go/build: support vendor directories in Import

This fix, plus a one-line change to golang.org/x/tools/go/loader,
is sufficient to let that loader package process source code
using vendored packages. For example,

	GOPATH="" ssadump net/http # uses vendored http2

used to fail, not able to find net/http's import of the vendored
copy of golang.org/x/net/http2/hpack.

This CL plus the fix to loader (CL 17727) suffices to get ssadump working,
as well as - I expect - most other source code processing built
on golang.org/x/tools/go/loader.

Fixes #12278.

Change-Id: I83715e757419171159f67d49bb453636afdd91f0
Reviewed-on: https://go-review.googlesource.com/17726
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/pkg.go

@@ -118,7 +118,7 @@ func (p *Package) vendored(imports []string) []string {
 	seen := make(map[string]bool)
 	var all []string
 	for _, path := range imports {
-		path, _ = vendoredImportPath(p, path)
+		path = vendoredImportPath(p, path)
 		if !seen[path] {
 			seen[path] = true
 			all = append(all, path)
@@ -256,6 +256,7 @@ func reloadPackage(arg string, stk *importStack) *Package {
 // The variable is obnoxiously long so that years from now when people find it in
 // their profiles and wonder what it does, there is some chance that a web search
 // might answer the question.
+// There is a copy of this variable in src/go/build/build.go. Delete that one when this one goes away.
 var go15VendorExperiment = os.Getenv("GO15VENDOREXPERIMENT") != "0"
 
 // dirToImportPath returns the pseudo-import path we use for a package
@@ -312,11 +313,14 @@ func loadImport(path, srcDir string, parent *Package, stk *importStack, importPo
 	importPath := path
 	origPath := path
 	isLocal := build.IsLocalImport(path)
-	var vendorSearch []string
 	if isLocal {
 		importPath = dirToImportPath(filepath.Join(srcDir, path))
 	} else if mode&useVendor != 0 {
-		path, vendorSearch = vendoredImportPath(parent, path)
+		// We do our own vendor resolution, because we want to
+		// find out the key to use in packageCache without the
+		// overhead of repeated calls to buildContext.Import.
+		// The code is also needed in a few other places anyway.
+		path = vendoredImportPath(parent, path)
 		importPath = path
 	}
 
@@ -343,29 +347,14 @@ func loadImport(path, srcDir string, parent *Package, stk *importStack, importPo
 	//
 	// TODO: After Go 1, decide when to pass build.AllowBinary here.
 	// See issue 3268 for mistakes to avoid.
-	bp, err := buildContext.Import(path, srcDir, build.ImportComment)
-
-	// If we got an error from go/build about package not found,
-	// it contains the directories from $GOROOT and $GOPATH that
-	// were searched. Add to that message the vendor directories
-	// that were searched.
-	if err != nil && len(vendorSearch) > 0 {
-		// NOTE(rsc): The direct text manipulation here is fairly awful,
-		// but it avoids defining new go/build API (an exported error type)
-		// late in the Go 1.5 release cycle. If this turns out to be a more general
-		// problem we could define a real error type when the decision can be
-		// considered more carefully.
-		text := err.Error()
-		if strings.Contains(text, "cannot find package \"") && strings.Contains(text, "\" in any of:\n\t") {
-			old := strings.SplitAfter(text, "\n")
-			lines := []string{old[0]}
-			for _, dir := range vendorSearch {
-				lines = append(lines, "\t"+dir+" (vendor tree)\n")
-			}
-			lines = append(lines, old[1:]...)
-			err = errors.New(strings.Join(lines, ""))
-		}
+	buildMode := build.ImportComment
+	if go15VendorExperiment && mode&useVendor != 0 && path == origPath {
+		// We've already searched the vendor directories and didn't find anything.
+		// Let Import search them again so that, if the package is not found anywhere,
+		// the error includes the vendor directories in the list of places considered.
+		buildMode |= build.AllowVendor
 	}
+	bp, err := buildContext.Import(path, srcDir, buildMode)
 	bp.ImportPath = importPath
 	if gobin != "" {
 		bp.BinDir = gobin
@@ -411,12 +400,9 @@ func isDir(path string) bool {
 // If parent is x/y/z, then path might expand to x/y/z/vendor/path, x/y/vendor/path,
 // x/vendor/path, vendor/path, or else stay path if none of those exist.
 // vendoredImportPath returns the expanded path or, if no expansion is found, the original.
-// If no expansion is found, vendoredImportPath also returns a list of vendor directories
-// it searched along the way, to help prepare a useful error message should path turn
-// out not to exist.
-func vendoredImportPath(parent *Package, path string) (found string, searched []string) {
+func vendoredImportPath(parent *Package, path string) (found string) {
 	if parent == nil || parent.Root == "" || !go15VendorExperiment {
-		return path, nil
+		return path
 	}
 	dir := filepath.Clean(parent.Dir)
 	root := filepath.Join(parent.Root, "src")
@@ -451,14 +437,12 @@ func vendoredImportPath(parent *Package, path string) (found string, searched []
 				// and found c:\gopath\src\vendor\path.
 				// We chopped \foo\bar (length 8) but the import path is "foo/bar" (length 7).
 				// Use "vendor/path" without any prefix.
-				return vpath, nil
+				return vpath
 			}
-			return parent.ImportPath[:len(parent.ImportPath)-chopped] + "/" + vpath, nil
+			return parent.ImportPath[:len(parent.ImportPath)-chopped] + "/" + vpath
 		}
-		// Note the existence of a vendor directory in case path is not found anywhere.
-		searched = append(searched, targ)
 	}
-	return path, searched
+	return path
 }
 
