internal/backport/go/build/read.go - website - Git at Google

 // Copyright 2012 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 build

 import (
 	"bufio"
 	"bytes"
 	"errors"
 	"fmt"
 	"golang.org/x/website/internal/backport/go/ast"
 	"golang.org/x/website/internal/backport/go/parser"
 	"golang.org/x/website/internal/backport/go/token"
 	"io"
 	"strconv"
 	"strings"
 	"unicode"
 	"unicode/utf8"
 )

 type importReader struct {
 	b    *bufio.Reader
 	buf  []byte
 	peek byte
 	err  error
 	eof  bool
 	nerr int
 	pos  token.Position
 }

 var bom = []byte{0xef, 0xbb, 0xbf}

 func newImportReader(name string, r io.Reader) *importReader {
 	b := bufio.NewReader(r)
 	// Remove leading UTF-8 BOM.
 	// Per https://golang.org/ref/spec#Source_code_representation:
 	// a compiler may ignore a UTF-8-encoded byte order mark (U+FEFF)
 	// if it is the first Unicode code point in the source text.
 	if leadingBytes, err := b.Peek(3); err == nil && bytes.Equal(leadingBytes, bom) {
 		b.Discard(3)
 	}
 	return &importReader{
 		b: b,
 		pos: token.Position{
 			Filename: name,
 			Line:     1,
 			Column:   1,
 		},
 	}
 }

 func isIdent(c byte) bool {
 	return 'A' <= c && c <= 'Z' || 'a' <= c && c <= 'z' || '0' <= c && c <= '9' || c == '_' || c >= utf8.RuneSelf
 }

 var (
 	errSyntax = errors.New("syntax error")
 	errNUL    = errors.New("unexpected NUL in input")
 )

 // syntaxError records a syntax error, but only if an I/O error has not already been recorded.
 func (r *importReader) syntaxError() {
 	if r.err == nil {
 		r.err = errSyntax
 	}
 }

 // readByte reads the next byte from the input, saves it in buf, and returns it.
 // If an error occurs, readByte records the error in r.err and returns 0.
 func (r *importReader) readByte() byte {
 	c, err := r.b.ReadByte()
 	if err == nil {
 		r.buf = append(r.buf, c)
 		if c == 0 {
 			err = errNUL
 		}
 	}
 	if err != nil {
 		if err == io.EOF {
 			r.eof = true
 		} else if r.err == nil {
 			r.err = err
 		}
 		c = 0
 	}
 	return c
 }

 // readByteNoBuf is like readByte but doesn't buffer the byte.
 // It exhausts r.buf before reading from r.b.
 func (r *importReader) readByteNoBuf() byte {
 	var c byte
 	var err error
 	if len(r.buf) > 0 {
 		c = r.buf[0]
 		r.buf = r.buf[1:]
 	} else {
 		c, err = r.b.ReadByte()
 		if err == nil && c == 0 {
 			err = errNUL
 		}
 	}

 	if err != nil {
 		if err == io.EOF {
 			r.eof = true
 		} else if r.err == nil {
 			r.err = err
 		}
 		return 0
 	}
 	r.pos.Offset++
 	if c == '\n' {
 		r.pos.Line++
 		r.pos.Column = 1
 	} else {
 		r.pos.Column++
 	}
 	return c
 }

 // peekByte returns the next byte from the input reader but does not advance beyond it.
 // If skipSpace is set, peekByte skips leading spaces and comments.
 func (r *importReader) peekByte(skipSpace bool) byte {
 	if r.err != nil {
 		if r.nerr++; r.nerr > 10000 {
 			panic("go/build: import reader looping")
 		}
 		return 0
 	}

 	// Use r.peek as first input byte.
 	// Don't just return r.peek here: it might have been left by peekByte(false)
 	// and this might be peekByte(true).
 	c := r.peek
 	if c == 0 {
 		c = r.readByte()
 	}
 	for r.err == nil && !r.eof {
 		if skipSpace {
 			// For the purposes of this reader, semicolons are never necessary to
 			// understand the input and are treated as spaces.
 			switch c {
 			case ' ', '\f', '\t', '\r', '\n', ';':
 				c = r.readByte()
 				continue

 			case '/':
 				c = r.readByte()
 				if c == '/' {
 					for c != '\n' && r.err == nil && !r.eof {
 						c = r.readByte()
 					}
 				} else if c == '*' {
 					var c1 byte
 					for (c != '*' || c1 != '/') && r.err == nil {
 						if r.eof {
 							r.syntaxError()
 						}
 						c, c1 = c1, r.readByte()
 					}
 				} else {
 					r.syntaxError()
 				}
 				c = r.readByte()
 				continue
 			}
 		}
 		break
 	}
 	r.peek = c
 	return r.peek
 }

