cmd/go: test remote lookup of packages with leading dots in path elements

Follow-up to CL 297530.

For #43985
For #34992

Change-Id: I2cfa6c41c013e627c3464c383ca42f5c9ebe521a
Reviewed-on: https://go-review.googlesource.com/c/go/+/297634
Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/cmd/go.mod

@@ -6,7 +6,7 @@ require (
 	github.com/google/pprof v0.0.0-20201203190320-1bf35d6f28c2
 	golang.org/x/arch v0.0.0-20201008161808-52c3e6f60cff
 	golang.org/x/crypto v0.0.0-20201016220609-9e8e0b390897
-	golang.org/x/mod v0.4.2-0.20210309222212-d6ab96f2441f
+	golang.org/x/mod v0.4.3-0.20210310185834-19d50cac98aa
 	golang.org/x/sys v0.0.0-20210218145245-beda7e5e158e // indirect
 	golang.org/x/tools v0.1.1-0.20210220032852-2363391a5b2f
 )

src/cmd/go.sum

@@ -14,8 +14,8 @@ golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPh
 golang.org/x/crypto v0.0.0-20201016220609-9e8e0b390897 h1:pLI5jrR7OSLijeIDcmRxNmw2api+jEfxLoykJVice/E=
 golang.org/x/crypto v0.0.0-20201016220609-9e8e0b390897/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
 golang.org/x/mod v0.4.1/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
-golang.org/x/mod v0.4.2-0.20210309222212-d6ab96f2441f h1:mQozKYYFIVK0MXcDB8Dvw0dR3rxKLnkSCJHWznfaodQ=
-golang.org/x/mod v0.4.2-0.20210309222212-d6ab96f2441f/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
+golang.org/x/mod v0.4.3-0.20210310185834-19d50cac98aa h1:++oSKjoJSsXNHyhUdK1BtBKMAaMHER+GWyKN3319OZA=
+golang.org/x/mod v0.4.3-0.20210310185834-19d50cac98aa/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/net v0.0.0-20201021035429-f5854403a974/go.mod h1:sp8m0HH+o8qH0wwXwYZr8TS3Oi6o0r6Gce1SSxlDquU=

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

@@ -695,7 +695,9 @@ func QueryPattern(ctx context.Context, pattern, query string, current func(strin
 
 // modulePrefixesExcludingTarget returns all prefixes of path that may plausibly
 // exist as a module, excluding targetPrefix but otherwise including path
-// itself, sorted by descending length.
+// itself, sorted by descending length. Prefixes that are not valid module paths
+// but are valid package paths (like "m" or "example.com/.gen") are included,
+// since they might be replaced.
 func modulePrefixesExcludingTarget(path string) []string {
 	prefixes := make([]string, 0, strings.Count(path, "/")+1)
 
@@ -747,6 +749,7 @@ func queryPrefixModules(ctx context.Context, candidateModules []string, queryMod
 		noPackage   *PackageNotInModuleError
 		noVersion   *NoMatchingVersionError
 		noPatchBase *NoPatchBaseError
+		invalidPath *module.InvalidPathError // see comment in case below
 		notExistErr error
 	)
 	for _, r := range results {
@@ -767,6 +770,17 @@ func queryPrefixModules(ctx context.Context, candidateModules []string, queryMod
 			if noPatchBase == nil {
 				noPatchBase = rErr
 			}
+		case *module.InvalidPathError:
+			// The prefix was not a valid module path, and there was no replacement.
+			// Prefixes like this may appear in candidateModules, since we handle
+			// replaced modules that weren't required in the repo lookup process
+			// (see lookupRepo).
+			//
+			// A shorter prefix may be a valid module path and may contain a valid
+			// import path, so this is a low-priority error.
+			if invalidPath == nil {
+				invalidPath = rErr
+			}
 		default:
 			if errors.Is(rErr, fs.ErrNotExist) {
 				if notExistErr == nil {
@@ -800,6 +814,8 @@ func queryPrefixModules(ctx context.Context, candidateModules []string, queryMod
 			err = noVersion
 		case noPatchBase != nil:
 			err = noPatchBase
+		case invalidPath != nil:
+			err = invalidPath
 		case notExistErr != nil:
 			err = notExistErr
 		default:

