cmd/go: resolve non-standard imports from within GOROOT/src using vendor directories

Updates #30228
Fixes #26924

Change-Id: Ie625c64721559c7633396342320536396cd1fcf5
Reviewed-on: https://go-review.googlesource.com/c/go/+/164621
Run-TryBot: Bryan C. Mills <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Jay Conrod <[email protected]>

Author: Bryan C. Mills

src/cmd/go/internal/cfg/cfg.go

@@ -38,7 +38,7 @@ var (
 	BuildWork              bool // -work flag
 	BuildX                 bool // -x flag
 
-	CmdName string // "build", "install", "list", etc.
+	CmdName string // "build", "install", "list", "mod tidy", etc.
 
 	DebugActiongraph string // -debug-actiongraph flag (undocumented, unstable)
 )

src/cmd/go/internal/load/pkg.go

@@ -32,14 +32,14 @@ var (
 	ModInit func()
 
 	// module hooks; nil if module use is disabled
-	ModBinDir            func() string                                       // return effective bin directory
-	ModLookup            func(path string) (dir, realPath string, err error) // lookup effective meaning of import
-	ModPackageModuleInfo func(path string) *modinfo.ModulePublic             // return module info for Package struct
-	ModImportPaths       func(args []string) []*search.Match                 // expand import paths
-	ModPackageBuildInfo  func(main string, deps []string) string             // return module info to embed in binary
-	ModInfoProg          func(info string) []byte                            // wrap module info in .go code for binary
-	ModImportFromFiles   func([]string)                                      // update go.mod to add modules for imports in these files
-	ModDirImportPath     func(string) string                                 // return effective import path for directory
+	ModBinDir            func() string                                                                            // return effective bin directory
+	ModLookup            func(parentPath string, parentIsStd bool, path string) (dir, realPath string, err error) // lookup effective meaning of import
+	ModPackageModuleInfo func(path string) *modinfo.ModulePublic                                                  // return module info for Package struct
+	ModImportPaths       func(args []string) []*search.Match                                                      // expand import paths
+	ModPackageBuildInfo  func(main string, deps []string) string                                                  // return module info to embed in binary
+	ModInfoProg          func(info string) []byte                                                                 // wrap module info in .go code for binary
+	ModImportFromFiles   func([]string)                                                                           // update go.mod to add modules for imports in these files
+	ModDirImportPath     func(string) string                                                                      // return effective import path for directory
 )
 
 var IgnoreImports bool // control whether we ignore imports in packages
@@ -483,8 +483,10 @@ func LoadImport(path, srcDir string, parent *Package, stk *ImportStack, importPo
 	}
 
 	parentPath := ""
+	parentIsStd := false
 	if parent != nil {
 		parentPath = parent.ImportPath
+		parentIsStd = parent.Standard
 	}
 
 	// Determine canonical identifier for this package.
@@ -501,7 +503,7 @@ func LoadImport(path, srcDir string, parent *Package, stk *ImportStack, importPo
 		importPath = dirToImportPath(filepath.Join(srcDir, path))
 	} else if cfg.ModulesEnabled {
 		var p string
-		modDir, p, modErr = ModLookup(path)
+		modDir, p, modErr = ModLookup(parentPath, parentIsStd, path)
 		if modErr == nil {
 			importPath = p
 		}
@@ -641,7 +643,13 @@ func isDir(path string) bool {
 // Go 1.11 module legacy conversion (golang.org/issue/25069).
 func ResolveImportPath(parent *Package, path string) (found string) {
 	if cfg.ModulesEnabled {
-		if _, p, e := ModLookup(path); e == nil {
+		parentPath := ""
+		parentIsStd := false
+		if parent != nil {
+			parentPath = parent.ImportPath
+			parentIsStd = parent.Standard
+		}
+		if _, p, e := ModLookup(parentPath, parentIsStd, path); e == nil {
 			return p
 		}
 		return path
@@ -1401,16 +1409,6 @@ func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 			continue
 		}
 		p1 := LoadImport(path, p.Dir, p, stk, p.Internal.Build.ImportPos[path], ResolveImport)
-		if p.Standard && p.Error == nil && !p1.Standard && p1.Error == nil {
-			p.Error = &PackageError{
-				ImportStack: stk.Copy(),
-				Err:         fmt.Sprintf("non-standard import %q in standard package %q", path, p.ImportPath),
-			}
-			pos := p.Internal.Build.ImportPos[path]
-			if len(pos) > 0 {
-				p.Error.Pos = pos[0].String()
-			}
-		}
 
 		path = p1.ImportPath
 		importPaths[i] = path

src/cmd/go/internal/modload/build.go

@@ -38,9 +38,6 @@ func findStandardImportPath(path string) string {
 		if goroot.IsStandardPackage(cfg.GOROOT, cfg.BuildContext.Compiler, path) {
 			return filepath.Join(cfg.GOROOT, "src", path)
 		}
-		if goroot.IsStandardPackage(cfg.GOROOT, cfg.BuildContext.Compiler, "vendor/"+path) {
-			return filepath.Join(cfg.GOROOT, "src/vendor", path)
-		}
 	}
 	return ""
 }

