1 files changed, 267 insertions, 0 deletions
diff --git a/dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/ebnf/ebnf.go b/dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/ebnf/ebnf.go
new file mode 100644
index 0000000..a4e20f0
--- /dev/null
+++ b/dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/ebnf/ebnf.go
@@ -0,0 +1,267 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package ebnf is a library for EBNF grammars. The input is text ([]byte)
+// satisfying the following grammar (represented itself in EBNF):
+//
+//	Production  = name "=" [ Expression ] "." .
+//	Expression  = Alternative { "|" Alternative } .
+//	Alternative = Term { Term } .
+//	Term        = name | token [ "…" token ] | Group | Option | Repetition .
+//	Group       = "(" Expression ")" .
+//	Option      = "[" Expression "]" .
+//	Repetition  = "{" Expression "}" .
+//
+// A name is a Go identifier, a token is a Go string, and comments
+// and white space follow the same rules as for the Go language.
+// Production names starting with an uppercase Unicode letter denote
+// non-terminal productions (i.e., productions which allow white-space
+// and comments between tokens); all other production names denote
+// lexical productions.
+package ebnf // import "golang.org/x/exp/ebnf"
+
+import (
+	"errors"
+	"fmt"
+	"text/scanner"
+	"unicode"
+	"unicode/utf8"
+)
+
+// ----------------------------------------------------------------------------
+// Error handling
+
+type errorList []error
+
+func (list errorList) Err() error {
+	if len(list) == 0 {
+		return nil
+	}
+	return list
+}
+
+func (list errorList) Error() string {
+	switch len(list) {
+	case 0:
+		return "no errors"
+	case 1:
+		return list[0].Error()
+	}
+	return fmt.Sprintf("%s (and %d more errors)", list[0], len(list)-1)
+}
+
+func newError(pos scanner.Position, msg string) error {
+	return errors.New(fmt.Sprintf("%s: %s", pos, msg))
+}
+
+// ----------------------------------------------------------------------------
+// Internal representation
+
+type (
+	// An Expression node represents a production expression.
+	Expression interface {
+		// Pos is the position of the first character of the syntactic construct
+		Pos() scanner.Position
+	}
+
+	// An Alternative node represents a non-empty list of alternative expressions.
+	Alternative []Expression // x | y | z
+
+	// A Sequence node represents a non-empty list of sequential expressions.
+	Sequence []Expression // x y z
+
+	// A Name node represents a production name.
+	Name struct {
+		StringPos scanner.Position
+		String    string
+	}
+
+	// A Token node represents a literal.
+	Token struct {
+		StringPos scanner.Position
+		String    string
+	}
+
+	// A List node represents a range of characters.
+	Range struct {
+		Begin, End *Token // begin ... end
+	}
+
+	// A Group node represents a grouped expression.
+	Group struct {
+		Lparen scanner.Position
+		Body   Expression // (body)
+	}
+
+	// An Option node represents an optional expression.
+	Option struct {
+		Lbrack scanner.Position
+		Body   Expression // [body]
+	}
+
+	// A Repetition node represents a repeated expression.
+	Repetition struct {
+		Lbrace scanner.Position
+		Body   Expression // {body}
+	}
+
+	// A Production node represents an EBNF production.
+	Production struct {
+		Name *Name
+		Expr Expression
+	}
+
+	// A Bad node stands for pieces of source code that lead to a parse error.
+	Bad struct {
+		TokPos scanner.Position
+		Error  string // parser error message
+	}
+
+	// A Grammar is a set of EBNF productions. The map
+	// is indexed by production name.
