import.go

Documentation: cmd/go/internal/modload

     1  // Copyright 2018 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 modload
     6  
     7  import (
     8  	"context"
     9  	"errors"
    10  	"fmt"
    11  	"go/build"
    12  	"internal/goroot"
    13  	"io/fs"
    14  	"os"
    15  	"path/filepath"
    16  	"sort"
    17  	"strings"
    18  
    19  	"cmd/go/internal/cfg"
    20  	"cmd/go/internal/fsys"
    21  	"cmd/go/internal/modfetch"
    22  	"cmd/go/internal/par"
    23  	"cmd/go/internal/search"
    24  
    25  	"golang.org/x/mod/module"
    26  	"golang.org/x/mod/semver"
    27  )
    28  
    29  type ImportMissingError struct {
    30  	Path     string
    31  	Module   module.Version
    32  	QueryErr error
    33  
    34  	// isStd indicates whether we would expect to find the package in the standard
    35  	// library. This is normally true for all dotless import paths, but replace
    36  	// directives can cause us to treat the replaced paths as also being in
    37  	// modules.
    38  	isStd bool
    39  
    40  	// replaced the highest replaced version of the module where the replacement
    41  	// contains the package. replaced is only set if the replacement is unused.
    42  	replaced module.Version
    43  
    44  	// newMissingVersion is set to a newer version of Module if one is present
    45  	// in the build list. When set, we can't automatically upgrade.
    46  	newMissingVersion string
    47  }
    48  
    49  func (e *ImportMissingError) Error() string {
    50  	if e.Module.Path == "" {
    51  		if e.isStd {
    52  			return fmt.Sprintf("package %s is not in GOROOT (%s)", e.Path, filepath.Join(cfg.GOROOT, "src", e.Path))
    53  		}
    54  		if e.QueryErr != nil {
    55  			return fmt.Sprintf("cannot find module providing package %s: %v", e.Path, e.QueryErr)
    56  		}
    57  		if cfg.BuildMod == "mod" || (cfg.BuildMod == "readonly" && allowMissingModuleImports) {
    58  			return "cannot find module providing package " + e.Path
    59  		}
    60  
    61  		if e.replaced.Path != "" {
    62  			suggestArg := e.replaced.Path
    63  			if !modfetch.IsZeroPseudoVersion(e.replaced.Version) {
    64  				suggestArg = e.replaced.String()
    65  			}
    66  			return fmt.Sprintf("module %s provides package %s and is replaced but not required; to add it:\n\tgo get %s", e.replaced.Path, e.Path, suggestArg)
    67  		}
    68  
    69  		suggestion := ""
    70  		if !HasModRoot() {
    71  			suggestion = ": working directory is not part of a module"
    72  		} else {
    73  			suggestion = fmt.Sprintf("; to add it:\n\tgo get %s", e.Path)
    74  		}
    75  		return fmt.Sprintf("no required module provides package %s%s", e.Path, suggestion)
    76  	}
    77  
    78  	if e.newMissingVersion != "" {
    79  		return fmt.Sprintf("package %s provided by %s at latest version %s but not at required version %s", e.Path, e.Module.Path, e.Module.Version, e.newMissingVersion)
    80  	}
    81  
    82  	return fmt.Sprintf("missing module for import: %s@%s provides %s", e.Module.Path, e.Module.Version, e.Path)
    83  }
    84  
    85  func (e *ImportMissingError) Unwrap() error {
    86  	return e.QueryErr
    87  }
    88  
    89  func (e *ImportMissingError) ImportPath() string {
    90  	return e.Path
    91  }
    92  
    93  // An AmbiguousImportError indicates an import of a package found in multiple
    94  // modules in the build list, or found in both the main module and its vendor
    95  // directory.
