internal/internal.go - cue - Git at Google

 // 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
 //
 //     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.

 // Package internal exposes some cue internals to other packages.
 //
 // A better name for this package would be technicaldebt.
 package internal // import "cuelang.org/go/internal"

 // TODO: refactor packages as to make this package unnecessary.

 import (
 	"bufio"
 	"fmt"
 	"os"
 	"path/filepath"
 	"strings"

 	"github.com/cockroachdb/apd/v2"
 	"golang.org/x/xerrors"

 	"cuelang.org/go/cue/ast"
 	"cuelang.org/go/cue/ast/astutil"
 	"cuelang.org/go/cue/errors"
 	"cuelang.org/go/cue/token"
 )

 // A Decimal is an arbitrary-precision binary-coded decimal number.
 //
 // Right now Decimal is aliased to apd.Decimal. This may change in the future.
 type Decimal = apd.Decimal

 // DebugStr prints a syntax node.
 var DebugStr func(x interface{}) string

 // ErrIncomplete can be used by builtins to signal the evaluation was
 // incomplete.
 var ErrIncomplete = errors.New("incomplete value")

 // EvalExpr evaluates an expression within an existing struct value.
 // Identifiers only resolve to values defined within the struct.
 //
 // Expressions may refer to builtin packages if they can be uniquely identified
 //
 // Both value and result are of type cue.Value, but are an interface to prevent
 // cyclic dependencies.
 //
 // TODO: extract interface
 var EvalExpr func(value, expr interface{}) (result interface{})

 // FromGoValue converts an arbitrary Go value to the corresponding CUE value.
 // instance must be of type *cue.Instance.
 // The returned value is a cue.Value, which the caller must cast to.
 var FromGoValue func(instance, x interface{}, allowDefault bool) interface{}

 // FromGoType converts an arbitrary Go type to the corresponding CUE value.
 // instance must be of type *cue.Instance.
 // The returned value is a cue.Value, which the caller must cast to.
 var FromGoType func(instance, x interface{}) interface{}

 // UnifyBuiltin returns the given Value unified with the given builtin template.
 var UnifyBuiltin func(v interface{}, kind string) interface{}

 // GetRuntime reports the runtime for an Instance or Value.
 var GetRuntime func(instance interface{}) interface{}

 // MakeInstance makes a new instance from a value.
 var MakeInstance func(value interface{}) (instance interface{})

 // CheckAndForkRuntime checks that value is created using runtime, panicking
 // if it does not, and returns a forked runtime that will discard additional
 // keys.
 var CheckAndForkRuntime func(runtime, value interface{}) interface{}

 // BaseContext is used as CUEs default context for arbitrary-precision decimals
 var BaseContext = apd.BaseContext.WithPrecision(24)

 // ListEllipsis reports the list type and remaining elements of a list. If we
 // ever relax the usage of ellipsis, this function will likely change. Using
 // this function will ensure keeping correct behavior or causing a compiler
 // failure.
 func ListEllipsis(n *ast.ListLit) (elts []ast.Expr, e *ast.Ellipsis) {
 	elts = n.Elts
 	if n := len(elts); n > 0 {
 		var ok bool
 		if e, ok = elts[n-1].(*ast.Ellipsis); ok {
 			elts = elts[:n-1]
 		}
 	}
 	return elts, e
 }

 func Imports(f *ast.File) (a []ast.Decl) {
 	for _, d := range f.Decls {
 		switch x := d.(type) {
 		case *ast.CommentGroup:
 		case *ast.Package:
 		case *ast.Attribute:
 		case *ast.ImportDecl:
 			a = append(a, x)
 		default:
 			return a
 		}
 	}
 	return a
 }

 func PackageInfo(f *ast.File) (p *ast.Package, name string, tok token.Pos) {
 	for _, d := range f.Decls {
 		switch x := d.(type) {
 		case *ast.CommentGroup:
 		case *ast.Package:
 			if x.Name == nil {
 				break
 			}
 			return x, x.Name.Name, x.Name.Pos()
 		}
 	}
 	return nil, "", f.Pos()
 }

 func SetPackage(f *ast.File, name string, overwrite bool) {
 	p, str, _ := PackageInfo(f)
 	if p != nil {
 		if !overwrite || str == name {
 			return
 		}
 		ident := ast.NewIdent(name)
 		astutil.CopyMeta(ident, p.Name)
 		return
 	}

 	decls := make([]ast.Decl, len(f.Decls)+1)
 	k := 0
 	for _, d := range f.Decls {
 		if _, ok := d.(*ast.CommentGroup); ok {
 			decls[k] = d
 			k++
 			continue
 		}
 		break
 	}
 	decls[k] = &ast.Package{Name: ast.NewIdent(name)}
 	copy(decls[k+1:], f.Decls[k:])
 	f.Decls = decls
 }