src/cmd/go/proxy_test.go

@@ -362,7 +362,7 @@ func proxyHandler(w http.ResponseWriter, r *http.Request) {
 			var buf bytes.Buffer
 			z := zip.NewWriter(&buf)
 			for _, f := range a.Files {
-				if strings.HasPrefix(f.Name, ".") {
+				if f.Name == ".info" || f.Name == ".mod" || f.Name == ".zip" {
 					continue
 				}
 				var zipName string

src/cmd/go/testdata/mod/example.com_dotname_v1.0.0.txt

@@ -0,0 +1,12 @@
+-- .info --
+{"Version":"v1.0.0"}
+-- .mod --
+module example.com/dotname
+
+go 1.16
+-- go.mod --
+module example.com/dotname
+
+go 1.16
+-- .dot/dot.go --
+package dot

src/cmd/go/testdata/script/mod_invalid_path_dotname.txt

@@ -0,0 +1,46 @@
+# Test that an import path containing an element with a leading dot
+# in another module is valid.
+
+# 'go get' works with no version query.
+cp go.mod.empty go.mod
+go get -d example.com/dotname/.dot
+go list -m example.com/dotname
+stdout '^example.com/dotname v1.0.0$'
+
+# 'go get' works with a version query.
+cp go.mod.empty go.mod
+go get -d example.com/dotname/.dot@latest
+go list -m example.com/dotname
+stdout '^example.com/dotname v1.0.0$'
+
+# 'go get' works on an importing package.
+cp go.mod.empty go.mod
+go get -d .
+go list -m example.com/dotname
+stdout '^example.com/dotname v1.0.0$'
+
+# 'go list' works on the dotted package.
+go list example.com/dotname/.dot
+stdout '^example.com/dotname/.dot$'
+
+# 'go list' works on an importing package.
+go list .
+stdout '^m$'
+
+# 'go mod tidy' works.
+cp go.mod.empty go.mod
+go mod tidy
+go list -m example.com/dotname
+stdout '^example.com/dotname v1.0.0$'
+
+-- go.mod.empty --
+module m
+
+go 1.16
+-- go.sum --
+example.com/dotname v1.0.0 h1:Q0JMAn464CnwFVCshs1n4+f5EFiW/eRhnx/fTWjw2Ag=
+example.com/dotname v1.0.0/go.mod h1:7K4VLT7QylRI8H7yZwUkeDH2s19wQnyfp/3oBlItWJ0=
+-- use.go --
+package use
+
+import _ "example.com/dotname/.dot"

src/cmd/go/testdata/script/mod_invalid_path_plus.txt

@@ -2,18 +2,22 @@
 # The '+' character should be disallowed in module paths, but allowed in package
 # paths within valid modules.
 
+# 'go list' accepts package paths with pluses.
+cp go.mod.orig go.mod
 go get -d example.net/cmd
 go list example.net/cmd/x++
 
+# 'go list -m' rejects module paths with pluses.
 ! go list -versions -m 'example.net/bad++'
 stderr '^go list -m: malformed module path "example.net/bad\+\+": invalid char ''\+''$'
 
-# TODO(bcmills): 'go get -d example.net/cmd/x++' should also work, but currently
-# it does not. This might be fixed by https://golang.org/cl/297891.
-! go get -d example.net/cmd/x++
-stderr '^go get: malformed module path "example.net/cmd/x\+\+": invalid char ''\+''$'
+# 'go get' accepts package paths with pluses.
+cp go.mod.orig go.mod
+go get -d example.net/cmd/x++
+go list -m example.net/cmd
+stdout '^example.net/cmd v0.0.0-00010101000000-000000000000 => ./cmd$'
 
