[gostls13.git] / src / cmd / go / internal / modindex / build.go

// Copyright 2011 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.

// This file is a lightly modified copy go/build/build.go with unused parts
// removed.

package modindex

import (
        "bytes"
        "cmd/go/internal/fsys"
        "cmd/go/internal/str"
        "errors"
        "fmt"
        "go/ast"
        "go/build"
        "go/build/constraint"
        "go/token"
        "io"
        "io/fs"
        "path/filepath"
        "sort"
        "strings"
        "unicode"
        "unicode/utf8"
)

// A Context specifies the supporting context for a build.
type Context struct {
        GOARCH string // target architecture
        GOOS   string // target operating system
        GOROOT string // Go root
        GOPATH string // Go paths

        // Dir is the caller's working directory, or the empty string to use
        // the current directory of the running process. In module mode, this is used
        // to locate the main module.
        //
        // If Dir is non-empty, directories passed to Import and ImportDir must
        // be absolute.
        Dir string

        CgoEnabled  bool   // whether cgo files are included
        UseAllFiles bool   // use files regardless of +build lines, file names
        Compiler    string // compiler to assume when computing target paths

        // The build, tool, and release tags specify build constraints
        // that should be considered satisfied when processing +build lines.
        // Clients creating a new context may customize BuildTags, which
        // defaults to empty, but it is usually an error to customize ToolTags or ReleaseTags.
        // ToolTags defaults to build tags appropriate to the current Go toolchain configuration.
        // ReleaseTags defaults to the list of Go releases the current release is compatible with.
        // BuildTags is not set for the Default build Context.
        // In addition to the BuildTags, ToolTags, and ReleaseTags, build constraints
        // consider the values of GOARCH and GOOS as satisfied tags.
        // The last element in ReleaseTags is assumed to be the current release.
        BuildTags   []string
        ToolTags    []string
        ReleaseTags []string

        // The install suffix specifies a suffix to use in the name of the installation
        // directory. By default it is empty, but custom builds that need to keep
        // their outputs separate can set InstallSuffix to do so. For example, when
        // using the race detector, the go command uses InstallSuffix = "race", so
        // that on a Linux/386 system, packages are written to a directory named
        // "linux_386_race" instead of the usual "linux_386".
        InstallSuffix string

        // By default, Import uses the operating system's file system calls
        // to read directories and files. To read from other sources,
        // callers can set the following functions. They all have default
        // behaviors that use the local file system, so clients need only set
        // the functions whose behaviors they wish to change.

        // JoinPath joins the sequence of path fragments into a single path.
        // If JoinPath is nil, Import uses filepath.Join.
        JoinPath func(elem ...string) string

        // SplitPathList splits the path list into a slice of individual paths.
        // If SplitPathList is nil, Import uses filepath.SplitList.
        SplitPathList func(list string) []string

        // IsAbsPath reports whether path is an absolute path.
        // If IsAbsPath is nil, Import uses filepath.IsAbs.
        IsAbsPath func(path string) bool

        // IsDir reports whether the path names a directory.
        // If IsDir is nil, Import calls os.Stat and uses the result's IsDir method.
        IsDir func(path string) bool

        // HasSubdir reports whether dir is lexically a subdirectory of
        // root, perhaps multiple levels below. It does not try to check
        // whether dir exists.
        // If so, HasSubdir sets rel to a slash-separated path that
        // can be joined to root to produce a path equivalent to dir.
        // If HasSubdir is nil, Import uses an implementation built on
        // filepath.EvalSymlinks.
        HasSubdir func(root, dir string) (rel string, ok bool)

        // ReadDir returns a slice of fs.FileInfo, sorted by Name,
        // describing the content of the named directory.
        // If ReadDir is nil, Import uses ioutil.ReadDir.
        ReadDir func(dir string) ([]fs.FileInfo, error)

        // OpenFile opens a file (not a directory) for reading.
        // If OpenFile is nil, Import uses os.Open.
        OpenFile func(path string) (io.ReadCloser, error)
}

// joinPath calls ctxt.JoinPath (if not nil) or else filepath.Join.
func (ctxt *Context) joinPath(elem ...string) string {
        if f := ctxt.JoinPath; f != nil {
                return f(elem...)
        }
        return filepath.Join(elem...)
}