 // nextByte is like peekByte but advances beyond the returned byte.
 func (r *importReader) nextByte(skipSpace bool) byte {
 	c := r.peekByte(skipSpace)
 	r.peek = 0
 	return c
 }

 var goEmbed = []byte("go:embed")

 // findEmbed advances the input reader to the next //go:embed comment.
 // It reports whether it found a comment.
 // (Otherwise it found an error or EOF.)
 func (r *importReader) findEmbed(first bool) bool {
 	// The import block scan stopped after a non-space character,
 	// so the reader is not at the start of a line on the first call.
 	// After that, each //go:embed extraction leaves the reader
 	// at the end of a line.
 	startLine := !first
 	var c byte
 	for r.err == nil && !r.eof {
 		c = r.readByteNoBuf()
 	Reswitch:
 		switch c {
 		default:
 			startLine = false

 		case '\n':
 			startLine = true

 		case ' ', '\t':
 			// leave startLine alone

 		case '"':
 			startLine = false
 			for r.err == nil {
 				if r.eof {
 					r.syntaxError()
 				}
 				c = r.readByteNoBuf()
 				if c == '\\' {
 					r.readByteNoBuf()
 					if r.err != nil {
 						r.syntaxError()
 						return false
 					}
 					continue
 				}
 				if c == '"' {
 					c = r.readByteNoBuf()
 					goto Reswitch
 				}
 			}
 			goto Reswitch

 		case '`':
 			startLine = false
 			for r.err == nil {
 				if r.eof {
 					r.syntaxError()
 				}
 				c = r.readByteNoBuf()
 				if c == '`' {
 					c = r.readByteNoBuf()
 					goto Reswitch
 				}
 			}

 		case '\'':
 			startLine = false
 			for r.err == nil {
 				if r.eof {
 					r.syntaxError()
 				}
 				c = r.readByteNoBuf()
 				if c == '\\' {
 					r.readByteNoBuf()
 					if r.err != nil {
 						r.syntaxError()
 						return false
 					}
 					continue
 				}
 				if c == '\'' {
 					c = r.readByteNoBuf()
 					goto Reswitch
 				}
 			}

 		case '/':
 			c = r.readByteNoBuf()
 			switch c {
 			default:
 				startLine = false
 				goto Reswitch

 			case '*':
 				var c1 byte
 				for (c != '*' || c1 != '/') && r.err == nil {
 					if r.eof {
 						r.syntaxError()
 					}
 					c, c1 = c1, r.readByteNoBuf()
 				}
 				startLine = false

 			case '/':
 				if startLine {
 					// Try to read this as a //go:embed comment.
 					for i := range goEmbed {
 						c = r.readByteNoBuf()
 						if c != goEmbed[i] {
 							goto SkipSlashSlash
 						}
 					}
 					c = r.readByteNoBuf()
 					if c == ' ' || c == '\t' {
 						// Found one!
 						return true
 					}
 				}
 			SkipSlashSlash:
 				for c != '\n' && r.err == nil && !r.eof {
 					c = r.readByteNoBuf()
 				}
 				startLine = true
 			}
 		}
 	}
 	return false
 }

 // readKeyword reads the given keyword from the input.
 // If the keyword is not present, readKeyword records a syntax error.
 func (r *importReader) readKeyword(kw string) {
 	r.peekByte(true)
 	for i := 0; i < len(kw); i++ {
 		if r.nextByte(false) != kw[i] {
 			r.syntaxError()
 			return
 		}
 	}
 	if isIdent(r.peekByte(false)) {
 		r.syntaxError()
 	}
 }

 // readIdent reads an identifier from the input.
 // If an identifier is not present, readIdent records a syntax error.
 func (r *importReader) readIdent() {
 	c := r.peekByte(true)
 	if !isIdent(c) {
 		r.syntaxError()
 		return
 	}
 	for isIdent(r.peekByte(false)) {
 		r.peek = 0
 	}
 }

