loader.go

Documentation: golang.org/x/tools/go/loader

     1  // Copyright 2013 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  package loader
     6  
     7  // See doc.go for package documentation and implementation notes.
     8  
     9  import (
    10  	"errors"
    11  	"fmt"
    12  	"go/ast"
    13  	"go/build"
    14  	"go/parser"
    15  	"go/token"
    16  	"go/types"
    17  	"os"
    18  	"path/filepath"
    19  	"sort"
    20  	"strings"
    21  	"sync"
    22  	"time"
    23  
    24  	"golang.org/x/tools/go/ast/astutil"
    25  	"golang.org/x/tools/go/internal/cgo"
    26  	"golang.org/x/tools/internal/typeparams"
    27  )
    28  
    29  var ignoreVendor build.ImportMode
    30  
    31  const trace = false // show timing info for type-checking
    32  
    33  // Config specifies the configuration for loading a whole program from
    34  // Go source code.
    35  // The zero value for Config is a ready-to-use default configuration.
    36  type Config struct {
    37  	// Fset is the file set for the parser to use when loading the
    38  	// program.  If nil, it may be lazily initialized by any
    39  	// method of Config.
    40  	Fset *token.FileSet
    41  
    42  	// ParserMode specifies the mode to be used by the parser when
    43  	// loading source packages.
    44  	ParserMode parser.Mode
    45  
    46  	// TypeChecker contains options relating to the type checker.
    47  	//
    48  	// The supplied IgnoreFuncBodies is not used; the effective
    49  	// value comes from the TypeCheckFuncBodies func below.
    50  	// The supplied Import function is not used either.
    51  	TypeChecker types.Config
    52  
    53  	// TypeCheckFuncBodies is a predicate over package paths.
    54  	// A package for which the predicate is false will
    55  	// have its package-level declarations type checked, but not
    56  	// its function bodies; this can be used to quickly load
    57  	// dependencies from source.  If nil, all func bodies are type
    58  	// checked.
    59  	TypeCheckFuncBodies func(path string) bool
    60  
    61  	// If Build is non-nil, it is used to locate source packages.
    62  	// Otherwise &build.Default is used.
    63  	//
    64  	// By default, cgo is invoked to preprocess Go files that
    65  	// import the fake package "C".  This behaviour can be
    66  	// disabled by setting CGO_ENABLED=0 in the environment prior
    67  	// to startup, or by setting Build.CgoEnabled=false.
    68  	Build *build.Context
    69  
    70  	// The current directory, used for resolving relative package
    71  	// references such as "./go/loader".  If empty, os.Getwd will be
    72  	// used instead.
    73  	Cwd string
    74  
    75  	// If DisplayPath is non-nil, it is used to transform each
    76  	// file name obtained from Build.Import().  This can be used
    77  	// to prevent a virtualized build.Config's file names from
    78  	// leaking into the user interface.
    79  	DisplayPath func(path string) string
    80  
    81  	// If AllowErrors is true, Load will return a Program even
    82  	// if some of the its packages contained I/O, parser or type
    83  	// errors; such errors are accessible via PackageInfo.Errors.  If
    84  	// false, Load will fail if any package had an error.
    85  	AllowErrors bool
    86  
    87  	// CreatePkgs specifies a list of non-importable initial
    88  	// packages to create.  The resulting packages will appear in
    89  	// the corresponding elements of the Program.Created slice.
    90  	CreatePkgs []PkgSpec
    91  
    92  	// ImportPkgs specifies a set of initial packages to load.
    93  	// The map keys are package paths.
    94  	//
    95  	// The map value indicates whether to load tests.  If true, Load
    96  	// will add and type-check two lists of files to the package:
    97  	// non-test files followed by in-package *_test.go files.  In
    98  	// addition, it will append the external test package (if any)
    99  	// to Program.Created.
   100  	ImportPkgs map[string]bool
   101  
   102  	// FindPackage is called during Load to create the build.Package
   103  	// for a given import path from a given directory.
   104  	// If FindPackage is nil, (*build.Context).Import is used.
   105  	// A client may use this hook to adapt to a proprietary build
   106  	// system that does not follow the "go build" layout
   107  	// conventions, for example.
   108  	//
   109  	// It must be safe to call concurrently from multiple goroutines.
   110  	FindPackage func(ctxt *build.Context, importPath, fromDir string, mode build.ImportMode) (*build.Package, error)
   111  
   112  	// AfterTypeCheck is called immediately after a list of files
   113  	// has been type-checked and appended to info.Files.
   114  	//
   115  	// This optional hook function is the earliest opportunity for
   116  	// the client to observe the output of the type checker,
   117  	// which may be useful to reduce analysis latency when loading
   118  	// a large program.
   119  	//
   120  	// The function is permitted to modify info.Info, for instance
   121  	// to clear data structures that are no longer needed, which can
   122  	// dramatically reduce peak memory consumption.
   123  	//
   124  	// The function may be called twice for the same PackageInfo:
   125  	// once for the files of the package and again for the
   126  	// in-package test files.
   127  	//
   128  	// It must be safe to call concurrently from multiple goroutines.
   129  	AfterTypeCheck func(info *PackageInfo, files []*ast.File)
   130  }
   131  
   132  // A PkgSpec specifies a non-importable package to be created by Load.
   133  // Files are processed first, but typically only one of Files and
   134  // Filenames is provided.  The path needn't be globally unique.
