Add generic deprecation warnings code for CRDs to find deprecated fields

gen/deprecations/cmd.go

@@ -0,0 +1,120 @@
+// Copyright 2025 Redpanda Data, Inc.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.md
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0
+
+package deprecations
+
+import (
+	_ "embed"
+	"fmt"
+	"go/ast"
+	"os"
+	"path/filepath"
+	"strings"
+	"text/template"
+	"time"
+
+	"github.com/spf13/cobra"
+)
+
+const DeprecationPrefix = "Deprecated"
+
+var (
+	testGenerator *template.Template
+	//go:embed templates/test.tpl
+	testTemplate string
+)
+
+func init() {
+	helpers := map[string]any{
+		"year": func() string {
+			return time.Now().Format("2006")
+		},
+	}
+	testGenerator = template.Must(template.New("tests").Funcs(helpers).Parse(testTemplate))
+}
+
+type DeprecationConfig struct {
+	Directory   string
+	PackageName string
+	OutputFile  string
+	Verbose     bool
+}
+
+type fieldRef struct {
+	GoPath   []string // Go field names e.g. [Spec ClusterSpec DeprecatedFullNameOverride]
+	JsonPath []string // JSON names e.g. [spec clusterSpec fullNameOverride]
+	TypeExpr ast.Expr
+}
+
+type objSpec struct {
+	Name     string
+	Literal  string
+	Warnings []string
+}
+
+// Debugf emits debug output when the config's Verbose flag is set.
+func (c DeprecationConfig) Debugf(format string, a ...interface{}) {
+	if !c.Verbose {
+		return
+	}
+	fmt.Fprintf(os.Stderr, format, a...)
+}
+
+func Cmd() *cobra.Command {
+	var config DeprecationConfig
+
+	cmd := &cobra.Command{
+		Use:     "deprecations",
+		Short:   "Generate tests for deprecated API fields",
+		Example: "gen deprecations --directory ./operator/api/redpanda/v1alpha2",
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return Render(config)
+		},
+	}
+
+	cmd.Flags().StringVar(&config.Directory, "directory", ".", "The directory to scan for deprecated fields")
+	cmd.Flags().StringVar(&config.PackageName, "package", "", "The name of the package, if not specified we try and figure it out dynamically")
+	cmd.Flags().StringVar(&config.OutputFile, "output-file", "zz_generated.deprecations_test.go", "The name of the file to output in the given directory")
+	cmd.Flags().BoolVarP(&config.Verbose, "verbose", "v", false, "Enable debug output.")
+
+	return cmd
+}
+
+func Render(config DeprecationConfig) error {
+	dir := config.Directory
+
+	if config.PackageName == "" {
+		config.PackageName = strings.Trim(filepath.Base(dir), ".")
+		config.PackageName = strings.Trim(filepath.Base(dir), "/")
+	}
+
+	if config.PackageName == "" {
+		return fmt.Errorf("could not determine package name")
+	}
+
+	parser := NewParser(config)
+
+	if err := parser.Parse(); err != nil {
+		return err
+	}
+
+	contents, err := parser.Compile()
+	if err != nil {
+		return err
+	}
+
+	outPath := filepath.Join(dir, config.OutputFile)
+	if err := os.WriteFile(outPath, contents, 0o644); err != nil {
+		return fmt.Errorf("failed to write output file: %w", err)
+	}
+
+	fmt.Printf("wrote %s\n", outPath)
+
+	return nil
+}