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// 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.

package build

import (
        "bytes"
        "errors"
        "fmt"
        "go/ast"
        "go/parser"
        "go/token"
        "io/ioutil"
        "log"
        "os"
        "path"
        "path/filepath"
        "runtime"
        "sort"
        "strconv"
        "strings"
        "unicode"
)

// A Context specifies the supporting context for a build.
type Context struct {
        GOARCH     string   // target architecture
        GOOS       string   // target operating system
        CgoEnabled bool     // whether cgo can be used
        BuildTags  []string // additional tags to recognize in +build lines

        // By default, ScanDir uses the operating system's
        // file system calls to read directories and files.
        // Callers can override those calls to provide other
        // ways to read data by setting ReadDir and ReadFile.
        // ScanDir does not make any assumptions about the
        // format of the strings dir and file: they can be
        // slash-separated, backslash-separated, even URLs.

        // ReadDir returns a slice of os.FileInfo, sorted by Name,
        // describing the content of the named directory.
        // The dir argument is the argument to ScanDir.
        // If ReadDir is nil, ScanDir uses io.ReadDir.
        ReadDir func(dir string) (fi []os.FileInfo, err error)

        // ReadFile returns the content of the file named file
        // in the directory named dir.  The dir argument is the
        // argument to ScanDir, and the file argument is the
        // Name field from an os.FileInfo returned by ReadDir.
        // The returned path is the full name of the file, to be
        // used in error messages.
        //
        // If ReadFile is nil, ScanDir uses filepath.Join(dir, file)
        // as the path and ioutil.ReadFile to read the data.
        ReadFile func(dir, file string) (path string, content []byte, err error)
}

func (ctxt *Context) readDir(dir string) ([]os.FileInfo, error) {
        if f := ctxt.ReadDir; f != nil {
                return f(dir)
        }
        return ioutil.ReadDir(dir)
}

func (ctxt *Context) readFile(dir, file string) (string, []byte, error) {
        if f := ctxt.ReadFile; f != nil {
                return f(dir, file)
        }
        p := filepath.Join(dir, file)
        content, err := ioutil.ReadFile(p)
        return p, content, err
}

// The DefaultContext is the default Context for builds.
// It uses the GOARCH and GOOS environment variables
// if set, or else the compiled code's GOARCH and GOOS.
var DefaultContext Context = defaultContext()

var cgoEnabled = map[string]bool{
        "darwin/386":    true,
        "darwin/amd64":  true,
        "linux/386":     true,
        "linux/amd64":   true,
        "freebsd/386":   true,
        "freebsd/amd64": true,
        "windows/386":   true,
        "windows/amd64": true,
}

func defaultContext() Context {
        var c Context

        c.GOARCH = envOr("GOARCH", runtime.GOARCH)
        c.GOOS = envOr("GOOS", runtime.GOOS)

        s := os.Getenv("CGO_ENABLED")
        switch s {
        case "1":
                c.CgoEnabled = true
        case "0":
                c.CgoEnabled = false
        default:
                c.CgoEnabled = cgoEnabled[c.GOOS+"/"+c.GOARCH]
        }

        return c
}

func envOr(name, def string) string {
        s := os.Getenv(name)
        if s == "" {
                return def
        }
        return s
}

type DirInfo struct {
        Package        string                      // Name of package in dir
        PackageComment *ast.CommentGroup           // Package comments from GoFiles
        ImportPath     string                      // Import path of package in dir
        Imports        []string                    // All packages imported by GoFiles
        ImportPos      map[string][]token.Position // Source code location of imports

        // Source files
        GoFiles  []string // .go files in dir (excluding CgoFiles, TestGoFiles, XTestGoFiles)
        HFiles   []string // .h files in dir
        CFiles   []string // .c files in dir
        SFiles   []string // .s (and, when using cgo, .S files in dir)
        CgoFiles []string // .go files that import "C"

        // Cgo directives
        CgoPkgConfig []string // Cgo pkg-config directives
        CgoCFLAGS    []string // Cgo CFLAGS directives
        CgoLDFLAGS   []string // Cgo LDFLAGS directives

        // Test information
        TestGoFiles   []string // _test.go files in package
        XTestGoFiles  []string // _test.go files outside package
        TestImports   []string // All packages imported by (X)TestGoFiles
        TestImportPos map[string][]token.Position
}

func (d *DirInfo) IsCommand() bool {
        // TODO(rsc): This is at least a little bogus.
        return d.Package == "main"
}

// ScanDir calls DefaultContext.ScanDir.
func ScanDir(dir string) (info *DirInfo, err error) {
        return DefaultContext.ScanDir(dir)
}

// TODO(rsc): Move this comment to a more appropriate place.