   135  //
   136  // For vendoring purposes, the package's directory is the one that
   137  // contains the first file.
   138  type PkgSpec struct {
   139  	Path      string      // package path ("" => use package declaration)
   140  	Files     []*ast.File // ASTs of already-parsed files
   141  	Filenames []string    // names of files to be parsed
   142  }
   143  
   144  // A Program is a Go program loaded from source as specified by a Config.
   145  type Program struct {
   146  	Fset *token.FileSet // the file set for this program
   147  
   148  	// Created[i] contains the initial package whose ASTs or
   149  	// filenames were supplied by Config.CreatePkgs[i], followed by
   150  	// the external test package, if any, of each package in
   151  	// Config.ImportPkgs ordered by ImportPath.
   152  	//
   153  	// NOTE: these files must not import "C".  Cgo preprocessing is
   154  	// only performed on imported packages, not ad hoc packages.
   155  	//
   156  	// TODO(adonovan): we need to copy and adapt the logic of
   157  	// goFilesPackage (from $GOROOT/src/cmd/go/build.go) and make
   158  	// Config.Import and Config.Create methods return the same kind
   159  	// of entity, essentially a build.Package.
   160  	// Perhaps we can even reuse that type directly.
   161  	Created []*PackageInfo
   162  
   163  	// Imported contains the initially imported packages,
   164  	// as specified by Config.ImportPkgs.
   165  	Imported map[string]*PackageInfo
   166  
   167  	// AllPackages contains the PackageInfo of every package
   168  	// encountered by Load: all initial packages and all
   169  	// dependencies, including incomplete ones.
   170  	AllPackages map[*types.Package]*PackageInfo
   171  
   172  	// importMap is the canonical mapping of package paths to
   173  	// packages.  It contains all Imported initial packages, but not
   174  	// Created ones, and all imported dependencies.
   175  	importMap map[string]*types.Package
   176  }
   177  
   178  // PackageInfo holds the ASTs and facts derived by the type-checker
   179  // for a single package.
   180  //
   181  // Not mutated once exposed via the API.
   182  type PackageInfo struct {
   183  	Pkg                   *types.Package
   184  	Importable            bool        // true if 'import "Pkg.Path()"' would resolve to this
   185  	TransitivelyErrorFree bool        // true if Pkg and all its dependencies are free of errors
   186  	Files                 []*ast.File // syntax trees for the package's files
   187  	Errors                []error     // non-nil if the package had errors
   188  	types.Info                        // type-checker deductions.
   189  	dir                   string      // package directory
   190  
   191  	checker   *types.Checker // transient type-checker state
   192  	errorFunc func(error)
   193  }
   194  
   195  func (info *PackageInfo) String() string { return info.Pkg.Path() }
   196  
   197  func (info *PackageInfo) appendError(err error) {
   198  	if info.errorFunc != nil {
   199  		info.errorFunc(err)
   200  	} else {
   201  		fmt.Fprintln(os.Stderr, err)
   202  	}
   203  	info.Errors = append(info.Errors, err)
   204  }
   205  
   206  func (conf *Config) fset() *token.FileSet {
   207  	if conf.Fset == nil {
   208  		conf.Fset = token.NewFileSet()
   209  	}
   210  	return conf.Fset
   211  }
   212  
   213  // ParseFile is a convenience function (intended for testing) that invokes
   214  // the parser using the Config's FileSet, which is initialized if nil.
   215  //
   216  // src specifies the parser input as a string, []byte, or io.Reader, and
   217  // filename is its apparent name.  If src is nil, the contents of
   218  // filename are read from the file system.
   219  func (conf *Config) ParseFile(filename string, src interface{}) (*ast.File, error) {
   220  	// TODO(adonovan): use conf.build() etc like parseFiles does.
   221  	return parser.ParseFile(conf.fset(), filename, src, conf.ParserMode)
   222  }
   223  
   224  // FromArgsUsage is a partial usage message that applications calling
   225  // FromArgs may wish to include in their -help output.
   226  const FromArgsUsage = `
   227  <args> is a list of arguments denoting a set of initial packages.
   228  It may take one of two forms:
   229  
   230  1. A list of *.go source files.
   231  
   232     All of the specified files are loaded, parsed and type-checked
   233     as a single package.  All the files must belong to the same directory.
   234  
   235  2. A list of import paths, each denoting a package.
   236  
   237     The package's directory is found relative to the $GOROOT and
   238     $GOPATH using similar logic to 'go build', and the *.go files in
   239     that directory are loaded, parsed and type-checked as a single
   240     package.
   241  
   242     In addition, all *_test.go files in the directory are then loaded
   243     and parsed.  Those files whose package declaration equals that of
   244     the non-*_test.go files are included in the primary package.  Test
   245     files whose package declaration ends with "_test" are type-checked
   246     as another package, the 'external' test package, so that a single
   247     import path may denote two packages.  (Whether this behaviour is
   248     enabled is tool-specific, and may depend on additional flags.)
   249  
   250  A '--' argument terminates the list of packages.
   251  `
   252  
   253  // FromArgs interprets args as a set of initial packages to load from
   254  // source and updates the configuration.  It returns the list of
   255  // unconsumed arguments.
   256  //
   257  // It is intended for use in command-line interfaces that require a
   258  // set of initial packages to be specified; see FromArgsUsage message
   259  // for details.
