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// Copyright 2019 The LUCI 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
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
package lucicfg
import (
luciflag ""
// Meta contains configuration for the configuration generator itself.
// It influences how generator produces output configs. It is settable through
// lucicfg.config(...) statements on the Starlark side or through command line
// flags. Command line flags override what was set via lucicfg.config(...).
// See @stdlib//internal/ for full meaning of fields.
type Meta struct {
ConfigServiceHost string `json:"config_service_host"` // LUCI config host name
ConfigDir string `json:"config_dir"` // output directory to place generated files or '-' for stdout
TrackedFiles []string `json:"tracked_files"` // e.g. ["*.cfg", "!*-dev.cfg"]
FailOnWarnings bool `json:"fail_on_warnings"` // true to treat validation warnings as errors
// FlagSet passed to AddFlags and AddOutputFlags.
fs *flag.FlagSet
// Pointers to fields that were touched. Used when merging two Metas together.
touched map[interface{}]struct{}
// True if detectTouchedFlags() was already called.
detectedTouchedFlags bool
// Log logs the values of the meta parameters to Debug logger.
func (m *Meta) Log(ctx context.Context) {
logging.Debugf(ctx, "Meta config:")
logging.Debugf(ctx, " config_service_host = %q", m.ConfigServiceHost)
logging.Debugf(ctx, " config_dir = %q", m.ConfigDir)
logging.Debugf(ctx, " tracked_files = %v", m.TrackedFiles)
logging.Debugf(ctx, " fail_on_warnings = %v", m.FailOnWarnings)
// RebaseConfigDir changes ConfigDir, if it is set, to be absolute by appending
// it to the given root.
// Doesn't touch "-", which indicates "stdout".
func (m *Meta) RebaseConfigDir(root string) {
if m.ConfigDir != "" && m.ConfigDir != "-" {
m.ConfigDir = filepath.Join(root, filepath.FromSlash(m.ConfigDir))
// AddFlags registers command line flags that correspond to Meta fields.
func (m *Meta) AddFlags(fs *flag.FlagSet) {
m.fs = fs
fs.StringVar(&m.ConfigServiceHost, "config-service-host", m.ConfigServiceHost, "Hostname of a LUCI config service to use for validation.")
fs.StringVar(&m.ConfigDir, "config-dir", m.ConfigDir,
`A directory to place generated configs into (relative to cwd if given as a
flag otherwise relative to the main script). If '-', generated configs are just
printed to stdout in a format useful for debugging.`)
fs.Var(luciflag.CommaList(&m.TrackedFiles), "tracked-files", "Globs for files considered generated, see lucicfg.config(...) doc for more info.")
fs.BoolVar(&m.FailOnWarnings, "fail-on-warnings", m.FailOnWarnings, "Treat validation warnings as errors.")
// detectTouchedFlags is called after flags are parsed to figure out what flags
// were explicitly set and what were left at their defaults.
// It updates Meta with information about touched flags which is later used
// by PopulateFromTouchedIn and WasTouched functions.
func (m *Meta) detectTouchedFlags() {
switch {
case m.fs == nil:
return // not using CLI flags at all
case m.detectedTouchedFlags:
return // already did this
case !m.fs.Parsed():
panic("detectTouchedFlags should be called after flags are parsed")
m.detectedTouchedFlags = true
fields := m.fieldsMap()
m.fs.Visit(func(f *flag.Flag) {
if ptr := fields[strings.Replace(f.Name, "-", "_", -1)]; ptr != nil {
// PopulateFromTouchedIn takes all touched values in `t` and copies them to
// `m`, overriding what's in `m`.
func (m *Meta) PopulateFromTouchedIn(t *Meta) {
left := m.fieldsMap()
right := t.fieldsMap()
for k, l := range left {
r := right[k]
if _, yes := t.touched[r]; yes {
// Do *l = *r.
switch l.(type) {
case *string:
*(l.(*string)) = *(r.(*string))
case *bool:
*(l.(*bool)) = *(r.(*bool))
case *[]string:
*(l.(*[]string)) = append([]string(nil), *(r.(*[]string))...)
// WasTouched returns true if the field (given by its Starlark snake_case name)
// was explicitly set via CLI flags or via lucicfg.config(...) in Starlark.
// Panics if the field is unrecognized.
func (m *Meta) WasTouched(field string) bool {
ptr, ok := m.fieldsMap()[field]
if !ok {
panic(fmt.Sprintf("no such meta field %s", field))
_, yes := m.touched[ptr]
return yes
// touch takes a pointer to some Meta field and marks it as explicitly set.
func (m *Meta) touch(ptr interface{}) {
if m.touched == nil {
m.touched = make(map[interface{}]struct{}, 1)
m.touched[ptr] = struct{}{}
// fieldsMap returns a mapping from a snake_case name of a field to a pointer to
// this field inside 'm'.
// This is used by both Starlark accessors and for processing CLI flags.
func (m *Meta) fieldsMap() map[string]interface{} {
return map[string]interface{}{
"config_service_host": &m.ConfigServiceHost,
"config_dir": &m.ConfigDir,
"tracked_files": &m.TrackedFiles,
"fail_on_warnings": &m.FailOnWarnings,
// setField sets the field k to v.
func (m *Meta) setField(k string, v starlark.Value) (err error) {
ptr := m.fieldsMap()[k]
if ptr == nil {
return fmt.Errorf("set_meta: no such meta key %q", k)
// On success, mark the field as modified.
defer func() {
if err == nil {
switch ptr := ptr.(type) {
case *string:
if str, ok := v.(starlark.String); ok {
*ptr = str.GoString()
return nil
return fmt.Errorf("set_meta: got %s, expecting string", v.Type())
case *bool:
if b, ok := v.(starlark.Bool); ok {
*ptr = bool(b)
return nil
return fmt.Errorf("set_meta: got %s, expecting bool", v.Type())
case *[]string:
if iterable, ok := v.(starlark.Iterable); ok {
iter := iterable.Iterate()
defer iter.Done()
var vals []string
for x := starlark.Value(nil); iter.Next(&x); {
if str, ok := x.(starlark.String); ok {
vals = append(vals, str.GoString())
} else {
return fmt.Errorf("set_meta: got %s, expecting string", x.Type())
*ptr = vals
return nil
return fmt.Errorf("set_meta: got %s, expecting an iterable", v.Type())
func init() {
// set_meta(k, v) sets the value of the corresponding field in Meta.
declNative("set_meta", func(call nativeCall) (starlark.Value, error) {
var k starlark.String
var v starlark.Value
if err := call.unpack(2, &k, &v); err != nil {
return nil, err
return starlark.None, call.State.Meta.setField(k.GoString(), v)