TUN-7227: Migrate to devincarr/quic-go

The lucas-clemente/quic-go package moved namespaces and our branch
went stale, this new fork provides support for the new quic-go repo
and applies the max datagram frame size change.

Until the max datagram frame size support gets upstreamed into quic-go,
this can be used to unblock go 1.20 support as the old
lucas-clemente/quic-go will not get go 1.20 support.

vendor/golang.org/x/exp/LICENSE

@@ -0,0 +1,27 @@
+Copyright (c) 2009 The Go Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+   * Neither the name of Google Inc. nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

vendor/golang.org/x/exp/PATENTS

@@ -0,0 +1,22 @@
+Additional IP Rights Grant (Patents)
+
+"This implementation" means the copyrightable works distributed by
+Google as part of the Go project.
+
+Google hereby grants to You a perpetual, worldwide, non-exclusive,
+no-charge, royalty-free, irrevocable (except as stated in this section)
+patent license to make, have made, use, offer to sell, sell, import,
+transfer and otherwise run, modify and propagate the contents of this
+implementation of Go, where such license applies only to those patent
+claims, both currently owned or controlled by Google and acquired in
+the future, licensable by Google that are necessarily infringed by this
+implementation of Go.  This grant does not include claims that would be
+infringed only as a consequence of further modification of this
+implementation.  If you or your agent or exclusive licensee institute or
+order or agree to the institution of patent litigation against any
+entity (including a cross-claim or counterclaim in a lawsuit) alleging
+that this implementation of Go or any code incorporated within this
+implementation of Go constitutes direct or contributory patent
+infringement, or inducement of patent infringement, then any patent
+rights granted to you under this License for this implementation of Go
+shall terminate as of the date such litigation is filed.

vendor/golang.org/x/exp/constraints/constraints.go

@@ -0,0 +1,50 @@
+// Copyright 2021 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 constraints defines a set of useful constraints to be used
+// with type parameters.
+package constraints
+
+// Signed is a constraint that permits any signed integer type.
+// If future releases of Go add new predeclared signed integer types,
+// this constraint will be modified to include them.
+type Signed interface {
+	~int | ~int8 | ~int16 | ~int32 | ~int64
+}
+
+// Unsigned is a constraint that permits any unsigned integer type.
+// If future releases of Go add new predeclared unsigned integer types,
+// this constraint will be modified to include them.
+type Unsigned interface {
+	~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr
+}
+
+// Integer is a constraint that permits any integer type.
+// If future releases of Go add new predeclared integer types,
+// this constraint will be modified to include them.
+type Integer interface {
+	Signed | Unsigned
+}
+
+// Float is a constraint that permits any floating-point type.
+// If future releases of Go add new predeclared floating-point types,
+// this constraint will be modified to include them.
+type Float interface {
+	~float32 | ~float64
+}
+
+// Complex is a constraint that permits any complex numeric type.
+// If future releases of Go add new predeclared complex numeric types,
+// this constraint will be modified to include them.
+type Complex interface {
+	~complex64 | ~complex128
+}
+
+// Ordered is a constraint that permits any ordered type: any type
+// that supports the operators < <= >= >.
+// If future releases of Go add new ordered types,
+// this constraint will be modified to include them.
+type Ordered interface {
+	Integer | Float | ~string
+}

vendor/golang.org/x/mod/modfile/print.go

@@ -0,0 +1,174 @@
+// Copyright 2018 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.
+
+// Module file printer.
+
+package modfile
+
+import (
+	"bytes"
+	"fmt"
+	"strings"
+)
+
+// Format returns a go.mod file as a byte slice, formatted in standard style.
+func Format(f *FileSyntax) []byte {
+	pr := &printer{}
+	pr.file(f)
+	return pr.Bytes()
+}
+
+// A printer collects the state during printing of a file or expression.
+type printer struct {
+	bytes.Buffer           // output buffer
+	comment      []Comment // pending end-of-line comments
+	margin       int       // left margin (indent), a number of tabs
+}
+
+// printf prints to the buffer.
+func (p *printer) printf(format string, args ...interface{}) {
+	fmt.Fprintf(p, format, args...)
+}
+
+// indent returns the position on the current line, in bytes, 0-indexed.
+func (p *printer) indent() int {
+	b := p.Bytes()
+	n := 0
+	for n < len(b) && b[len(b)-1-n] != '\n' {
+		n++
+	}
+	return n
+}
+
+// newline ends the current line, flushing end-of-line comments.
+func (p *printer) newline() {
+	if len(p.comment) > 0 {
+		p.printf(" ")
+		for i, com := range p.comment {
+			if i > 0 {
+				p.trim()
+				p.printf("\n")
+				for i := 0; i < p.margin; i++ {
+					p.printf("\t")
+				}
+			}
+			p.printf("%s", strings.TrimSpace(com.Token))
+		}
+		p.comment = p.comment[:0]
+	}
+
+	p.trim()
+	p.printf("\n")
+	for i := 0; i < p.margin; i++ {
+		p.printf("\t")
+	}
+}
+
+// trim removes trailing spaces and tabs from the current line.
+func (p *printer) trim() {
+	// Remove trailing spaces and tabs from line we're about to end.
+	b := p.Bytes()
+	n := len(b)
+	for n > 0 && (b[n-1] == '\t' || b[n-1] == ' ') {
+		n--
+	}
+	p.Truncate(n)
+}
+
+// file formats the given file into the print buffer.