 // readString reads a quoted string literal from the input.
 // If an identifier is not present, readString records a syntax error.
 func (r *importReader) readString() {
 	switch r.nextByte(true) {
 	case '`':
 		for r.err == nil {
 			if r.nextByte(false) == '`' {
 				break
 			}
 			if r.eof {
 				r.syntaxError()
 			}
 		}
 	case '"':
 		for r.err == nil {
 			c := r.nextByte(false)
 			if c == '"' {
 				break
 			}
 			if r.eof || c == '\n' {
 				r.syntaxError()
 			}
 			if c == '\\' {
 				r.nextByte(false)
 			}
 		}
 	default:
 		r.syntaxError()
 	}
 }

 // readImport reads an import clause - optional identifier followed by quoted string -
 // from the input.
 func (r *importReader) readImport() {
 	c := r.peekByte(true)
 	if c == '.' {
 		r.peek = 0
 	} else if isIdent(c) {
 		r.readIdent()
 	}
 	r.readString()
 }

 // readComments is like io.ReadAll, except that it only reads the leading
 // block of comments in the file.
 func readComments(f io.Reader) ([]byte, error) {
 	r := newImportReader("", f)
 	r.peekByte(true)
 	if r.err == nil && !r.eof {
 		// Didn't reach EOF, so must have found a non-space byte. Remove it.
 		r.buf = r.buf[:len(r.buf)-1]
 	}
 	return r.buf, r.err
 }

 // readGoInfo expects a Go file as input and reads the file up to and including the import section.
 // It records what it learned in *info.
 // If info.fset is non-nil, readGoInfo parses the file and sets info.parsed, info.parseErr,
 // info.imports, info.embeds, and info.embedErr.
 //
 // It only returns an error if there are problems reading the file,
 // not for syntax errors in the file itself.
 func readGoInfo(f io.Reader, info *fileInfo) error {
 	r := newImportReader(info.name, f)

 	r.readKeyword("package")
 	r.readIdent()
 	for r.peekByte(true) == 'i' {
 		r.readKeyword("import")
 		if r.peekByte(true) == '(' {
 			r.nextByte(false)
 			for r.peekByte(true) != ')' && r.err == nil {
 				r.readImport()
 			}
 			r.nextByte(false)
 		} else {
 			r.readImport()
 		}
 	}

 	info.header = r.buf

 	// If we stopped successfully before EOF, we read a byte that told us we were done.
 	// Return all but that last byte, which would cause a syntax error if we let it through.
 	if r.err == nil && !r.eof {
 		info.header = r.buf[:len(r.buf)-1]
 	}

 	// If we stopped for a syntax error, consume the whole file so that
 	// we are sure we don't change the errors that go/parser returns.
 	if r.err == errSyntax {
 		r.err = nil
 		for r.err == nil && !r.eof {
 			r.readByte()
 		}
 		info.header = r.buf
 	}
 	if r.err != nil {
 		return r.err
 	}

 	if info.fset == nil {
 		return nil
 	}

 	// Parse file header & record imports.
 	info.parsed, info.parseErr = parser.ParseFile(info.fset, info.name, info.header, parser.ImportsOnly|parser.ParseComments)
 	if info.parseErr != nil {
 		return nil
 	}

 	hasEmbed := false
 	for _, decl := range info.parsed.Decls {
 		d, ok := decl.(*ast.GenDecl)
 		if !ok {
 			continue
 		}
 		for _, dspec := range d.Specs {
 			spec, ok := dspec.(*ast.ImportSpec)
 			if !ok {
 				continue
 			}
 			quoted := spec.Path.Value
 			path, err := strconv.Unquote(quoted)
 			if err != nil {
 				return fmt.Errorf("parser returned invalid quoted string: <%s>", quoted)
 			}
 			if path == "embed" {
 				hasEmbed = true
 			}

 			doc := spec.Doc
 			if doc == nil && len(d.Specs) == 1 {
 				doc = d.Doc
 			}
 			info.imports = append(info.imports, fileImport{path, spec.Pos(), doc})
 		}
 	}

