test: add import compliance tests

vms/evm/imports_test.go

@@ -0,0 +1,118 @@
+// Copyright (C) 2019-2025, Ava Labs, Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package evm
+
+import (
+	"fmt"
+	"go/parser"
+	"go/token"
+	"io/fs"
+	"path/filepath"
+	"slices"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// TestImportViolations ensures proper import rules:
+// - graft/coreth can be imported anywhere EXCEPT vms/evm (but vms/evm/emulate is an exception)
+// - graft/subnet-evm can only be imported within graft/subnet-evm itself and vms/evm/emulate
+// - github.com/ava-labs/libevm/libevm/pseudo cannot be imported anywhere
+//
+// The rationale for these rules are as follows:
+//
+// coreth can be imported in AvalancheGo, because it was already imported by Avalanche prior to
+// grafting
+//
+// coreth can NOT be imported in the vms/evm package, because the goal is that vms/evm should
+// only contain the 'clean' properly uplifted code, that meets AvalancheGo quality standards.
+//
+// subnet-evm can NOT be imported anywhere in AvalancheGo besides graft/subnet-evm itself,
+// because it must not become a direct dependency of AvalancheGo or mix directly with coreth.
+//
+// both coreth and subnet-evm can be imported in the vms/evm/emulate package, because it
+// allows consumers to use both coreth and subnet-evm registration at the same time.
+//
+// github.com/ava-labs/libevm/libevm/pseudo cannot be imported anywhere, without review from any of
+// @StephenButtolph, @ARR4N, or @joshua-kim. There is almost certainly a better option, and it exists
+// only because libevm can't pollute the code base with generic type parameters.
+//
+// TODO(jonathanoppenheimer): remove the graft functionality once the graft package will be removed.
+func TestImportViolations(t *testing.T) {
+	const root = ".."
+	repoRoot, err := filepath.Abs(root)
+	require.NoError(t, err)
+
+	graftDir := filepath.Join(repoRoot, "graft")
+	graftSubnetEVMDir := filepath.Join(repoRoot, "graft", "subnet-evm")
+	emulateDir := filepath.Join(repoRoot, "vms", "evm", "emulate")
+	vmsEVMDir := filepath.Join(repoRoot, "vms", "evm")
+
+	var violations []string
+
+	err = filepath.Walk(root, func(file string, _ fs.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+		if strings.ToLower(filepath.Ext(file)) != ".go" {
+			return nil
+		}
+
+		absFile, err := filepath.Abs(file)
+		if err != nil {
+			return err
+		}
+
+		node, err := parser.ParseFile(token.NewFileSet(), file, nil, parser.ImportsOnly)
+		if err != nil {
+			return fmt.Errorf("parser.ParseFile(..., %q, ...): %w", file, err)
+		}
+
+		for _, spec := range node.Imports {
+			if spec.Path == nil {
+				continue
+			}
+			importPath := strings.Trim(spec.Path.Value, `"`)
+
+			inGraft := strings.HasPrefix(absFile, graftDir)
+			inGraftSubnetEVM := strings.HasPrefix(absFile, graftSubnetEVMDir)
+			inEmulate := strings.HasPrefix(absFile, emulateDir)
+			inVMsEVM := strings.HasPrefix(absFile, vmsEVMDir)
+			importsPseudo := isImportIn(importPath, "github.com/ava-labs/libevm/libevm/pseudo")
+			importsCoreth := isImportIn(importPath, "github.com/ava-labs/avalanchego/graft/coreth")
+			importsSubnetEVM := isImportIn(importPath, "github.com/ava-labs/avalanchego/graft/subnet-evm")
+
+			hasViolation := []bool{
+				importsPseudo,
+				!inGraft && importsCoreth && inVMsEVM && !inEmulate,
+				!inGraftSubnetEVM && importsSubnetEVM && !inEmulate,
+			}
+			if slices.Contains(hasViolation, true) {
+				violations = append(violations, fmt.Sprintf("File %q imports %q", file, importPath))
+			}
+		}
+		return nil
+	})
+
+	require.NoErrorf(t, err, "filepath.Walk(%q)", root)
+	require.Empty(t, violations, "import violations found")
+}
+
+func isImportIn(importPath, targetedImport string) bool {
+	if importPath == targetedImport {
+		return true
+	}
+
+	// importPath must be at least len(targetedImport) + 1 to be a subpackage
+	// (e.g., "github.com/foo/x" is len("github.com/foo") + 2, minimum subpackage length)
+	if len(importPath) < len(targetedImport)+1 {
+		return false
+	}
+
+	// Check if importPath is a subpackage by ensuring it has the targetedImport prefix
+	// AND the next character is '/'. This is to prevent false positives where one
+	// package name is a prefix of another like "github.com/foo" vs "github.com/foobar".
+	return strings.HasPrefix(importPath, targetedImport) && importPath[len(targetedImport)] == '/'
+}