+func (p *printer) file(f *FileSyntax) {
+	for _, com := range f.Before {
+		p.printf("%s", strings.TrimSpace(com.Token))
+		p.newline()
+	}
+
+	for i, stmt := range f.Stmt {
+		switch x := stmt.(type) {
+		case *CommentBlock:
+			// comments already handled
+			p.expr(x)
+
+		default:
+			p.expr(x)
+			p.newline()
+		}
+
+		for _, com := range stmt.Comment().After {
+			p.printf("%s", strings.TrimSpace(com.Token))
+			p.newline()
+		}
+
+		if i+1 < len(f.Stmt) {
+			p.newline()
+		}
+	}
+}
+
+func (p *printer) expr(x Expr) {
+	// Emit line-comments preceding this expression.
+	if before := x.Comment().Before; len(before) > 0 {
+		// Want to print a line comment.
+		// Line comments must be at the current margin.
+		p.trim()
+		if p.indent() > 0 {
+			// There's other text on the line. Start a new line.
+			p.printf("\n")
+		}
+		// Re-indent to margin.
+		for i := 0; i < p.margin; i++ {
+			p.printf("\t")
+		}
+		for _, com := range before {
+			p.printf("%s", strings.TrimSpace(com.Token))
+			p.newline()
+		}
+	}
+
+	switch x := x.(type) {
+	default:
+		panic(fmt.Errorf("printer: unexpected type %T", x))
+
+	case *CommentBlock:
+		// done
+
+	case *LParen:
+		p.printf("(")
+	case *RParen:
+		p.printf(")")
+
+	case *Line:
+		p.tokens(x.Token)
+
+	case *LineBlock:
+		p.tokens(x.Token)
+		p.printf(" ")
+		p.expr(&x.LParen)
+		p.margin++
+		for _, l := range x.Line {
+			p.newline()
+			p.expr(l)
+		}
+		p.margin--
+		p.newline()
+		p.expr(&x.RParen)
+	}
+
+	// Queue end-of-line comments for printing when we
+	// reach the end of the line.
+	p.comment = append(p.comment, x.Comment().Suffix...)
+}
+
+func (p *printer) tokens(tokens []string) {
+	sep := ""
+	for _, t := range tokens {
+		if t == "," || t == ")" || t == "]" || t == "}" {
+			sep = ""
+		}
+		p.printf("%s%s", sep, t)
+		sep = " "
+		if t == "(" || t == "[" || t == "{" {
+			sep = ""
+		}
+	}
+}

vendor/golang.org/x/mod/modfile/read.go

@@ -0,0 +1,958 @@
+// Copyright 2018 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 modfile
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+// A Position describes an arbitrary source position in a file, including the
+// file, line, column, and byte offset.
+type Position struct {
+	Line     int // line in input (starting at 1)
+	LineRune int // rune in line (starting at 1)
+	Byte     int // byte in input (starting at 0)
+}
+
+// add returns the position at the end of s, assuming it starts at p.
+func (p Position) add(s string) Position {
+	p.Byte += len(s)
+	if n := strings.Count(s, "\n"); n > 0 {
+		p.Line += n
+		s = s[strings.LastIndex(s, "\n")+1:]
+		p.LineRune = 1
+	}
+	p.LineRune += utf8.RuneCountInString(s)
+	return p
+}
+
+// An Expr represents an input element.
+type Expr interface {
+	// Span returns the start and end position of the expression,
+	// excluding leading or trailing comments.
+	Span() (start, end Position)
+
+	// Comment returns the comments attached to the expression.
+	// This method would normally be named 'Comments' but that
+	// would interfere with embedding a type of the same name.
+	Comment() *Comments
+}
+
+// A Comment represents a single // comment.
+type Comment struct {
+	Start  Position
+	Token  string // without trailing newline
+	Suffix bool   // an end of line (not whole line) comment
+}
+
+// Comments collects the comments associated with an expression.
+type Comments struct {
+	Before []Comment // whole-line comments before this expression
+	Suffix []Comment // end-of-line comments after this expression
+
+	// For top-level expressions only, After lists whole-line
+	// comments following the expression.
+	After []Comment
+}
+
+// Comment returns the receiver. This isn't useful by itself, but
+// a Comments struct is embedded into all the expression
+// implementation types, and this gives each of those a Comment
+// method to satisfy the Expr interface.
+func (c *Comments) Comment() *Comments {
+	return c
+}
+
+// A FileSyntax represents an entire go.mod file.
+type FileSyntax struct {
+	Name string // file path
+	Comments
+	Stmt []Expr
+}
+
+func (x *FileSyntax) Span() (start, end Position) {
+	if len(x.Stmt) == 0 {
+		return
+	}
+	start, _ = x.Stmt[0].Span()
+	_, end = x.Stmt[len(x.Stmt)-1].Span()
+	return start, end
+}
+
+// addLine adds a line containing the given tokens to the file.
+//
+// If the first token of the hint matches the first token of the
+// line, the new line is added at the end of the block containing hint,
+// extracting hint into a new block if it is not yet in one.
+//
+// If the hint is non-nil buts its first token does not match,
+// the new line is added after the block containing hint
+// (or hint itself, if not in a block).
+//
+// If no hint is provided, addLine appends the line to the end of
+// the last block with a matching first token,
+// or to the end of the file if no such block exists.
+func (x *FileSyntax) addLine(hint Expr, tokens ...string) *Line {
+	if hint == nil {
+		// If no hint given, add to the last statement of the given type.