--- go.mod --
+-- go.mod.orig --
 module example.com/m
 
 go 1.16

src/cmd/vendor/golang.org/x/mod/module/module.go

@@ -192,6 +192,21 @@ func (e *InvalidVersionError) Error() string {
 
 func (e *InvalidVersionError) Unwrap() error { return e.Err }
 
+// An InvalidPathError indicates a module, import, or file path doesn't
+// satisfy all naming constraints. See CheckPath, CheckImportPath,
+// and CheckFilePath for specific restrictions.
+type InvalidPathError struct {
+	Kind string // "module", "import", or "file"
+	Path string
+	Err  error
+}
+
+func (e *InvalidPathError) Error() string {
+	return fmt.Sprintf("malformed %s path %q: %v", e.Kind, e.Path, e.Err)
+}
+
+func (e *InvalidPathError) Unwrap() error { return e.Err }
+
 // Check checks that a given module path, version pair is valid.
 // In addition to the path being a valid module path
 // and the version being a valid semantic version,
@@ -296,30 +311,36 @@ func fileNameOK(r rune) bool {
 // this second requirement is replaced by a requirement that the path
 // follow the gopkg.in server's conventions.
 // Third, no path element may begin with a dot.
-func CheckPath(path string) error {
+func CheckPath(path string) (err error) {
+	defer func() {
+		if err != nil {
+			err = &InvalidPathError{Kind: "module", Path: path, Err: err}
+		}
+	}()
+
 	if err := checkPath(path, modulePath); err != nil {
-		return fmt.Errorf("malformed module path %q: %v", path, err)
+		return err
 	}
 	i := strings.Index(path, "/")
 	if i < 0 {
 		i = len(path)
 	}
 	if i == 0 {
-		return fmt.Errorf("malformed module path %q: leading slash", path)
+		return fmt.Errorf("leading slash")
 	}
 	if !strings.Contains(path[:i], ".") {
-		return fmt.Errorf("malformed module path %q: missing dot in first path element", path)
+		return fmt.Errorf("missing dot in first path element")
 	}
 	if path[0] == '-' {
-		return fmt.Errorf("malformed module path %q: leading dash in first path element", path)
+		return fmt.Errorf("leading dash in first path element")
 	}
 	for _, r := range path[:i] {
 		if !firstPathOK(r) {
-			return fmt.Errorf("malformed module path %q: invalid char %q in first path element", path, r)
+			return fmt.Errorf("invalid char %q in first path element", r)
 		}
 	}
 	if _, _, ok := SplitPathVersion(path); !ok {
-		return fmt.Errorf("malformed module path %q: invalid version", path)
+		return fmt.Errorf("invalid version")
 	}
 	return nil
 }
@@ -343,7 +364,7 @@ func CheckPath(path string) error {
 // subtleties of Unicode.
 func CheckImportPath(path string) error {
 	if err := checkPath(path, importPath); err != nil {
-		return fmt.Errorf("malformed import path %q: %v", path, err)
+		return &InvalidPathError{Kind: "import", Path: path, Err: err}
 	}
 	return nil
 }
@@ -358,12 +379,13 @@ const (
 	filePath
 )
 
-// checkPath checks that a general path is valid.
-// It returns an error describing why but not mentioning path.
-// Because these checks apply to both module paths and import paths,
-// the caller is expected to add the "malformed ___ path %q: " prefix.
-// fileName indicates whether the final element of the path is a file name
-// (as opposed to a directory name).
+// checkPath checks that a general path is valid. kind indicates what
+// specific constraints should be applied.
+//
+// checkPath returns an error describing why the path is not valid.
+// Because these checks apply to module, import, and file paths,
+// and because other checks may be applied, the caller is expected to wrap
+// this error with InvalidPathError.
 func checkPath(path string, kind pathKind) error {
 	if !utf8.ValidString(path) {
 		return fmt.Errorf("invalid UTF-8")
@@ -477,7 +499,7 @@ func checkElem(elem string, kind pathKind) error {
 // subtleties of Unicode.
 func CheckFilePath(path string) error {
 	if err := checkPath(path, filePath); err != nil {
-		return fmt.Errorf("malformed file path %q: %v", path, err)
+		return &InvalidPathError{Kind: "file", Path: path, Err: err}
 	}
 	return nil
 }

src/cmd/vendor/modules.txt

@@ -28,7 +28,7 @@ golang.org/x/arch/x86/x86asm
 golang.org/x/crypto/ed25519
 golang.org/x/crypto/ed25519/internal/edwards25519
 golang.org/x/crypto/ssh/terminal
-# golang.org/x/mod v0.4.2-0.20210309222212-d6ab96f2441f
+# golang.org/x/mod v0.4.3-0.20210310185834-19d50cac98aa
 ## explicit
 golang.org/x/mod/internal/lazyregexp
 golang.org/x/mod/modfile