github.com/gnolang/gno@v0.0.0-20240520182011-228e9d0192ce/gnovm/pkg/gnomod/read.go

// 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 here[1].
//
// [1]: https://cs.opensource.google/go/x/mod/+/master:LICENSE
//
// Mostly copied and modified from:
// - golang.org/x/mod/modfile/read.go
// - golang.org/x/mod/modfile/rule.go

package gnomod

import (
	"bytes"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"unicode"
	"unicode/utf8"

	"golang.org/x/mod/modfile"
	"golang.org/x/mod/module"
)

// 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        modfile.Position  // current input position
	comments   []modfile.Comment // accumulated comments

	// Parser state.
	file        *modfile.FileSyntax // returned top-level syntax tree
	parseErrors modfile.ErrorList   // errors encountered during parsing

	// Comment assignment state.
	pre  []modfile.Expr // all expressions, in preorder traversal
	post []modfile.Expr // all expressions, in postorder traversal
}

func newInput(filename string, data []byte) *input {
	return &input{
		filename:  filename,
		complete:  data,
		remaining: data,
		pos:       modfile.Position{Line: 1, LineRune: 1, Byte: 0},
	}
}

// parse parses the input file.
func parse(file string, data []byte) (f *modfile.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, modfile.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, modfile.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    modfile.Position
	endPos modfile.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 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, modfile.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 modfile.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 *modfile.LParen, *modfile.RParen:
		// nothing
	case *modfile.CommentBlock:
		// nothing
	case *modfile.Line:
		// nothing
	case *modfile.FileSyntax:
		for _, stmt := range x.Stmt {
			in.order(stmt)
		}
	case *modfile.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 []modfile.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 *modfile.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 []modfile.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(modfile.FileSyntax)
	var cb *modfile.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 = &modfile.CommentBlock{Start: tok.pos}
			}
			com := cb.Comment()
			com.Before = append(com.Before, modfile.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, &modfile.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, &modfile.LineBlock{
						Start:  start,
						Token:  tokens,
						LParen: modfile.LParen{Pos: tok.pos},
						RParen: modfile.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 modfile.Position, token []string, lparen token) *modfile.LineBlock {
	x := &modfile.LineBlock{
		Start:  start,
		Token:  token,
		LParen: modfile.LParen{Pos: lparen.pos},
	}
	var comments []modfile.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, modfile.Comment{})
			}
		case _COMMENT:
			tok := in.lex()
			comments = append(comments, modfile.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() *modfile.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 &modfile.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
}

func modulePathMajor(path string) (string, error) {
	_, major, ok := module.SplitPathVersion(path)
	if !ok {
		return "", fmt.Errorf("invalid module path")
	}
	return major, nil
}

func parseString(s *string) (string, error) {
	t := *s
	if strings.HasPrefix(t, `"`) {
		var err error
		if t, err = strconv.Unquote(t); err != nil {
			return "", err
		}
	} else if strings.ContainsAny(t, "\"'`") {
		// Other quotes are reserved both for possible future expansion
		// and to avoid confusion. For example if someone types 'x'
		// we want that to be a syntax error and not a literal x in literal quotation marks.
		return "", fmt.Errorf("unquoted string cannot contain quote")
	}
	*s = modfile.AutoQuote(t)
	return t, nil
}

func parseVersion(verb string, path string, s *string) (string, error) {
	t, err := parseString(s)
	if err != nil {
		return "", &modfile.Error{
			Verb:    verb,
			ModPath: path,
			Err: &module.InvalidVersionError{
				Version: *s,
				Err:     err,
			},
		}
	}

	cv := module.CanonicalVersion(t)
	if cv == "" {
		return "", &modfile.Error{
			Verb:    verb,
			ModPath: path,
			Err: &module.InvalidVersionError{
				Version: t,
				Err:     errors.New("must be of the form v1.2.3"),
			},
		}
	}

	*s = cv
	return *s, nil
}

func parseReplace(filename string, line *modfile.Line, verb string, args []string) (*modfile.Replace, *modfile.Error) {
	wrapModPathError := func(modPath string, err error) *modfile.Error {
		return &modfile.Error{
			Filename: filename,
			Pos:      line.Start,
			ModPath:  modPath,
			Verb:     verb,
			Err:      err,
		}
	}
	wrapError := func(err error) *modfile.Error {
		return &modfile.Error{
			Filename: filename,
			Pos:      line.Start,
			Err:      err,
		}
	}
	errorf := func(format string, args ...interface{}) *modfile.Error {
		return wrapError(fmt.Errorf(format, args...))
	}