+	Loop:
+		for i := len(x.Stmt) - 1; i >= 0; i-- {
+			stmt := x.Stmt[i]
+			switch stmt := stmt.(type) {
+			case *Line:
+				if stmt.Token != nil && stmt.Token[0] == tokens[0] {
+					hint = stmt
+					break Loop
+				}
+			case *LineBlock:
+				if stmt.Token[0] == tokens[0] {
+					hint = stmt
+					break Loop
+				}
+			}
+		}
+	}
+
+	newLineAfter := func(i int) *Line {
+		new := &Line{Token: tokens}
+		if i == len(x.Stmt) {
+			x.Stmt = append(x.Stmt, new)
+		} else {
+			x.Stmt = append(x.Stmt, nil)
+			copy(x.Stmt[i+2:], x.Stmt[i+1:])
+			x.Stmt[i+1] = new
+		}
+		return new
+	}
+
+	if hint != nil {
+		for i, stmt := range x.Stmt {
+			switch stmt := stmt.(type) {
+			case *Line:
+				if stmt == hint {
+					if stmt.Token == nil || stmt.Token[0] != tokens[0] {
+						return newLineAfter(i)
+					}
+
+					// Convert line to line block.
+					stmt.InBlock = true
+					block := &LineBlock{Token: stmt.Token[:1], Line: []*Line{stmt}}
+					stmt.Token = stmt.Token[1:]
+					x.Stmt[i] = block
+					new := &Line{Token: tokens[1:], InBlock: true}
+					block.Line = append(block.Line, new)
+					return new
+				}
+
+			case *LineBlock:
+				if stmt == hint {
+					if stmt.Token[0] != tokens[0] {
+						return newLineAfter(i)
+					}
+
+					new := &Line{Token: tokens[1:], InBlock: true}
+					stmt.Line = append(stmt.Line, new)
+					return new
+				}
+
+				for j, line := range stmt.Line {
+					if line == hint {
+						if stmt.Token[0] != tokens[0] {
+							return newLineAfter(i)
+						}
+
+						// Add new line after hint within the block.
+						stmt.Line = append(stmt.Line, nil)
+						copy(stmt.Line[j+2:], stmt.Line[j+1:])
+						new := &Line{Token: tokens[1:], InBlock: true}
+						stmt.Line[j+1] = new
+						return new
+					}
+				}
+			}
+		}
+	}
+
+	new := &Line{Token: tokens}
+	x.Stmt = append(x.Stmt, new)
+	return new
+}
+
+func (x *FileSyntax) updateLine(line *Line, tokens ...string) {
+	if line.InBlock {
+		tokens = tokens[1:]
+	}
+	line.Token = tokens
+}
+
+// markRemoved modifies line so that it (and its end-of-line comment, if any)
+// will be dropped by (*FileSyntax).Cleanup.
+func (line *Line) markRemoved() {
+	line.Token = nil
+	line.Comments.Suffix = nil
+}
+
+// Cleanup cleans up the file syntax x after any edit operations.
+// To avoid quadratic behavior, (*Line).markRemoved marks the line as dead
+// by setting line.Token = nil but does not remove it from the slice
+// in which it appears. After edits have all been indicated,
+// calling Cleanup cleans out the dead lines.
+func (x *FileSyntax) Cleanup() {
+	w := 0
+	for _, stmt := range x.Stmt {
+		switch stmt := stmt.(type) {
+		case *Line:
+			if stmt.Token == nil {
+				continue
+			}
+		case *LineBlock:
+			ww := 0
+			for _, line := range stmt.Line {
+				if line.Token != nil {
+					stmt.Line[ww] = line
+					ww++
+				}
+			}
+			if ww == 0 {
+				continue
+			}
+			if ww == 1 {
+				// Collapse block into single line.
+				line := &Line{
+					Comments: Comments{
+						Before: commentsAdd(stmt.Before, stmt.Line[0].Before),
+						Suffix: commentsAdd(stmt.Line[0].Suffix, stmt.Suffix),
+						After:  commentsAdd(stmt.Line[0].After, stmt.After),
+					},
+					Token: stringsAdd(stmt.Token, stmt.Line[0].Token),
+				}
+				x.Stmt[w] = line
+				w++
+				continue
+			}
+			stmt.Line = stmt.Line[:ww]
+		}
+		x.Stmt[w] = stmt
+		w++
+	}
+	x.Stmt = x.Stmt[:w]
+}
+
+func commentsAdd(x, y []Comment) []Comment {
+	return append(x[:len(x):len(x)], y...)
+}
+
+func stringsAdd(x, y []string) []string {
+	return append(x[:len(x):len(x)], y...)
+}
+
+// A CommentBlock represents a top-level block of comments separate
+// from any rule.
+type CommentBlock struct {
+	Comments
+	Start Position
+}
+
+func (x *CommentBlock) Span() (start, end Position) {
+	return x.Start, x.Start
+}
+
+// A Line is a single line of tokens.
+type Line struct {
+	Comments
+	Start   Position
+	Token   []string
+	InBlock bool
+	End     Position
+}
+
+func (x *Line) Span() (start, end Position) {
+	return x.Start, x.End
+}
+
+// A LineBlock is a factored block of lines, like
+//
+//	require (
+//		"x"
+//		"y"
+//	)
+type LineBlock struct {
+	Comments
+	Start  Position
+	LParen LParen
+	Token  []string
+	Line   []*Line
+	RParen RParen
+}
+
+func (x *LineBlock) Span() (start, end Position) {
+	return x.Start, x.RParen.Pos.add(")")
+}
+
+// An LParen represents the beginning of a parenthesized line block.