// ScanDir returns a structure with details about the Go package
// found in the given directory.
//
// Most .go, .c, .h, and .s files in the directory are considered part
// of the package.  The exceptions are:
//
//      - .go files in package main (unless no other package is found)
//      - .go files in package documentation
//      - files starting with _ or .
//      - files with build constraints not satisfied by the context
//
// Build Constraints
//
// A build constraint is a line comment beginning with the directive +build
// that lists the conditions under which a file should be included in the package.
// Constraints may appear in any kind of source file (not just Go), but
// they must be appear near the top of the file, preceded
// only by blank lines and other line comments.
//
// A build constraint is evaluated as the OR of space-separated options;
// each option evaluates as the AND of its comma-separated terms;
// and each term is an alphanumeric word or, preceded by !, its negation.
// That is, the build constraint:
//
//      // +build linux,386 darwin,!cgo
//
// corresponds to the boolean formula:
//
//      (linux AND 386) OR (darwin AND (NOT cgo))
//
// During a particular build, the following words are satisfied:
//
//      - the target operating system, as spelled by runtime.GOOS
//      - the target architecture, as spelled by runtime.GOARCH
//      - "cgo", if ctxt.CgoEnabled is true
//      - any additional words listed in ctxt.BuildTags
//
// If a file's name, after stripping the extension and a possible _test suffix,
// matches *_GOOS, *_GOARCH, or *_GOOS_GOARCH for any known operating
// system and architecture values, then the file is considered to have an implicit
// build constraint requiring those terms.
//
// Examples
//
// To keep a file from being considered for the build:
//
//      // +build ignore
//
// (any other unsatisfied word will work as well, but ``ignore'' is conventional.)
//
// To build a file only when using cgo, and only on Linux and OS X:
//
//      // +build linux,cgo darwin,cgo
// 
// Such a file is usually paired with another file implementing the
// default functionality for other systems, which in this case would
// carry the constraint:
//
//      // +build !linux !darwin !cgo
//
// Naming a file dns_windows.go will cause it to be included only when
// building the package for Windows; similarly, math_386.s will be included
// only when building the package for 32-bit x86.
//
func (ctxt *Context) ScanDir(dir string) (info *DirInfo, err error) {
        dirs, err := ctxt.readDir(dir)
        if err != nil {
                return nil, err
        }

        var Sfiles []string // files with ".S" (capital S)
        var di DirInfo
        imported := make(map[string][]token.Position)
        testImported := make(map[string][]token.Position)
        fset := token.NewFileSet()
        for _, d := range dirs {
                if d.IsDir() {
                        continue
                }
                name := d.Name()
                if strings.HasPrefix(name, "_") ||
                        strings.HasPrefix(name, ".") {
                        continue
                }
                if !ctxt.goodOSArchFile(name) {
                        continue
                }

                ext := path.Ext(name)
                switch ext {
                case ".go", ".c", ".s", ".h", ".S":
                        // tentatively okay
                default:
                        // skip
                        continue
                }

                // Look for +build comments to accept or reject the file.
                filename, data, err := ctxt.readFile(dir, name)
                if err != nil {
                        return nil, err
                }
                if !ctxt.shouldBuild(data) {
                        continue
                }

                // Going to save the file.  For non-Go files, can stop here.
                switch ext {
                case ".c":
                        di.CFiles = append(di.CFiles, name)
                        continue
                case ".h":
                        di.HFiles = append(di.HFiles, name)
                        continue
                case ".s":
                        di.SFiles = append(di.SFiles, name)
                        continue
                case ".S":
                        Sfiles = append(Sfiles, name)
                        continue
                }

                pf, err := parser.ParseFile(fset, filename, data, parser.ImportsOnly|parser.ParseComments)
                if err != nil {
                        return nil, err
                }

                pkg := string(pf.Name.Name)
                if pkg == "main" && di.Package != "" && di.Package != "main" {
                        continue
                }
                if pkg == "documentation" {
                        continue
                }