// splitPathList calls ctxt.SplitPathList (if not nil) or else filepath.SplitList.
func (ctxt *Context) splitPathList(s string) []string {
        if f := ctxt.SplitPathList; f != nil {
                return f(s)
        }
        return filepath.SplitList(s)
}

// isAbsPath calls ctxt.IsAbsPath (if not nil) or else filepath.IsAbs.
func (ctxt *Context) isAbsPath(path string) bool {
        if f := ctxt.IsAbsPath; f != nil {
                return f(path)
        }
        return filepath.IsAbs(path)
}

// isDir calls ctxt.IsDir (if not nil) or else uses fsys.Stat.
func isDir(path string) bool {
        fi, err := fsys.Stat(path)
        return err == nil && fi.IsDir()
}

// hasSubdir calls ctxt.HasSubdir (if not nil) or else uses
// the local file system to answer the question.
func (ctxt *Context) hasSubdir(root, dir string) (rel string, ok bool) {
        if f := ctxt.HasSubdir; f != nil {
                return f(root, dir)
        }

        // Try using paths we received.
        if rel, ok = hasSubdir(root, dir); ok {
                return
        }

        // Try expanding symlinks and comparing
        // expanded against unexpanded and
        // expanded against expanded.
        rootSym, _ := filepath.EvalSymlinks(root)
        dirSym, _ := filepath.EvalSymlinks(dir)

        if rel, ok = hasSubdir(rootSym, dir); ok {
                return
        }
        if rel, ok = hasSubdir(root, dirSym); ok {
                return
        }
        return hasSubdir(rootSym, dirSym)
}

// hasSubdir reports if dir is within root by performing lexical analysis only.
func hasSubdir(root, dir string) (rel string, ok bool) {
        root = str.WithFilePathSeparator(filepath.Clean(root))
        dir = filepath.Clean(dir)
        if !strings.HasPrefix(dir, root) {
                return "", false
        }
        return filepath.ToSlash(dir[len(root):]), true
}

// gopath returns the list of Go path directories.
func (ctxt *Context) gopath() []string {
        var all []string
        for _, p := range ctxt.splitPathList(ctxt.GOPATH) {
                if p == "" || p == ctxt.GOROOT {
                        // Empty paths are uninteresting.
                        // If the path is the GOROOT, ignore it.
                        // People sometimes set GOPATH=$GOROOT.
                        // Do not get confused by this common mistake.
                        continue
                }
                if strings.HasPrefix(p, "~") {
                        // Path segments starting with ~ on Unix are almost always
                        // users who have incorrectly quoted ~ while setting GOPATH,
                        // preventing it from expanding to $HOME.
                        // The situation is made more confusing by the fact that
                        // bash allows quoted ~ in $PATH (most shells do not).
                        // Do not get confused by this, and do not try to use the path.
                        // It does not exist, and printing errors about it confuses
                        // those users even more, because they think "sure ~ exists!".
                        // The go command diagnoses this situation and prints a
                        // useful error.
                        // On Windows, ~ is used in short names, such as c:\progra~1
                        // for c:\program files.
                        continue
                }
                all = append(all, p)
        }
        return all
}

var defaultToolTags, defaultReleaseTags []string

// NoGoError is the error used by Import to describe a directory
// containing no buildable Go source files. (It may still contain
// test files, files hidden by build tags, and so on.)
type NoGoError struct {
        Dir string
}

func (e *NoGoError) Error() string {
        return "no buildable Go source files in " + e.Dir
}

// MultiplePackageError describes a directory containing
// multiple buildable Go source files for multiple packages.
type MultiplePackageError struct {
        Dir      string   // directory containing files
        Packages []string // package names found
        Files    []string // corresponding files: Files[i] declares package Packages[i]
}

func (e *MultiplePackageError) Error() string {
        // Error string limited to two entries for compatibility.
        return fmt.Sprintf("found packages %s (%s) and %s (%s) in %s", e.Packages[0], e.Files[0], e.Packages[1], e.Files[1], e.Dir)
}

func nameExt(name string) string {
        i := strings.LastIndex(name, ".")
        if i < 0 {
                return ""
        }
        return name[i:]
}

func fileListForExt(p *build.Package, ext string) *[]string {
        switch ext {
        case ".c":
                return &p.CFiles
        case ".cc", ".cpp", ".cxx":
                return &p.CXXFiles
        case ".m":
                return &p.MFiles
        case ".h", ".hh", ".hpp", ".hxx":
                return &p.HFiles
        case ".f", ".F", ".for", ".f90":
                return &p.FFiles
        case ".s", ".S", ".sx":
                return &p.SFiles
        case ".swig":
                return &p.SwigFiles
        case ".swigcxx":
                return &p.SwigCXXFiles
        case ".syso":
                return &p.SysoFiles
        }
        return nil
}

var errNoModules = errors.New("not using modules")

func findImportComment(data []byte) (s string, line int) {
        // expect keyword package
        word, data := parseWord(data)
        if string(word) != "package" {
                return "", 0
        }