+// It is a place to store suffix comments.
+type LParen struct {
+	Comments
+	Pos Position
+}
+
+func (x *LParen) Span() (start, end Position) {
+	return x.Pos, x.Pos.add(")")
+}
+
+// An RParen represents the end of a parenthesized line block.
+// It is a place to store whole-line (before) comments.
+type RParen struct {
+	Comments
+	Pos Position
+}
+
+func (x *RParen) Span() (start, end Position) {
+	return x.Pos, x.Pos.add(")")
+}
+
+// An input represents a single input file being parsed.
+type input struct {
+	// Lexing state.
+	filename   string    // name of input file, for errors
+	complete   []byte    // entire input
+	remaining  []byte    // remaining input
+	tokenStart []byte    // token being scanned to end of input
+	token      token     // next token to be returned by lex, peek
+	pos        Position  // current input position
+	comments   []Comment // accumulated comments
+
+	// Parser state.
+	file        *FileSyntax // returned top-level syntax tree
+	parseErrors ErrorList   // errors encountered during parsing
+
+	// Comment assignment state.
+	pre  []Expr // all expressions, in preorder traversal
+	post []Expr // all expressions, in postorder traversal
+}
+
+func newInput(filename string, data []byte) *input {
+	return &input{
+		filename:  filename,
+		complete:  data,
+		remaining: data,
+		pos:       Position{Line: 1, LineRune: 1, Byte: 0},
+	}
+}
+
+// parse parses the input file.
+func parse(file string, data []byte) (f *FileSyntax, err error) {
+	// The parser panics for both routine errors like syntax errors
+	// and for programmer bugs like array index errors.
+	// Turn both into error returns. Catching bug panics is
+	// especially important when processing many files.
+	in := newInput(file, data)
+	defer func() {
+		if e := recover(); e != nil && e != &in.parseErrors {
+			in.parseErrors = append(in.parseErrors, Error{
+				Filename: in.filename,
+				Pos:      in.pos,
+				Err:      fmt.Errorf("internal error: %v", e),
+			})
+		}
+		if err == nil && len(in.parseErrors) > 0 {
+			err = in.parseErrors
+		}
+	}()
+
+	// Prime the lexer by reading in the first token. It will be available
+	// in the next peek() or lex() call.
+	in.readToken()
+
+	// Invoke the parser.
+	in.parseFile()
+	if len(in.parseErrors) > 0 {
+		return nil, in.parseErrors
+	}
+	in.file.Name = in.filename
+
+	// Assign comments to nearby syntax.
+	in.assignComments()
+
+	return in.file, nil
+}
+
+// Error is called to report an error.
+// Error does not return: it panics.
+func (in *input) Error(s string) {
+	in.parseErrors = append(in.parseErrors, Error{
+		Filename: in.filename,
+		Pos:      in.pos,
+		Err:      errors.New(s),
+	})
+	panic(&in.parseErrors)
+}
+
+// eof reports whether the input has reached end of file.
+func (in *input) eof() bool {
+	return len(in.remaining) == 0
+}
+
+// peekRune returns the next rune in the input without consuming it.
+func (in *input) peekRune() int {
+	if len(in.remaining) == 0 {
+		return 0
+	}
+	r, _ := utf8.DecodeRune(in.remaining)
+	return int(r)
+}
+
+// peekPrefix reports whether the remaining input begins with the given prefix.
+func (in *input) peekPrefix(prefix string) bool {
+	// This is like bytes.HasPrefix(in.remaining, []byte(prefix))
+	// but without the allocation of the []byte copy of prefix.
+	for i := 0; i < len(prefix); i++ {
+		if i >= len(in.remaining) || in.remaining[i] != prefix[i] {
+			return false
+		}
+	}
+	return true
+}
+
+// readRune consumes and returns the next rune in the input.
+func (in *input) readRune() int {
+	if len(in.remaining) == 0 {
+		in.Error("internal lexer error: readRune at EOF")
+	}
+	r, size := utf8.DecodeRune(in.remaining)
+	in.remaining = in.remaining[size:]
+	if r == '\n' {
+		in.pos.Line++
+		in.pos.LineRune = 1
+	} else {
+		in.pos.LineRune++
+	}
+	in.pos.Byte += size
+	return int(r)
+}
+
+type token struct {
+	kind   tokenKind
+	pos    Position
+	endPos Position
+	text   string
+}
+
+type tokenKind int
+
+const (
+	_EOF tokenKind = -(iota + 1)
+	_EOLCOMMENT
+	_IDENT
+	_STRING
+	_COMMENT
+
+	// newlines and punctuation tokens are allowed as ASCII codes.
+)
+
+func (k tokenKind) isComment() bool {
+	return k == _COMMENT || k == _EOLCOMMENT
+}
+
+// isEOL returns whether a token terminates a line.
+func (k tokenKind) isEOL() bool {
+	return k == _EOF || k == _EOLCOMMENT || k == '\n'
+}
+
+// startToken marks the beginning of the next input token.
+// It must be followed by a call to endToken, once the token's text has
+// been consumed using readRune.
+func (in *input) startToken() {
+	in.tokenStart = in.remaining
+	in.token.text = ""
+	in.token.pos = in.pos
+}
+
+// endToken marks the end of an input token.