src/cmd/go/internal/modload/import.go

@@ -64,6 +64,19 @@ func Import(path string) (m module.Version, dir string, err error) {
 	if search.IsStandardImportPath(path) {
 		if goroot.IsStandardPackage(cfg.GOROOT, cfg.BuildContext.Compiler, path) {
 			dir := filepath.Join(cfg.GOROOT, "src", path)
+
+			// If the main module is in the standard library, attribute its packages
+			// to that module.
+			switch Target.Path {
+			case "cmd":
+				if strings.HasPrefix(path, "cmd") {
+					return Target, dir, nil
+				}
+			case "std":
+				if !strings.HasPrefix(path, "cmd") {
+					return Target, dir, nil
+				}
+			}
 			return module.Version{}, dir, nil
 		}
 	}

src/cmd/go/internal/modload/init.go

@@ -18,6 +18,7 @@ import (
 	"cmd/go/internal/mvs"
 	"cmd/go/internal/renameio"
 	"cmd/go/internal/search"
+	"cmd/go/internal/str"
 	"encoding/json"
 	"fmt"
 	"go/build"
@@ -380,6 +381,11 @@ func InitMod() {
 // modFileToBuildList initializes buildList from the modFile.
 func modFileToBuildList() {
 	Target = modFile.Module.Mod
+	if (str.HasPathPrefix(Target.Path, "std") || str.HasPathPrefix(Target.Path, "cmd")) &&
+		search.InDir(cwd, cfg.GOROOTsrc) == "" {
+		base.Fatalf("go: reserved module path %s not allow outside of GOROOT/src", Target.Path)
+	}
+
 	list := []module.Version{Target}
 	for _, r := range modFile.Require {
 		list = append(list, r.Mod)

src/cmd/go/internal/modload/load.go

@@ -12,6 +12,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path"
+	pathpkg "path"
 	"path/filepath"
 	"sort"
 	"strings"
@@ -90,7 +91,9 @@ func ImportPaths(patterns []string) []*search.Match {
 				// the exact version of a particular module increases during
 				// the loader iterations.
 				m.Pkgs = str.StringList(fsDirs[i])
-				for j, pkg := range m.Pkgs {
+				pkgs := m.Pkgs
+				m.Pkgs = m.Pkgs[:0]
+				for _, pkg := range pkgs {
 					dir := pkg
 					if !filepath.IsAbs(dir) {
 						dir = filepath.Join(cwd, pkg)
@@ -108,6 +111,16 @@ func ImportPaths(patterns []string) []*search.Match {
 						if strings.HasPrefix(suffix, "/vendor/") {
 							// TODO getmode vendor check
 							pkg = strings.TrimPrefix(suffix, "/vendor/")
+						} else if Target.Path == "std" {
+							// Don't add the prefix "std/" to packages in the "std" module.
+							// It's the one module path that isn't a prefix of its packages.
+							pkg = strings.TrimPrefix(suffix, "/")
+							if pkg == "builtin" {
+								// "builtin" is a pseudo-package with a real source file.
+								// It's not included in "std", so it shouldn't be included in
+								// "./..." within module "std" either.
+								continue
+							}
 						} else {
 							pkg = Target.Path + suffix
 						}
@@ -129,10 +142,10 @@ func ImportPaths(patterns []string) []*search.Match {
 						// After loader is done iterating, we still need to return the
 						// path, so that "go list -e" produces valid output.
 						if iterating {
-							pkg = ""
+							continue
 						}
 					}
-					m.Pkgs[j] = pkg
+					m.Pkgs = append(m.Pkgs, pkg)
 				}
 
 			case strings.Contains(m.Pattern, "..."):
@@ -163,9 +176,7 @@ func ImportPaths(patterns []string) []*search.Match {
 		updateMatches(true)
 		for _, m := range matches {
 			for _, pkg := range m.Pkgs {
-				if pkg != "" {
-					roots = append(roots, pkg)
-				}
+				roots = append(roots, pkg)
 			}
 		}
 		return roots
@@ -394,13 +405,17 @@ func ModuleUsedDirectly(path string) bool {
 }
 
