(go/v4): Simplify init directory validation to only block PROJECT fil

Remove overly restrictive directory validation that was blocking legitimate
files like mise.toml and other configuration files. The previous logic
attempted to allow only specific file types but had inverted logic that
blocked most files unnecessarily.

At this stage, we don't have a maintainable way to accurately predict all
possible file conflicts. The only file that definitively conflicts with
scaffolding is the PROJECT file, which kubebuilder generates.

This allows users to run kubebuilder init in directories with legitimate
configuration files (mise.toml, .envrc, .tool-versions, etc.) without
encountering false validation errors.

Author: camilamacedo86

pkg/plugins/golang/v4/init.go

@@ -22,7 +22,6 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
-	"unicode"
 
 	"github.com/spf13/pflag"
 
@@ -159,53 +158,24 @@ func (p *initSubcommand) PostScaffold() error {
 }
 
 // checkDir will return error if the current directory has files which are not allowed.
-// Note that, it is expected that the directory to scaffold the project is cleaned.
-// Otherwise, it might face issues to do the scaffold.
+// Only the PROJECT file is disallowed as it will be generated by the scaffolding tool.
 func checkDir() error {
 	err := filepath.Walk(".",
 		func(path string, info os.FileInfo, err error) error {
 			if err != nil {
 				return fmt.Errorf("error walking path %q: %w", path, err)
 			}
-			// Allow directory trees starting with '.'
+			// Skip dot directories
 			if info.IsDir() && strings.HasPrefix(info.Name(), ".") && info.Name() != "." {
 				return filepath.SkipDir
 			}
-			// Allow files starting with '.'
-			if strings.HasPrefix(info.Name(), ".") {
-				return nil
+			// Only block PROJECT file (reserved for scaffolding)
+			if !info.IsDir() && info.Name() == "PROJECT" {
+				return fmt.Errorf("PROJECT file found in target directory. " +
+					"This file is reserved and will be generated by kubebuilder")
 			}
-			// Allow files ending with '.md' extension
-			if strings.HasSuffix(info.Name(), ".md") && !info.IsDir() {
-				return nil
-			}
-			// Allow capitalized files except PROJECT
-			isCapitalized := true
-			for _, l := range info.Name() {
-				if !unicode.IsUpper(l) {
-					isCapitalized = false
-					break
-				}
-			}
-			if isCapitalized && info.Name() != "PROJECT" {
-				return nil
-			}
-			disallowedExtensions := []string{
-				".go",
-				".yaml",
-				".mod",
-				".sum",
-			}
-			// Deny files with .go or .yaml or .mod or .sum extensions
-			for _, ext := range disallowedExtensions {
-				if strings.HasSuffix(info.Name(), ext) {
-					return nil
-				}
-			}
-			// Do not allow any other file
-			return fmt.Errorf("target directory is not empty and contains a disallowed file %q. "+
-				"files with the following extensions [%s] are not allowed to avoid conflicts with the tooling",
-				path, strings.Join(disallowedExtensions, ", "))
+			// Allow everything else
+			return nil
 		})
 	if err != nil {
 		return fmt.Errorf("error walking directory: %w", err)