+// It records the actual token string in tok.text.
+// A single trailing newline (LF or CRLF) will be removed from comment tokens.
+func (in *input) endToken(kind tokenKind) {
+	in.token.kind = kind
+	text := string(in.tokenStart[:len(in.tokenStart)-len(in.remaining)])
+	if kind.isComment() {
+		if strings.HasSuffix(text, "\r\n") {
+			text = text[:len(text)-2]
+		} else {
+			text = strings.TrimSuffix(text, "\n")
+		}
+	}
+	in.token.text = text
+	in.token.endPos = in.pos
+}
+
+// peek returns the kind of the next token returned by lex.
+func (in *input) peek() tokenKind {
+	return in.token.kind
+}
+
+// lex is called from the parser to obtain the next input token.
+func (in *input) lex() token {
+	tok := in.token
+	in.readToken()
+	return tok
+}
+
+// readToken lexes the next token from the text and stores it in in.token.
+func (in *input) readToken() {
+	// Skip past spaces, stopping at non-space or EOF.
+	for !in.eof() {
+		c := in.peekRune()
+		if c == ' ' || c == '\t' || c == '\r' {
+			in.readRune()
+			continue
+		}
+
+		// Comment runs to end of line.
+		if in.peekPrefix("//") {
+			in.startToken()
+
+			// Is this comment the only thing on its line?
+			// Find the last \n before this // and see if it's all
+			// spaces from there to here.
+			i := bytes.LastIndex(in.complete[:in.pos.Byte], []byte("\n"))
+			suffix := len(bytes.TrimSpace(in.complete[i+1:in.pos.Byte])) > 0
+			in.readRune()
+			in.readRune()
+
+			// Consume comment.
+			for len(in.remaining) > 0 && in.readRune() != '\n' {
+			}
+
+			// If we are at top level (not in a statement), hand the comment to
+			// the parser as a _COMMENT token. The grammar is written
+			// to handle top-level comments itself.
+			if !suffix {
+				in.endToken(_COMMENT)
+				return
+			}
+
+			// Otherwise, save comment for later attachment to syntax tree.
+			in.endToken(_EOLCOMMENT)
+			in.comments = append(in.comments, Comment{in.token.pos, in.token.text, suffix})
+			return
+		}
+
+		if in.peekPrefix("/*") {
+			in.Error("mod files must use // comments (not /* */ comments)")
+		}
+
+		// Found non-space non-comment.
+		break
+	}
+
+	// Found the beginning of the next token.
+	in.startToken()
+
+	// End of file.
+	if in.eof() {
+		in.endToken(_EOF)
+		return
+	}
+
+	// Punctuation tokens.
+	switch c := in.peekRune(); c {
+	case '\n', '(', ')', '[', ']', '{', '}', ',':
+		in.readRune()
+		in.endToken(tokenKind(c))
+		return
+
+	case '"', '`': // quoted string
+		quote := c
+		in.readRune()
+		for {
+			if in.eof() {
+				in.pos = in.token.pos
+				in.Error("unexpected EOF in string")
+			}
+			if in.peekRune() == '\n' {
+				in.Error("unexpected newline in string")
+			}
+			c := in.readRune()
+			if c == quote {
+				break
+			}
+			if c == '\\' && quote != '`' {
+				if in.eof() {
+					in.pos = in.token.pos
+					in.Error("unexpected EOF in string")
+				}
+				in.readRune()
+			}
+		}
+		in.endToken(_STRING)
+		return
+	}
+
+	// Checked all punctuation. Must be identifier token.
+	if c := in.peekRune(); !isIdent(c) {
+		in.Error(fmt.Sprintf("unexpected input character %#q", c))
+	}
+
+	// Scan over identifier.
+	for isIdent(in.peekRune()) {
+		if in.peekPrefix("//") {
+			break
+		}
+		if in.peekPrefix("/*") {
+			in.Error("mod files must use // comments (not /* */ comments)")
+		}
+		in.readRune()
+	}
+	in.endToken(_IDENT)
+}
+
+// isIdent reports whether c is an identifier rune.
+// We treat most printable runes as identifier runes, except for a handful of
+// ASCII punctuation characters.
+func isIdent(c int) bool {
+	switch r := rune(c); r {
+	case ' ', '(', ')', '[', ']', '{', '}', ',':
+		return false
+	default:
+		return !unicode.IsSpace(r) && unicode.IsPrint(r)
+	}
+}
+
+// Comment assignment.
+// We build two lists of all subexpressions, preorder and postorder.
+// The preorder list is ordered by start location, with outer expressions first.
+// The postorder list is ordered by end location, with outer expressions last.
+// We use the preorder list to assign each whole-line comment to the syntax
+// immediately following it, and we use the postorder list to assign each
+// end-of-line comment to the syntax immediately preceding it.
+
+// order walks the expression adding it and its subexpressions to the
+// preorder and postorder lists.
+func (in *input) order(x Expr) {
+	if x != nil {
+		in.pre = append(in.pre, x)
+	}
+	switch x := x.(type) {
+	default:
+		panic(fmt.Errorf("order: unexpected type %T", x))
+	case nil:
+		// nothing
+	case *LParen, *RParen:
+		// nothing
+	case *CommentBlock:
+		// nothing
+	case *Line:
+		// nothing
+	case *FileSyntax:
+		for _, stmt := range x.Stmt {
+			in.order(stmt)
+		}
+	case *LineBlock:
+		in.order(&x.LParen)
+		for _, l := range x.Line {
+			in.order(l)
+		}
+		in.order(&x.RParen)
+	}
+	if x != nil {
+		in.post = append(in.post, x)
+	}
+}
+
+// assignComments attaches comments to nearby syntax.