        // expect package name
        _, data = parseWord(data)

        // now ready for import comment, a // or /* */ comment
        // beginning and ending on the current line.
        for len(data) > 0 && (data[0] == ' ' || data[0] == '\t' || data[0] == '\r') {
                data = data[1:]
        }

        var comment []byte
        switch {
        case bytes.HasPrefix(data, slashSlash):
                comment, _, _ = bytes.Cut(data[2:], newline)
        case bytes.HasPrefix(data, slashStar):
                var ok bool
                comment, _, ok = bytes.Cut(data[2:], starSlash)
                if !ok {
                        // malformed comment
                        return "", 0
                }
                if bytes.Contains(comment, newline) {
                        return "", 0
                }
        }
        comment = bytes.TrimSpace(comment)

        // split comment into `import`, `"pkg"`
        word, arg := parseWord(comment)
        if string(word) != "import" {
                return "", 0
        }

        line = 1 + bytes.Count(data[:cap(data)-cap(arg)], newline)
        return strings.TrimSpace(string(arg)), line
}

var (
        slashSlash = []byte("//")
        slashStar  = []byte("/*")
        starSlash  = []byte("*/")
        newline    = []byte("\n")
)

// skipSpaceOrComment returns data with any leading spaces or comments removed.
func skipSpaceOrComment(data []byte) []byte {
        for len(data) > 0 {
                switch data[0] {
                case ' ', '\t', '\r', '\n':
                        data = data[1:]
                        continue
                case '/':
                        if bytes.HasPrefix(data, slashSlash) {
                                i := bytes.Index(data, newline)
                                if i < 0 {
                                        return nil
                                }
                                data = data[i+1:]
                                continue
                        }
                        if bytes.HasPrefix(data, slashStar) {
                                data = data[2:]
                                i := bytes.Index(data, starSlash)
                                if i < 0 {
                                        return nil
                                }
                                data = data[i+2:]
                                continue
                        }
                }
                break
        }
        return data
}

// parseWord skips any leading spaces or comments in data
// and then parses the beginning of data as an identifier or keyword,
// returning that word and what remains after the word.
func parseWord(data []byte) (word, rest []byte) {
        data = skipSpaceOrComment(data)

        // Parse past leading word characters.
        rest = data
        for {
                r, size := utf8.DecodeRune(rest)
                if unicode.IsLetter(r) || '0' <= r && r <= '9' || r == '_' {
                        rest = rest[size:]
                        continue
                }
                break
        }

        word = data[:len(data)-len(rest)]
        if len(word) == 0 {
                return nil, nil
        }

        return word, rest
}

var dummyPkg build.Package

// fileInfo records information learned about a file included in a build.
type fileInfo struct {
        name     string // full name including dir
        header   []byte
        fset     *token.FileSet
        parsed   *ast.File
        parseErr error
        imports  []fileImport
        embeds   []fileEmbed

        // Additional fields added to go/build's fileinfo for the purposes of the modindex package.
        binaryOnly           bool
        goBuildConstraint    string
        plusBuildConstraints []string
}

type fileImport struct {
        path string
        pos  token.Pos
        doc  *ast.CommentGroup
}

type fileEmbed struct {
        pattern string
        pos     token.Position
}

var errNonSource = errors.New("non source file")

// getFileInfo extracts the information needed from each go file for the module
// index.
//
// If Name denotes a Go program, matchFile reads until the end of the
// Imports and returns that section of the file in the FileInfo's Header field,
// even though it only considers text until the first non-comment
// for +build lines.
//
// getFileInfo will return errNonSource if the file is not a source or object
// file and shouldn't even be added to IgnoredFiles.
func getFileInfo(dir, name string, fset *token.FileSet) (*fileInfo, error) {
        if strings.HasPrefix(name, "_") ||
                strings.HasPrefix(name, ".") {
                return nil, nil
        }

        i := strings.LastIndex(name, ".")
        if i < 0 {
                i = len(name)
        }
        ext := name[i:]

        if ext != ".go" && fileListForExt(&dummyPkg, ext) == nil {
                // skip
                return nil, errNonSource
        }

        info := &fileInfo{name: filepath.Join(dir, name), fset: fset}
        if ext == ".syso" {
                // binary, no reading
                return info, nil
        }

        f, err := fsys.Open(info.name)
        if err != nil {
                return nil, err
        }