 	// If the file imports "embed",
 	// we have to look for //go:embed comments
 	// in the remainder of the file.
 	// The compiler will enforce the mapping of comments to
 	// declared variables. We just need to know the patterns.
 	// If there were //go:embed comments earlier in the file
 	// (near the package statement or imports), the compiler
 	// will reject them. They can be (and have already been) ignored.
 	if hasEmbed {
 		var line []byte
 		for first := true; r.findEmbed(first); first = false {
 			line = line[:0]
 			pos := r.pos
 			for {
 				c := r.readByteNoBuf()
 				if c == '\n' || r.err != nil || r.eof {
 					break
 				}
 				line = append(line, c)
 			}
 			// Add args if line is well-formed.
 			// Ignore badly-formed lines - the compiler will report them when it finds them,
 			// and we can pretend they are not there to help go list succeed with what it knows.
 			embs, err := parseGoEmbed(string(line), pos)
 			if err == nil {
 				info.embeds = append(info.embeds, embs...)
 			}
 		}
 	}

 	return nil
 }

 // parseGoEmbed parses the text following "//go:embed" to extract the glob patterns.
 // It accepts unquoted space-separated patterns as well as double-quoted and back-quoted Go strings.
 // This is based on a similar function in cmd/compile/internal/gc/noder.go;
 // this version calculates position information as well.
 func parseGoEmbed(args string, pos token.Position) ([]fileEmbed, error) {
 	trimBytes := func(n int) {
 		pos.Offset += n
 		pos.Column += utf8.RuneCountInString(args[:n])
 		args = args[n:]
 	}
 	trimSpace := func() {
 		trim := strings.TrimLeftFunc(args, unicode.IsSpace)
 		trimBytes(len(args) - len(trim))
 	}

 	var list []fileEmbed
 	for trimSpace(); args != ""; trimSpace() {
 		var path string
 		pathPos := pos
 	Switch:
 		switch args[0] {
 		default:
 			i := len(args)
 			for j, c := range args {
 				if unicode.IsSpace(c) {
 					i = j
 					break
 				}
 			}
 			path = args[:i]
 			trimBytes(i)

 		case '`':
 			var ok bool
 			path, _, ok = stringsCut(args[1:], "`")
 			if !ok {
 				return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args)
 			}
 			trimBytes(1 + len(path) + 1)

 		case '"':
 			i := 1
 			for ; i < len(args); i++ {
 				if args[i] == '\\' {
 					i++
 					continue
 				}
 				if args[i] == '"' {
 					q, err := strconv.Unquote(args[:i+1])
 					if err != nil {
 						return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args[:i+1])
 					}
 					path = q
 					trimBytes(i + 1)
 					break Switch
 				}
 			}
 			if i >= len(args) {
 				return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args)
 			}
 		}

 		if args != "" {
 			r, _ := utf8.DecodeRuneInString(args)
 			if !unicode.IsSpace(r) {
 				return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args)
 			}
 		}
 		list = append(list, fileEmbed{path, pathPos})
 	}
 	return list, nil
 }
	// Copyright 2012 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 build

	import (
	"bufio"
	"bytes"
	"errors"
	"fmt"
	"golang.org/x/website/internal/backport/go/ast"
	"golang.org/x/website/internal/backport/go/parser"
	"golang.org/x/website/internal/backport/go/token"
	"io"
	"strconv"
	"strings"
	"unicode"
	"unicode/utf8"
	)

	type importReader struct {
	b *bufio.Reader
	buf []byte
	peek byte
	err error
	eof bool
	nerr int
	pos token.Position
	}

	var bom = []byte{0xef, 0xbb, 0xbf}

	func newImportReader(name string, r io.Reader) *importReader {
	b := bufio.NewReader(r)
	// Remove leading UTF-8 BOM.
	// Per https://golang.org/ref/spec#Source_code_representation:
	// a compiler may ignore a UTF-8-encoded byte order mark (U+FEFF)
	// if it is the first Unicode code point in the source text.
	if leadingBytes, err := b.Peek(3); err == nil && bytes.Equal(leadingBytes, bom) {
	b.Discard(3)
	}
	return &importReader{
	b: b,
	pos: token.Position{
	Filename: name,
	Line: 1,
	Column: 1,
	},
	}
	}

	func isIdent(c byte) bool {
	return 'A' <= c && c <= 'Z' \|\| 'a' <= c && c <= 'z' \|\| '0' <= c && c <= '9' \|\| c == '_' \|\| c >= utf8.RuneSelf
	}

	var (
	errSyntax = errors.New("syntax error")
	errNUL = errors.New("unexpected NUL in input")
	)