+func (in *input) assignComments() {
+	const debug = false
+
+	// Generate preorder and postorder lists.
+	in.order(in.file)
+
+	// Split into whole-line comments and suffix comments.
+	var line, suffix []Comment
+	for _, com := range in.comments {
+		if com.Suffix {
+			suffix = append(suffix, com)
+		} else {
+			line = append(line, com)
+		}
+	}
+
+	if debug {
+		for _, c := range line {
+			fmt.Fprintf(os.Stderr, "LINE %q :%d:%d #%d\n", c.Token, c.Start.Line, c.Start.LineRune, c.Start.Byte)
+		}
+	}
+
+	// Assign line comments to syntax immediately following.
+	for _, x := range in.pre {
+		start, _ := x.Span()
+		if debug {
+			fmt.Fprintf(os.Stderr, "pre %T :%d:%d #%d\n", x, start.Line, start.LineRune, start.Byte)
+		}
+		xcom := x.Comment()
+		for len(line) > 0 && start.Byte >= line[0].Start.Byte {
+			if debug {
+				fmt.Fprintf(os.Stderr, "ASSIGN LINE %q #%d\n", line[0].Token, line[0].Start.Byte)
+			}
+			xcom.Before = append(xcom.Before, line[0])
+			line = line[1:]
+		}
+	}
+
+	// Remaining line comments go at end of file.
+	in.file.After = append(in.file.After, line...)
+
+	if debug {
+		for _, c := range suffix {
+			fmt.Fprintf(os.Stderr, "SUFFIX %q :%d:%d #%d\n", c.Token, c.Start.Line, c.Start.LineRune, c.Start.Byte)
+		}
+	}
+
+	// Assign suffix comments to syntax immediately before.
+	for i := len(in.post) - 1; i >= 0; i-- {
+		x := in.post[i]
+
+		start, end := x.Span()
+		if debug {
+			fmt.Fprintf(os.Stderr, "post %T :%d:%d #%d :%d:%d #%d\n", x, start.Line, start.LineRune, start.Byte, end.Line, end.LineRune, end.Byte)
+		}
+
+		// Do not assign suffix comments to end of line block or whole file.
+		// Instead assign them to the last element inside.
+		switch x.(type) {
+		case *FileSyntax:
+			continue
+		}
+
+		// Do not assign suffix comments to something that starts
+		// on an earlier line, so that in
+		//
+		//	x ( y
+		//		z ) // comment
+		//
+		// we assign the comment to z and not to x ( ... ).
+		if start.Line != end.Line {
+			continue
+		}
+		xcom := x.Comment()
+		for len(suffix) > 0 && end.Byte <= suffix[len(suffix)-1].Start.Byte {
+			if debug {
+				fmt.Fprintf(os.Stderr, "ASSIGN SUFFIX %q #%d\n", suffix[len(suffix)-1].Token, suffix[len(suffix)-1].Start.Byte)
+			}
+			xcom.Suffix = append(xcom.Suffix, suffix[len(suffix)-1])
+			suffix = suffix[:len(suffix)-1]
+		}
+	}
+
+	// We assigned suffix comments in reverse.
+	// If multiple suffix comments were appended to the same
+	// expression node, they are now in reverse. Fix that.
+	for _, x := range in.post {
+		reverseComments(x.Comment().Suffix)
+	}
+
+	// Remaining suffix comments go at beginning of file.
+	in.file.Before = append(in.file.Before, suffix...)
+}
+
+// reverseComments reverses the []Comment list.
+func reverseComments(list []Comment) {
+	for i, j := 0, len(list)-1; i < j; i, j = i+1, j-1 {
+		list[i], list[j] = list[j], list[i]
+	}
+}
+
+func (in *input) parseFile() {
+	in.file = new(FileSyntax)
+	var cb *CommentBlock
+	for {
+		switch in.peek() {
+		case '\n':
+			in.lex()
+			if cb != nil {
+				in.file.Stmt = append(in.file.Stmt, cb)
+				cb = nil
+			}
+		case _COMMENT:
+			tok := in.lex()
+			if cb == nil {
+				cb = &CommentBlock{Start: tok.pos}
+			}
+			com := cb.Comment()
+			com.Before = append(com.Before, Comment{Start: tok.pos, Token: tok.text})
+		case _EOF:
+			if cb != nil {
+				in.file.Stmt = append(in.file.Stmt, cb)
+			}
+			return
+		default:
+			in.parseStmt()
+			if cb != nil {
+				in.file.Stmt[len(in.file.Stmt)-1].Comment().Before = cb.Before
+				cb = nil
+			}
+		}
+	}
+}
+
+func (in *input) parseStmt() {
+	tok := in.lex()
+	start := tok.pos
+	end := tok.endPos
+	tokens := []string{tok.text}
+	for {
+		tok := in.lex()
+		switch {
+		case tok.kind.isEOL():
+			in.file.Stmt = append(in.file.Stmt, &Line{
+				Start: start,
+				Token: tokens,
+				End:   end,
+			})
+			return
+
+		case tok.kind == '(':
+			if next := in.peek(); next.isEOL() {
+				// Start of block: no more tokens on this line.