   260  //
   261  // Only superficial errors are reported at this stage; errors dependent
   262  // on I/O are detected during Load.
   263  func (conf *Config) FromArgs(args []string, xtest bool) ([]string, error) {
   264  	var rest []string
   265  	for i, arg := range args {
   266  		if arg == "--" {
   267  			rest = args[i+1:]
   268  			args = args[:i]
   269  			break // consume "--" and return the remaining args
   270  		}
   271  	}
   272  
   273  	if len(args) > 0 && strings.HasSuffix(args[0], ".go") {
   274  		// Assume args is a list of a *.go files
   275  		// denoting a single ad hoc package.
   276  		for _, arg := range args {
   277  			if !strings.HasSuffix(arg, ".go") {
   278  				return nil, fmt.Errorf("named files must be .go files: %s", arg)
   279  			}
   280  		}
   281  		conf.CreateFromFilenames("", args...)
   282  	} else {
   283  		// Assume args are directories each denoting a
   284  		// package and (perhaps) an external test, iff xtest.
   285  		for _, arg := range args {
   286  			if xtest {
   287  				conf.ImportWithTests(arg)
   288  			} else {
   289  				conf.Import(arg)
   290  			}
   291  		}
   292  	}
   293  
   294  	return rest, nil
   295  }
   296  
   297  // CreateFromFilenames is a convenience function that adds
   298  // a conf.CreatePkgs entry to create a package of the specified *.go
   299  // files.
   300  func (conf *Config) CreateFromFilenames(path string, filenames ...string) {
   301  	conf.CreatePkgs = append(conf.CreatePkgs, PkgSpec{Path: path, Filenames: filenames})
   302  }
   303  
   304  // CreateFromFiles is a convenience function that adds a conf.CreatePkgs
   305  // entry to create package of the specified path and parsed files.
   306  func (conf *Config) CreateFromFiles(path string, files ...*ast.File) {
   307  	conf.CreatePkgs = append(conf.CreatePkgs, PkgSpec{Path: path, Files: files})
   308  }
   309  
   310  // ImportWithTests is a convenience function that adds path to
   311  // ImportPkgs, the set of initial source packages located relative to
   312  // $GOPATH.  The package will be augmented by any *_test.go files in
   313  // its directory that contain a "package x" (not "package x_test")
   314  // declaration.
   315  //
   316  // In addition, if any *_test.go files contain a "package x_test"
   317  // declaration, an additional package comprising just those files will
   318  // be added to CreatePkgs.
   319  func (conf *Config) ImportWithTests(path string) { conf.addImport(path, true) }
   320  
   321  // Import is a convenience function that adds path to ImportPkgs, the
   322  // set of initial packages that will be imported from source.
   323  func (conf *Config) Import(path string) { conf.addImport(path, false) }
   324  
   325  func (conf *Config) addImport(path string, tests bool) {
   326  	if path == "C" {
   327  		return // ignore; not a real package
   328  	}
   329  	if conf.ImportPkgs == nil {
   330  		conf.ImportPkgs = make(map[string]bool)
   331  	}
   332  	conf.ImportPkgs[path] = conf.ImportPkgs[path] || tests
   333  }
   334  
   335  // PathEnclosingInterval returns the PackageInfo and ast.Node that
   336  // contain source interval [start, end), and all the node's ancestors
   337  // up to the AST root.  It searches all ast.Files of all packages in prog.
   338  // exact is defined as for astutil.PathEnclosingInterval.
   339  //
   340  // The zero value is returned if not found.
   341  func (prog *Program) PathEnclosingInterval(start, end token.Pos) (pkg *PackageInfo, path []ast.Node, exact bool) {
   342  	for _, info := range prog.AllPackages {
   343  		for _, f := range info.Files {
   344  			if f.Pos() == token.NoPos {
   345  				// This can happen if the parser saw
   346  				// too many errors and bailed out.
   347  				// (Use parser.AllErrors to prevent that.)
   348  				continue
   349  			}
   350  			if !tokenFileContainsPos(prog.Fset.File(f.Pos()), start) {
   351  				continue
   352  			}
   353  			if path, exact := astutil.PathEnclosingInterval(f, start, end); path != nil {
   354  				return info, path, exact
   355  			}
   356  		}
   357  	}
   358  	return nil, nil, false
   359  }
   360  
   361  // InitialPackages returns a new slice containing the set of initial
   362  // packages (Created + Imported) in unspecified order.
   363  func (prog *Program) InitialPackages() []*PackageInfo {
   364  	infos := make([]*PackageInfo, 0, len(prog.Created)+len(prog.Imported))
   365  	infos = append(infos, prog.Created...)
   366  	for _, info := range prog.Imported {
   367  		infos = append(infos, info)
   368  	}
   369  	return infos
   370  }
   371  
   372  // Package returns the ASTs and results of type checking for the
   373  // specified package.
   374  func (prog *Program) Package(path string) *PackageInfo {
   375  	if info, ok := prog.AllPackages[prog.importMap[path]]; ok {
   376  		return info
   377  	}
   378  	for _, info := range prog.Created {
   379  		if path == info.Pkg.Path() {
   380  			return info
   381  		}
   382  	}
   383  	return nil
   384  }
   385  
   386  // ---------- Implementation ----------
   387  
   388  // importer holds the working state of the algorithm.
