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// Copyright 2018 The CUE 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 load
import (
pathpkg "path"
goruntime "runtime"
const (
cueSuffix = ".cue"
modDir = "cue.mod"
configFile = "module.cue"
pkgDir = "pkg"
// FromArgsUsage is a partial usage message that applications calling
// FromArgs may wish to include in their -help output.
// Some of the aspects of this documentation, like flags and handling '--' need
// to be implemented by the tools.
const FromArgsUsage = `
<args> is a list of arguments denoting a set of instances of the form:
<package>* <file_args>*
1. A list of source files
CUE files are parsed, loaded and unified into a single instance. All files
must have the same package name.
Data files, like YAML or JSON, are handled in one of two ways:
a. Explicitly mapped into a single CUE namespace, using the --path, --files
and --list flags. In this case these are unified into a single instance
along with any other CUE files.
b. Treated as a stream of data elements that each is optionally unified with
a single instance, which either consists of the other CUE files specified
on the command line or a single package.
By default, the format of files is derived from the file extension.
This behavior may be modified with file arguments of the form <qualifiers>:
For instance,
cue eval foo.cue json:
indicates that the file should be interpreted as a JSON file.
A qualifier applies to all files following it until the next qualifier.
The following qualifiers are available:
cue CUE definitions and data
json JSON data, one value only
jsonl newline-separated JSON values
yaml a YAML file, may contain a stream
proto Protobuf definitions
jsonschema data encoding describes JSON Schema
openapi data encoding describes Open API
data output as -- or only accept -- data
graph data allowing references or anchors
schema output as schema; defaults JSON files to JSON Schema
def full definitions, including documentation
2. A list of relative directories to denote a package instance.
Each directory matching the pattern is loaded as a separate instance.
The instance contains all files in this directory and ancestor directories,
up to the module root, with the same package name. The package name must
be either uniquely determined by the files in the given directory, or
explicitly defined using a package name qualifier. For instance, ./...:foo
selects all packages named foo in the any subdirectory of the current
working directory.
3. An import path referring to a directory within the current module
All CUE files in that directory, and all the ancestor directories up to the
module root (if applicable), with a package name corresponding to the base
name of the directory or the optional explicit package name are loaded into
a single instance.
Examples, assume a module name of package in cue.mod
./foo package corresponding to foo directory
.:bar package in current directory with package name bar
// GenPath reports the directory in which to store generated
// files.
func GenPath(root string) string {
return internal.GenPath(root)
// A Config configures load behavior.
type Config struct {
// Context specifies the context for the load operation.
// If the context is cancelled, the loader may stop early
// and return an ErrCancelled error.
// If Context is nil, the load cannot be cancelled.
Context *build.Context
loader *loader
// A Module is a collection of packages and instances that are within the
// directory hierarchy rooted at the module root. The module root can be
// marked with a cue.mod file.
ModuleRoot string
// Module specifies the module prefix. If not empty, this value must match
// the module field of an existing cue.mod file.
Module string
// Package defines the name of the package to be loaded. If this is not set,
// the package must be uniquely defined from its context. Special values:
// _ load files without a package
// * load all packages. Files without packages are loaded
// in the _ package.
Package string
// Dir is the directory in which to run the build system's query tool
// that provides information about the packages.
// If Dir is empty, the tool is run in the current directory.
Dir string
// Tags defines boolean tags or key-value pairs to select files to build
// or be injected as values in fields.
// Each string is of the form
// key [ "=" value ]
// where key is a valid CUE identifier and value valid CUE scalar.
// The Tags values are used to both select which files get included in a
// build and to inject values into the AST.
// File selection
// Files with an attribute of the form @if(expr) before a package clause
// are conditionally included if expr resolves to true, where expr refers to
// boolean values in Tags.
// It is an error for a file to have more than one @if attribute or to
// have a @if attribute without or after a package clause.
// Value injection
// The Tags values are also used to inject values into fields with a
// @tag attribute.