 // NewComment creates a new CommentGroup from the given text.
 // Each line is prefixed with "//" and the last newline is removed.
 // Useful for ASTs generated by code other than the CUE parser.
 func NewComment(isDoc bool, s string) *ast.CommentGroup {
 	if s == "" {
 		return nil
 	}
 	cg := &ast.CommentGroup{Doc: isDoc}
 	if !isDoc {
 		cg.Line = true
 		cg.Position = 10
 	}
 	scanner := bufio.NewScanner(strings.NewReader(s))
 	for scanner.Scan() {
 		scanner := bufio.NewScanner(strings.NewReader(scanner.Text()))
 		scanner.Split(bufio.ScanWords)
 		const maxRunesPerLine = 66
 		count := 2
 		buf := strings.Builder{}
 		buf.WriteString("//")
 		for scanner.Scan() {
 			s := scanner.Text()
 			n := len([]rune(s)) + 1
 			if count+n > maxRunesPerLine && count > 3 {
 				cg.List = append(cg.List, &ast.Comment{Text: buf.String()})
 				count = 3
 				buf.Reset()
 				buf.WriteString("//")
 			}
 			buf.WriteString(" ")
 			buf.WriteString(s)
 			count += n
 		}
 		cg.List = append(cg.List, &ast.Comment{Text: buf.String()})
 	}
 	if last := len(cg.List) - 1; cg.List[last].Text == "//" {
 		cg.List = cg.List[:last]
 	}
 	return cg
 }

 func FileComment(f *ast.File) *ast.CommentGroup {
 	pkg, _, _ := PackageInfo(f)
 	var cgs []*ast.CommentGroup
 	if pkg != nil {
 		cgs = pkg.Comments()
 	} else if cgs = f.Comments(); len(cgs) > 0 {
 		// Use file comment.
 	} else {
 		// Use first comment before any declaration.
 		for _, d := range f.Decls {
 			if cg, ok := d.(*ast.CommentGroup); ok {
 				return cg
 			}
 			if cgs = ast.Comments(d); cgs != nil {
 				break
 			}
 			if _, ok := d.(*ast.Attribute); !ok {
 				break
 			}
 		}
 	}
 	var cg *ast.CommentGroup
 	for _, c := range cgs {
 		if c.Position == 0 {
 			cg = c
 		}
 	}
 	return cg
 }

 func NewAttr(name, str string) *ast.Attribute {
 	buf := &strings.Builder{}
 	buf.WriteByte('@')
 	buf.WriteString(name)
 	buf.WriteByte('(')
 	fmt.Fprintf(buf, str)
 	buf.WriteByte(')')

 	return &ast.Attribute{Text: buf.String()}
 }

 // ToExpr converts a node to an expression. If it is a file, it will return
 // it as a struct. If is an expression, it will return it as is. Otherwise
 // it panics.
 func ToExpr(n ast.Node) ast.Expr {
 	switch x := n.(type) {
 	case nil:
 		return nil

 	case ast.Expr:
 		return x

 	case *ast.File:
 		start := 0
 	outer:
 		for i, d := range x.Decls {
 			switch d.(type) {
 			case *ast.Package, *ast.ImportDecl:
 				start = i + 1
 			case *ast.CommentGroup, *ast.Attribute:
 			default:
 				break outer
 			}
 		}
 		return &ast.StructLit{Elts: x.Decls[start:]}

