main.go

Documentation: cmd/doc

     1  // Copyright 2015 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Doc (usually run as go doc) accepts zero, one or two arguments.
     6  //
     7  // Zero arguments:
     8  //
     9  //	go doc
    10  //
    11  // Show the documentation for the package in the current directory.
    12  //
    13  // One argument:
    14  //
    15  //	go doc <pkg>
    16  //	go doc <sym>[.<methodOrField>]
    17  //	go doc [<pkg>.]<sym>[.<methodOrField>]
    18  //	go doc [<pkg>.][<sym>.]<methodOrField>
    19  //
    20  // The first item in this list that succeeds is the one whose documentation
    21  // is printed. If there is a symbol but no package, the package in the current
    22  // directory is chosen. However, if the argument begins with a capital
    23  // letter it is always assumed to be a symbol in the current directory.
    24  //
    25  // Two arguments:
    26  //
    27  //	go doc <pkg> <sym>[.<methodOrField>]
    28  //
    29  // Show the documentation for the package, symbol, and method or field. The
    30  // first argument must be a full package path. This is similar to the
    31  // command-line usage for the godoc command.
    32  //
    33  // For commands, unless the -cmd flag is present "go doc command"
    34  // shows only the package-level docs for the package.
    35  //
    36  // The -src flag causes doc to print the full source code for the symbol, such
    37  // as the body of a struct, function or method.
    38  //
    39  // The -all flag causes doc to print all documentation for the package and
    40  // all its visible symbols. The argument must identify a package.
    41  //
    42  // For complete documentation, run "go help doc".
    43  package main
    44  
    45  import (
    46  	"bytes"
    47  	"flag"
    48  	"fmt"
    49  	"go/build"
    50  	"go/token"
    51  	"io"
    52  	"log"
    53  	"os"
    54  	"path"
    55  	"path/filepath"
    56  	"strings"
    57  
    58  	"cmd/internal/telemetry/counter"
    59  )
    60  
    61  var (
    62  	unexported bool   // -u flag
    63  	matchCase  bool   // -c flag
    64  	chdir      string // -C flag
    65  	showAll    bool   // -all flag
    66  	showCmd    bool   // -cmd flag
    67  	showSrc    bool   // -src flag
    68  	short      bool   // -short flag
    69  )
    70  
    71  // usage is a replacement usage function for the flags package.
    72  func usage() {
    73  	fmt.Fprintf(os.Stderr, "Usage of [go] doc:\n")
    74  	fmt.Fprintf(os.Stderr, "\tgo doc\n")
    75  	fmt.Fprintf(os.Stderr, "\tgo doc <pkg>\n")
    76  	fmt.Fprintf(os.Stderr, "\tgo doc <sym>[.<methodOrField>]\n")
    77  	fmt.Fprintf(os.Stderr, "\tgo doc [<pkg>.]<sym>[.<methodOrField>]\n")
    78  	fmt.Fprintf(os.Stderr, "\tgo doc [<pkg>.][<sym>.]<methodOrField>\n")
    79  	fmt.Fprintf(os.Stderr, "\tgo doc <pkg> <sym>[.<methodOrField>]\n")
    80  	fmt.Fprintf(os.Stderr, "For more information run\n")
    81  	fmt.Fprintf(os.Stderr, "\tgo help doc\n\n")
    82  	fmt.Fprintf(os.Stderr, "Flags:\n")
    83  	flag.PrintDefaults()
    84  	os.Exit(2)
    85  }
    86  
    87  func main() {
    88  	log.SetFlags(0)
    89  	log.SetPrefix("doc: ")
    90  	counter.Open()
    91  	dirsInit()
    92  	err := do(os.Stdout, flag.CommandLine, os.Args[1:])
    93  	if err != nil {
    94  		log.Fatal(err)
    95  	}
    96  }
    97  
    98  // do is the workhorse, broken out of main to make testing easier.