// For any field of the form
// field: x @tag(key)
// and Tags value for which the name matches key, the field will be
// modified to
// field: x & "value"
// By default, the injected value is treated as a string. Alternatively, a
// "type" option of the @tag attribute allows a value to be interpreted as
// an int, number, or bool. For instance, for a field
// field: x @tag(key,type=int)
// an entry "key=2" modifies the field to
// field: x & 2
// Valid values for type are "int", "number", "bool", and "string".
// A @tag attribute can also define shorthand values, which can be injected
// into the fields without having to specify the key. For instance, for
// environment: string @tag(env,short=prod|staging)
// the Tags entry "prod" sets the environment field to the value "prod".
// This is equivalent to a Tags entry of "env=prod".
// The use of @tag does not preclude using any of the usual CUE constraints
// to limit the possible values of a field. For instance
// environment: "prod" | "staging" @tag(env,short=prod|staging)
// ensures the user may only specify "prod" or "staging".
Tags []string
// TagVars defines a set of key value pair the values of which may be
// referenced by tags.
// Use DefaultTagVars to get a pre-loaded map with supported values.
TagVars map[string]TagVar
// Include all files, regardless of tags.
AllCUEFiles bool
// Deprecated: use Tags
BuildTags []string
releaseTags []string
// If Tests is set, the loader includes not just the packages
// matching a particular pattern but also any related test packages.
Tests bool
// If Tools is set, the loader includes tool files associated with
// a package.
Tools bool
// filesMode indicates that files are specified
// explicitly on the command line.
filesMode bool
// If DataFiles is set, the loader includes entries for directories that
// have no CUE files, but have recognized data files that could be converted
// to CUE.
DataFiles bool
// StdRoot specifies an alternative directory for standard libaries.
// This is mostly used for bootstrapping.
StdRoot string
// ParseFile is called to read and parse each file when preparing a
// package's syntax tree. It must be safe to call ParseFile simultaneously
// from multiple goroutines. If ParseFile is nil, the loader will uses
// parser.ParseFile.
// ParseFile should parse the source from src and use filename only for
// recording position information.
// An application may supply a custom implementation of ParseFile to change
// the effective file contents or the behavior of the parser, or to modify
// the syntax tree.
ParseFile func(name string, src interface{}) (*ast.File, error)
// Overlay provides a mapping of absolute file paths to file contents. If
// the file with the given path already exists, the parser will use the
// alternative file contents provided by the map.
Overlay map[string]Source
// Stdin defines an alternative for os.Stdin for the file "-". When used,
// the corresponding build.File will be associated with the full buffer.
Stdin io.Reader
loadFunc build.LoadFunc
func (c *Config) stdin() io.Reader {
if c.Stdin == nil {
return os.Stdin
return c.Stdin
func (c *Config) newInstance(pos token.Pos, p importPath) *build.Instance {
dir, name, err := c.absDirFromImportPath(pos, p)
i := c.Context.NewInstance(dir, c.loadFunc)
i.Dir = dir
i.PkgName = name
i.DisplayPath = string(p)
i.ImportPath = string(p)
i.Root = c.ModuleRoot
i.Module = c.Module
i.Err = errors.Append(i.Err, err)
return i
func (c *Config) newRelInstance(pos token.Pos, path, pkgName string) *build.Instance {
fs := c.fileSystem
var err errors.Error
dir := path
p := c.Context.NewInstance(path, c.loadFunc)
p.PkgName = pkgName
p.DisplayPath = filepath.ToSlash(path)
// p.ImportPath = string(dir) // compute unique ID.
p.Root = c.ModuleRoot
p.Module = c.Module
if isLocalImport(path) {
if c.Dir == "" {
err = errors.Append(err, errors.Newf(pos, "cwd unknown"))
dir = filepath.Join(c.Dir, filepath.FromSlash(path))
if path == "" {
err = errors.Append(err, errors.Newf(pos,
"import %q: invalid import path", path))
} else if path != cleanImport(path) {
err = errors.Append(err, c.loader.errPkgf(nil,
"non-canonical import path: %q should be %q", path, pathpkg.Clean(path)))
if importPath, e := c.importPathFromAbsDir(fsPath(dir), path); e != nil {
// Detect later to keep error messages consistent.