 	default:
 		panic(fmt.Sprintf("Unsupported node type %T", x))
 	}
 }

 // ToFile converts an expression to a file.
 //
 // Adjusts the spacing of x when needed.
 func ToFile(n ast.Node) *ast.File {
 	switch x := n.(type) {
 	case nil:
 		return nil
 	case *ast.StructLit:
 		return &ast.File{Decls: x.Elts}
 	case ast.Expr:
 		ast.SetRelPos(x, token.NoSpace)
 		return &ast.File{Decls: []ast.Decl{&ast.EmbedDecl{Expr: x}}}
 	case *ast.File:
 		return x
 	default:
 		panic(fmt.Sprintf("Unsupported node type %T", x))
 	}
 }

 func IsBulkField(d ast.Decl) bool {
 	if f, ok := d.(*ast.Field); ok {
 		if _, ok := f.Label.(*ast.ListLit); ok {
 			return true
 		}
 	}
 	return false
 }

 func IsDef(s string) bool {
 	return strings.HasPrefix(s, "#") || strings.HasPrefix(s, "_#")
 }

 func IsHidden(s string) bool {
 	return strings.HasPrefix(s, "_")
 }

 func IsDefOrHidden(s string) bool {
 	return strings.HasPrefix(s, "#") || strings.HasPrefix(s, "_")
 }

 func IsDefinition(label ast.Label) bool {
 	switch x := label.(type) {
 	case *ast.Alias:
 		if ident, ok := x.Expr.(*ast.Ident); ok {
 			return IsDef(ident.Name)
 		}
 	case *ast.Ident:
 		return IsDef(x.Name)
 	}
 	return false
 }

 func IsRegularField(f *ast.Field) bool {
 	if f.Token == token.ISA {
 		return false
 	}
 	var ident *ast.Ident
 	switch x := f.Label.(type) {
 	case *ast.Alias:
 		ident, _ = x.Expr.(*ast.Ident)
 	case *ast.Ident:
 		ident = x
 	}
 	if ident == nil {
 		return true
 	}
 	if strings.HasPrefix(ident.Name, "#") || strings.HasPrefix(ident.Name, "_") {
 		return false
 	}
 	return true
 }

 func EmbedStruct(s *ast.StructLit) *ast.EmbedDecl {
 	e := &ast.EmbedDecl{Expr: s}
 	if len(s.Elts) == 1 {
 		d := s.Elts[0]
 		astutil.CopyPosition(e, d)
 		ast.SetRelPos(d, token.NoSpace)
 		astutil.CopyComments(e, d)
 		ast.SetComments(d, nil)
 		if f, ok := d.(*ast.Field); ok {
 			ast.SetRelPos(f.Label, token.NoSpace)
 		}
 	}
 	s.Lbrace = token.Newline.Pos()
 	s.Rbrace = token.NoSpace.Pos()
 	return e
 }

 // IsEllipsis reports whether the declaration can be represented as an ellipsis.
 func IsEllipsis(x ast.Decl) bool {
 	// ...
 	if _, ok := x.(*ast.Ellipsis); ok {
 		return true
 	}

 	// [string]: _ or [_]: _
 	f, ok := x.(*ast.Field)
 	if !ok {
 		return false
 	}
 	v, ok := f.Value.(*ast.Ident)
 	if !ok || v.Name != "_" {
 		return false
 	}
 	l, ok := f.Label.(*ast.ListLit)
 	if !ok || len(l.Elts) != 1 {
 		return false
 	}
 	i, ok := l.Elts[0].(*ast.Ident)
 	if !ok {
 		return false
 	}
 	return i.Name == "string" || i.Name == "_"
 }

 // GenPath reports the directory in which to store generated files.
 func GenPath(root string) string {
 	info, err := os.Stat(filepath.Join(root, "cue.mod"))
 	if os.IsNotExist(err) || !info.IsDir() {
 		// Try legacy pkgDir mode
 		pkgDir := filepath.Join(root, "pkg")
 		if err == nil && !info.IsDir() {
 			return pkgDir
 		}
 		if info, err := os.Stat(pkgDir); err == nil && info.IsDir() {
 			return pkgDir
 		}
 	}
 	return filepath.Join(root, "cue.mod", "gen")
 }

 var ErrInexact = errors.New("inexact subsumption")

 func DecorateError(info error, err errors.Error) errors.Error {
 	return &decorated{cueError: err, info: info}
 }

 type cueError = errors.Error

 type decorated struct {
 	cueError

 	info error
 }

 func (e *decorated) Is(err error) bool {
 	return xerrors.Is(e.info, err) || xerrors.Is(e.cueError, err)
 }

 // MaxDepth indicates the maximum evaluation depth. This is there to break
 // cycles in the absence of cycle detection.
 //
 // It is registered in a central place to make it easy to find all spots where
 // cycles are broken in this brute-force manner.
 //
 // TODO(eval): have cycle detection.
 const MaxDepth = 20
	// 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
	//
	// 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.