   389  type importer struct {
   390  	conf  *Config   // the client configuration
   391  	start time.Time // for logging
   392  
   393  	progMu sync.Mutex // guards prog
   394  	prog   *Program   // the resulting program
   395  
   396  	// findpkg is a memoization of FindPackage.
   397  	findpkgMu sync.Mutex // guards findpkg
   398  	findpkg   map[findpkgKey]*findpkgValue
   399  
   400  	importedMu sync.Mutex             // guards imported
   401  	imported   map[string]*importInfo // all imported packages (incl. failures) by import path
   402  
   403  	// import dependency graph: graph[x][y] => x imports y
   404  	//
   405  	// Since non-importable packages cannot be cyclic, we ignore
   406  	// their imports, thus we only need the subgraph over importable
   407  	// packages.  Nodes are identified by their import paths.
   408  	graphMu sync.Mutex
   409  	graph   map[string]map[string]bool
   410  }
   411  
   412  type findpkgKey struct {
   413  	importPath string
   414  	fromDir    string
   415  	mode       build.ImportMode
   416  }
   417  
   418  type findpkgValue struct {
   419  	ready chan struct{} // closed to broadcast readiness
   420  	bp    *build.Package
   421  	err   error
   422  }
   423  
   424  // importInfo tracks the success or failure of a single import.
   425  //
   426  // Upon completion, exactly one of info and err is non-nil:
   427  // info on successful creation of a package, err otherwise.
   428  // A successful package may still contain type errors.
   429  type importInfo struct {
   430  	path     string        // import path
   431  	info     *PackageInfo  // results of typechecking (including errors)
   432  	complete chan struct{} // closed to broadcast that info is set.
   433  }
   434  
   435  // awaitCompletion blocks until ii is complete,
   436  // i.e. the info field is safe to inspect.
   437  func (ii *importInfo) awaitCompletion() {
   438  	<-ii.complete // wait for close
   439  }
   440  
   441  // Complete marks ii as complete.
   442  // Its info and err fields will not be subsequently updated.
   443  func (ii *importInfo) Complete(info *PackageInfo) {
   444  	if info == nil {
   445  		panic("info == nil")
   446  	}
   447  	ii.info = info
   448  	close(ii.complete)
   449  }
   450  
   451  type importError struct {
   452  	path string // import path
   453  	err  error  // reason for failure to create a package
   454  }
   455  
   456  // Load creates the initial packages specified by conf.{Create,Import}Pkgs,
   457  // loading their dependencies packages as needed.
   458  //
   459  // On success, Load returns a Program containing a PackageInfo for
   460  // each package.  On failure, it returns an error.
   461  //
   462  // If AllowErrors is true, Load will return a Program even if some
   463  // packages contained I/O, parser or type errors, or if dependencies
   464  // were missing.  (Such errors are accessible via PackageInfo.Errors.  If
   465  // false, Load will fail if any package had an error.
   466  //
   467  // It is an error if no packages were loaded.
   468  func (conf *Config) Load() (*Program, error) {
   469  	// Create a simple default error handler for parse/type errors.
   470  	if conf.TypeChecker.Error == nil {
   471  		conf.TypeChecker.Error = func(e error) { fmt.Fprintln(os.Stderr, e) }
   472  	}
   473  
   474  	// Set default working directory for relative package references.
   475  	if conf.Cwd == "" {
   476  		var err error
   477  		conf.Cwd, err = os.Getwd()
   478  		if err != nil {
   479  			return nil, err
   480  		}
   481  	}
   482  
   483  	// Install default FindPackage hook using go/build logic.
   484  	if conf.FindPackage == nil {
   485  		conf.FindPackage = (*build.Context).Import
   486  	}
   487  
   488  	prog := &Program{
   489  		Fset:        conf.fset(),
   490  		Imported:    make(map[string]*PackageInfo),
   491  		importMap:   make(map[string]*types.Package),
   492  		AllPackages: make(map[*types.Package]*PackageInfo),
   493  	}
   494  
   495  	imp := importer{
   496  		conf:     conf,
   497  		prog:     prog,
   498  		findpkg:  make(map[findpkgKey]*findpkgValue),
   499  		imported: make(map[string]*importInfo),
   500  		start:    time.Now(),
   501  		graph:    make(map[string]map[string]bool),
   502  	}
   503  
   504  	// -- loading proper (concurrent phase) --------------------------------
   505  
   506  	var errpkgs []string // packages that contained errors
   507  
   508  	// Load the initially imported packages and their dependencies,
   509  	// in parallel.
   510  	// No vendor check on packages imported from the command line.
   511  	infos, importErrors := imp.importAll("", conf.Cwd, conf.ImportPkgs, ignoreVendor)
   512  	for _, ie := range importErrors {
   513  		conf.TypeChecker.Error(ie.err) // failed to create package
   514  		errpkgs = append(errpkgs, ie.path)
   515  	}
   516  	for _, info := range infos {
   517  		prog.Imported[info.Pkg.Path()] = info
   518  	}
   519  
   520  	// Augment the designated initial packages by their tests.
   521  	// Dependencies are loaded in parallel.
   522  	var xtestPkgs []*build.Package
   523  	for importPath, augment := range conf.ImportPkgs {
   524  		if !augment {
   525  			continue
   526  		}
   527  
   528  		// No vendor check on packages imported from command line.
   529  		bp, err := imp.findPackage(importPath, conf.Cwd, ignoreVendor)
   530  		if err != nil {
   531  			// Package not found, or can't even parse package declaration.