 // reusePackage reuses package p to satisfy the import at the top

src/cmd/go/vendor_test.go

@@ -102,7 +102,7 @@ func TestVendorImportError(t *testing.T) {
 
 	re := regexp.MustCompile(`cannot find package "notfound" in any of:
 	.*[\\/]testdata[\\/]src[\\/]vend[\\/]x[\\/]vendor[\\/]notfound \(vendor tree\)
-	.*[\\/]testdata[\\/]src[\\/]vend[\\/]vendor[\\/]notfound \(vendor tree\)
+	.*[\\/]testdata[\\/]src[\\/]vend[\\/]vendor[\\/]notfound
 	.*[\\/]src[\\/]notfound \(from \$GOROOT\)
 	.*[\\/]testdata[\\/]src[\\/]notfound \(from \$GOPATH\)`)
 

src/go/build/build.go

@@ -110,7 +110,7 @@ func (ctxt *Context) splitPathList(s string) []string {
 	return filepath.SplitList(s)
 }
 
-// isAbsPath calls ctxt.IsAbsSPath (if not nil) or else filepath.IsAbs.
+// isAbsPath calls ctxt.IsAbsPath (if not nil) or else filepath.IsAbs.
 func (ctxt *Context) isAbsPath(path string) bool {
 	if f := ctxt.IsAbsPath; f != nil {
 		return f(path)
@@ -343,6 +343,19 @@ const (
 	// or finds conflicting comments in multiple source files.
 	// See golang.org/s/go14customimport for more information.
 	ImportComment
+
+	// If AllowVendor is set, Import searches vendor directories
+	// that apply in the given source directory before searching
+	// the GOROOT and GOPATH roots.
+	// If an Import finds and returns a package using a vendor
+	// directory, the resulting ImportPath is the complete path
+	// to the package, including the path elements leading up
+	// to and including "vendor".
+	// For example, if Import("y", "x/subdir", AllowVendor) finds
+	// "x/vendor/y", the returned package's ImportPath is "x/vendor/y",
+	// not plain "y".
+	// See golang.org/s/go15vendor for more information.
+	AllowVendor
 )
 
 // A Package describes the Go package found in a directory.
@@ -474,15 +487,22 @@ func (ctxt *Context) Import(path string, srcDir string, mode ImportMode) (*Packa
 	switch ctxt.Compiler {
 	case "gccgo":
 		pkgtargetroot = "pkg/gccgo_" + ctxt.GOOS + "_" + ctxt.GOARCH + suffix
-		dir, elem := pathpkg.Split(p.ImportPath)
-		pkga = pkgtargetroot + "/" + dir + "lib" + elem + ".a"
 	case "gc":
 		pkgtargetroot = "pkg/" + ctxt.GOOS + "_" + ctxt.GOARCH + suffix
-		pkga = pkgtargetroot + "/" + p.ImportPath + ".a"
 	default:
 		// Save error for end of function.
 		pkgerr = fmt.Errorf("import %q: unknown compiler %q", path, ctxt.Compiler)
 	}
+	setPkga := func() {
+		switch ctxt.Compiler {
+		case "gccgo":
+			dir, elem := pathpkg.Split(p.ImportPath)
+			pkga = pkgtargetroot + "/" + dir + "lib" + elem + ".a"
+		case "gc":
+			pkga = pkgtargetroot + "/" + p.ImportPath + ".a"
+		}
+	}
+	setPkga()
 
 	binaryOnly := false
 	if IsLocalImport(path) {
@@ -543,9 +563,50 @@ func (ctxt *Context) Import(path string, srcDir string, mode ImportMode) (*Packa
 
