            TyKind::InferenceVar(_, TyVariableKind::Integer)
-            | TyKind::InferenceVar(_, TyVariableKind::Float) => rhs_ty,
+        BinaryOp::ArithOp(_) => match (lhs_ty.kind(&Interner), rhs_ty.kind(&Interner)) {
+            // (int, int) | (uint, uint) | (float, float)
+            (TyKind::Scalar(Scalar::Int(_)), TyKind::Scalar(Scalar::Int(_)))
+            | (TyKind::Scalar(Scalar::Uint(_)), TyKind::Scalar(Scalar::Uint(_)))
+            | (TyKind::Scalar(Scalar::Float(_)), TyKind::Scalar(Scalar::Float(_))) => rhs_ty,
+            // ({int}, int) | ({int}, uint)
+            (TyKind::InferenceVar(_, TyVariableKind::Integer), TyKind::Scalar(Scalar::Int(_)))
+            | (TyKind::InferenceVar(_, TyVariableKind::Integer), TyKind::Scalar(Scalar::Uint(_))) => {
+                rhs_ty
+            }
+            // (int, {int}) | (uint, {int})
+            (TyKind::Scalar(Scalar::Int(_)), TyKind::InferenceVar(_, TyVariableKind::Integer))
+            | (TyKind::Scalar(Scalar::Uint(_)), TyKind::InferenceVar(_, TyVariableKind::Integer)) => {
+                lhs_ty
+            }
+            // ({float} | float)
+            (TyKind::InferenceVar(_, TyVariableKind::Float), TyKind::Scalar(Scalar::Float(_))) => {
+                rhs_ty
+            }
+            // (float, {float})
+            (TyKind::Scalar(Scalar::Float(_)), TyKind::InferenceVar(_, TyVariableKind::Float)) => {
+                lhs_ty
+            }
+            // ({int}, {int}) | ({float}, {float})
+            (
+                TyKind::InferenceVar(_, TyVariableKind::Integer),
+                TyKind::InferenceVar(_, TyVariableKind::Integer),
+            )
+            | (
+                TyKind::InferenceVar(_, TyVariableKind::Float),
+                TyKind::InferenceVar(_, TyVariableKind::Float),
+            ) => rhs_ty,
             _ => TyKind::Error.intern(&Interner),
         },
     }
-- 
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