   532  			// Already reported by previous loop; ignore it.
   533  			continue
   534  		}
   535  
   536  		// Needs external test package?
   537  		if len(bp.XTestGoFiles) > 0 {
   538  			xtestPkgs = append(xtestPkgs, bp)
   539  		}
   540  
   541  		// Consult the cache using the canonical package path.
   542  		path := bp.ImportPath
   543  		imp.importedMu.Lock() // (unnecessary, we're sequential here)
   544  		ii, ok := imp.imported[path]
   545  		// Paranoid checks added due to issue #11012.
   546  		if !ok {
   547  			// Unreachable.
   548  			// The previous loop called importAll and thus
   549  			// startLoad for each path in ImportPkgs, which
   550  			// populates imp.imported[path] with a non-zero value.
   551  			panic(fmt.Sprintf("imported[%q] not found", path))
   552  		}
   553  		if ii == nil {
   554  			// Unreachable.
   555  			// The ii values in this loop are the same as in
   556  			// the previous loop, which enforced the invariant
   557  			// that at least one of ii.err and ii.info is non-nil.
   558  			panic(fmt.Sprintf("imported[%q] == nil", path))
   559  		}
   560  		if ii.info == nil {
   561  			// Unreachable.
   562  			// awaitCompletion has the postcondition
   563  			// ii.info != nil.
   564  			panic(fmt.Sprintf("imported[%q].info = nil", path))
   565  		}
   566  		info := ii.info
   567  		imp.importedMu.Unlock()
   568  
   569  		// Parse the in-package test files.
   570  		files, errs := imp.conf.parsePackageFiles(bp, 't')
   571  		for _, err := range errs {
   572  			info.appendError(err)
   573  		}
   574  
   575  		// The test files augmenting package P cannot be imported,
   576  		// but may import packages that import P,
   577  		// so we must disable the cycle check.
   578  		imp.addFiles(info, files, false)
   579  	}
   580  
   581  	createPkg := func(path, dir string, files []*ast.File, errs []error) {
   582  		info := imp.newPackageInfo(path, dir)
   583  		for _, err := range errs {
   584  			info.appendError(err)
   585  		}
   586  
   587  		// Ad hoc packages are non-importable,
   588  		// so no cycle check is needed.
   589  		// addFiles loads dependencies in parallel.
   590  		imp.addFiles(info, files, false)
   591  		prog.Created = append(prog.Created, info)
   592  	}
   593  
   594  	// Create packages specified by conf.CreatePkgs.
   595  	for _, cp := range conf.CreatePkgs {
   596  		files, errs := parseFiles(conf.fset(), conf.build(), nil, conf.Cwd, cp.Filenames, conf.ParserMode)
   597  		files = append(files, cp.Files...)
   598  
   599  		path := cp.Path
   600  		if path == "" {
   601  			if len(files) > 0 {
   602  				path = files[0].Name.Name
   603  			} else {
   604  				path = "(unnamed)"
   605  			}
   606  		}
   607  
   608  		dir := conf.Cwd
   609  		if len(files) > 0 && files[0].Pos().IsValid() {
   610  			dir = filepath.Dir(conf.fset().File(files[0].Pos()).Name())
   611  		}
   612  		createPkg(path, dir, files, errs)
   613  	}
   614  
   615  	// Create external test packages.
   616  	sort.Sort(byImportPath(xtestPkgs))
   617  	for _, bp := range xtestPkgs {
   618  		files, errs := imp.conf.parsePackageFiles(bp, 'x')
   619  		createPkg(bp.ImportPath+"_test", bp.Dir, files, errs)
   620  	}
   621  
   622  	// -- finishing up (sequential) ----------------------------------------
   623  
   624  	if len(prog.Imported)+len(prog.Created) == 0 {
   625  		return nil, errors.New("no initial packages were loaded")
   626  	}
   627  
   628  	// Create infos for indirectly imported packages.
   629  	// e.g. incomplete packages without syntax, loaded from export data.
   630  	for _, obj := range prog.importMap {
   631  		info := prog.AllPackages[obj]
   632  		if info == nil {
   633  			prog.AllPackages[obj] = &PackageInfo{Pkg: obj, Importable: true}
   634  		} else {
   635  			// finished
   636  			info.checker = nil
   637  			info.errorFunc = nil
   638  		}
   639  	}
   640  
   641  	if !conf.AllowErrors {
   642  		// Report errors in indirectly imported packages.
   643  		for _, info := range prog.AllPackages {
   644  			if len(info.Errors) > 0 {
   645  				errpkgs = append(errpkgs, info.Pkg.Path())
   646  			}
   647  		}
   648  		if errpkgs != nil {
   649  			var more string
   650  			if len(errpkgs) > 3 {
   651  				more = fmt.Sprintf(" and %d more", len(errpkgs)-3)
   652  				errpkgs = errpkgs[:3]
   653  			}
   654  			return nil, fmt.Errorf("couldn't load packages due to errors: %s%s",
   655  				strings.Join(errpkgs, ", "), more)
   656  		}
   657  	}
   658  
   659  	markErrorFreePackages(prog.AllPackages)
   660  
   661  	return prog, nil
   662  }
   663  
   664  type byImportPath []*build.Package
   665  
   666  func (b byImportPath) Len() int           { return len(b) }
   667  func (b byImportPath) Less(i, j int) bool { return b[i].ImportPath < b[j].ImportPath }
   668  func (b byImportPath) Swap(i, j int)      { b[i], b[j] = b[j], b[i] }
   669  
   670  // markErrorFreePackages sets the TransitivelyErrorFree flag on all
   671  // applicable packages.