 		// tried records the location of unsuccessful package lookups
 		var tried struct {
+			vendor []string
 			goroot string
 			gopath []string
 		}
+		gopath := ctxt.gopath()
+
+		// Vendor directories get first chance to satisfy import.
+		if mode&AllowVendor != 0 && srcDir != "" {
+			searchVendor := func(root string, isGoroot bool) bool {
+				sub, ok := ctxt.hasSubdir(root, srcDir)
+				if !ok || !strings.HasPrefix(sub, "src/") || strings.Contains(sub, "/testdata/") {
+					return false
+				}
+				for {
+					vendor := ctxt.joinPath(root, sub, "vendor")
+					if ctxt.isDir(vendor) {
+						dir := ctxt.joinPath(vendor, path)
+						if ctxt.isDir(dir) {
+							p.Dir = dir
+							p.ImportPath = strings.TrimPrefix(pathpkg.Join(sub, "vendor", path), "src/")
+							p.Goroot = isGoroot
+							p.Root = root
+							setPkga() // p.ImportPath changed
+							return true
+						}
+						tried.vendor = append(tried.vendor, dir)
+					}
+					i := strings.LastIndex(sub, "/")
+					if i < 0 {
+						break
+					}
+					sub = sub[:i]
+				}
+				return false
+			}
+			if searchVendor(ctxt.GOROOT, true) {
+				goto Found
+			}
+			for _, root := range gopath {
+				if searchVendor(root, false) {
+					goto Found
+				}
+			}
+		}
 
 		// Determine directory from import path.
 		if ctxt.GOROOT != "" {
@@ -560,7 +621,7 @@ func (ctxt *Context) Import(path string, srcDir string, mode ImportMode) (*Packa
 			}
 			tried.goroot = dir
 		}
-		for _, root := range ctxt.gopath() {
+		for _, root := range gopath {
 			dir := ctxt.joinPath(root, "src", path)
 			isDir := ctxt.isDir(dir)
 			binaryOnly = !isDir && mode&AllowBinary != 0 && pkga != "" && ctxt.isFile(ctxt.joinPath(root, pkga))
@@ -574,20 +635,22 @@ func (ctxt *Context) Import(path string, srcDir string, mode ImportMode) (*Packa
 
 		// package was not found
 		var paths []string
+		format := "\t%s (vendor tree)"
+		for _, dir := range tried.vendor {
+			paths = append(paths, fmt.Sprintf(format, dir))
+			format = "\t%s"
+		}
 		if tried.goroot != "" {
 			paths = append(paths, fmt.Sprintf("\t%s (from $GOROOT)", tried.goroot))
 		} else {
 			paths = append(paths, "\t($GOROOT not set)")
 		}
-		var i int
-		var format = "\t%s (from $GOPATH)"
-		for ; i < len(tried.gopath); i++ {
-			if i > 0 {
-				format = "\t%s"
-			}
-			paths = append(paths, fmt.Sprintf(format, tried.gopath[i]))
+		format = "\t%s (from $GOPATH)"
+		for _, dir := range tried.gopath {
+			paths = append(paths, fmt.Sprintf(format, dir))
+			format = "\t%s"
 		}
-		if i == 0 {
+		if len(tried.gopath) == 0 {
 			paths = append(paths, "\t($GOPATH not set)")
 		}
 		return p, fmt.Errorf("cannot find package %q in any of:\n%s", path, strings.Join(paths, "\n"))

src/go/build/build_test.go

@@ -297,3 +297,30 @@ func TestShellSafety(t *testing.T) {
 		}
 	}
 }
+
+func TestImportVendor(t *testing.T) {
+	ctxt := Default
+	ctxt.GOPATH = ""
+	p, err := ctxt.Import("golang.org/x/net/http2/hpack", filepath.Join(ctxt.GOROOT, "src/net/http"), AllowVendor)
+	if err != nil {
+		t.Fatalf("cannot find vendored golang.org/x/net/http2/hpack from net/http directory: %v", err)
+	}
+	want := "vendor/golang.org/x/net/http2/hpack"
+	if p.ImportPath != want {
+		t.Fatalf("Import succeeded but found %q, want %q", p.ImportPath, want)
+	}
+}
+
+func TestImportVendorFailure(t *testing.T) {
+	ctxt := Default
+	ctxt.GOPATH = ""
+	p, err := ctxt.Import("x.com/y/z", filepath.Join(ctxt.GOROOT, "src/net/http"), AllowVendor)
+	if err == nil {
+		t.Fatalf("found made-up package x.com/y/z in %s", p.Dir)
+	}
+
+	e := err.Error()
+	if !strings.Contains(e, " (vendor tree)") {
+		t.Fatalf("error on failed import does not mention GOROOT/src/vendor directory:\n%s", e)
+	}
+}