        // TODO(matloob) should we decide whether to ignore binary only here or earlier
        // when we create the index file?
        var ignoreBinaryOnly bool
        if strings.HasSuffix(name, ".go") {
                err = readGoInfo(f, info)
                if strings.HasSuffix(name, "_test.go") {
                        ignoreBinaryOnly = true // ignore //go:binary-only-package comments in _test.go files
                }
        } else {
                info.header, err = readComments(f)
        }
        f.Close()
        if err != nil {
                return nil, fmt.Errorf("read %s: %v", info.name, err)
        }

        // Look for +build comments to accept or reject the file.
        info.goBuildConstraint, info.plusBuildConstraints, info.binaryOnly, err = getConstraints(info.header)
        if err != nil {
                return nil, fmt.Errorf("%s: %v", name, err)
        }

        if ignoreBinaryOnly && info.binaryOnly {
                info.binaryOnly = false // override info.binaryOnly
        }

        return info, nil
}

func cleanDecls(m map[string][]token.Position) ([]string, map[string][]token.Position) {
        all := make([]string, 0, len(m))
        for path := range m {
                all = append(all, path)
        }
        sort.Strings(all)
        return all, m
}

var (
        bSlashSlash = []byte(slashSlash)
        bStarSlash  = []byte(starSlash)
        bSlashStar  = []byte(slashStar)
        bPlusBuild  = []byte("+build")

        goBuildComment = []byte("//go:build")

        errMultipleGoBuild = errors.New("multiple //go:build comments")
)

func isGoBuildComment(line []byte) bool {
        if !bytes.HasPrefix(line, goBuildComment) {
                return false
        }
        line = bytes.TrimSpace(line)
        rest := line[len(goBuildComment):]
        return len(rest) == 0 || len(bytes.TrimSpace(rest)) < len(rest)
}

// Special comment denoting a binary-only package.
// See https://golang.org/design/2775-binary-only-packages
// for more about the design of binary-only packages.
var binaryOnlyComment = []byte("//go:binary-only-package")

func getConstraints(content []byte) (goBuild string, plusBuild []string, binaryOnly bool, err error) {
        // Identify leading run of // comments and blank lines,
        // which must be followed by a blank line.
        // Also identify any //go:build comments.
        content, goBuildBytes, sawBinaryOnly, err := parseFileHeader(content)
        if err != nil {
                return "", nil, false, err
        }

        // If //go:build line is present, it controls, so no need to look for +build .
        // Otherwise, get plusBuild constraints.
        if goBuildBytes == nil {
                p := content
                for len(p) > 0 {
                        line := p
                        if i := bytes.IndexByte(line, '\n'); i >= 0 {
                                line, p = line[:i], p[i+1:]
                        } else {
                                p = p[len(p):]
                        }
                        line = bytes.TrimSpace(line)
                        if !bytes.HasPrefix(line, bSlashSlash) || !bytes.Contains(line, bPlusBuild) {
                                continue
                        }
                        text := string(line)
                        if !constraint.IsPlusBuild(text) {
                                continue
                        }
                        plusBuild = append(plusBuild, text)
                }
        }

        return string(goBuildBytes), plusBuild, sawBinaryOnly, nil
}

func parseFileHeader(content []byte) (trimmed, goBuild []byte, sawBinaryOnly bool, err error) {
        end := 0
        p := content
        ended := false       // found non-blank, non-// line, so stopped accepting // +build lines
        inSlashStar := false // in /* */ comment