	// Package internal exposes some cue internals to other packages.
	//
	// A better name for this package would be technicaldebt.
	package internal // import "cuelang.org/go/internal"

	// TODO: refactor packages as to make this package unnecessary.

	import (
	"bufio"
	"fmt"
	"os"
	"path/filepath"
	"strings"

	"github.com/cockroachdb/apd/v2"
	"golang.org/x/xerrors"

	"cuelang.org/go/cue/ast"
	"cuelang.org/go/cue/ast/astutil"
	"cuelang.org/go/cue/errors"
	"cuelang.org/go/cue/token"
	)

	// A Decimal is an arbitrary-precision binary-coded decimal number.
	//
	// Right now Decimal is aliased to apd.Decimal. This may change in the future.
	type Decimal = apd.Decimal

	// DebugStr prints a syntax node.
	var DebugStr func(x interface{}) string

	// ErrIncomplete can be used by builtins to signal the evaluation was
	// incomplete.
	var ErrIncomplete = errors.New("incomplete value")

	// EvalExpr evaluates an expression within an existing struct value.
	// Identifiers only resolve to values defined within the struct.
	//
	// Expressions may refer to builtin packages if they can be uniquely identified
	//
	// Both value and result are of type cue.Value, but are an interface to prevent
	// cyclic dependencies.
	//
	// TODO: extract interface
	var EvalExpr func(value, expr interface{}) (result interface{})

	// FromGoValue converts an arbitrary Go value to the corresponding CUE value.
	// instance must be of type *cue.Instance.
	// The returned value is a cue.Value, which the caller must cast to.
	var FromGoValue func(instance, x interface{}, allowDefault bool) interface{}

	// FromGoType converts an arbitrary Go type to the corresponding CUE value.
	// instance must be of type *cue.Instance.
	// The returned value is a cue.Value, which the caller must cast to.
	var FromGoType func(instance, x interface{}) interface{}

	// UnifyBuiltin returns the given Value unified with the given builtin template.
	var UnifyBuiltin func(v interface{}, kind string) interface{}

	// GetRuntime reports the runtime for an Instance or Value.
	var GetRuntime func(instance interface{}) interface{}

	// MakeInstance makes a new instance from a value.
	var MakeInstance func(value interface{}) (instance interface{})

	// CheckAndForkRuntime checks that value is created using runtime, panicking
	// if it does not, and returns a forked runtime that will discard additional
	// keys.
	var CheckAndForkRuntime func(runtime, value interface{}) interface{}

	// BaseContext is used as CUEs default context for arbitrary-precision decimals
	var BaseContext = apd.BaseContext.WithPrecision(24)

	// ListEllipsis reports the list type and remaining elements of a list. If we
	// ever relax the usage of ellipsis, this function will likely change. Using
	// this function will ensure keeping correct behavior or causing a compiler
	// failure.
	func ListEllipsis(n ast.ListLit) (elts []ast.Expr, e ast.Ellipsis) {
	elts = n.Elts
	if n := len(elts); n > 0 {
	var ok bool
	if e, ok = elts[n-1].(*ast.Ellipsis); ok {
	elts = elts[:n-1]
	}
	}
	return elts, e
	}

	func Imports(f *ast.File) (a []ast.Decl) {
	for _, d := range f.Decls {
	switch x := d.(type) {
	case *ast.CommentGroup:
	case *ast.Package:
	case *ast.Attribute:
	case *ast.ImportDecl:
	a = append(a, x)
	default:
	return a
	}
	}
	return a
	}

	func PackageInfo(f ast.File) (p ast.Package, name string, tok token.Pos) {
	for _, d := range f.Decls {
	switch x := d.(type) {
	case *ast.CommentGroup:
	case *ast.Package:
	if x.Name == nil {
	break
	}
	return x, x.Name.Name, x.Name.Pos()
	}
	}
	return nil, "", f.Pos()
	}