    99  func do(writer io.Writer, flagSet *flag.FlagSet, args []string) (err error) {
   100  	flagSet.Usage = usage
   101  	unexported = false
   102  	matchCase = false
   103  	flagSet.StringVar(&chdir, "C", "", "change to `dir` before running command")
   104  	flagSet.BoolVar(&unexported, "u", false, "show unexported symbols as well as exported")
   105  	flagSet.BoolVar(&matchCase, "c", false, "symbol matching honors case (paths not affected)")
   106  	flagSet.BoolVar(&showAll, "all", false, "show all documentation for package")
   107  	flagSet.BoolVar(&showCmd, "cmd", false, "show symbols with package docs even if package is a command")
   108  	flagSet.BoolVar(&showSrc, "src", false, "show source code for symbol")
   109  	flagSet.BoolVar(&short, "short", false, "one-line representation for each symbol")
   110  	flagSet.Parse(args)
   111  	counter.Inc("doc/invocations")
   112  	counter.CountFlags("doc/flag:", *flag.CommandLine)
   113  	if chdir != "" {
   114  		if err := os.Chdir(chdir); err != nil {
   115  			return err
   116  		}
   117  	}
   118  	var paths []string
   119  	var symbol, method string
   120  	// Loop until something is printed.
   121  	dirs.Reset()
   122  	for i := 0; ; i++ {
   123  		buildPackage, userPath, sym, more := parseArgs(flagSet.Args())
   124  		if i > 0 && !more { // Ignore the "more" bit on the first iteration.
   125  			return failMessage(paths, symbol, method)
   126  		}
   127  		if buildPackage == nil {
   128  			return fmt.Errorf("no such package: %s", userPath)
   129  		}
   130  
   131  		// The builtin package needs special treatment: its symbols are lower
   132  		// case but we want to see them, always.
   133  		if buildPackage.ImportPath == "builtin" {
   134  			unexported = true
   135  		}
   136  
   137  		symbol, method = parseSymbol(sym)
   138  		pkg := parsePackage(writer, buildPackage, userPath)
   139  		paths = append(paths, pkg.prettyPath())
   140  
   141  		defer func() {
   142  			pkg.flush()
   143  			e := recover()
   144  			if e == nil {
   145  				return
   146  			}
   147  			pkgError, ok := e.(PackageError)
   148  			if ok {
   149  				err = pkgError
   150  				return
   151  			}
   152  			panic(e)
   153  		}()
   154  
   155  		switch {
   156  		case symbol == "":
   157  			pkg.packageDoc() // The package exists, so we got some output.
   158  			return
   159  		case method == "":
   160  			if pkg.symbolDoc(symbol) {
   161  				return
   162  			}
   163  		case pkg.printMethodDoc(symbol, method):
   164  			return
   165  		case pkg.printFieldDoc(symbol, method):
   166  			return
   167  		}
   168  	}
   169  }
   170  
   171  // failMessage creates a nicely formatted error message when there is no result to show.
   172  func failMessage(paths []string, symbol, method string) error {
   173  	var b bytes.Buffer
   174  	if len(paths) > 1 {
   175  		b.WriteString("s")
   176  	}
   177  	b.WriteString(" ")
   178  	for i, path := range paths {
   179  		if i > 0 {
   180  			b.WriteString(", ")
   181  		}
   182  		b.WriteString(path)
   183  	}
   184  	if method == "" {
   185  		return fmt.Errorf("no symbol %s in package%s", symbol, &b)
   186  	}
   187  	return fmt.Errorf("no method or field %s.%s in package%s", symbol, method, &b)
   188  }
   189  
   190  // parseArgs analyzes the arguments (if any) and returns the package
   191  // it represents, the part of the argument the user used to identify
   192  // the path (or "" if it's the current package) and the symbol
   193  // (possibly with a .method) within that package.
   194  // parseSymbol is used to analyze the symbol itself.
   195  // The boolean final argument reports whether it is possible that
   196  // there may be more directories worth looking at. It will only
   197  // be true if the package path is a partial match for some directory
   198  // and there may be more matches. For example, if the argument
   199  // is rand.Float64, we must scan both crypto/rand and math/rand
   200  // to find the symbol, and the first call will return crypto/rand, true.