	arrow := 2
	if len(args) >= 2 && args[1] == "=>" {
		arrow = 1
	}
	if len(args) < arrow+2 || len(args) > arrow+3 || args[arrow] != "=>" {
		return nil, errorf("usage: %s module/path [v1.2.3] => other/module v1.4\n\t or %s module/path [v1.2.3] => ../local/directory", verb, verb)
	}
	s, err := parseString(&args[0])
	if err != nil {
		return nil, errorf("invalid quoted string: %v", err)
	}
	pathMajor, err := modulePathMajor(s)
	if err != nil {
		return nil, wrapModPathError(s, err)
	}
	var v string
	if arrow == 2 {
		v, err = parseVersion(verb, s, &args[1])
		if err != nil {
			return nil, wrapError(err)
		}
		if err := module.CheckPathMajor(v, pathMajor); err != nil {
			return nil, wrapModPathError(s, err)
		}
	}
	ns, err := parseString(&args[arrow+1])
	if err != nil {
		return nil, errorf("invalid quoted string: %v", err)
	}
	nv := ""
	if len(args) == arrow+2 {
		if !modfile.IsDirectoryPath(ns) {
			if strings.Contains(ns, "@") {
				return nil, errorf("replacement module must match format 'path version', not 'path@version'")
			}
			return nil, errorf("replacement module without version must be directory path (rooted or starting with . or ..)")
		}
		if filepath.Separator == '/' && strings.Contains(ns, `\`) {
			return nil, errorf("replacement directory appears to be Windows path (on a non-windows system)")
		}
	}
	if len(args) == arrow+3 {
		nv, err = parseVersion(verb, ns, &args[arrow+2])
		if err != nil {
			return nil, wrapError(err)
		}
		if modfile.IsDirectoryPath(ns) {
			return nil, errorf("replacement module directory path %q cannot have version", ns)
		}
	}
	return &modfile.Replace{
		Old:    module.Version{Path: s, Version: v},
		New:    module.Version{Path: ns, Version: nv},
		Syntax: line,
	}, nil
}

var reDeprecation = regexp.MustCompile(`(?s)(?:^|\n\n)Deprecated: *(.*?)(?:$|\n\n)`)

// parseDeprecation extracts the text of comments on a "module" directive and
// extracts a deprecation message from that.
//
// A deprecation message is contained in a paragraph within a block of comments
// that starts with "Deprecated:" (case sensitive). The message runs until the
// end of the paragraph and does not include the "Deprecated:" prefix. If the
// comment block has multiple paragraphs that start with "Deprecated:",
// parseDeprecation returns the message from the first.
func parseDeprecation(block *modfile.LineBlock, line *modfile.Line) string {
	text := parseDirectiveComment(block, line)
	m := reDeprecation.FindStringSubmatch(text)
	if m == nil {
		return ""
	}
	return m[1]
}

// parseDirectiveComment extracts the text of comments on a directive.
// If the directive's lien does not have comments and is part of a block that
// does have comments, the block's comments are used.
func parseDirectiveComment(block *modfile.LineBlock, line *modfile.Line) string {
	comments := line.Comment()
	if block != nil && len(comments.Before) == 0 && len(comments.Suffix) == 0 {
		comments = block.Comment()
	}
	groups := [][]modfile.Comment{comments.Before, comments.Suffix}
	var lines []string
	for _, g := range groups {
		for _, c := range g {
			if !strings.HasPrefix(c.Token, "//") {
				continue // blank line
			}
			lines = append(lines, strings.TrimSpace(strings.TrimPrefix(c.Token, "//")))
		}
	}
	return strings.Join(lines, "\n")
}

// parseDraft returns whether the module is marked as draft.
func parseDraft(block *modfile.CommentBlock) bool {
	if len(block.Before) != 1 {
		return false
	}
	comment := block.Before[0]
	if strings.TrimSpace(strings.TrimPrefix(comment.Token, "//")) != "Draft" {
		return false
	}
	return true
}

// markLineAsRemoved modifies line so that it (and its end-of-line comment, if any)
// will be dropped by (*FileSyntax).Cleanup.
func markLineAsRemoved(line *modfile.Line) {
	line.Token = nil
	line.Comments.Suffix = nil
}

func updateLine(line *modfile.Line, tokens ...string) {
	if line.InBlock {
		tokens = tokens[1:]
	}
	line.Token = tokens
}

