[Compiler] Support basic casting operations in VM

bbq/compiler/compiler.go

@@ -1149,14 +1149,25 @@ func (c *Compiler[_]) VisitCastingExpression(expression *ast.CastingExpression)
 	castingTypes := c.ExtendedElaboration.CastingExpressionTypes(expression)
 	index := c.getOrAddType(castingTypes.TargetType)
 
-	castKind := opcode.CastKindFrom(expression.Operation)
-
-	c.codeGen.Emit(
-		opcode.InstructionCast{
+	var castInstruction opcode.Instruction
+	switch expression.Operation {
+	case ast.OperationCast:
+		castInstruction = opcode.InstructionSimpleCast{
 			TypeIndex: index,
-			Kind:      castKind,
-		},
-	)
+		}
+	case ast.OperationFailableCast:
+		castInstruction = opcode.InstructionFailableCast{
+			TypeIndex: index,
+		}
+	case ast.OperationForceCast:
+		castInstruction = opcode.InstructionForceCast{
+			TypeIndex: index,
+		}
+	default:
+		panic(errors.NewUnreachableError())
+	}
+
+	c.codeGen.Emit(castInstruction)
 	return
 }
 

bbq/opcode/instruction.go

@@ -1,4 +1,4 @@
 /*
  * Cadence - The resource-oriented smart contract programming language
  *
  * Copyright Flow Foundation
@@ -94,16 +94,6 @@
 	emitByte(code, byte(domain))
 }
 
-// CastKind
-
-func decodeCastKind(ip *uint16, code []byte) CastKind {
-	return CastKind(decodeByte(ip, code))
-}
-
-func emitCastKind(code *[]byte, kind CastKind) {
-	emitByte(code, byte(kind))
-}
-
 // CompositeKind
 
 func decodeCompositeKind(ip *uint16, code []byte) common.CompositeKind {

bbq/opcode/instructions.yml

@@ -331,14 +331,43 @@
       - name: "value"
         type: "value"
 
-- name: "cast"
+- name: "simpleCast"
   description:
     Pops a value off the stack, casts it to the given type, and then pushes it back on to the stack.
   operands:
     - name: "typeIndex"
       type: "index"
-    - name: "kind"
-      type: "castKind"
+  valueEffects:
+    pop:
+      - name: "value"
+        type: "value"
+    push:
+      - name: "value"
+        type: "value"
+
+- name: "failableCast"
+  description:
+    Pops a value off the stack and casts it to the given type.
+    If the value is a subtype of the given type, then casted value is pushed back on to the stack.
+    If the value is not a subtype of the given type, then a `nil` is pushed to the stack instead.
+  operands:
+    - name: "typeIndex"
+      type: "index"
+  valueEffects:
+    pop:
+      - name: "value"
+        type: "value"
+    push:
+      - name: "value"
+        type: "optional"
+
+- name: "forceCast"
+  description:
+    Pops a value off the stack, force-casts it to the given type, and then pushes it back on to the stack.
+    Panics if the value is not a subtype of the given type.
+  operands:
+    - name: "typeIndex"
+      type: "index"
   valueEffects:
     pop:
       - name: "value"

bbq/opcode/opcode.go

@@ -72,7 +72,12 @@ const (
 	Unwrap
 	Destroy
 	Transfer
-	Cast
+	SimpleCast
+	FailableCast
+	ForceCast
+	_
+	_
+	_
 	_
 	_
 	_