cuelang.org/go@v0.10.1/cue/ast/ident.go (about)

     1  // Copyright 2019 CUE Authors
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package ast
    16  
    17  import (
    18  	"strconv"
    19  	"strings"
    20  	"unicode"
    21  	"unicode/utf8"
    22  
    23  	"cuelang.org/go/cue/errors"
    24  	"cuelang.org/go/cue/token"
    25  )
    26  
    27  func isLetter(ch rune) bool {
    28  	return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch >= utf8.RuneSelf && unicode.IsLetter(ch)
    29  }
    30  
    31  func isDigit(ch rune) bool {
    32  	// TODO(mpvl): Is this correct?
    33  	return '0' <= ch && ch <= '9' || ch >= utf8.RuneSelf && unicode.IsDigit(ch)
    34  }
    35  
    36  // IsValidIdent reports whether str is a valid identifier.
    37  // Note that the underscore "_" string is considered valid, for top.
    38  func IsValidIdent(ident string) bool {
    39  	if ident == "" {
    40  		return false
    41  	}
    42  
    43  	consumed := false
    44  	if strings.HasPrefix(ident, "_") {
    45  		ident = ident[1:]
    46  		consumed = true
    47  		if len(ident) == 0 {
    48  			return true
    49  		}
    50  	}
    51  	if strings.HasPrefix(ident, "#") {
    52  		ident = ident[1:]
    53  		// Note: _#0 is not allowed by the spec, although _0 is.
    54  		// TODO: set consumed to true here to allow #0.
    55  		consumed = false
    56  	}
    57  
    58  	if !consumed {
    59  		if r, _ := utf8.DecodeRuneInString(ident); isDigit(r) {
    60  			return false
    61  		}
    62  	}
    63  
    64  	for _, r := range ident {
    65  		if isLetter(r) || isDigit(r) || r == '_' || r == '$' {
    66  			continue
    67  		}
    68  		return false
    69  	}
    70  	return true
    71  }
    72  
    73  // LabelName reports the name of a label, whether it is an identifier
    74  // (it binds a value to a scope), and whether it is valid.
    75  // Keywords that are allowed in label positions are interpreted accordingly.
    76  //
    77  // Examples:
    78  //
    79  //	Label   Result
    80  //	foo     "foo"  true   nil
    81  //	true    "true" true   nil
    82  //	"foo"   "foo"  false  nil
    83  //	"x-y"   "x-y"  false  nil
    84  //	"foo    ""     false  invalid string
    85  //	"\(x)"  ""     false  errors.Is(err, ErrIsExpression)
    86  //	X=foo   "foo"  true   nil
    87  func LabelName(l Label) (name string, isIdent bool, err error) {
    88  	if a, ok := l.(*Alias); ok {
    89  		l, _ = a.Expr.(Label)
    90  	}
    91  	switch n := l.(type) {
    92  	case *ListLit:
    93  		// An expression, but not one that can evaluated.
    94  		return "", false, errors.Newf(l.Pos(),
    95  			"cannot reference fields with square brackets labels outside the field value")
    96  
    97  	case *Ident:
    98  		name = n.Name
    99  		if !IsValidIdent(name) {
   100  			return "", false, errors.Newf(l.Pos(), "invalid identifier")
   101  		}
   102  		return name, true, err
   103  
   104  	case *BasicLit:
   105  		switch n.Kind {
   106  		case token.STRING:
   107  			// Use strconv to only allow double-quoted, single-line strings.
   108  			name, err = strconv.Unquote(n.Value)
   109  			if err != nil {
   110  				err = errors.Newf(l.Pos(), "invalid")
   111  			}
   112  
   113  		case token.NULL, token.TRUE, token.FALSE:
   114  			name = n.Value
   115  			isIdent = true
   116  
   117  		default:
   118  			// TODO: allow numbers to be fields
   119  			// This includes interpolation and template labels.
   120  			return "", false, errors.Wrapf(ErrIsExpression, l.Pos(),
   121  				"cannot use numbers as fields")
   122  		}
   123  		return name, isIdent, err
   124  
   125  	default:
   126  		// This includes interpolation and template labels.
   127  		return "", false, errors.Wrapf(ErrIsExpression, l.Pos(),
   128  			"label is an expression")
   129  	}
   130  }
   131  
   132  // ErrIsExpression reports whether a label is an expression.
   133  // This error is never returned directly. Use errors.Is.
   134  var ErrIsExpression = errors.New("not a concrete label")