Lines:
        for len(p) > 0 {
                line := p
                if i := bytes.IndexByte(line, '\n'); i >= 0 {
                        line, p = line[:i], p[i+1:]
                } else {
                        p = p[len(p):]
                }
                line = bytes.TrimSpace(line)
                if len(line) == 0 && !ended { // Blank line
                        // Remember position of most recent blank line.
                        // When we find the first non-blank, non-// line,
                        // this "end" position marks the latest file position
                        // where a // +build line can appear.
                        // (It must appear _before_ a blank line before the non-blank, non-// line.
                        // Yes, that's confusing, which is part of why we moved to //go:build lines.)
                        // Note that ended==false here means that inSlashStar==false,
                        // since seeing a /* would have set ended==true.
                        end = len(content) - len(p)
                        continue Lines
                }
                if !bytes.HasPrefix(line, slashSlash) { // Not comment line
                        ended = true
                }

                if !inSlashStar && isGoBuildComment(line) {
                        if goBuild != nil {
                                return nil, nil, false, errMultipleGoBuild
                        }
                        goBuild = line
                }
                if !inSlashStar && bytes.Equal(line, binaryOnlyComment) {
                        sawBinaryOnly = true
                }

        Comments:
                for len(line) > 0 {
                        if inSlashStar {
                                if i := bytes.Index(line, starSlash); i >= 0 {
                                        inSlashStar = false
                                        line = bytes.TrimSpace(line[i+len(starSlash):])
                                        continue Comments
                                }
                                continue Lines
                        }
                        if bytes.HasPrefix(line, bSlashSlash) {
                                continue Lines
                        }
                        if bytes.HasPrefix(line, bSlashStar) {
                                inSlashStar = true
                                line = bytes.TrimSpace(line[len(bSlashStar):])
                                continue Comments
                        }
                        // Found non-comment text.
                        break Lines
                }
        }

        return content[:end], goBuild, sawBinaryOnly, nil
}

// saveCgo saves the information from the #cgo lines in the import "C" comment.
// These lines set CFLAGS, CPPFLAGS, CXXFLAGS and LDFLAGS and pkg-config directives
// that affect the way cgo's C code is built.
func (ctxt *Context) saveCgo(filename string, di *build.Package, text string) error {
        for _, line := range strings.Split(text, "\n") {
                orig := line

                // Line is
                //      #cgo [GOOS/GOARCH...] LDFLAGS: stuff
                //
                line = strings.TrimSpace(line)
                if len(line) < 5 || line[:4] != "#cgo" || (line[4] != ' ' && line[4] != '\t') {
                        continue
                }

                // Split at colon.
                line, argstr, ok := strings.Cut(strings.TrimSpace(line[4:]), ":")
                if !ok {
                        return fmt.Errorf("%s: invalid #cgo line: %s", filename, orig)
                }

                // Parse GOOS/GOARCH stuff.
                f := strings.Fields(line)
                if len(f) < 1 {
                        return fmt.Errorf("%s: invalid #cgo line: %s", filename, orig)
                }

                cond, verb := f[:len(f)-1], f[len(f)-1]
                if len(cond) > 0 {
                        ok := false
                        for _, c := range cond {
                                if ctxt.matchAuto(c, nil) {
                                        ok = true
                                        break
                                }
                        }
                        if !ok {
                                continue
                        }
                }

                args, err := splitQuoted(argstr)
                if err != nil {
                        return fmt.Errorf("%s: invalid #cgo line: %s", filename, orig)
                }
                for i, arg := range args {
                        if arg, ok = expandSrcDir(arg, di.Dir); !ok {
                                return fmt.Errorf("%s: malformed #cgo argument: %s", filename, arg)
                        }
                        args[i] = arg
                }

                switch verb {
                case "CFLAGS", "CPPFLAGS", "CXXFLAGS", "FFLAGS", "LDFLAGS":
                        // Change relative paths to absolute.
                        ctxt.makePathsAbsolute(args, di.Dir)
                }

                switch verb {
                case "CFLAGS":
                        di.CgoCFLAGS = append(di.CgoCFLAGS, args...)
                case "CPPFLAGS":
                        di.CgoCPPFLAGS = append(di.CgoCPPFLAGS, args...)
                case "CXXFLAGS":
                        di.CgoCXXFLAGS = append(di.CgoCXXFLAGS, args...)
                case "FFLAGS":
                        di.CgoFFLAGS = append(di.CgoFFLAGS, args...)
                case "LDFLAGS":
                        di.CgoLDFLAGS = append(di.CgoLDFLAGS, args...)
                case "pkg-config":
                        di.CgoPkgConfig = append(di.CgoPkgConfig, args...)
                default:
                        return fmt.Errorf("%s: invalid #cgo verb: %s", filename, orig)
                }
        }
        return nil
}