   201  func parseArgs(args []string) (pkg *build.Package, path, symbol string, more bool) {
   202  	wd, err := os.Getwd()
   203  	if err != nil {
   204  		log.Fatal(err)
   205  	}
   206  	if len(args) == 0 {
   207  		// Easy: current directory.
   208  		return importDir(wd), "", "", false
   209  	}
   210  	arg := args[0]
   211  	// We have an argument. If it is a directory name beginning with . or ..,
   212  	// use the absolute path name. This discriminates "./errors" from "errors"
   213  	// if the current directory contains a non-standard errors package.
   214  	if isDotSlash(arg) {
   215  		arg = filepath.Join(wd, arg)
   216  	}
   217  	switch len(args) {
   218  	default:
   219  		usage()
   220  	case 1:
   221  		// Done below.
   222  	case 2:
   223  		// Package must be findable and importable.
   224  		pkg, err := build.Import(args[0], wd, build.ImportComment)
   225  		if err == nil {
   226  			return pkg, args[0], args[1], false
   227  		}
   228  		for {
   229  			packagePath, ok := findNextPackage(arg)
   230  			if !ok {
   231  				break
   232  			}
   233  			if pkg, err := build.ImportDir(packagePath, build.ImportComment); err == nil {
   234  				return pkg, arg, args[1], true
   235  			}
   236  		}
   237  		return nil, args[0], args[1], false
   238  	}
   239  	// Usual case: one argument.
   240  	// If it contains slashes, it begins with either a package path
   241  	// or an absolute directory.
   242  	// First, is it a complete package path as it is? If so, we are done.
   243  	// This avoids confusion over package paths that have other
   244  	// package paths as their prefix.
   245  	var importErr error
   246  	if filepath.IsAbs(arg) {
   247  		pkg, importErr = build.ImportDir(arg, build.ImportComment)
   248  		if importErr == nil {
   249  			return pkg, arg, "", false
   250  		}
   251  	} else {
   252  		pkg, importErr = build.Import(arg, wd, build.ImportComment)
   253  		if importErr == nil {
   254  			return pkg, arg, "", false
   255  		}
   256  	}
   257  	// Another disambiguator: If the argument starts with an upper
   258  	// case letter, it can only be a symbol in the current directory.
   259  	// Kills the problem caused by case-insensitive file systems
   260  	// matching an upper case name as a package name.
   261  	if !strings.ContainsAny(arg, `/\`) && token.IsExported(arg) {
   262  		pkg, err := build.ImportDir(".", build.ImportComment)
   263  		if err == nil {
   264  			return pkg, "", arg, false
   265  		}
   266  	}
   267  	// If it has a slash, it must be a package path but there is a symbol.
   268  	// It's the last package path we care about.
   269  	slash := strings.LastIndex(arg, "/")
   270  	// There may be periods in the package path before or after the slash
   271  	// and between a symbol and method.
   272  	// Split the string at various periods to see what we find.
   273  	// In general there may be ambiguities but this should almost always
   274  	// work.
   275  	var period int
   276  	// slash+1: if there's no slash, the value is -1 and start is 0; otherwise
   277  	// start is the byte after the slash.
   278  	for start := slash + 1; start < len(arg); start = period + 1 {
   279  		period = strings.Index(arg[start:], ".")
   280  		symbol := ""
   281  		if period < 0 {
   282  			period = len(arg)
   283  		} else {
   284  			period += start
   285  			symbol = arg[period+1:]
   286  		}
   287  		// Have we identified a package already?
   288  		pkg, err := build.Import(arg[0:period], wd, build.ImportComment)
   289  		if err == nil {
   290  			return pkg, arg[0:period], symbol, false
   291  		}
   292  		// See if we have the basename or tail of a package, as in json for encoding/json
   293  		// or ivy/value for robpike.io/ivy/value.
   294  		pkgName := arg[:period]
   295  		for {
   296  			path, ok := findNextPackage(pkgName)
   297  			if !ok {
   298  				break
   299  			}
   300  			if pkg, err = build.ImportDir(path, build.ImportComment); err == nil {
   301  				return pkg, arg[0:period], symbol, true
   302  			}
   303  		}
   304  		dirs.Reset() // Next iteration of for loop must scan all the directories again.