    96  type AmbiguousImportError struct {
    97  	importPath string
    98  	Dirs       []string
    99  	Modules    []module.Version // Either empty or 1:1 with Dirs.
   100  }
   101  
   102  func (e *AmbiguousImportError) ImportPath() string {
   103  	return e.importPath
   104  }
   105  
   106  func (e *AmbiguousImportError) Error() string {
   107  	locType := "modules"
   108  	if len(e.Modules) == 0 {
   109  		locType = "directories"
   110  	}
   111  
   112  	var buf strings.Builder
   113  	fmt.Fprintf(&buf, "ambiguous import: found package %s in multiple %s:", e.importPath, locType)
   114  
   115  	for i, dir := range e.Dirs {
   116  		buf.WriteString("\n\t")
   117  		if i < len(e.Modules) {
   118  			m := e.Modules[i]
   119  			buf.WriteString(m.Path)
   120  			if m.Version != "" {
   121  				fmt.Fprintf(&buf, " %s", m.Version)
   122  			}
   123  			fmt.Fprintf(&buf, " (%s)", dir)
   124  		} else {
   125  			buf.WriteString(dir)
   126  		}
   127  	}
   128  
   129  	return buf.String()
   130  }
   131  
   132  // ImportMissingSumError is reported in readonly mode when we need to check
   133  // if a module contains a package, but we don't have a sum for its .zip file.
   134  // We might need sums for multiple modules to verify the package is unique.
   135  //
   136  // TODO(#43653): consolidate multiple errors of this type into a single error
   137  // that suggests a 'go get' command for root packages that transtively import
   138  // packages from modules with missing sums. load.CheckPackageErrors would be
   139  // a good place to consolidate errors, but we'll need to attach the import
   140  // stack here.
   141  type ImportMissingSumError struct {
   142  	importPath                string
   143  	found                     bool
   144  	mods                      []module.Version
   145  	importer, importerVersion string // optional, but used for additional context
   146  	importerIsTest            bool
   147  }
   148  
   149  func (e *ImportMissingSumError) Error() string {
   150  	var importParen string
   151  	if e.importer != "" {
   152  		importParen = fmt.Sprintf(" (imported by %s)", e.importer)
   153  	}
   154  	var message string
   155  	if e.found {
   156  		message = fmt.Sprintf("missing go.sum entry needed to verify package %s%s is provided by exactly one module", e.importPath, importParen)
   157  	} else {
   158  		message = fmt.Sprintf("missing go.sum entry for module providing package %s%s", e.importPath, importParen)
   159  	}
   160  	var hint string
   161  	if e.importer == "" {
   162  		// Importing package is unknown, or the missing package was named on the
   163  		// command line. Recommend 'go mod download' for the modules that could
   164  		// provide the package, since that shouldn't change go.mod.
   165  		args := make([]string, len(e.mods))
   166  		for i, mod := range e.mods {
   167  			args[i] = mod.Path
   168  		}
   169  		hint = fmt.Sprintf("; to add:\n\tgo mod download %s", strings.Join(args, " "))
   170  	} else {
   171  		// Importing package is known (common case). Recommend 'go get' on the
   172  		// current version of the importing package.
   173  		tFlag := ""
   174  		if e.importerIsTest {
   175  			tFlag = " -t"
   176  		}
   177  		version := ""
   178  		if e.importerVersion != "" {
   179  			version = "@" + e.importerVersion
   180  		}
   181  		hint = fmt.Sprintf("; to add:\n\tgo get%s %s%s", tFlag, e.importer, version)
   182  	}
   183  	return message + hint
   184  }
   185  
   186  func (e *ImportMissingSumError) ImportPath() string {
   187  	return e.importPath
   188  }
   189  
   190  type invalidImportError struct {
   191  	importPath string
   192  	err        error
   193  }
   194  
   195  func (e *invalidImportError) ImportPath() string {
   196  	return e.importPath
   197  }
   198  
   199  func (e *invalidImportError) Error() string {
   200  	return e.err.Error()
   201  }
   202  
   203  func (e *invalidImportError) Unwrap() error {
   204  	return e.err
   205  }
   206  
   207  // importFromBuildList finds the module and directory in the build list
   208  // containing the package with the given import path. The answer must be unique:
   209  // importFromBuildList returns an error if multiple modules attempt to provide
   210  // the same package.
   211  //
   212  // importFromBuildList can return a module with an empty m.Path, for packages in
   213  // the standard library.
   214  //
   215  // importFromBuildList can return an empty directory string, for fake packages
   216  // like "C" and "unsafe".
   217  //
   218  // If the package cannot be found in buildList,
   219  // importFromBuildList returns an *ImportMissingError.