+	//
+	Grammar map[string]*Production
+)
+
+func (x Alternative) Pos() scanner.Position { return x[0].Pos() } // the parser always generates non-empty Alternative
+func (x Sequence) Pos() scanner.Position    { return x[0].Pos() } // the parser always generates non-empty Sequences
+func (x *Name) Pos() scanner.Position       { return x.StringPos }
+func (x *Token) Pos() scanner.Position      { return x.StringPos }
+func (x *Range) Pos() scanner.Position      { return x.Begin.Pos() }
+func (x *Group) Pos() scanner.Position      { return x.Lparen }
+func (x *Option) Pos() scanner.Position     { return x.Lbrack }
+func (x *Repetition) Pos() scanner.Position { return x.Lbrace }
+func (x *Production) Pos() scanner.Position { return x.Name.Pos() }
+func (x *Bad) Pos() scanner.Position        { return x.TokPos }
+
+// ----------------------------------------------------------------------------
+// Grammar verification
+
+func isLexical(name string) bool {
+	ch, _ := utf8.DecodeRuneInString(name)
+	return !unicode.IsUpper(ch)
+}
+
+type verifier struct {
+	errors   errorList
+	worklist []*Production
+	reached  Grammar // set of productions reached from (and including) the root production
+	grammar  Grammar
+}
+
+func (v *verifier) error(pos scanner.Position, msg string) {
+	v.errors = append(v.errors, newError(pos, msg))
+}
+
+func (v *verifier) push(prod *Production) {
+	name := prod.Name.String
+	if _, found := v.reached[name]; !found {
+		v.worklist = append(v.worklist, prod)
+		v.reached[name] = prod
+	}
+}
+
+func (v *verifier) verifyChar(x *Token) rune {
+	s := x.String
+	if utf8.RuneCountInString(s) != 1 {
+		v.error(x.Pos(), "single char expected, found "+s)
+		return 0
+	}
+	ch, _ := utf8.DecodeRuneInString(s)
+	return ch
+}
+
+func (v *verifier) verifyExpr(expr Expression, lexical bool) {
+	switch x := expr.(type) {
+	case nil:
+		// empty expression
+	case Alternative:
+		for _, e := range x {
+			v.verifyExpr(e, lexical)
+		}
+	case Sequence:
+		for _, e := range x {
+			v.verifyExpr(e, lexical)
+		}
+	case *Name:
+		// a production with this name must exist;
+		// add it to the worklist if not yet processed
+		if prod, found := v.grammar[x.String]; found {
+			v.push(prod)
+		} else {
+			v.error(x.Pos(), "missing production "+x.String)
+		}
+		// within a lexical production references
+		// to non-lexical productions are invalid
+		if lexical && !isLexical(x.String) {
+			v.error(x.Pos(), "reference to non-lexical production "+x.String)
+		}
+	case *Token:
+		// nothing to do for now
+	case *Range:
+		i := v.verifyChar(x.Begin)
+		j := v.verifyChar(x.End)
+		if i >= j {
+			v.error(x.Pos(), "decreasing character range")
+		}
+	case *Group:
+		v.verifyExpr(x.Body, lexical)
+	case *Option:
+		v.verifyExpr(x.Body, lexical)
+	case *Repetition:
+		v.verifyExpr(x.Body, lexical)
+	case *Bad:
+		v.error(x.Pos(), x.Error)
+	default:
+		panic(fmt.Sprintf("internal error: unexpected type %T", expr))
+	}
+}
+
+func (v *verifier) verify(grammar Grammar, start string) {
+	// find root production
+	root, found := grammar[start]
+	if !found {
+		var noPos scanner.Position
+		v.error(noPos, "no start production "+start)
+		return
+	}
+
+	// initialize verifier
+	v.worklist = v.worklist[0:0]
+	v.reached = make(Grammar)
+	v.grammar = grammar
+
+	// work through the worklist
+	v.push(root)
+	for {
+		n := len(v.worklist) - 1
+		if n < 0 {
+			break
+		}
+		prod := v.worklist[n]
+		v.worklist = v.worklist[0:n]
+		v.verifyExpr(prod.Expr, isLexical(prod.Name.String))
+	}
+
+	// check if all productions were reached
+	if len(v.reached) < len(v.grammar) {
+		for name, prod := range v.grammar {
+			if _, found := v.reached[name]; !found {
+				v.error(prod.Pos(), name+" is unreachable")
+			}
+		}
+	}
+}
+
+// Verify checks that:
+//   - all productions used are defined
+//   - all productions defined are used when beginning at start
+//   - lexical productions refer only to other lexical productions
+//
+// Position information is interpreted relative to the file set fset.
+func Verify(grammar Grammar, start string) error {
+	var v verifier
+	v.verify(grammar, start)
+	return v.errors.Err()
+}