   305  	}
   306  	// If it has a slash, we've failed.
   307  	if slash >= 0 {
   308  		// build.Import should always include the path in its error message,
   309  		// and we should avoid repeating it. Unfortunately, build.Import doesn't
   310  		// return a structured error. That can't easily be fixed, since it
   311  		// invokes 'go list' and returns the error text from the loaded package.
   312  		// TODO(golang.org/issue/34750): load using golang.org/x/tools/go/packages
   313  		// instead of go/build.
   314  		importErrStr := importErr.Error()
   315  		if strings.Contains(importErrStr, arg[:period]) {
   316  			log.Fatal(importErrStr)
   317  		} else {
   318  			log.Fatalf("no such package %s: %s", arg[:period], importErrStr)
   319  		}
   320  	}
   321  	// Guess it's a symbol in the current directory.
   322  	return importDir(wd), "", arg, false
   323  }
   324  
   325  // dotPaths lists all the dotted paths legal on Unix-like and
   326  // Windows-like file systems. We check them all, as the chance
   327  // of error is minute and even on Windows people will use ./
   328  // sometimes.
   329  var dotPaths = []string{
   330  	`./`,
   331  	`../`,
   332  	`.\`,
   333  	`..\`,
   334  }
   335  
   336  // isDotSlash reports whether the path begins with a reference
   337  // to the local . or .. directory.
   338  func isDotSlash(arg string) bool {
   339  	if arg == "." || arg == ".." {
   340  		return true
   341  	}
   342  	for _, dotPath := range dotPaths {
   343  		if strings.HasPrefix(arg, dotPath) {
   344  			return true
   345  		}
   346  	}
   347  	return false
   348  }
   349  
   350  // importDir is just an error-catching wrapper for build.ImportDir.
   351  func importDir(dir string) *build.Package {
   352  	pkg, err := build.ImportDir(dir, build.ImportComment)
   353  	if err != nil {
   354  		log.Fatal(err)
   355  	}
   356  	return pkg
   357  }
   358  
   359  // parseSymbol breaks str apart into a symbol and method.
   360  // Both may be missing or the method may be missing.
   361  // If present, each must be a valid Go identifier.
   362  func parseSymbol(str string) (symbol, method string) {
   363  	if str == "" {
   364  		return
   365  	}
   366  	elem := strings.Split(str, ".")
   367  	switch len(elem) {
   368  	case 1:
   369  	case 2:
   370  		method = elem[1]
   371  	default:
   372  		log.Printf("too many periods in symbol specification")
   373  		usage()
   374  	}
   375  	symbol = elem[0]
   376  	return
   377  }
   378  
   379  // isExported reports whether the name is an exported identifier.
   380  // If the unexported flag (-u) is true, isExported returns true because
   381  // it means that we treat the name as if it is exported.
   382  func isExported(name string) bool {
   383  	return unexported || token.IsExported(name)
   384  }
   385  
   386  // findNextPackage returns the next full file name path that matches the
   387  // (perhaps partial) package path pkg. The boolean reports if any match was found.
   388  func findNextPackage(pkg string) (string, bool) {
   389  	if filepath.IsAbs(pkg) {
   390  		if dirs.offset == 0 {
   391  			dirs.offset = -1
   392  			return pkg, true
   393  		}
   394  		return "", false
   395  	}
   396  	if pkg == "" || token.IsExported(pkg) { // Upper case symbol cannot be a package name.
   397  		return "", false
   398  	}
   399  	pkg = path.Clean(pkg)
   400  	pkgSuffix := "/" + pkg
   401  	for {
   402  		d, ok := dirs.Next()
   403  		if !ok {
   404  			return "", false
   405  		}
   406  		if d.importPath == pkg || strings.HasSuffix(d.importPath, pkgSuffix) {
   407  			return d.dir, true
   408  		}
   409  	}
   410  }
   411  
   412  var buildCtx = build.Default
   413  
   414  // splitGopath splits $GOPATH into a list of roots.
   415  func splitGopath() []string {
   416  	return filepath.SplitList(buildCtx.GOPATH)
   417  }
   418
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