 // Lookup returns the source directory, import path, and any loading error for
-// the package at path.
+// the package at path as imported from the package in parentDir.
 // Lookup requires that one of the Load functions in this package has already
 // been called.
-func Lookup(path string) (dir, realPath string, err error) {
+func Lookup(parentPath string, parentIsStd bool, path string) (dir, realPath string, err error) {
 	if path == "" {
 		panic("Lookup called with empty package path")
 	}
+
+	if parentIsStd {
+		path = loaded.stdVendor(parentPath, path)
+	}
 	pkg, ok := loaded.pkgCache.Get(path).(*loadPkg)
 	if !ok {
 		// The loader should have found all the relevant paths.
@@ -434,10 +449,11 @@ func Lookup(path string) (dir, realPath string, err error) {
 // TODO(rsc): It might be nice to make the loader take and return
 // a buildList rather than hard-coding use of the global.
 type loader struct {
-	tags      map[string]bool // tags for scanDir
-	testRoots bool            // include tests for roots
-	isALL     bool            // created with LoadALL
-	testAll   bool            // include tests for all packages
+	tags           map[string]bool // tags for scanDir
+	testRoots      bool            // include tests for roots
+	isALL          bool            // created with LoadALL
+	testAll        bool            // include tests for all packages
+	forceStdVendor bool            // if true, load standard-library dependencies from the vendor subtree
 
 	// reset on each iteration
 	roots    []*loadPkg
@@ -457,6 +473,17 @@ func newLoader() *loader {
 	ld := new(loader)
 	ld.tags = imports.Tags()
 	ld.testRoots = LoadTests
+
+	switch Target.Path {
+	case "std", "cmd":
+		// Inside the "std" and "cmd" modules, we prefer to use the vendor directory
+		// unless the command explicitly changes the module graph.
+		// TODO(golang.org/issue/30240): Remove this special case.
+		if cfg.CmdName != "get" && !strings.HasPrefix(cfg.CmdName, "mod ") {
+			ld.forceStdVendor = true
+		}
+	}
+
 	return ld
 }
 
@@ -631,7 +658,11 @@ func (ld *loader) doPkg(item interface{}) {
 		}
 	}
 
+	inStd := (search.IsStandardImportPath(pkg.path) && search.InDir(pkg.dir, cfg.GOROOTsrc) != "")
 	for _, path := range imports {
+		if inStd {
+			path = ld.stdVendor(pkg.path, path)
+		}
 		pkg.imports = append(pkg.imports, ld.pkg(path, false))
 	}
 
@@ -642,6 +673,30 @@ func (ld *loader) doPkg(item interface{}) {
 	}
 }
 
+// stdVendor returns the canonical import path for the package with the given
+// path when imported from the standard-library package at parentPath.
+func (ld *loader) stdVendor(parentPath, path string) string {
+	if search.IsStandardImportPath(path) {
+		return path
+	}
+
+	if str.HasPathPrefix(parentPath, "cmd") && (Target.Path != "cmd" || ld.forceStdVendor) {
+		vendorPath := pathpkg.Join("cmd", "vendor", path)
+		if _, err := os.Stat(filepath.Join(cfg.GOROOTsrc, filepath.FromSlash(vendorPath))); err == nil {
+			return vendorPath
+		}
+	}
+	if Target.Path != "std" || ld.forceStdVendor {
+		vendorPath := pathpkg.Join("vendor", path)
+		if _, err := os.Stat(filepath.Join(cfg.GOROOTsrc, filepath.FromSlash(vendorPath))); err == nil {
+			return vendorPath
+		}
+	}
+
+	// Not vendored: resolve from modules.
+	return path
+}
+
 // computePatternAll returns the list of packages matching pattern "all",
 // starting with a list of the import paths for the packages in the main module.
 func (ld *loader) computePatternAll(paths []string) []string {
@@ -932,6 +987,20 @@ func (r *mvsReqs) required(mod module.Version) ([]module.Version, error) {
 		return vendorList, nil
 	}
 
+	switch Target.Path {
+	case "std", "cmd":
+		// When inside "std" or "cmd", only fetch and read go.mod files if we're
+		// explicitly running a command that can change the module graph. If we have
+		// to resolve a new dependency, we might pick the wrong version, but 'go mod
+		// tidy' will fix it — and new standard-library dependencies should be rare
+		// anyway.
+		//
+		// TODO(golang.org/issue/30240): Drop this special-case.
+		if cfg.CmdName != "get" && !strings.HasPrefix(cfg.CmdName, "mod ") {
+			return nil, nil
+		}
+	}
+
 	origPath := mod.Path
 	if repl := Replacement(mod); repl.Path != "" {
 		if repl.Version == "" {

src/cmd/go/internal/modload/query.go

@@ -9,6 +9,7 @@ import (
 	"cmd/go/internal/modfetch/codehost"
 	"cmd/go/internal/module"
 	"cmd/go/internal/semver"
+	"cmd/go/internal/str"
 	"fmt"
 	pathpkg "path"
 	"strings"
@@ -131,6 +132,10 @@ func Query(path, query string, allowed func(module.Version) bool) (*modfetch.Rev
 		return &modfetch.RevInfo{Version: Target.Version}, nil
 	}
 
+	if str.HasPathPrefix(path, "std") || str.HasPathPrefix(path, "cmd") {
+		return nil, fmt.Errorf("explicit requirement on standard-library module %s not allowed", path)
+	}
+
 	// Load versions and execute query.
 	repo, err := modfetch.Lookup(path)
 	if err != nil {