refactor: improve the lock copy.sh script

* separate the script into a template file so it's easier to shellcheck
  and syntax highlight in editors.

* shellcheck the script and remove all SC2086 warnings
  ("Double quote to prevent globbing and word splitting")

* improve the buildozer help messages in the copy.sh script:
  * reduce duplication of buildozer command
  * add a more clear autofix bazel run command that can be easily
    copy-pasted

* change some of the variable names in the copy.sh template for longer,
  easier to understand names (repo_name >> name, lock_label >> label)

* move repo_name and workspace_relative_path into variables to reduce
  line length and improve readability

apt/private/BUILD.bazel

@@ -3,6 +3,7 @@ load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
 exports_files([
     "dpkg_statusd.sh",
     "dpkg_status.sh",
+    "copy.sh.tmpl",
     "package.BUILD.tmpl",
 ])
 

apt/private/copy.sh.tmpl

@@ -0,0 +1,51 @@
+#!/usr/bin/env bash
+
+set -o pipefail -o errexit -o nounset
+
+lock=$(realpath "$1")
+autofix=${{2:-}}
+
+cd "$BUILD_WORKING_DIRECTORY"
+
+echo
+echo "Writing lockfile to {workspace_relative_path}"
+cp "$lock" "{workspace_relative_path}"
+
+# Detect which file we wish the user to edit
+if [ -e "$BUILD_WORKSPACE_DIRECTORY/WORKSPACE" ]; then
+     wksp_file="WORKSPACE"
+elif [ -e "$BUILD_WORKSPACE_DIRECTORY/WORKSPACE.bazel" ]; then
+     wksp_file="WORKSPACE.bazel"
+elif [ -e "$BUILD_WORKSPACE_DIRECTORY/MODULE.bazel" ]; then
+    wksp_file="MODULE.bazel"
+else
+    echo>&2 "Error: no MODULE.bazel or WORKSPACE file was found"
+    exit 1
+fi
+
+# Detect a vendored buildozer binary in canonical location (tools/buildozer)
+if [ -e "$BUILD_WORKSPACE_DIRECTORY/tools/buildozer" ]; then
+    buildozer="tools/buildozer"
+else
+    # Assume it's on the $PATH
+    buildozer="buildozer"
+fi
+
+echo
+
+cmd="$buildozer 'set lock \"{lock_label}\"' $wksp_file:{repo_name}"
+
+if [[ "$autofix" == "--autofix" ]]; then
+    eval "$cmd"
+else
+    cat <<EOF
+Run the following command to add the 'lock' attribute
+to the "{repo_name}" repo in $wksp_file:
+
+    $cmd
+
+or run the following command to do it automatically:
+
+    bazel run @{repo_name}//:lock -- --autofix
+EOF
+fi

apt/private/resolve.bzl

@@ -83,50 +83,6 @@ def internal_resolve(rctx, yq_toolchain_prefix, manifest, include_transitive):
                 lockf.add_package_dependency(package, dep, arch)
     return lockf
 
-_COPY_SH_TMPL = """\
-#!/usr/bin/env bash
-set -o pipefail -o errexit -o nounset
-
-lock=$(realpath $1)
-
-cd $BUILD_WORKING_DIRECTORY
-
-echo ''
-echo 'Writing lockfile to {workspace_relative_path}' 
-cp $lock {workspace_relative_path}
-
-# Detect which file we wish the user to edit
-if [ -e $BUILD_WORKSPACE_DIRECTORY/WORKSPACE ]; then
-    wksp_file="WORKSPACE"
-elif [ -e $BUILD_WORKSPACE_DIRECTORY/WORKSPACE.bazel ]; then
-    wksp_file="WORKSPACE.bazel"
-elif [ -e $BUILD_WORKSPACE_DIRECTORY/MODULE.bazel ]; then
-    wksp_file="MODULE.bazel"
-else
-    echo>&2 "Error: no MODULE.bazel or WORKSPACE file was found"
-    exit 1
-fi
-
-# Detect a vendored buildozer binary in canonical location (tools/buildozer)
-if [ -e $BUILD_WORKSPACE_DIRECTORY/tools/buildozer ]; then
-    buildozer="tools/buildozer"
-else
-    # Assume it's on the $PATH
-    buildozer="buildozer"
-fi
-
-if [[ "${{2:-}}" == "--autofix" ]]; then
-    echo ''
-    ${{buildozer}} 'set lock \"{label}\"' ${{wksp_file}}:{name}
-else
-    cat <<EOF
-Run the following command to add the lockfile or pass --autofix flag to do it automatically.
-
-   ${{buildozer}} 'set lock \"{label}\"' ${{wksp_file}}:{name}
-EOF
-fi
-"""
-
 _BUILD_TMPL = """
 filegroup(
     name = "lockfile",
@@ -149,16 +105,22 @@ def _deb_resolve_impl(rctx):
     lockf = internal_resolve(rctx, rctx.attr.yq_toolchain_prefix, rctx.attr.manifest, rctx.attr.resolve_transitive)
     lockf.write("lock.json")
 
-    locklabel = rctx.attr.manifest.relative(rctx.attr.manifest.name.replace(".yaml", ".lock.json"))
+    lock_filename = rctx.attr.manifest.name.replace(".yaml", ".lock.json")
+    lock_label = rctx.attr.manifest.relative(lock_filename)
+    workspace_relative_path = "{}{}".format(
+        ("%s/" % lock_label.package) if lock_label.package else "",
+        lock_label.name,
+    )
+
     rctx.file(
         "copy.sh",
-        _COPY_SH_TMPL.format(
+        rctx.read(Label("//apt/private:copy.sh.tmpl")).format(
             # NOTE: the split("~") is needed when we run bazel from another
             # directory, e.g. when running e2e tests we change dir to e2e/smoke
             # and then rctx.name is 'rules_distroless~~apt~bullseye'
-            name = rctx.name.split("~")[-1].replace("_resolve", ""),
-            label = locklabel,
-            workspace_relative_path = (("%s/" % locklabel.package) if locklabel.package else "") + locklabel.name,
+            repo_name = rctx.name.split("~")[-1].replace("_resolve", ""),
+            lock_label = lock_label,
+            workspace_relative_path = workspace_relative_path,
         ),
         executable = True,
     )