	// syntaxError records a syntax error, but only if an I/O error has not already been recorded.
	func (r *importReader) syntaxError() {
	if r.err == nil {
	r.err = errSyntax
	}
	}

	// readByte reads the next byte from the input, saves it in buf, and returns it.
	// If an error occurs, readByte records the error in r.err and returns 0.
	func (r *importReader) readByte() byte {
	c, err := r.b.ReadByte()
	if err == nil {
	r.buf = append(r.buf, c)
	if c == 0 {
	err = errNUL
	}
	}
	if err != nil {
	if err == io.EOF {
	r.eof = true
	} else if r.err == nil {
	r.err = err
	}
	c = 0
	}
	return c
	}

	// readByteNoBuf is like readByte but doesn't buffer the byte.
	// It exhausts r.buf before reading from r.b.
	func (r *importReader) readByteNoBuf() byte {
	var c byte
	var err error
	if len(r.buf) > 0 {
	c = r.buf[0]
	r.buf = r.buf[1:]
	} else {
	c, err = r.b.ReadByte()
	if err == nil && c == 0 {
	err = errNUL
	}
	}

	if err != nil {
	if err == io.EOF {
	r.eof = true
	} else if r.err == nil {
	r.err = err
	}
	return 0
	}
	r.pos.Offset++
	if c == '\n' {
	r.pos.Line++
	r.pos.Column = 1
	} else {
	r.pos.Column++
	}
	return c
	}

	// peekByte returns the next byte from the input reader but does not advance beyond it.
	// If skipSpace is set, peekByte skips leading spaces and comments.
	func (r *importReader) peekByte(skipSpace bool) byte {
	if r.err != nil {
	if r.nerr++; r.nerr > 10000 {
	panic("go/build: import reader looping")
	}
	return 0
	}

	// Use r.peek as first input byte.
	// Don't just return r.peek here: it might have been left by peekByte(false)
	// and this might be peekByte(true).
	c := r.peek
	if c == 0 {
	c = r.readByte()
	}
	for r.err == nil && !r.eof {
	if skipSpace {
	// For the purposes of this reader, semicolons are never necessary to
	// understand the input and are treated as spaces.
	switch c {
	case ' ', '\f', '\t', '\r', '\n', ';':
	c = r.readByte()
	continue

	case '/':
	c = r.readByte()
	if c == '/' {
	for c != '\n' && r.err == nil && !r.eof {
	c = r.readByte()
	}
	} else if c == '*' {
	var c1 byte
	for (c != '*' \|\| c1 != '/') && r.err == nil {
	if r.eof {
	r.syntaxError()
	}
	c, c1 = c1, r.readByte()
	}
	} else {
	r.syntaxError()
	}
	c = r.readByte()
	continue
	}
	}
	break
	}
	r.peek = c
	return r.peek
	}

	// nextByte is like peekByte but advances beyond the returned byte.
	func (r *importReader) nextByte(skipSpace bool) byte {
	c := r.peekByte(skipSpace)
	r.peek = 0
	return c
	}

	var goEmbed = []byte("go:embed")

	// findEmbed advances the input reader to the next //go:embed comment.
	// It reports whether it found a comment.
	// (Otherwise it found an error or EOF.)
	func (r *importReader) findEmbed(first bool) bool {
	// The import block scan stopped after a non-space character,
	// so the reader is not at the start of a line on the first call.
	// After that, each //go:embed extraction leaves the reader
	// at the end of a line.
	startLine := !first
	var c byte
	for r.err == nil && !r.eof {
	c = r.readByteNoBuf()
	Reswitch:
	switch c {
	default:
	startLine = false

	case '\n':
	startLine = true

	case ' ', '\t':
	// leave startLine alone

	case '"':
	startLine = false
	for r.err == nil {
	if r.eof {
	r.syntaxError()
	}
	c = r.readByteNoBuf()
	if c == '\\' {
	r.readByteNoBuf()
	if r.err != nil {
	r.syntaxError()
	return false
	}
	continue
	}
	if c == '"' {
	c = r.readByteNoBuf()
	goto Reswitch
	}
	}
	goto Reswitch

	case '`':
	startLine = false
	for r.err == nil {
	if r.eof {
	r.syntaxError()
	}
	c = r.readByteNoBuf()
	if c == '`' {
	c = r.readByteNoBuf()
	goto Reswitch
	}
	}