	func SetPackage(f *ast.File, name string, overwrite bool) {
	p, str, _ := PackageInfo(f)
	if p != nil {
	if !overwrite \|\| str == name {
	return
	}
	ident := ast.NewIdent(name)
	astutil.CopyMeta(ident, p.Name)
	return
	}

	decls := make([]ast.Decl, len(f.Decls)+1)
	k := 0
	for _, d := range f.Decls {
	if _, ok := d.(*ast.CommentGroup); ok {
	decls[k] = d
	k++
	continue
	}
	break
	}
	decls[k] = &ast.Package{Name: ast.NewIdent(name)}
	copy(decls[k+1:], f.Decls[k:])
	f.Decls = decls
	}

	// NewComment creates a new CommentGroup from the given text.
	// Each line is prefixed with "//" and the last newline is removed.
	// Useful for ASTs generated by code other than the CUE parser.
	func NewComment(isDoc bool, s string) *ast.CommentGroup {
	if s == "" {
	return nil
	}
	cg := &ast.CommentGroup{Doc: isDoc}
	if !isDoc {
	cg.Line = true
	cg.Position = 10
	}
	scanner := bufio.NewScanner(strings.NewReader(s))
	for scanner.Scan() {
	scanner := bufio.NewScanner(strings.NewReader(scanner.Text()))
	scanner.Split(bufio.ScanWords)
	const maxRunesPerLine = 66
	count := 2
	buf := strings.Builder{}
	buf.WriteString("//")
	for scanner.Scan() {
	s := scanner.Text()
	n := len([]rune(s)) + 1
	if count+n > maxRunesPerLine && count > 3 {
	cg.List = append(cg.List, &ast.Comment{Text: buf.String()})
	count = 3
	buf.Reset()
	buf.WriteString("//")
	}
	buf.WriteString(" ")
	buf.WriteString(s)
	count += n
	}
	cg.List = append(cg.List, &ast.Comment{Text: buf.String()})
	}
	if last := len(cg.List) - 1; cg.List[last].Text == "//" {
	cg.List = cg.List[:last]
	}
	return cg
	}

	func FileComment(f ast.File) ast.CommentGroup {
	pkg, _, _ := PackageInfo(f)
	var cgs []*ast.CommentGroup
	if pkg != nil {
	cgs = pkg.Comments()
	} else if cgs = f.Comments(); len(cgs) > 0 {
	// Use file comment.
	} else {
	// Use first comment before any declaration.
	for _, d := range f.Decls {
	if cg, ok := d.(*ast.CommentGroup); ok {
	return cg
	}
	if cgs = ast.Comments(d); cgs != nil {
	break
	}
	if _, ok := d.(*ast.Attribute); !ok {
	break
	}
	}
	}
	var cg *ast.CommentGroup
	for _, c := range cgs {
	if c.Position == 0 {
	cg = c
	}
	}
	return cg
	}

	func NewAttr(name, str string) *ast.Attribute {
	buf := &strings.Builder{}
	buf.WriteByte('@')
	buf.WriteString(name)
	buf.WriteByte('(')
	fmt.Fprintf(buf, str)
	buf.WriteByte(')')

	return &ast.Attribute{Text: buf.String()}
	}

	// ToExpr converts a node to an expression. If it is a file, it will return
	// it as a struct. If is an expression, it will return it as is. Otherwise
	// it panics.
	func ToExpr(n ast.Node) ast.Expr {
	switch x := n.(type) {
	case nil:
	return nil

	case ast.Expr:
	return x

	case *ast.File:
	start := 0
	outer:
	for i, d := range x.Decls {
	switch d.(type) {
	case ast.Package, ast.ImportDecl:
	start = i + 1
	case ast.CommentGroup, ast.Attribute:
	default:
	break outer
	}
	}
	return &ast.StructLit{Elts: x.Decls[start:]}

	default:
	panic(fmt.Sprintf("Unsupported node type %T", x))
	}
	}

	// ToFile converts an expression to a file.
	//
	// Adjusts the spacing of x when needed.
	func ToFile(n ast.Node) *ast.File {
	switch x := n.(type) {
	case nil:
	return nil
	case *ast.StructLit:
	return &ast.File{Decls: x.Elts}
	case ast.Expr:
	ast.SetRelPos(x, token.NoSpace)
	return &ast.File{Decls: []ast.Decl{&ast.EmbedDecl{Expr: x}}}
	case *ast.File:
	return x
	default:
	panic(fmt.Sprintf("Unsupported node type %T", x))
	}
	}