+				in.file.Stmt = append(in.file.Stmt, in.parseLineBlock(start, tokens, tok))
+				return
+			} else if next == ')' {
+				rparen := in.lex()
+				if in.peek().isEOL() {
+					// Empty block.
+					in.lex()
+					in.file.Stmt = append(in.file.Stmt, &LineBlock{
+						Start:  start,
+						Token:  tokens,
+						LParen: LParen{Pos: tok.pos},
+						RParen: RParen{Pos: rparen.pos},
+					})
+					return
+				}
+				// '( )' in the middle of the line, not a block.
+				tokens = append(tokens, tok.text, rparen.text)
+			} else {
+				// '(' in the middle of the line, not a block.
+				tokens = append(tokens, tok.text)
+			}
+
+		default:
+			tokens = append(tokens, tok.text)
+			end = tok.endPos
+		}
+	}
+}
+
+func (in *input) parseLineBlock(start Position, token []string, lparen token) *LineBlock {
+	x := &LineBlock{
+		Start:  start,
+		Token:  token,
+		LParen: LParen{Pos: lparen.pos},
+	}
+	var comments []Comment
+	for {
+		switch in.peek() {
+		case _EOLCOMMENT:
+			// Suffix comment, will be attached later by assignComments.
+			in.lex()
+		case '\n':
+			// Blank line. Add an empty comment to preserve it.
+			in.lex()
+			if len(comments) == 0 && len(x.Line) > 0 || len(comments) > 0 && comments[len(comments)-1].Token != "" {
+				comments = append(comments, Comment{})
+			}
+		case _COMMENT:
+			tok := in.lex()
+			comments = append(comments, Comment{Start: tok.pos, Token: tok.text})
+		case _EOF:
+			in.Error(fmt.Sprintf("syntax error (unterminated block started at %s:%d:%d)", in.filename, x.Start.Line, x.Start.LineRune))
+		case ')':
+			rparen := in.lex()
+			x.RParen.Before = comments
+			x.RParen.Pos = rparen.pos
+			if !in.peek().isEOL() {
+				in.Error("syntax error (expected newline after closing paren)")
+			}
+			in.lex()
+			return x
+		default:
+			l := in.parseLine()
+			x.Line = append(x.Line, l)
+			l.Comment().Before = comments
+			comments = nil
+		}
+	}
+}
+
+func (in *input) parseLine() *Line {
+	tok := in.lex()
+	if tok.kind.isEOL() {
+		in.Error("internal parse error: parseLine at end of line")
+	}
+	start := tok.pos
+	end := tok.endPos
+	tokens := []string{tok.text}
+	for {
+		tok := in.lex()
+		if tok.kind.isEOL() {
+			return &Line{
+				Start:   start,
+				Token:   tokens,
+				End:     end,
+				InBlock: true,
+			}
+		}
+		tokens = append(tokens, tok.text)
+		end = tok.endPos
+	}
+}
+
+var (
+	slashSlash = []byte("//")
+	moduleStr  = []byte("module")
+)
+
+// ModulePath returns the module path from the gomod file text.
+// If it cannot find a module path, it returns an empty string.
+// It is tolerant of unrelated problems in the go.mod file.
+func ModulePath(mod []byte) string {
+	for len(mod) > 0 {
+		line := mod
+		mod = nil
+		if i := bytes.IndexByte(line, '\n'); i >= 0 {
+			line, mod = line[:i], line[i+1:]
+		}
+		if i := bytes.Index(line, slashSlash); i >= 0 {
+			line = line[:i]
+		}
+		line = bytes.TrimSpace(line)
+		if !bytes.HasPrefix(line, moduleStr) {
+			continue
+		}
+		line = line[len(moduleStr):]
+		n := len(line)
+		line = bytes.TrimSpace(line)
+		if len(line) == n || len(line) == 0 {
+			continue
+		}
+
+		if line[0] == '"' || line[0] == '`' {
+			p, err := strconv.Unquote(string(line))
+			if err != nil {
+				return "" // malformed quoted string or multiline module path
+			}
+			return p
+		}
+
+		return string(line)
+	}
+	return "" // missing module path
+}

vendor/golang.org/x/mod/modfile/work.go

@@ -0,0 +1,234 @@
+// Copyright 2021 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 modfile
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+)
+
+// A WorkFile is the parsed, interpreted form of a go.work file.
+type WorkFile struct {
+	Go      *Go
+	Use     []*Use
+	Replace []*Replace
+
+	Syntax *FileSyntax
+}
+
+// A Use is a single directory statement.
+type Use struct {
+	Path       string // Use path of module.
+	ModulePath string // Module path in the comment.
+	Syntax     *Line
+}
+
+// ParseWork parses and returns a go.work file.
+//
+// file is the name of the file, used in positions and errors.
+//
+// data is the content of the file.
+//
+// fix is an optional function that canonicalizes module versions.
+// If fix is nil, all module versions must be canonical (module.CanonicalVersion
+// must return the same string).