	case '\'':
	startLine = false
	for r.err == nil {
	if r.eof {
	r.syntaxError()
	}
	c = r.readByteNoBuf()
	if c == '\\' {
	r.readByteNoBuf()
	if r.err != nil {
	r.syntaxError()
	return false
	}
	continue
	}
	if c == '\'' {
	c = r.readByteNoBuf()
	goto Reswitch
	}
	}

	case '/':
	c = r.readByteNoBuf()
	switch c {
	default:
	startLine = false
	goto Reswitch

	case '*':
	var c1 byte
	for (c != '*' \|\| c1 != '/') && r.err == nil {
	if r.eof {
	r.syntaxError()
	}
	c, c1 = c1, r.readByteNoBuf()
	}
	startLine = false

	case '/':
	if startLine {
	// Try to read this as a //go:embed comment.
	for i := range goEmbed {
	c = r.readByteNoBuf()
	if c != goEmbed[i] {
	goto SkipSlashSlash
	}
	}
	c = r.readByteNoBuf()
	if c == ' ' \|\| c == '\t' {
	// Found one!
	return true
	}
	}
	SkipSlashSlash:
	for c != '\n' && r.err == nil && !r.eof {
	c = r.readByteNoBuf()
	}
	startLine = true
	}
	}
	}
	return false
	}

	// readKeyword reads the given keyword from the input.
	// If the keyword is not present, readKeyword records a syntax error.
	func (r *importReader) readKeyword(kw string) {
	r.peekByte(true)
	for i := 0; i < len(kw); i++ {
	if r.nextByte(false) != kw[i] {
	r.syntaxError()
	return
	}
	}
	if isIdent(r.peekByte(false)) {
	r.syntaxError()
	}
	}

	// readIdent reads an identifier from the input.
	// If an identifier is not present, readIdent records a syntax error.
	func (r *importReader) readIdent() {
	c := r.peekByte(true)
	if !isIdent(c) {
	r.syntaxError()
	return
	}
	for isIdent(r.peekByte(false)) {
	r.peek = 0
	}
	}

	// readString reads a quoted string literal from the input.
	// If an identifier is not present, readString records a syntax error.
	func (r *importReader) readString() {
	switch r.nextByte(true) {
	case '`':
	for r.err == nil {
	if r.nextByte(false) == '`' {
	break
	}
	if r.eof {
	r.syntaxError()
	}
	}
	case '"':
	for r.err == nil {
	c := r.nextByte(false)
	if c == '"' {
	break
	}
	if r.eof \|\| c == '\n' {
	r.syntaxError()
	}
	if c == '\\' {
	r.nextByte(false)
	}
	}
	default:
	r.syntaxError()
	}
	}

	// readImport reads an import clause - optional identifier followed by quoted string -
	// from the input.
	func (r *importReader) readImport() {
	c := r.peekByte(true)
	if c == '.' {
	r.peek = 0
	} else if isIdent(c) {
	r.readIdent()
	}
	r.readString()
	}

	// readComments is like io.ReadAll, except that it only reads the leading
	// block of comments in the file.
	func readComments(f io.Reader) ([]byte, error) {
	r := newImportReader("", f)
	r.peekByte(true)
	if r.err == nil && !r.eof {
	// Didn't reach EOF, so must have found a non-space byte. Remove it.
	r.buf = r.buf[:len(r.buf)-1]
	}
	return r.buf, r.err
	}

	// readGoInfo expects a Go file as input and reads the file up to and including the import section.
	// It records what it learned in *info.
	// If info.fset is non-nil, readGoInfo parses the file and sets info.parsed, info.parseErr,
	// info.imports, info.embeds, and info.embedErr.
	//
	// It only returns an error if there are problems reading the file,
	// not for syntax errors in the file itself.
	func readGoInfo(f io.Reader, info *fileInfo) error {
	r := newImportReader(info.name, f)

	r.readKeyword("package")
	r.readIdent()
	for r.peekByte(true) == 'i' {
	r.readKeyword("import")
	if r.peekByte(true) == '(' {
	r.nextByte(false)
	for r.peekByte(true) != ')' && r.err == nil {
	r.readImport()
	}
	r.nextByte(false)
	} else {
	r.readImport()
	}
	}

	info.header = r.buf

	// If we stopped successfully before EOF, we read a byte that told us we were done.
	// Return all but that last byte, which would cause a syntax error if we let it through.
	if r.err == nil && !r.eof {
	info.header = r.buf[:len(r.buf)-1]
	}