// expandSrcDir expands any occurrence of ${SRCDIR}, making sure
// the result is safe for the shell.
func expandSrcDir(str string, srcdir string) (string, bool) {
        // "\" delimited paths cause safeCgoName to fail
        // so convert native paths with a different delimiter
        // to "/" before starting (eg: on windows).
        srcdir = filepath.ToSlash(srcdir)

        chunks := strings.Split(str, "${SRCDIR}")
        if len(chunks) < 2 {
                return str, safeCgoName(str)
        }
        ok := true
        for _, chunk := range chunks {
                ok = ok && (chunk == "" || safeCgoName(chunk))
        }
        ok = ok && (srcdir == "" || safeCgoName(srcdir))
        res := strings.Join(chunks, srcdir)
        return res, ok && res != ""
}

// makePathsAbsolute looks for compiler options that take paths and
// makes them absolute. We do this because through the 1.8 release we
// ran the compiler in the package directory, so any relative -I or -L
// options would be relative to that directory. In 1.9 we changed to
// running the compiler in the build directory, to get consistent
// build results (issue #19964). To keep builds working, we change any
// relative -I or -L options to be absolute.
//
// Using filepath.IsAbs and filepath.Join here means the results will be
// different on different systems, but that's OK: -I and -L options are
// inherently system-dependent.
func (ctxt *Context) makePathsAbsolute(args []string, srcDir string) {
        nextPath := false
        for i, arg := range args {
                if nextPath {
                        if !filepath.IsAbs(arg) {
                                args[i] = filepath.Join(srcDir, arg)
                        }
                        nextPath = false
                } else if strings.HasPrefix(arg, "-I") || strings.HasPrefix(arg, "-L") {
                        if len(arg) == 2 {
                                nextPath = true
                        } else {
                                if !filepath.IsAbs(arg[2:]) {
                                        args[i] = arg[:2] + filepath.Join(srcDir, arg[2:])
                                }
                        }
                }
        }
}

// NOTE: $ is not safe for the shell, but it is allowed here because of linker options like -Wl,$ORIGIN.
// We never pass these arguments to a shell (just to programs we construct argv for), so this should be okay.
// See golang.org/issue/6038.
// The @ is for OS X. See golang.org/issue/13720.
// The % is for Jenkins. See golang.org/issue/16959.
// The ! is because module paths may use them. See golang.org/issue/26716.
// The ~ and ^ are for sr.ht. See golang.org/issue/32260.
const safeString = "+-.,/0123456789=ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz:$@%! ~^"

func safeCgoName(s string) bool {
        if s == "" {
                return false
        }
        for i := 0; i < len(s); i++ {
                if c := s[i]; c < utf8.RuneSelf && strings.IndexByte(safeString, c) < 0 {
                        return false
                }
        }
        return true
}

// splitQuoted splits the string s around each instance of one or more consecutive
// white space characters while taking into account quotes and escaping, and
// returns an array of substrings of s or an empty list if s contains only white space.
// Single quotes and double quotes are recognized to prevent splitting within the
// quoted region, and are removed from the resulting substrings. If a quote in s
// isn't closed err will be set and r will have the unclosed argument as the
// last element. The backslash is used for escaping.
//
// For example, the following string:
//
//      a b:"c d" 'e''f'  "g\""
//
// Would be parsed as:
//
//      []string{"a", "b:c d", "ef", `g"`}
func splitQuoted(s string) (r []string, err error) {
        var args []string
        arg := make([]rune, len(s))
        escaped := false
        quoted := false
        quote := '\x00'
        i := 0
        for _, rune := range s {
                switch {
                case escaped:
                        escaped = false
                case rune == '\\':
                        escaped = true
                        continue
                case quote != '\x00':
                        if rune == quote {
                                quote = '\x00'
                                continue
                        }
                case rune == '"' || rune == '\'':
                        quoted = true
                        quote = rune
                        continue
                case unicode.IsSpace(rune):
                        if quoted || i > 0 {
                                quoted = false
                                args = append(args, string(arg[:i]))
                                i = 0
                        }
                        continue
                }
                arg[i] = rune
                i++
        }
        if quoted || i > 0 {
                args = append(args, string(arg[:i]))
        }
        if quote != 0 {
                err = errors.New("unclosed quote")
        } else if escaped {
                err = errors.New("unfinished escaping")
        }
        return args, err
}

