compiler: disallow generic method receiver

Either non-pointer or pointer, both cases are disallowed to be generic.
Need to be reverted and properly handled within the scope of #2376.

Signed-off-by: Anna Shaleva <shaleva.ann@nspcc.ru>

Author: AnnaShaleva

pkg/compiler/analysis.go

@@ -19,6 +19,8 @@ var (
 	ErrMissingExportedParamName = errors.New("exported method is not allowed to have unnamed parameter")
 	// ErrInvalidExportedRetCount is returned when exported contract method has invalid return values count.
 	ErrInvalidExportedRetCount = errors.New("exported method is not allowed to have more than one return value")
+	// ErrGenericsUnsuppored is returned when generics-related tokens are encountered.
+	ErrGenericsUnsuppored = errors.New("generics are currently unsupported, please, see the https://github.com/nspcc-dev/neo-go/issues/2376")
 )
 
 var (
@@ -361,6 +363,13 @@ func (c *codegen) analyzeFuncAndGlobalVarUsage() funcUsage {
 			case *ast.FuncDecl:
 				name := c.getFuncNameFromDecl(pkgPath, n)
 
+				// filter out generic functions
+				err := c.checkGenericsFuncDecl(n, name)
+				if err != nil {
+					c.prog.Err = err
+					return false // Program is invalid.
+				}
+
 				// exported functions and methods are always assumed to be used
 				if isMain && n.Name.IsExported() || isInitFunc(n) || isDeployFunc(n) {
 					diff[name] = true
@@ -535,6 +544,32 @@ func (c *codegen) analyzeFuncAndGlobalVarUsage() funcUsage {
 	return usage
 }
 
+// checkGenericFuncDecl checks whether provided ast.FuncDecl has generic code.
+func (c *codegen) checkGenericsFuncDecl(n *ast.FuncDecl, funcName string) error {
+	var errGenerics error
+
+	// Generic function receiver.
+	if n.Recv != nil {
+		switch t := n.Recv.List[0].Type.(type) {
+		case *ast.StarExpr:
+			switch t.X.(type) {
+			case *ast.IndexExpr:
+				// func (x *Pointer[T]) Load() *T
+				errGenerics = errors.New("generic pointer function receiver")
+			}
+		case *ast.IndexExpr:
+			// func (x Structure[T]) Load() *T
+			errGenerics = errors.New("generic function receiver")
+		}
+	}
+
+	if errGenerics != nil {
+		return fmt.Errorf("%w: %s has %s", ErrGenericsUnsuppored, funcName, errGenerics.Error())
+	}
+
+	return nil
+}
+
 // nodeContext contains ast node with the corresponding import map, type info and package information
 // required to retrieve fully qualified node name (if so).
 type nodeContext struct {

pkg/compiler/generics_test.go

@@ -0,0 +1,38 @@
+package compiler_test
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/nspcc-dev/neo-go/pkg/compiler"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGenericMethodReceiver(t *testing.T) {
+	t.Run("star expression", func(t *testing.T) {
+		src := `
+		package receiver
+		type Pointer[T any] struct {
+			value T
+		}
+		func (x *Pointer[T]) Load() *T {
+			return &x.value
+		}
+`
+		_, _, err := compiler.CompileWithOptions("foo.go", strings.NewReader(src), nil)
+		require.ErrorIs(t, err, compiler.ErrGenericsUnsuppored)
+	})
+	t.Run("ident expression", func(t *testing.T) {
+		src := `
+		package receiver
+		type Pointer[T any] struct {
+			value T
+		}
+		func (x Pointer[T]) Load() *T {
+			return &x.value
+		}
+`
+		_, _, err := compiler.CompileWithOptions("foo.go", strings.NewReader(src), nil)
+		require.ErrorIs(t, err, compiler.ErrGenericsUnsuppored)
+	})
+}