   672  func markErrorFreePackages(allPackages map[*types.Package]*PackageInfo) {
   673  	// Build the transpose of the import graph.
   674  	importedBy := make(map[*types.Package]map[*types.Package]bool)
   675  	for P := range allPackages {
   676  		for _, Q := range P.Imports() {
   677  			clients, ok := importedBy[Q]
   678  			if !ok {
   679  				clients = make(map[*types.Package]bool)
   680  				importedBy[Q] = clients
   681  			}
   682  			clients[P] = true
   683  		}
   684  	}
   685  
   686  	// Find all packages reachable from some error package.
   687  	reachable := make(map[*types.Package]bool)
   688  	var visit func(*types.Package)
   689  	visit = func(p *types.Package) {
   690  		if !reachable[p] {
   691  			reachable[p] = true
   692  			for q := range importedBy[p] {
   693  				visit(q)
   694  			}
   695  		}
   696  	}
   697  	for _, info := range allPackages {
   698  		if len(info.Errors) > 0 {
   699  			visit(info.Pkg)
   700  		}
   701  	}
   702  
   703  	// Mark the others as "transitively error-free".
   704  	for _, info := range allPackages {
   705  		if !reachable[info.Pkg] {
   706  			info.TransitivelyErrorFree = true
   707  		}
   708  	}
   709  }
   710  
   711  // build returns the effective build context.
   712  func (conf *Config) build() *build.Context {
   713  	if conf.Build != nil {
   714  		return conf.Build
   715  	}
   716  	return &build.Default
   717  }
   718  
   719  // parsePackageFiles enumerates the files belonging to package path,
   720  // then loads, parses and returns them, plus a list of I/O or parse
   721  // errors that were encountered.
   722  //
   723  // 'which' indicates which files to include:
   724  //
   725  //	'g': include non-test *.go source files (GoFiles + processed CgoFiles)
   726  //	't': include in-package *_test.go source files (TestGoFiles)
   727  //	'x': include external *_test.go source files. (XTestGoFiles)
   728  func (conf *Config) parsePackageFiles(bp *build.Package, which rune) ([]*ast.File, []error) {
   729  	if bp.ImportPath == "unsafe" {
   730  		return nil, nil
   731  	}
   732  	var filenames []string
   733  	switch which {
   734  	case 'g':
   735  		filenames = bp.GoFiles
   736  	case 't':
   737  		filenames = bp.TestGoFiles
   738  	case 'x':
   739  		filenames = bp.XTestGoFiles
   740  	default:
   741  		panic(which)
   742  	}
   743  
   744  	files, errs := parseFiles(conf.fset(), conf.build(), conf.DisplayPath, bp.Dir, filenames, conf.ParserMode)
   745  
   746  	// Preprocess CgoFiles and parse the outputs (sequentially).
   747  	if which == 'g' && bp.CgoFiles != nil {
   748  		cgofiles, err := cgo.ProcessFiles(bp, conf.fset(), conf.DisplayPath, conf.ParserMode)
   749  		if err != nil {
   750  			errs = append(errs, err)
   751  		} else {
   752  			files = append(files, cgofiles...)
   753  		}
   754  	}
   755  
   756  	return files, errs
   757  }
   758  
   759  // doImport imports the package denoted by path.
   760  // It implements the types.Importer signature.
   761  //
   762  // It returns an error if a package could not be created
   763  // (e.g. go/build or parse error), but type errors are reported via
   764  // the types.Config.Error callback (the first of which is also saved
   765  // in the package's PackageInfo).
   766  //
   767  // Idempotent.
   768  func (imp *importer) doImport(from *PackageInfo, to string) (*types.Package, error) {
   769  	if to == "C" {
   770  		// This should be unreachable, but ad hoc packages are
   771  		// not currently subject to cgo preprocessing.
   772  		// See https://golang.org/issue/11627.
   773  		return nil, fmt.Errorf(`the loader doesn't cgo-process ad hoc packages like %q; see Go issue 11627`,
   774  			from.Pkg.Path())
   775  	}
   776  
   777  	bp, err := imp.findPackage(to, from.dir, 0)
   778  	if err != nil {
   779  		return nil, err
   780  	}
   781  
   782  	// The standard unsafe package is handled specially,
   783  	// and has no PackageInfo.
   784  	if bp.ImportPath == "unsafe" {
   785  		return types.Unsafe, nil
   786  	}
   787  
   788  	// Look for the package in the cache using its canonical path.
   789  	path := bp.ImportPath
   790  	imp.importedMu.Lock()
   791  	ii := imp.imported[path]
   792  	imp.importedMu.Unlock()
   793  	if ii == nil {
   794  		panic("internal error: unexpected import: " + path)
   795  	}
   796  	if ii.info != nil {
   797  		return ii.info.Pkg, nil
   798  	}
   799  
   800  	// Import of incomplete package: this indicates a cycle.
   801  	fromPath := from.Pkg.Path()
   802  	if cycle := imp.findPath(path, fromPath); cycle != nil {
   803  		// Normalize cycle: start from alphabetically largest node.