} else {
p.ImportPath = string(importPath)
p.Dir = dir
if fs.isAbsPath(path) || strings.HasPrefix(path, "/") {
err = errors.Append(err, errors.Newf(pos,
"absolute import path %q not allowed", path))
if err != nil {
p.Err = errors.Append(p.Err, err)
p.Incomplete = true
return p
func (c Config) newErrInstance(pos token.Pos, path importPath, err error) *build.Instance {
i := c.newInstance(pos, path)
i.Err = errors.Promote(err, "instance")
return i
func toImportPath(dir string) importPath {
return importPath(filepath.ToSlash(dir))
type importPath string
type fsPath string
func (c *Config) importPathFromAbsDir(absDir fsPath, key string) (importPath, errors.Error) {
if c.ModuleRoot == "" {
return "", errors.Newf(token.NoPos,
"cannot determine import path for %q (root undefined)", key)
dir := filepath.Clean(string(absDir))
if !strings.HasPrefix(dir, c.ModuleRoot) {
return "", errors.Newf(token.NoPos,
"cannot determine import path for %q (dir outside of root)", key)
pkg := filepath.ToSlash(dir[len(c.ModuleRoot):])
switch {
case strings.HasPrefix(pkg, "/cue.mod/"):
pkg = pkg[len("/cue.mod/"):]
if pkg == "" {
return "", errors.Newf(token.NoPos,
"invalid package %q (root of %s)", key, modDir)
// TODO(legacy): remove.
case strings.HasPrefix(pkg, "/pkg/"):
pkg = pkg[len("/pkg/"):]
if pkg == "" {
return "", errors.Newf(token.NoPos,
"invalid package %q (root of %s)", key, pkgDir)
case c.Module == "":
return "", errors.Newf(token.NoPos,
"cannot determine import path for %q (no module)", key)
pkg = c.Module + pkg
name := c.Package
switch name {
case "_", "*":
name = ""
return addImportQualifier(importPath(pkg), name)
func addImportQualifier(pkg importPath, name string) (importPath, errors.Error) {
if name != "" {
s := string(pkg)
if i := strings.LastIndexByte(s, '/'); i >= 0 {
s = s[i+1:]
if i := strings.LastIndexByte(s, ':'); i >= 0 {
// should never happen, but just in case.
s = s[i+1:]
if s != name {
return "", errors.Newf(token.NoPos,
"non-matching package names (%s != %s)", s, name)
} else if s != name {
pkg += importPath(":" + name)
return pkg, nil
// absDirFromImportPath converts a giving import path to an absolute directory
// and a package name. The root directory must be set.
// The returned directory may not exist.
func (c *Config) absDirFromImportPath(pos token.Pos, p importPath) (absDir, name string, err errors.Error) {
if c.ModuleRoot == "" {
return "", "", errors.Newf(pos, "cannot import %q (root undefined)", p)
// Extract the package name.
name = string(p)
switch i := strings.LastIndexAny(name, "/:"); {
case i < 0:
case p[i] == ':':
name = string(p[i+1:])
p = p[:i]
default: // p[i] == '/'
name = string(p[i+1:])
// TODO: fully test that name is a valid identifier.
if name == "" {
err = errors.Newf(pos, "empty package name in import path %q", p)
} else if strings.IndexByte(name, '.') >= 0 {
err = errors.Newf(pos,
"cannot determine package name for %q (set explicitly with ':')", p)
// Determine the directory.
sub := filepath.FromSlash(string(p))
switch hasPrefix := strings.HasPrefix(string(p), c.Module); {
case hasPrefix && len(sub) == len(c.Module):
absDir = c.ModuleRoot
case hasPrefix && p[len(c.Module)] == '/':
absDir = filepath.Join(c.ModuleRoot, sub[len(c.Module)+1:])
absDir = filepath.Join(GenPath(c.ModuleRoot), sub)
return absDir, name, err
// Complete updates the configuration information. After calling complete,
// the following invariants hold:
// - c.ModuleRoot != ""
// - c.Module is set to the module import prefix if there is a cue.mod file
// with the module property.