   220  func importFromBuildList(ctx context.Context, path string, buildList []module.Version) (m module.Version, dir string, err error) {
   221  	if strings.Contains(path, "@") {
   222  		return module.Version{}, "", fmt.Errorf("import path should not have @version")
   223  	}
   224  	if build.IsLocalImport(path) {
   225  		return module.Version{}, "", fmt.Errorf("relative import not supported")
   226  	}
   227  	if path == "C" || path == "unsafe" {
   228  		// There's no directory for import "C" or import "unsafe".
   229  		return module.Version{}, "", nil
   230  	}
   231  	// Before any further lookup, check that the path is valid.
   232  	if err := module.CheckImportPath(path); err != nil {
   233  		return module.Version{}, "", &invalidImportError{importPath: path, err: err}
   234  	}
   235  
   236  	// Is the package in the standard library?
   237  	pathIsStd := search.IsStandardImportPath(path)
   238  	if pathIsStd && goroot.IsStandardPackage(cfg.GOROOT, cfg.BuildContext.Compiler, path) {
   239  		if targetInGorootSrc {
   240  			if dir, ok, err := dirInModule(path, targetPrefix, ModRoot(), true); err != nil {
   241  				return module.Version{}, dir, err
   242  			} else if ok {
   243  				return Target, dir, nil
   244  			}
   245  		}
   246  		dir := filepath.Join(cfg.GOROOT, "src", path)
   247  		return module.Version{}, dir, nil
   248  	}
   249  
   250  	// -mod=vendor is special.
   251  	// Everything must be in the main module or the main module's vendor directory.
   252  	if cfg.BuildMod == "vendor" {
   253  		mainDir, mainOK, mainErr := dirInModule(path, targetPrefix, ModRoot(), true)
   254  		vendorDir, vendorOK, _ := dirInModule(path, "", filepath.Join(ModRoot(), "vendor"), false)
   255  		if mainOK && vendorOK {
   256  			return module.Version{}, "", &AmbiguousImportError{importPath: path, Dirs: []string{mainDir, vendorDir}}
   257  		}
   258  		// Prefer to return main directory if there is one,
   259  		// Note that we're not checking that the package exists.
   260  		// We'll leave that for load.
   261  		if !vendorOK && mainDir != "" {
   262  			return Target, mainDir, nil
   263  		}
   264  		if mainErr != nil {
   265  			return module.Version{}, "", mainErr
   266  		}
   267  		readVendorList()
   268  		return vendorPkgModule[path], vendorDir, nil
   269  	}
   270  
   271  	// Check each module on the build list.
   272  	var dirs []string
   273  	var mods []module.Version
   274  	var sumErrMods []module.Version
   275  	for _, m := range buildList {
   276  		if !maybeInModule(path, m.Path) {
   277  			// Avoid possibly downloading irrelevant modules.
   278  			continue
   279  		}
   280  		needSum := true
   281  		root, isLocal, err := fetch(ctx, m, needSum)
   282  		if err != nil {
   283  			if sumErr := (*sumMissingError)(nil); errors.As(err, &sumErr) {
   284  				// We are missing a sum needed to fetch a module in the build list.
   285  				// We can't verify that the package is unique, and we may not find
   286  				// the package at all. Keep checking other modules to decide which
   287  				// error to report. Multiple sums may be missing if we need to look in
   288  				// multiple nested modules to resolve the import.
   289  				sumErrMods = append(sumErrMods, m)
   290  				continue
   291  			}
   292  			// Report fetch error.
   293  			// Note that we don't know for sure this module is necessary,
   294  			// but it certainly _could_ provide the package, and even if we
   295  			// continue the loop and find the package in some other module,
   296  			// we need to look at this module to make sure the import is
   297  			// not ambiguous.