// setIndirect sets line to have (or not have) a "// indirect" comment.
func setIndirect(r *modfile.Require, indirect bool) {
	r.Indirect = indirect
	line := r.Syntax
	if isIndirect(line) == indirect {
		return
	}
	if indirect {
		// Adding comment.
		if len(line.Suffix) == 0 {
			// New comment.
			line.Suffix = []modfile.Comment{{Token: "// indirect", Suffix: true}}
			return
		}

		com := &line.Suffix[0]
		text := strings.TrimSpace(strings.TrimPrefix(com.Token, string(slashSlash)))
		if text == "" {
			// Empty comment.
			com.Token = "// indirect"
			return
		}

		// Insert at beginning of existing comment.
		com.Token = "// indirect; " + text
		return
	}

	// Removing comment.
	f := strings.TrimSpace(strings.TrimPrefix(line.Suffix[0].Token, string(slashSlash)))
	if f == "indirect" {
		// Remove whole comment.
		line.Suffix = nil
		return
	}

	// Remove comment prefix.
	com := &line.Suffix[0]
	i := strings.Index(com.Token, "indirect;")
	com.Token = "//" + com.Token[i+len("indirect;"):]
}

// isIndirect reports whether line has a "// indirect" comment,
// meaning it is in go.mod only for its effect on indirect dependencies,
// so that it can be dropped entirely once the effective version of the
// indirect dependency reaches the given minimum version.
func isIndirect(line *modfile.Line) bool {
	if len(line.Suffix) == 0 {
		return false
	}
	f := strings.Fields(strings.TrimPrefix(line.Suffix[0].Token, string(slashSlash)))
	return (len(f) == 1 && f[0] == "indirect" || len(f) > 1 && f[0] == "indirect;")
}

// 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 addLine(x *modfile.FileSyntax, hint modfile.Expr, tokens ...string) *modfile.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 *modfile.Line:
				if stmt.Token != nil && stmt.Token[0] == tokens[0] {
					hint = stmt
					break Loop
				}
			case *modfile.LineBlock:
				if stmt.Token[0] == tokens[0] {
					hint = stmt
					break Loop
				}
			}
		}
	}

	newLineAfter := func(i int) *modfile.Line {
		newl := &modfile.Line{Token: tokens}
		if i == len(x.Stmt) {
			x.Stmt = append(x.Stmt, newl)
		} else {
			x.Stmt = append(x.Stmt, nil)
			copy(x.Stmt[i+2:], x.Stmt[i+1:])
			x.Stmt[i+1] = newl
		}
		return newl
	}

	if hint != nil {
		for i, stmt := range x.Stmt {
			switch stmt := stmt.(type) {
			case *modfile.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 := &modfile.LineBlock{Token: stmt.Token[:1], Line: []*modfile.Line{stmt}}
					stmt.Token = stmt.Token[1:]
					x.Stmt[i] = block
					newl := &modfile.Line{Token: tokens[1:], InBlock: true}
					block.Line = append(block.Line, newl)
					return newl
				}

			case *modfile.LineBlock:
				if stmt == hint {
					if stmt.Token[0] != tokens[0] {
						return newLineAfter(i)
					}

					newl := &modfile.Line{Token: tokens[1:], InBlock: true}
					stmt.Line = append(stmt.Line, newl)
					return newl
				}

				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:])
						newl := &modfile.Line{Token: tokens[1:], InBlock: true}
						stmt.Line[j+1] = newl
						return newl
					}
				}
			}
		}
	}

	newl := &modfile.Line{Token: tokens}
	x.Stmt = append(x.Stmt, newl)
	return newl
}

func addReplace(syntax *modfile.FileSyntax, replace *[]*modfile.Replace, oldPath, oldVers, newPath, newVers string) error {
	need := true
	oldv := module.Version{Path: oldPath, Version: oldVers}
	newv := module.Version{Path: newPath, Version: newVers}
	tokens := []string{"replace", modfile.AutoQuote(oldPath)}
	if oldVers != "" {
		tokens = append(tokens, oldVers)
	}
	tokens = append(tokens, "=>", modfile.AutoQuote(newPath))
	if newVers != "" {
		tokens = append(tokens, newVers)
	}

	var hint *modfile.Line
	for _, r := range *replace {
		if r.Old.Path == oldPath && (oldVers == "" || r.Old.Version == oldVers) {
			if need {
				// Found replacement for old; update to use new.
				r.New = newv
				updateLine(r.Syntax, tokens...)
				need = false
				continue
			}
			// Already added; delete other replacements for same.
			markLineAsRemoved(r.Syntax)
			*r = modfile.Replace{}
		}
		if r.Old.Path == oldPath {
			hint = r.Syntax
		}
	}
	if need {
		*replace = append(*replace, &modfile.Replace{Old: oldv, New: newv, Syntax: addLine(syntax, hint, tokens...)})
	}
	return nil
}