Added code generator for DefaultRESTMapper

We need to fork upstream's DefaultRESTMapper to be able
to update and delete its contents dynamically inside
our DynamicRESTMapper. The script added in this commit
does it automatically.

On-behalf-of: @SAP [email protected]
Signed-off-by: Robert Vasek <[email protected]>

Author: gman0

hack/gen-patch-defaultrestmapper.sh

@@ -0,0 +1,109 @@
+#!/usr/bin/env bash
+
+# Copyright 2025 The KCP Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -o errexit
+set -o nounset
+set -o pipefail
+
+REPO_ROOT=$(cd "$(dirname "${BASH_SOURCE[0]}")"/.. && pwd)
+DEFAULTRESTMAPPER_FILEPATH="${DEFAULTRESTMAPPER_FILEPATH:-$( go list -m -json k8s.io/apimachinery | jq -r .Dir )/pkg/api/meta/restmapper.go}"
+DEFAULTRESTMAPPER_PATCH_FILEPATH="${DEFAULTRESTMAPPER_PATCH_FILEPATH:-${REPO_ROOT}/pkg/reconciler/dynamicrestmapper/defaultrestmapper_kcp.go}"
+
+function usage {
+    echo "gen-patch-defaultrestmapper copies upstream's DefaultRESTMapper,"
+    echo "makes the changes needed by our DynamicRESTMapper, and stores"
+    echo "the result in ${DEFAULTRESTMAPPER_PATCH_FILEPATH}."
+    echo
+    echo "By default, gen-patch-defaultrestmapper tries to look for"
+    echo "restmapper.go in:"
+    echo
+    printf "\t%s,\n" "${DEFAULTRESTMAPPER_FILEPATH}"
+    echo
+    echo "as detected by 'go list -m -json k8s.io/apimachinery'."
+    echo "If you wish to use a different path, pass it in through"
+    echo "DEFAULTRESTMAPPER_FILEPATH environment variable."
+    echo
+    echo "Usage:"
+    echo
+    printf "\t%s\n" "${0}"
+    exit 0
+}
+
+# Script input validation.
+
+[[ $# != 0 ]] && usage
+[[ -f "${DEFAULTRESTMAPPER_FILEPATH}" ]] || { echo "Error: ${DEFAULTRESTMAPPER_FILEPATH} (from DEFAULTRESTMAPPER_FILEPATH) is not a file" 1>&2 ; exit 1 ; }
+touch "${DEFAULTRESTMAPPER_PATCH_FILEPATH}"
+[[ -f "${DEFAULTRESTMAPPER_PATCH_FILEPATH}" ]] || { echo "Error: ${DEFAULTRESTMAPPER_PATCH_FILEPATH} (from DEFAULTRESTMAPPER_PATCH_FILEPATH) is not a file" 1>&2 ; exit 1 ; }
+
+# File generation.
+
+# First, we generate the preamble with our package name, and
+# paste upstream's defaultrestmapper.go contents, starting right
+# after its `package meta` declaration.
+
+cat "${REPO_ROOT}/hack/boilerplate/boilerplate.go.txt" > "${DEFAULTRESTMAPPER_PATCH_FILEPATH}"
+sed -i "s/YEAR/$(date +'%Y')/" "${DEFAULTRESTMAPPER_PATCH_FILEPATH}"
+cat >> "${DEFAULTRESTMAPPER_PATCH_FILEPATH}" << Header_EOF
+
+package dynamicrestmapper
+
+// Code generated by hack/gen-patch-defaultrestmapper.sh
+// Original file in k8s.io/apimachinery/pkg/api/meta/restmapper.go.
+
+// We need this DefaultRESTMapper fork to be able to modify its
+// internal mappings, to support update and deletion operations.
+// These are implemented separately, in defaultrestmapper_mutable.go.
+
+import "k8s.io/apimachinery/pkg/api/meta" // Import the source package of the original file.
+
+Header_EOF
+
+awk '/^package meta$/ {flag=1; next} flag' "${DEFAULTRESTMAPPER_FILEPATH}" >> "${DEFAULTRESTMAPPER_PATCH_FILEPATH}"
+
+# Next, we need to replace symbols that were local to the meta
+# package with their package-qualified names and fix the imports
+# in the resulting file.
+
+# This is the list of all symbols that need to be referenced inside
+# the k8s.io/apimachinery/pkg/api/meta package.
+#
+# Please keep it up-to-date and sorted.
+symbols_from_meta_pkg=(
+    AmbiguousResourceError
+    NoKindMatchError
+    NoResourceMatchError
+    ResettableRESTMapper
+    RESTMapper
+    RESTMapping
+    RESTScope
+    RESTScopeName
+    RESTScopeNameNamespace
+    RESTScopeNameRoot
+)
+
+for sym in ${symbols_from_meta_pkg[@]}; do
+    gofmt -w -r "${sym} -> meta.${sym}" "${DEFAULTRESTMAPPER_PATCH_FILEPATH}"
+done
+
+# Inform the caller if there were changes. Something could have broken.
+
+git diff --quiet -- "${DEFAULTRESTMAPPER_PATCH_FILEPATH}" || {
+    echo "Warning: ${DEFAULTRESTMAPPER_PATCH_FILEPATH} was modified." 1>&2
+    echo "Warning: Please inspect the changes before continuing. Run:" 1>&2
+    printf "\n\tgit diff -- %s\n\n" "${DEFAULTRESTMAPPER_PATCH_FILEPATH}" 1>&2
+    exit 0
+}