cmd/go: fix go get -t -u path/... containing vendor directories

A lot of things had to line up to make this break,
but the caching of download results interacted badly
with vendor directories, "go get -t -u", and wildcard
expansion.

Fixes #18219.

Change-Id: I2676498d2f714eaeb69f399e9ed527640c12e60d
Reviewed-on: https://go-review.googlesource.com/34201
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/get.go

@@ -205,6 +205,10 @@ var downloadRootCache = map[string]bool{}
 // download runs the download half of the get command
 // for the package named by the argument.
 func download(arg string, parent *Package, stk *importStack, mode int) {
+	if mode&useVendor != 0 {
+		// Caller is responsible for expanding vendor paths.
+		panic("internal error: download mode has useVendor set")
+	}
 	load := func(path string, mode int) *Package {
 		if parent == nil {
 			return loadPackage(path, stk)
@@ -315,33 +319,43 @@ func download(arg string, parent *Package, stk *importStack, mode int) {
 		}
 
 		// Process dependencies, now that we know what they are.
-		for _, path := range p.Imports {
+		imports := p.Imports
+		if mode&getTestDeps != 0 {
+			// Process test dependencies when -t is specified.
+			// (But don't get test dependencies for test dependencies:
+			// we always pass mode 0 to the recursive calls below.)
+			imports = stringList(imports, p.TestImports, p.XTestImports)
+		}
+		for i, path := range imports {
 			if path == "C" {
 				continue
 			}
-			// Don't get test dependencies recursively.
-			// Imports is already vendor-expanded.
+			// Fail fast on import naming full vendor path.
+			// Otherwise expand path as needed for test imports.
+			// Note that p.Imports can have additional entries beyond p.build.Imports.
+			orig := path
+			if i < len(p.build.Imports) {
+				orig = p.build.Imports[i]
+			}
+			if j, ok := findVendor(orig); ok {
+				stk.push(path)
+				err := &PackageError{
+					ImportStack: stk.copy(),
+					Err:         "must be imported as " + path[j+len("vendor/"):],
+				}
+				stk.pop()
+				errorf("%s", err)
+				continue
+			}
+			// If this is a test import, apply vendor lookup now.
+			// We cannot pass useVendor to download, because
+			// download does caching based on the value of path,
+			// so it must be the fully qualified path already.
+			if i >= len(p.Imports) {
+				path = vendoredImportPath(p, path)
+			}
 			download(path, p, stk, 0)
 		}
-		if mode&getTestDeps != 0 {
-			// Process test dependencies when -t is specified.
-			// (Don't get test dependencies for test dependencies.)
-			// We pass useVendor here because p.load does not
-			// vendor-expand TestImports and XTestImports.
-			// The call to loadImport inside download needs to do that.
-			for _, path := range p.TestImports {
-				if path == "C" {
-					continue
-				}
-				download(path, p, stk, useVendor)
-			}
-			for _, path := range p.XTestImports {
-				if path == "C" {
-					continue
-				}
-				download(path, p, stk, useVendor)
-			}
-		}
 
 		if isWildcard {
 			stk.pop()

src/cmd/go/pkg.go

@@ -178,7 +178,9 @@ func (p *Package) copyBuild(pp *build.Package) {
 	p.CgoCXXFLAGS = pp.CgoCXXFLAGS
 	p.CgoLDFLAGS = pp.CgoLDFLAGS
 	p.CgoPkgConfig = pp.CgoPkgConfig
-	p.Imports = pp.Imports
+	// We modify p.Imports in place, so make copy now.
+	p.Imports = make([]string, len(pp.Imports))
+	copy(p.Imports, pp.Imports)
 	p.TestGoFiles = pp.TestGoFiles
 	p.TestImports = pp.TestImports
 	p.XTestGoFiles = pp.XTestGoFiles

src/cmd/go/vendor_test.go

@@ -188,6 +188,42 @@ func TestVendorGetUpdate(t *testing.T) {
 	tg.run("get", "-u", "github.com/rsc/go-get-issue-11864")
 }
 
+func TestVendorGetU(t *testing.T) {
+	testenv.MustHaveExternalNetwork(t)
+
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.makeTempdir()
+	tg.setenv("GOPATH", tg.path("."))
+	tg.run("get", "-u", "github.com/rsc/go-get-issue-11864")
+}
+
+func TestVendorGetTU(t *testing.T) {
+	testenv.MustHaveExternalNetwork(t)
+
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.makeTempdir()
+	tg.setenv("GOPATH", tg.path("."))
+	tg.run("get", "-t", "-u", "github.com/rsc/go-get-issue-11864/...")
+}
+
+func TestVendorGetBadVendor(t *testing.T) {
+	testenv.MustHaveExternalNetwork(t)
+
+	for _, suffix := range []string{"bad/imp", "bad/imp2", "bad/imp3", "..."} {
+		t.Run(suffix, func(t *testing.T) {
+			tg := testgo(t)
+			defer tg.cleanup()
+			tg.makeTempdir()
+			tg.setenv("GOPATH", tg.path("."))
+			tg.runFail("get", "-t", "-u", "github.com/rsc/go-get-issue-18219/"+suffix)
+			tg.grepStderr("must be imported as", "did not find error about vendor import")
+			tg.mustNotExist(tg.path("src/github.com/rsc/vendor"))
+		})
+	}
+}
+
 func TestGetSubmodules(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)