compiler: distinguish between type conversions and function calls

RN every identifier in call expression is considered to be lambda.
But it also can be type expression, so we need to distinguish between
these cases.

pkg/compiler/codegen.go

@@ -712,6 +712,7 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 			name      string
 			numArgs   = len(n.Args)
 			isBuiltin bool
+			isFunc    bool
 		)
 
 		switch fun := n.Fun.(type) {
@@ -721,6 +722,10 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 			if !ok && !isBuiltin {
 				name = fun.Name
 			}
+			// distinguish lambda invocations from type conversions
+			if fun.Obj != nil && fun.Obj.Kind == ast.Var {
+				isFunc = true
+			}
 		case *ast.SelectorExpr:
 			// If this is a method call we need to walk the AST to load the struct locally.
 			// Otherwise this is a function call from a imported package and we can call it
@@ -767,9 +772,11 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 			// We can be sure builtins are of type *ast.Ident.
 			c.convertBuiltin(n)
 		case name != "":
-			// Function was not found thus is can be only an invocation of func-typed variable.
-			c.emitLoadVar(name)
-			emit.Opcode(c.prog.BinWriter, opcode.CALLA)
+			// Function was not found thus is can be only an invocation of func-typed variable or type conversion.
+			if isFunc {
+				c.emitLoadVar(name)
+				emit.Opcode(c.prog.BinWriter, opcode.CALLA)
+			}
 		case isSyscall(f):
 			c.convertSyscall(n, f.selector.Name, f.name)
 		default:

pkg/compiler/convert_test.go

@@ -72,3 +72,17 @@ func TestTypeAssertion(t *testing.T) {
 	}`
 	eval(t, src, big.NewInt(1))
 }
+
+func TestTypeConversion(t *testing.T) {
+	src := `package foo
+	type myInt int
+	func Main() int32 {
+		var a int32 = 41
+		b := myInt(a)
+		incMy := func(x myInt) myInt { return x + 1 }
+		c := incMy(b)
+		return int32(c)
+	}`
+
+	eval(t, src, big.NewInt(42))
+}