                isTest := strings.HasSuffix(name, "_test.go")
                if isTest && strings.HasSuffix(pkg, "_test") {
                        pkg = pkg[:len(pkg)-len("_test")]
                }

                if pkg != di.Package && di.Package == "main" {
                        // Found non-main package but was recording
                        // information about package main.  Reset.
                        di = DirInfo{}
                }
                if di.Package == "" {
                        di.Package = pkg
                } else if pkg != di.Package {
                        return nil, fmt.Errorf("%s: found packages %s and %s", dir, pkg, di.Package)
                }
                if pf.Doc != nil {
                        if di.PackageComment != nil {
                                di.PackageComment.List = append(di.PackageComment.List, pf.Doc.List...)
                        } else {
                                di.PackageComment = pf.Doc
                        }
                }

                // Record imports and information about cgo.
                isCgo := false
                for _, decl := range pf.Decls {
                        d, ok := decl.(*ast.GenDecl)
                        if !ok {
                                continue
                        }
                        for _, dspec := range d.Specs {
                                spec, ok := dspec.(*ast.ImportSpec)
                                if !ok {
                                        continue
                                }
                                quoted := string(spec.Path.Value)
                                path, err := strconv.Unquote(quoted)
                                if err != nil {
                                        log.Panicf("%s: parser returned invalid quoted string: <%s>", filename, quoted)
                                }
                                if isTest {
                                        testImported[path] = append(testImported[path], fset.Position(spec.Pos()))
                                } else {
                                        imported[path] = append(imported[path], fset.Position(spec.Pos()))
                                }
                                if path == "C" {
                                        if isTest {
                                                return nil, fmt.Errorf("%s: use of cgo in test not supported", filename)
                                        }
                                        cg := spec.Doc
                                        if cg == nil && len(d.Specs) == 1 {
                                                cg = d.Doc
                                        }
                                        if cg != nil {
                                                if err := ctxt.saveCgo(filename, &di, cg); err != nil {
                                                        return nil, err
                                                }
                                        }
                                        isCgo = true
                                }
                        }
                }
                if isCgo {
                        if ctxt.CgoEnabled {
                                di.CgoFiles = append(di.CgoFiles, name)
                        }
                } else if isTest {
                        if pkg == string(pf.Name.Name) {
                                di.TestGoFiles = append(di.TestGoFiles, name)
                        } else {
                                di.XTestGoFiles = append(di.XTestGoFiles, name)
                        }
                } else {
                        di.GoFiles = append(di.GoFiles, name)
                }
        }
        if di.Package == "" {
                return nil, fmt.Errorf("%s: no Go source files", dir)
        }
        di.Imports = make([]string, len(imported))
        di.ImportPos = imported
        i := 0
        for p := range imported {
                di.Imports[i] = p
                i++
        }
        di.TestImports = make([]string, len(testImported))
        di.TestImportPos = testImported
        i = 0
        for p := range testImported {
                di.TestImports[i] = p
                i++
        }

        // add the .S files only if we are using cgo
        // (which means gcc will compile them).
        // The standard assemblers expect .s files.
        if len(di.CgoFiles) > 0 {
                di.SFiles = append(di.SFiles, Sfiles...)
                sort.Strings(di.SFiles)
        }

        // File name lists are sorted because ReadDir sorts.
        sort.Strings(di.Imports)
        sort.Strings(di.TestImports)
        return &di, nil
}

var slashslash = []byte("//")

// shouldBuild reports whether it is okay to use this file,
// The rule is that in the file's leading run of // comments
// and blank lines, which must be followed by a blank line
// (to avoid including a Go package clause doc comment),
// lines beginning with '// +build' are taken as build directives.
//
// The file is accepted only if each such line lists something
// matching the file.  For example:
//
//      // +build windows linux
//
// marks the file as applicable only on Windows and Linux.
//
func (ctxt *Context) shouldBuild(content []byte) bool {
        // Pass 1. Identify leading run of // comments and blank lines,
        // which must be followed by a blank line.
        end := 0
        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 len(line) == 0 { // Blank line
                        end = cap(content) - cap(line) // &line[0] - &content[0]
                        continue
                }
                if !bytes.HasPrefix(line, slashslash) { // Not comment line
                        break
                }
        }
        content = content[:end]