   298  			return module.Version{}, "", err
   299  		}
   300  		if dir, ok, err := dirInModule(path, m.Path, root, isLocal); err != nil {
   301  			return module.Version{}, "", err
   302  		} else if ok {
   303  			mods = append(mods, m)
   304  			dirs = append(dirs, dir)
   305  		}
   306  	}
   307  	if len(mods) > 1 {
   308  		return module.Version{}, "", &AmbiguousImportError{importPath: path, Dirs: dirs, Modules: mods}
   309  	}
   310  	if len(sumErrMods) > 0 {
   311  		return module.Version{}, "", &ImportMissingSumError{
   312  			importPath: path,
   313  			mods:       sumErrMods,
   314  			found:      len(mods) > 0,
   315  		}
   316  	}
   317  	if len(mods) == 1 {
   318  		return mods[0], dirs[0], nil
   319  	}
   320  
   321  	return module.Version{}, "", &ImportMissingError{Path: path, isStd: pathIsStd}
   322  }
   323  
   324  // queryImport attempts to locate a module that can be added to the current
   325  // build list to provide the package with the given import path.
   326  //
   327  // Unlike QueryPattern, queryImport prefers to add a replaced version of a
   328  // module *before* checking the proxies for a version to add.
   329  func queryImport(ctx context.Context, path string) (module.Version, error) {
   330  	// To avoid spurious remote fetches, try the latest replacement for each
   331  	// module (golang.org/issue/26241).
   332  	if index != nil {
   333  		var mods []module.Version
   334  		for mp, mv := range index.highestReplaced {
   335  			if !maybeInModule(path, mp) {
   336  				continue
   337  			}
   338  			if mv == "" {
   339  				// The only replacement is a wildcard that doesn't specify a version, so
   340  				// synthesize a pseudo-version with an appropriate major version and a
   341  				// timestamp below any real timestamp. That way, if the main module is
   342  				// used from within some other module, the user will be able to upgrade
   343  				// the requirement to any real version they choose.
   344  				if _, pathMajor, ok := module.SplitPathVersion(mp); ok && len(pathMajor) > 0 {
   345  					mv = modfetch.ZeroPseudoVersion(pathMajor[1:])
   346  				} else {
   347  					mv = modfetch.ZeroPseudoVersion("v0")
   348  				}
   349  			}
   350  			mods = append(mods, module.Version{Path: mp, Version: mv})
   351  		}
   352  
   353  		// Every module path in mods is a prefix of the import path.
   354  		// As in QueryPattern, prefer the longest prefix that satisfies the import.
   355  		sort.Slice(mods, func(i, j int) bool {
   356  			return len(mods[i].Path) > len(mods[j].Path)
   357  		})
   358  		for _, m := range mods {
   359  			needSum := true
   360  			root, isLocal, err := fetch(ctx, m, needSum)
   361  			if err != nil {
   362  				if sumErr := (*sumMissingError)(nil); errors.As(err, &sumErr) {
   363  					return module.Version{}, &ImportMissingSumError{importPath: path}
   364  				}
   365  				return module.Version{}, err
   366  			}
   367  			if _, ok, err := dirInModule(path, m.Path, root, isLocal); err != nil {
   368  				return m, err
   369  			} else if ok {
   370  				if cfg.BuildMod == "readonly" {
   371  					return module.Version{}, &ImportMissingError{Path: path, replaced: m}
   372  				}
   373  				return m, nil
   374  			}
   375  		}
   376  		if len(mods) > 0 && module.CheckPath(path) != nil {
   377  			// The package path is not valid to fetch remotely,
   378  			// so it can only exist in a replaced module,
   379  			// and we know from the above loop that it is not.
   380  			return module.Version{}, &PackageNotInModuleError{
   381  				Mod:         mods[0],
   382  				Query:       "latest",
   383  				Pattern:     path,
   384  				Replacement: Replacement(mods[0]),
   385  			}
   386  		}
   387  	}
   388  
   389  	if search.IsStandardImportPath(path) {
   390  		// This package isn't in the standard library, isn't in any module already
   391  		// in the build list, and isn't in any other module that the user has
   392  		// shimmed in via a "replace" directive.
   393  		// Moreover, the import path is reserved for the standard library, so
   394  		// QueryPattern cannot possibly find a module containing this package.
   395  		//
   396  		// Instead of trying QueryPattern, report an ImportMissingError immediately.
   397  		return module.Version{}, &ImportMissingError{Path: path, isStd: true}
   398  	}
   399  
   400  	if cfg.BuildMod == "readonly" && !allowMissingModuleImports {
   401  		// In readonly mode, we can't write go.mod, so we shouldn't try to look up
   402  		// the module. If readonly mode was enabled explicitly, include that in
   403  		// the error message.