// - c.loader != nil
// - c.cache != ""
func (c Config) complete() (cfg *Config, err error) {
// Each major CUE release should add a tag here.
// Old tags should not be removed. That is, the cue1.x tag is present
// in all releases >= CUE 1.x. Code that requires CUE 1.x or later should
// say "+build cue1.x", and code that should only be built before CUE 1.x
// (perhaps it is the stub to use in that case) should say "+build !cue1.x".
c.releaseTags = []string{"cue0.1"}
if c.Dir == "" {
c.Dir, err = os.Getwd()
if err != nil {
return nil, err
} else if c.Dir, err = filepath.Abs(c.Dir); err != nil {
return nil, err
// TODO: we could populate this already with absolute file paths,
// but relative paths cannot be added. Consider what is reasonable.
if err := c.fileSystem.init(&c); err != nil {
return nil, err
// TODO: determine root on a package basis. Maybe we even need a
// pkgname.cue.mod
// Look to see if there is a cue.mod.
if c.ModuleRoot == "" {
// Only consider the current directory by default
c.ModuleRoot = c.Dir
if root := c.findRoot(c.Dir); root != "" {
c.ModuleRoot = root
c.loader = &loader{
cfg: &c,
buildTags: make(map[string]bool),
// TODO: also make this work if run from outside the module?
switch {
case true:
mod := filepath.Join(c.ModuleRoot, modDir)
info, cerr := c.fileSystem.stat(mod)
if cerr != nil {
if info.IsDir() {
mod = filepath.Join(mod, configFile)
f, cerr := c.fileSystem.openFile(mod)
if cerr != nil {
// TODO: move to full build again
file, err := parser.ParseFile("load", f)
if err != nil {
return nil, errors.Wrapf(err, token.NoPos, "invalid cue.mod file")
r := runtime.New()
v, err := compile.Files(nil, r, "_", file)
if err != nil {
return nil, errors.Wrapf(err, token.NoPos, "invalid cue.mod file")
ctx := eval.NewContext(r, v)
prefix := v.Lookup(ctx.StringLabel("module"))
if prefix != nil {
name := ctx.StringValue(prefix.Value())
if err := ctx.Err(); err != nil {
return &c, err.Err
pos := token.NoPos
src := prefix.Value().Source()
if src != nil {
pos = src.Pos()
if c.Module != "" && c.Module != name {
return &c, errors.Newf(pos, "inconsistent modules: got %q, want %q", name, c.Module)
c.Module = name
c.loadFunc = c.loader.loadFunc()
if c.Context == nil {
c.Context = build.NewContext(
return &c, nil
func (c Config) isRoot(dir string) bool {
fs := &c.fileSystem
// Note: cue.mod used to be a file. We still allow both to match.
_, err := fs.stat(filepath.Join(dir, modDir))
return err == nil
// findRoot returns the module root or "" if none was found.
func (c Config) findRoot(dir string) string {
fs := &c.fileSystem
absDir, err := filepath.Abs(dir)
if err != nil {
return ""
abs := absDir
for {
if c.isRoot(abs) {
return abs
d := filepath.Dir(abs)
if filepath.Base(filepath.Dir(abs)) == modDir {
// The package was located within a "cue.mod" dir and there was
// not cue.mod found until now. So there is no root.
return ""
if len(d) >= len(abs) {
break // reached top of file system, no cue.mod
abs = d
abs = absDir
// TODO(legacy): remove this capability at some point.
for {
info, err := fs.stat(filepath.Join(abs, pkgDir))
if err == nil && info.IsDir() {
return abs
d := filepath.Dir(abs)
if len(d) >= len(abs) {
return "" // reached top of file system, no pkg dir.
abs = d
func home() string {
env := "HOME"
if goruntime.GOOS == "windows" {
} else if goruntime.GOOS == "plan9" {
env = "home"
return os.Getenv(env)