	func IsBulkField(d ast.Decl) bool {
	if f, ok := d.(*ast.Field); ok {
	if _, ok := f.Label.(*ast.ListLit); ok {
	return true
	}
	}
	return false
	}

	func IsDef(s string) bool {
	return strings.HasPrefix(s, "#") \|\| strings.HasPrefix(s, "_#")
	}

	func IsHidden(s string) bool {
	return strings.HasPrefix(s, "_")
	}

	func IsDefOrHidden(s string) bool {
	return strings.HasPrefix(s, "#") \|\| strings.HasPrefix(s, "_")
	}

	func IsDefinition(label ast.Label) bool {
	switch x := label.(type) {
	case *ast.Alias:
	if ident, ok := x.Expr.(*ast.Ident); ok {
	return IsDef(ident.Name)
	}
	case *ast.Ident:
	return IsDef(x.Name)
	}
	return false
	}

	func IsRegularField(f *ast.Field) bool {
	if f.Token == token.ISA {
	return false
	}
	var ident *ast.Ident
	switch x := f.Label.(type) {
	case *ast.Alias:
	ident, _ = x.Expr.(*ast.Ident)
	case *ast.Ident:
	ident = x
	}
	if ident == nil {
	return true
	}
	if strings.HasPrefix(ident.Name, "#") \|\| strings.HasPrefix(ident.Name, "_") {
	return false
	}
	return true
	}

	func EmbedStruct(s ast.StructLit) ast.EmbedDecl {
	e := &ast.EmbedDecl{Expr: s}
	if len(s.Elts) == 1 {
	d := s.Elts[0]
	astutil.CopyPosition(e, d)
	ast.SetRelPos(d, token.NoSpace)
	astutil.CopyComments(e, d)
	ast.SetComments(d, nil)
	if f, ok := d.(*ast.Field); ok {
	ast.SetRelPos(f.Label, token.NoSpace)
	}
	}
	s.Lbrace = token.Newline.Pos()
	s.Rbrace = token.NoSpace.Pos()
	return e
	}

	// IsEllipsis reports whether the declaration can be represented as an ellipsis.
	func IsEllipsis(x ast.Decl) bool {
	// ...
	if _, ok := x.(*ast.Ellipsis); ok {
	return true
	}

	// [string]: _ or [_]: _
	f, ok := x.(*ast.Field)
	if !ok {
	return false
	}
	v, ok := f.Value.(*ast.Ident)
	if !ok \|\| v.Name != "_" {
	return false
	}
	l, ok := f.Label.(*ast.ListLit)
	if !ok \|\| len(l.Elts) != 1 {
	return false
	}
	i, ok := l.Elts[0].(*ast.Ident)
	if !ok {
	return false
	}
	return i.Name == "string" \|\| i.Name == "_"
	}

	// GenPath reports the directory in which to store generated files.
	func GenPath(root string) string {
	info, err := os.Stat(filepath.Join(root, "cue.mod"))
	if os.IsNotExist(err) \|\| !info.IsDir() {
	// Try legacy pkgDir mode
	pkgDir := filepath.Join(root, "pkg")
	if err == nil && !info.IsDir() {
	return pkgDir
	}
	if info, err := os.Stat(pkgDir); err == nil && info.IsDir() {
	return pkgDir
	}
	}
	return filepath.Join(root, "cue.mod", "gen")
	}

	var ErrInexact = errors.New("inexact subsumption")

	func DecorateError(info error, err errors.Error) errors.Error {
	return &decorated{cueError: err, info: info}
	}

	type cueError = errors.Error

	type decorated struct {
	cueError

	info error
	}

	func (e *decorated) Is(err error) bool {
	return xerrors.Is(e.info, err) \|\| xerrors.Is(e.cueError, err)
	}

	// MaxDepth indicates the maximum evaluation depth. This is there to break
	// cycles in the absence of cycle detection.
	//
	// It is registered in a central place to make it easy to find all spots where
	// cycles are broken in this brute-force manner.
	//
	// TODO(eval): have cycle detection.
	const MaxDepth = 20