   404  		var queryErr error
   405  		if cfg.BuildModExplicit {
   406  			queryErr = fmt.Errorf("import lookup disabled by -mod=%s", cfg.BuildMod)
   407  		} else if cfg.BuildModReason != "" {
   408  			queryErr = fmt.Errorf("import lookup disabled by -mod=%s\n\t(%s)", cfg.BuildMod, cfg.BuildModReason)
   409  		}
   410  		return module.Version{}, &ImportMissingError{Path: path, QueryErr: queryErr}
   411  	}
   412  
   413  	// Look up module containing the package, for addition to the build list.
   414  	// Goal is to determine the module, download it to dir,
   415  	// and return m, dir, ImpportMissingError.
   416  	fmt.Fprintf(os.Stderr, "go: finding module for package %s\n", path)
   417  
   418  	candidates, err := QueryPackages(ctx, path, "latest", Selected, CheckAllowed)
   419  	if err != nil {
   420  		if errors.Is(err, fs.ErrNotExist) {
   421  			// Return "cannot find module providing package […]" instead of whatever
   422  			// low-level error QueryPattern produced.
   423  			return module.Version{}, &ImportMissingError{Path: path, QueryErr: err}
   424  		} else {
   425  			return module.Version{}, err
   426  		}
   427  	}
   428  
   429  	candidate0MissingVersion := ""
   430  	for i, c := range candidates {
   431  		cm := c.Mod
   432  		canAdd := true
   433  		for _, bm := range buildList {
   434  			if bm.Path == cm.Path && semver.Compare(bm.Version, cm.Version) > 0 {
   435  				// QueryPattern proposed that we add module cm to provide the package,
   436  				// but we already depend on a newer version of that module (and we don't
   437  				// have the package).
   438  				//
   439  				// This typically happens when a package is present at the "@latest"
   440  				// version (e.g., v1.0.0) of a module, but we have a newer version
   441  				// of the same module in the build list (e.g., v1.0.1-beta), and
   442  				// the package is not present there.
   443  				canAdd = false
   444  				if i == 0 {
   445  					candidate0MissingVersion = bm.Version
   446  				}
   447  				break
   448  			}
   449  		}
   450  		if canAdd {
   451  			return cm, nil
   452  		}
   453  	}
   454  	return module.Version{}, &ImportMissingError{
   455  		Path:              path,
   456  		Module:            candidates[0].Mod,
   457  		newMissingVersion: candidate0MissingVersion,
   458  	}
   459  }
   460  
   461  // maybeInModule reports whether, syntactically,
   462  // a package with the given import path could be supplied
   463  // by a module with the given module path (mpath).
   464  func maybeInModule(path, mpath string) bool {
   465  	return mpath == path ||
   466  		len(path) > len(mpath) && path[len(mpath)] == '/' && path[:len(mpath)] == mpath
   467  }
   468  
   469  var (
   470  	haveGoModCache   par.Cache // dir → bool
   471  	haveGoFilesCache par.Cache // dir → goFilesEntry
   472  )
   473  
   474  type goFilesEntry struct {
   475  	haveGoFiles bool
   476  	err         error
   477  }
   478  
   479  // dirInModule locates the directory that would hold the package named by the given path,
   480  // if it were in the module with module path mpath and root mdir.
   481  // If path is syntactically not within mpath,
   482  // or if mdir is a local file tree (isLocal == true) and the directory
   483  // that would hold path is in a sub-module (covered by a go.mod below mdir),
   484  // dirInModule returns "", false, nil.
   485  //
   486  // Otherwise, dirInModule returns the name of the directory where
   487  // Go source files would be expected, along with a boolean indicating
   488  // whether there are in fact Go source files in that directory.
   489  // A non-nil error indicates that the existence of the directory and/or
   490  // source files could not be determined, for example due to a permission error.
   491  func dirInModule(path, mpath, mdir string, isLocal bool) (dir string, haveGoFiles bool, err error) {
   492  	// Determine where to expect the package.