   804  		pos, start := -1, ""
   805  		for i, s := range cycle {
   806  			if pos < 0 || s > start {
   807  				pos, start = i, s
   808  			}
   809  		}
   810  		cycle = append(cycle, cycle[:pos]...)[pos:] // rotate cycle to start from largest
   811  		cycle = append(cycle, cycle[0])             // add start node to end to show cycliness
   812  		return nil, fmt.Errorf("import cycle: %s", strings.Join(cycle, " -> "))
   813  	}
   814  
   815  	panic("internal error: import of incomplete (yet acyclic) package: " + fromPath)
   816  }
   817  
   818  // findPackage locates the package denoted by the importPath in the
   819  // specified directory.
   820  func (imp *importer) findPackage(importPath, fromDir string, mode build.ImportMode) (*build.Package, error) {
   821  	// We use a non-blocking duplicate-suppressing cache (gopl.io §9.7)
   822  	// to avoid holding the lock around FindPackage.
   823  	key := findpkgKey{importPath, fromDir, mode}
   824  	imp.findpkgMu.Lock()
   825  	v, ok := imp.findpkg[key]
   826  	if ok {
   827  		// cache hit
   828  		imp.findpkgMu.Unlock()
   829  
   830  		<-v.ready // wait for entry to become ready
   831  	} else {
   832  		// Cache miss: this goroutine becomes responsible for
   833  		// populating the map entry and broadcasting its readiness.
   834  		v = &findpkgValue{ready: make(chan struct{})}
   835  		imp.findpkg[key] = v
   836  		imp.findpkgMu.Unlock()
   837  
   838  		ioLimit <- true
   839  		v.bp, v.err = imp.conf.FindPackage(imp.conf.build(), importPath, fromDir, mode)
   840  		<-ioLimit
   841  
   842  		if _, ok := v.err.(*build.NoGoError); ok {
   843  			v.err = nil // empty directory is not an error
   844  		}
   845  
   846  		close(v.ready) // broadcast ready condition
   847  	}
   848  	return v.bp, v.err
   849  }
   850  
   851  // importAll loads, parses, and type-checks the specified packages in
   852  // parallel and returns their completed importInfos in unspecified order.
   853  //
   854  // fromPath is the package path of the importing package, if it is
   855  // importable, "" otherwise.  It is used for cycle detection.
   856  //
   857  // fromDir is the directory containing the import declaration that
   858  // caused these imports.
   859  func (imp *importer) importAll(fromPath, fromDir string, imports map[string]bool, mode build.ImportMode) (infos []*PackageInfo, errors []importError) {
   860  	if fromPath != "" {
   861  		// We're loading a set of imports.
   862  		//
   863  		// We must record graph edges from the importing package
   864  		// to its dependencies, and check for cycles.
   865  		imp.graphMu.Lock()
   866  		deps, ok := imp.graph[fromPath]
   867  		if !ok {
   868  			deps = make(map[string]bool)
   869  			imp.graph[fromPath] = deps
   870  		}
   871  		for importPath := range imports {
   872  			deps[importPath] = true
   873  		}
   874  		imp.graphMu.Unlock()
   875  	}
   876  
   877  	var pending []*importInfo
   878  	for importPath := range imports {
   879  		if fromPath != "" {
   880  			if cycle := imp.findPath(importPath, fromPath); cycle != nil {
   881  				// Cycle-forming import: we must not check it
   882  				// since it would deadlock.
   883  				if trace {
   884  					fmt.Fprintf(os.Stderr, "import cycle: %q\n", cycle)
   885  				}
   886  				continue
   887  			}
   888  		}
   889  		bp, err := imp.findPackage(importPath, fromDir, mode)
   890  		if err != nil {
   891  			errors = append(errors, importError{
   892  				path: importPath,
   893  				err:  err,
   894  			})
   895  			continue
   896  		}
   897  		pending = append(pending, imp.startLoad(bp))
   898  	}
   899  
   900  	for _, ii := range pending {
   901  		ii.awaitCompletion()
   902  		infos = append(infos, ii.info)
   903  	}
   904  
   905  	return infos, errors
   906  }
   907  
   908  // findPath returns an arbitrary path from 'from' to 'to' in the import
   909  // graph, or nil if there was none.
   910  func (imp *importer) findPath(from, to string) []string {
   911  	imp.graphMu.Lock()
   912  	defer imp.graphMu.Unlock()
   913  
   914  	seen := make(map[string]bool)
   915  	var search func(stack []string, importPath string) []string
   916  	search = func(stack []string, importPath string) []string {
   917  		if !seen[importPath] {
   918  			seen[importPath] = true
   919  			stack = append(stack, importPath)
   920  			if importPath == to {
   921  				return stack
   922  			}
   923  			for x := range imp.graph[importPath] {
   924  				if p := search(stack, x); p != nil {
   925  					return p
   926  				}
   927  			}
   928  		}
   929  		return nil
   930  	}
   931  	return search(make([]string, 0, 20), from)
   932  }
   933  
   934  // startLoad initiates the loading, parsing and type-checking of the
   935  // specified package and its dependencies, if it has not already begun.
   936  //
   937  // It returns an importInfo, not necessarily in a completed state.  The
   938  // caller must call awaitCompletion() before accessing its info field.
   939  //
   940  // startLoad is concurrency-safe and idempotent.