	// If we stopped for a syntax error, consume the whole file so that
	// we are sure we don't change the errors that go/parser returns.
	if r.err == errSyntax {
	r.err = nil
	for r.err == nil && !r.eof {
	r.readByte()
	}
	info.header = r.buf
	}
	if r.err != nil {
	return r.err
	}

	if info.fset == nil {
	return nil
	}

	// Parse file header & record imports.
	info.parsed, info.parseErr = parser.ParseFile(info.fset, info.name, info.header, parser.ImportsOnly\|parser.ParseComments)
	if info.parseErr != nil {
	return nil
	}

	hasEmbed := false
	for _, decl := range info.parsed.Decls {
	d, ok := decl.(*ast.GenDecl)
	if !ok {
	continue
	}
	for _, dspec := range d.Specs {
	spec, ok := dspec.(*ast.ImportSpec)
	if !ok {
	continue
	}
	quoted := spec.Path.Value
	path, err := strconv.Unquote(quoted)
	if err != nil {
	return fmt.Errorf("parser returned invalid quoted string: <%s>", quoted)
	}
	if path == "embed" {
	hasEmbed = true
	}

	doc := spec.Doc
	if doc == nil && len(d.Specs) == 1 {
	doc = d.Doc
	}
	info.imports = append(info.imports, fileImport{path, spec.Pos(), doc})
	}
	}

	// If the file imports "embed",
	// we have to look for //go:embed comments
	// in the remainder of the file.
	// The compiler will enforce the mapping of comments to
	// declared variables. We just need to know the patterns.
	// If there were //go:embed comments earlier in the file
	// (near the package statement or imports), the compiler
	// will reject them. They can be (and have already been) ignored.
	if hasEmbed {
	var line []byte
	for first := true; r.findEmbed(first); first = false {
	line = line[:0]
	pos := r.pos
	for {
	c := r.readByteNoBuf()
	if c == '\n' \|\| r.err != nil \|\| r.eof {
	break
	}
	line = append(line, c)
	}
	// Add args if line is well-formed.
	// Ignore badly-formed lines - the compiler will report them when it finds them,
	// and we can pretend they are not there to help go list succeed with what it knows.
	embs, err := parseGoEmbed(string(line), pos)
	if err == nil {
	info.embeds = append(info.embeds, embs...)
	}
	}
	}

	return nil
	}

	// parseGoEmbed parses the text following "//go:embed" to extract the glob patterns.
	// It accepts unquoted space-separated patterns as well as double-quoted and back-quoted Go strings.
	// This is based on a similar function in cmd/compile/internal/gc/noder.go;
	// this version calculates position information as well.
	func parseGoEmbed(args string, pos token.Position) ([]fileEmbed, error) {
	trimBytes := func(n int) {
	pos.Offset += n
	pos.Column += utf8.RuneCountInString(args[:n])
	args = args[n:]
	}
	trimSpace := func() {
	trim := strings.TrimLeftFunc(args, unicode.IsSpace)
	trimBytes(len(args) - len(trim))
	}

	var list []fileEmbed
	for trimSpace(); args != ""; trimSpace() {
	var path string
	pathPos := pos
	Switch:
	switch args[0] {
	default:
	i := len(args)
	for j, c := range args {
	if unicode.IsSpace(c) {
	i = j
	break
	}
	}
	path = args[:i]
	trimBytes(i)

	case '`':
	var ok bool
	path, _, ok = stringsCut(args[1:], "`")
	if !ok {
	return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args)
	}
	trimBytes(1 + len(path) + 1)

	case '"':
	i := 1
	for ; i < len(args); i++ {
	if args[i] == '\\' {
	i++
	continue
	}
	if args[i] == '"' {
	q, err := strconv.Unquote(args[:i+1])
	if err != nil {
	return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args[:i+1])
	}
	path = q
	trimBytes(i + 1)
	break Switch
	}
	}
	if i >= len(args) {
	return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args)
	}
	}

	if args != "" {
	r, _ := utf8.DecodeRuneInString(args)
	if !unicode.IsSpace(r) {
	return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args)
	}
	}
	list = append(list, fileEmbed{path, pathPos})
	}
	return list, nil
	}