// matchAuto interprets text as either a +build or //go:build expression (whichever works),
// reporting whether the expression matches the build context.
//
// matchAuto is only used for testing of tag evaluation
// and in #cgo lines, which accept either syntax.
func (ctxt *Context) matchAuto(text string, allTags map[string]bool) bool {
        if strings.ContainsAny(text, "&|()") {
                text = "//go:build " + text
        } else {
                text = "// +build " + text
        }
        x, err := constraint.Parse(text)
        if err != nil {
                return false
        }
        return ctxt.eval(x, allTags)
}

func (ctxt *Context) eval(x constraint.Expr, allTags map[string]bool) bool {
        return x.Eval(func(tag string) bool { return ctxt.matchTag(tag, allTags) })
}

// matchTag reports whether the name is one of:
//
//      cgo (if cgo is enabled)
//      $GOOS
//      $GOARCH
//      boringcrypto
//      ctxt.Compiler
//      linux (if GOOS == android)
//      solaris (if GOOS == illumos)
//      tag (if tag is listed in ctxt.BuildTags or ctxt.ReleaseTags)
//
// It records all consulted tags in allTags.
func (ctxt *Context) matchTag(name string, allTags map[string]bool) bool {
        if allTags != nil {
                allTags[name] = true
        }

        // special tags
        if ctxt.CgoEnabled && name == "cgo" {
                return true
        }
        if name == ctxt.GOOS || name == ctxt.GOARCH || name == ctxt.Compiler {
                return true
        }
        if ctxt.GOOS == "android" && name == "linux" {
                return true
        }
        if ctxt.GOOS == "illumos" && name == "solaris" {
                return true
        }
        if ctxt.GOOS == "ios" && name == "darwin" {
                return true
        }
        if name == "unix" && unixOS[ctxt.GOOS] {
                return true
        }
        if name == "boringcrypto" {
                name = "goexperiment.boringcrypto" // boringcrypto is an old name for goexperiment.boringcrypto
        }

        // other tags
        for _, tag := range ctxt.BuildTags {
                if tag == name {
                        return true
                }
        }
        for _, tag := range ctxt.ToolTags {
                if tag == name {
                        return true
                }
        }
        for _, tag := range ctxt.ReleaseTags {
                if tag == name {
                        return true
                }
        }

        return false
}

// goodOSArchFile returns false if the name contains a $GOOS or $GOARCH
// suffix which does not match the current system.
// The recognized name formats are:
//
//      name_$(GOOS).*
//      name_$(GOARCH).*
//      name_$(GOOS)_$(GOARCH).*
//      name_$(GOOS)_test.*
//      name_$(GOARCH)_test.*
//      name_$(GOOS)_$(GOARCH)_test.*
//
// Exceptions:
// if GOOS=android, then files with GOOS=linux are also matched.
// if GOOS=illumos, then files with GOOS=solaris are also matched.
// if GOOS=ios, then files with GOOS=darwin are also matched.
func (ctxt *Context) goodOSArchFile(name string, allTags map[string]bool) bool {
        name, _, _ = strings.Cut(name, ".")

        // Before Go 1.4, a file called "linux.go" would be equivalent to having a
        // build tag "linux" in that file. For Go 1.4 and beyond, we require this
        // auto-tagging to apply only to files with a non-empty prefix, so
        // "foo_linux.go" is tagged but "linux.go" is not. This allows new operating
        // systems, such as android, to arrive without breaking existing code with
        // innocuous source code in "android.go". The easiest fix: cut everything
        // in the name before the initial _.
        i := strings.Index(name, "_")
        if i < 0 {
                return true
        }
        name = name[i:] // ignore everything before first _

        l := strings.Split(name, "_")
        if n := len(l); n > 0 && l[n-1] == "test" {
                l = l[:n-1]
        }
        n := len(l)
        if n >= 2 && knownOS[l[n-2]] && knownArch[l[n-1]] {
                if allTags != nil {
                        // In case we short-circuit on l[n-1].
                        allTags[l[n-2]] = true
                }
                return ctxt.matchTag(l[n-1], allTags) && ctxt.matchTag(l[n-2], allTags)
        }
        if n >= 1 && (knownOS[l[n-1]] || knownArch[l[n-1]]) {
                return ctxt.matchTag(l[n-1], allTags)
        }
        return true
}