   493  	if path == mpath {
   494  		dir = mdir
   495  	} else if mpath == "" { // vendor directory
   496  		dir = filepath.Join(mdir, path)
   497  	} else if len(path) > len(mpath) && path[len(mpath)] == '/' && path[:len(mpath)] == mpath {
   498  		dir = filepath.Join(mdir, path[len(mpath)+1:])
   499  	} else {
   500  		return "", false, nil
   501  	}
   502  
   503  	// Check that there aren't other modules in the way.
   504  	// This check is unnecessary inside the module cache
   505  	// and important to skip in the vendor directory,
   506  	// where all the module trees have been overlaid.
   507  	// So we only check local module trees
   508  	// (the main module, and any directory trees pointed at by replace directives).
   509  	if isLocal {
   510  		for d := dir; d != mdir && len(d) > len(mdir); {
   511  			haveGoMod := haveGoModCache.Do(d, func() interface{} {
   512  				fi, err := fsys.Stat(filepath.Join(d, "go.mod"))
   513  				return err == nil && !fi.IsDir()
   514  			}).(bool)
   515  
   516  			if haveGoMod {
   517  				return "", false, nil
   518  			}
   519  			parent := filepath.Dir(d)
   520  			if parent == d {
   521  				// Break the loop, as otherwise we'd loop
   522  				// forever if d=="." and mdir=="".
   523  				break
   524  			}
   525  			d = parent
   526  		}
   527  	}
   528  
   529  	// Now committed to returning dir (not "").
   530  
   531  	// Are there Go source files in the directory?
   532  	// We don't care about build tags, not even "+build ignore".
   533  	// We're just looking for a plausible directory.
   534  	res := haveGoFilesCache.Do(dir, func() interface{} {
   535  		ok, err := fsys.IsDirWithGoFiles(dir)
   536  		return goFilesEntry{haveGoFiles: ok, err: err}
   537  	}).(goFilesEntry)
   538  
   539  	return dir, res.haveGoFiles, res.err
   540  }
   541  
   542  // fetch downloads the given module (or its replacement)
   543  // and returns its location.
   544  //
   545  // needSum indicates whether the module may be downloaded in readonly mode
   546  // without a go.sum entry. It should only be false for modules fetched
   547  // speculatively (for example, for incompatible version filtering). The sum
   548  // will still be verified normally.
   549  //
   550  // The isLocal return value reports whether the replacement,
   551  // if any, is local to the filesystem.
   552  func fetch(ctx context.Context, mod module.Version, needSum bool) (dir string, isLocal bool, err error) {
   553  	if mod == Target {
   554  		return ModRoot(), true, nil
   555  	}
   556  	if r := Replacement(mod); r.Path != "" {
   557  		if r.Version == "" {
   558  			dir = r.Path
   559  			if !filepath.IsAbs(dir) {
   560  				dir = filepath.Join(ModRoot(), dir)
   561  			}
   562  			// Ensure that the replacement directory actually exists:
   563  			// dirInModule does not report errors for missing modules,
   564  			// so if we don't report the error now, later failures will be
   565  			// very mysterious.
   566  			if _, err := fsys.Stat(dir); err != nil {
   567  				if os.IsNotExist(err) {
   568  					// Semantically the module version itself “exists” — we just don't
   569  					// have its source code. Remove the equivalence to os.ErrNotExist,
   570  					// and make the message more concise while we're at it.
   571  					err = fmt.Errorf("replacement directory %s does not exist", r.Path)
   572  				} else {
   573  					err = fmt.Errorf("replacement directory %s: %w", r.Path, err)
   574  				}
   575  				return dir, true, module.VersionError(mod, err)
   576  			}
   577  			return dir, true, nil
   578  		}
   579  		mod = r
   580  	}
   581  
   582  	if HasModRoot() && cfg.BuildMod == "readonly" && needSum && !modfetch.HaveSum(mod) {
   583  		return "", false, module.VersionError(mod, &sumMissingError{})
   584  	}
   585  
   586  	dir, err = modfetch.Download(ctx, mod)
   587  	return dir, false, err
   588  }
   589  
   590  type sumMissingError struct {
   591  	suggestion string
   592  }
   593  
   594  func (e *sumMissingError) Error() string {
   595  	return "missing go.sum entry" + e.suggestion
   596  }
   597
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