   941  func (imp *importer) startLoad(bp *build.Package) *importInfo {
   942  	path := bp.ImportPath
   943  	imp.importedMu.Lock()
   944  	ii, ok := imp.imported[path]
   945  	if !ok {
   946  		ii = &importInfo{path: path, complete: make(chan struct{})}
   947  		imp.imported[path] = ii
   948  		go func() {
   949  			info := imp.load(bp)
   950  			ii.Complete(info)
   951  		}()
   952  	}
   953  	imp.importedMu.Unlock()
   954  
   955  	return ii
   956  }
   957  
   958  // load implements package loading by parsing Go source files
   959  // located by go/build.
   960  func (imp *importer) load(bp *build.Package) *PackageInfo {
   961  	info := imp.newPackageInfo(bp.ImportPath, bp.Dir)
   962  	info.Importable = true
   963  	files, errs := imp.conf.parsePackageFiles(bp, 'g')
   964  	for _, err := range errs {
   965  		info.appendError(err)
   966  	}
   967  
   968  	imp.addFiles(info, files, true)
   969  
   970  	imp.progMu.Lock()
   971  	imp.prog.importMap[bp.ImportPath] = info.Pkg
   972  	imp.progMu.Unlock()
   973  
   974  	return info
   975  }
   976  
   977  // addFiles adds and type-checks the specified files to info, loading
   978  // their dependencies if needed.  The order of files determines the
   979  // package initialization order.  It may be called multiple times on the
   980  // same package.  Errors are appended to the info.Errors field.
   981  //
   982  // cycleCheck determines whether the imports within files create
   983  // dependency edges that should be checked for potential cycles.
   984  func (imp *importer) addFiles(info *PackageInfo, files []*ast.File, cycleCheck bool) {
   985  	// Ensure the dependencies are loaded, in parallel.
   986  	var fromPath string
   987  	if cycleCheck {
   988  		fromPath = info.Pkg.Path()
   989  	}
   990  	// TODO(adonovan): opt: make the caller do scanImports.
   991  	// Callers with a build.Package can skip it.
   992  	imp.importAll(fromPath, info.dir, scanImports(files), 0)
   993  
   994  	if trace {
   995  		fmt.Fprintf(os.Stderr, "%s: start %q (%d)\n",
   996  			time.Since(imp.start), info.Pkg.Path(), len(files))
   997  	}
   998  
   999  	// Don't call checker.Files on Unsafe, even with zero files,
  1000  	// because it would mutate the package, which is a global.
  1001  	if info.Pkg == types.Unsafe {
  1002  		if len(files) > 0 {
  1003  			panic(`"unsafe" package contains unexpected files`)
  1004  		}
  1005  	} else {
  1006  		// Ignore the returned (first) error since we
  1007  		// already collect them all in the PackageInfo.
  1008  		info.checker.Files(files)
  1009  		info.Files = append(info.Files, files...)
  1010  	}
  1011  
  1012  	if imp.conf.AfterTypeCheck != nil {
  1013  		imp.conf.AfterTypeCheck(info, files)
  1014  	}
  1015  
  1016  	if trace {
  1017  		fmt.Fprintf(os.Stderr, "%s: stop %q\n",
  1018  			time.Since(imp.start), info.Pkg.Path())
  1019  	}
  1020  }
  1021  
  1022  func (imp *importer) newPackageInfo(path, dir string) *PackageInfo {
  1023  	var pkg *types.Package
  1024  	if path == "unsafe" {
  1025  		pkg = types.Unsafe
  1026  	} else {
  1027  		pkg = types.NewPackage(path, "")
  1028  	}
  1029  	info := &PackageInfo{
  1030  		Pkg: pkg,
  1031  		Info: types.Info{
  1032  			Types:      make(map[ast.Expr]types.TypeAndValue),
  1033  			Defs:       make(map[*ast.Ident]types.Object),
  1034  			Uses:       make(map[*ast.Ident]types.Object),
  1035  			Implicits:  make(map[ast.Node]types.Object),
  1036  			Scopes:     make(map[ast.Node]*types.Scope),
  1037  			Selections: make(map[*ast.SelectorExpr]*types.Selection),
  1038  		},
  1039  		errorFunc: imp.conf.TypeChecker.Error,
  1040  		dir:       dir,
  1041  	}
  1042  	typeparams.InitInstanceInfo(&info.Info)
  1043  
  1044  	// Copy the types.Config so we can vary it across PackageInfos.
  1045  	tc := imp.conf.TypeChecker
  1046  	tc.IgnoreFuncBodies = false
  1047  	if f := imp.conf.TypeCheckFuncBodies; f != nil {
  1048  		tc.IgnoreFuncBodies = !f(path)
  1049  	}
  1050  	tc.Importer = closure{imp, info}
  1051  	tc.Error = info.appendError // appendError wraps the user's Error function
  1052  
  1053  	info.checker = types.NewChecker(&tc, imp.conf.fset(), pkg, &info.Info)
  1054  	imp.progMu.Lock()
  1055  	imp.prog.AllPackages[pkg] = info
  1056  	imp.progMu.Unlock()
  1057  	return info
  1058  }
  1059  
  1060  type closure struct {
  1061  	imp  *importer
  1062  	info *PackageInfo
  1063  }
  1064  
  1065  func (c closure) Import(to string) (*types.Package, error) { return c.imp.doImport(c.info, to) }
  1066
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