+func ParseWork(file string, data []byte, fix VersionFixer) (*WorkFile, error) {
+	fs, err := parse(file, data)
+	if err != nil {
+		return nil, err
+	}
+	f := &WorkFile{
+		Syntax: fs,
+	}
+	var errs ErrorList
+
+	for _, x := range fs.Stmt {
+		switch x := x.(type) {
+		case *Line:
+			f.add(&errs, x, x.Token[0], x.Token[1:], fix)
+
+		case *LineBlock:
+			if len(x.Token) > 1 {
+				errs = append(errs, Error{
+					Filename: file,
+					Pos:      x.Start,
+					Err:      fmt.Errorf("unknown block type: %s", strings.Join(x.Token, " ")),
+				})
+				continue
+			}
+			switch x.Token[0] {
+			default:
+				errs = append(errs, Error{
+					Filename: file,
+					Pos:      x.Start,
+					Err:      fmt.Errorf("unknown block type: %s", strings.Join(x.Token, " ")),
+				})
+				continue
+			case "use", "replace":
+				for _, l := range x.Line {
+					f.add(&errs, l, x.Token[0], l.Token, fix)
+				}
+			}
+		}
+	}
+
+	if len(errs) > 0 {
+		return nil, errs
+	}
+	return f, nil
+}
+
+// Cleanup cleans up the file f after any edit operations.
+// To avoid quadratic behavior, modifications like DropRequire
+// clear the entry but do not remove it from the slice.
+// Cleanup cleans out all the cleared entries.
+func (f *WorkFile) Cleanup() {
+	w := 0
+	for _, r := range f.Use {
+		if r.Path != "" {
+			f.Use[w] = r
+			w++
+		}
+	}
+	f.Use = f.Use[:w]
+
+	w = 0
+	for _, r := range f.Replace {
+		if r.Old.Path != "" {
+			f.Replace[w] = r
+			w++
+		}
+	}
+	f.Replace = f.Replace[:w]
+
+	f.Syntax.Cleanup()
+}
+
+func (f *WorkFile) AddGoStmt(version string) error {
+	if !GoVersionRE.MatchString(version) {
+		return fmt.Errorf("invalid language version string %q", version)
+	}
+	if f.Go == nil {
+		stmt := &Line{Token: []string{"go", version}}
+		f.Go = &Go{
+			Version: version,
+			Syntax:  stmt,
+		}
+		// Find the first non-comment-only block that's and add
+		// the go statement before it. That will keep file comments at the top.
+		i := 0
+		for i = 0; i < len(f.Syntax.Stmt); i++ {
+			if _, ok := f.Syntax.Stmt[i].(*CommentBlock); !ok {
+				break
+			}
+		}
+		f.Syntax.Stmt = append(append(f.Syntax.Stmt[:i:i], stmt), f.Syntax.Stmt[i:]...)
+	} else {
+		f.Go.Version = version
+		f.Syntax.updateLine(f.Go.Syntax, "go", version)
+	}
+	return nil
+}
+
+func (f *WorkFile) AddUse(diskPath, modulePath string) error {
+	need := true
+	for _, d := range f.Use {
+		if d.Path == diskPath {
+			if need {
+				d.ModulePath = modulePath
+				f.Syntax.updateLine(d.Syntax, "use", AutoQuote(diskPath))
+				need = false
+			} else {
+				d.Syntax.markRemoved()
+				*d = Use{}
+			}
+		}
+	}
+
+	if need {
+		f.AddNewUse(diskPath, modulePath)
+	}
+	return nil
+}
+
+func (f *WorkFile) AddNewUse(diskPath, modulePath string) {
+	line := f.Syntax.addLine(nil, "use", AutoQuote(diskPath))
+	f.Use = append(f.Use, &Use{Path: diskPath, ModulePath: modulePath, Syntax: line})
+}
+
+func (f *WorkFile) SetUse(dirs []*Use) {
+	need := make(map[string]string)
+	for _, d := range dirs {
+		need[d.Path] = d.ModulePath
+	}
+
+	for _, d := range f.Use {
+		if modulePath, ok := need[d.Path]; ok {
+			d.ModulePath = modulePath
+		} else {
+			d.Syntax.markRemoved()
+			*d = Use{}
+		}
+	}
+
+	// TODO(#45713): Add module path to comment.
+
+	for diskPath, modulePath := range need {
+		f.AddNewUse(diskPath, modulePath)
+	}
+	f.SortBlocks()
+}
+
+func (f *WorkFile) DropUse(path string) error {
+	for _, d := range f.Use {
+		if d.Path == path {
+			d.Syntax.markRemoved()
+			*d = Use{}
+		}
+	}
+	return nil
+}
+
+func (f *WorkFile) AddReplace(oldPath, oldVers, newPath, newVers string) error {
+	return addReplace(f.Syntax, &f.Replace, oldPath, oldVers, newPath, newVers)
+}
+
+func (f *WorkFile) DropReplace(oldPath, oldVers string) error {
+	for _, r := range f.Replace {
+		if r.Old.Path == oldPath && r.Old.Version == oldVers {
+			r.Syntax.markRemoved()
+			*r = Replace{}
+		}
+	}
+	return nil
+}
+
+func (f *WorkFile) SortBlocks() {
+	f.removeDups() // otherwise sorting is unsafe
+
+	for _, stmt := range f.Syntax.Stmt {
+		block, ok := stmt.(*LineBlock)
+		if !ok {
+			continue
+		}
+		sort.SliceStable(block.Line, func(i, j int) bool {
+			return lineLess(block.Line[i], block.Line[j])
+		})
+	}
+}
+
+// removeDups removes duplicate replace directives.
+//
+// Later replace directives take priority.
+//
+// require directives are not de-duplicated. That's left up to higher-level
+// logic (MVS).
+//
+// retract directives are not de-duplicated since comments are
+// meaningful, and versions may be retracted multiple times.
+func (f *WorkFile) removeDups() {
+	removeDups(f.Syntax, nil, &f.Replace)
+}