        // Pass 2.  Process each line in the run.
        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, slashslash) {
                        line = bytes.TrimSpace(line[len(slashslash):])
                        if len(line) > 0 && line[0] == '+' {
                                // Looks like a comment +line.
                                f := strings.Fields(string(line))
                                if f[0] == "+build" {
                                        ok := false
                                        for _, tok := range f[1:] {
                                                if ctxt.match(tok) {
                                                        ok = true
                                                        break
                                                }
                                        }
                                        if !ok {
                                                return false // this one doesn't match
                                        }
                                }
                        }
                }
        }
        return true // everything matches
}

// saveCgo saves the information from the #cgo lines in the import "C" comment.
// These lines set CFLAGS and LDFLAGS and pkg-config directives that affect
// the way cgo's C code is built.
//
// TODO(rsc): This duplicates code in cgo.
// Once the dust settles, remove this code from cgo.
func (ctxt *Context) saveCgo(filename string, di *DirInfo, cg *ast.CommentGroup) error {
        text := cg.Text()
        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 = strings.TrimSpace(line[4:])
                i := strings.Index(line, ":")
                if i < 0 {
                        return fmt.Errorf("%s: invalid #cgo line: %s", filename, orig)
                }
                line, argstr := line[:i], line[i+1:]

                // 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.match(c) {
                                        ok = true
                                        break
                                }
                        }
                        if !ok {
                                continue
                        }
                }

                args, err := splitQuoted(argstr)
                if err != nil {
                        return fmt.Errorf("%s: invalid #cgo line: %s", filename, orig)
                }
                for _, arg := range args {
                        if !safeName(arg) {
                                return fmt.Errorf("%s: malformed #cgo argument: %s", filename, arg)
                        }
                }

                switch verb {
                case "CFLAGS":
                        di.CgoCFLAGS = append(di.CgoCFLAGS, 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
}

var safeBytes = []byte("+-.,/0123456789=ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz:")

func safeName(s string) bool {
        if s == "" {
                return false
        }
        for i := 0; i < len(s); i++ {
                if c := s[i]; c < 0x80 && bytes.IndexByte(safeBytes, 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
}

// match returns true if the name is one of:
//
//      $GOOS
//      $GOARCH
//      cgo (if cgo is enabled)
//      !cgo (if cgo is disabled)
//      tag (if tag is listed in ctxt.BuildTags)
//      !tag (if tag is not listed in ctxt.BuildTags)
//      a slash-separated list of any of these
//
func (ctxt *Context) match(name string) bool {
        if name == "" {
                return false
        }
        if i := strings.Index(name, ","); i >= 0 {
                // comma-separated list
                return ctxt.match(name[:i]) && ctxt.match(name[i+1:])
        }
        if strings.HasPrefix(name, "!!") { // bad syntax, reject always
                return false
        }
        if strings.HasPrefix(name, "!") { // negation
                return !ctxt.match(name[1:])
        }

        // Tags must be letters, digits, underscores.
        // Unlike in Go identifiers, all digits is fine (e.g., "386").
        for _, c := range name {
                if !unicode.IsLetter(c) && !unicode.IsDigit(c) && c != '_' {
                        return false
                }
        }

        // special tags
        if ctxt.CgoEnabled && name == "cgo" {
                return true
        }
        if name == ctxt.GOOS || name == ctxt.GOARCH {
                return true
        }

        // other tags
        for _, tag := range ctxt.BuildTags {
                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.*
//
func (ctxt *Context) goodOSArchFile(name string) bool {
        if dot := strings.Index(name, "."); dot != -1 {
                name = name[:dot]
        }
        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]] {
                return l[n-2] == ctxt.GOOS && l[n-1] == ctxt.GOARCH
        }
        if n >= 1 && knownOS[l[n-1]] {
                return l[n-1] == ctxt.GOOS
        }
        if n >= 1 && knownArch[l[n-1]] {
                return l[n-1] == ctxt.GOARCH
        }
        return true
}

var knownOS = make(map[string]bool)
var knownArch = make(map[string]bool)

func init() {
        for _, v := range strings.Fields(goosList) {
                knownOS[v] = true
        }
        for _, v := range strings.Fields(goarchList) {
                knownArch[v] = true
        }
}