internal/mod/module: add CheckPathWithoutVersion

This enables us to check that module path is valid when it doesn't
have a version suffix.

Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: Ia28e2fb305c1c3e63a7b06cf898be4c844201f1f
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1170841
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

internal/mod/module/module_test.go

@@ -43,6 +43,32 @@ func TestCheck(t *testing.T) {
 	}
 }
 
+var checkPathWithoutVersionTests = []struct {
+	path    string
+	wantErr string
+}{{
+	path:    "rsc io/quote",
+	wantErr: `invalid char ' '`,
+}, {
+	path:    "foo.com@v0",
+	wantErr: `module path inappropriately contains major version`,
+}, {
+	path: "foo.com/bar/baz",
+}}
+
+func TestCheckPathWithoutVersion(t *testing.T) {
+	for _, test := range checkPathWithoutVersionTests {
+		t.Run(test.path, func(t *testing.T) {
+			err := CheckPathWithoutVersion(test.path)
+			if test.wantErr != "" {
+				qt.Assert(t, qt.ErrorMatches(err, test.wantErr))
+				return
+			}
+			qt.Assert(t, qt.IsNil(err))
+		})
+	}
+}
+
 var newVersionTests = []struct {
 	path, vers   string
 	wantError    string

internal/mod/module/path.go

@@ -104,6 +104,40 @@ func fileNameOK(r rune) bool {
 	return unicode.IsLetter(r)
 }
 
+// CheckPathWithoutVersion is like CheckPath except that
+// it expects a module path without a major version.
+func CheckPathWithoutVersion(basePath string) (err error) {
+	if _, _, ok := SplitPathVersion(basePath); ok {
+		return fmt.Errorf("module path inappropriately contains major version")
+	}
+	if err := checkPath(basePath, modulePath); err != nil {
+		return err
+	}
+	i := strings.Index(basePath, "/")
+	if i < 0 {
+		i = len(basePath)
+	}
+	if i == 0 {
+		return fmt.Errorf("leading slash")
+	}
+	if !strings.Contains(basePath[:i], ".") {
+		return fmt.Errorf("missing dot in first path element")
+	}
+	if basePath[0] == '-' {
+		return fmt.Errorf("leading dash in first path element")
+	}
+	for _, r := range basePath[:i] {
+		if !firstPathOK(r) {
+			return fmt.Errorf("invalid char %q in first path element", r)
+		}
+	}
+	// Sanity check agreement with OCI specs.
+	if !basePathPat.MatchString(basePath) {
+		return fmt.Errorf("non-conforming path %q", basePath)
+	}
+	return nil
+}
+
 // CheckPath checks that a module path is valid.
 // A valid module path is a valid import path, as checked by CheckImportPath,
 // with three additional constraints.
@@ -135,32 +169,9 @@ func CheckPath(mpath string) (err error) {
 	if semver.Major(vers) != vers {
 		return fmt.Errorf("path can contain major version only")
 	}
-
-	if err := checkPath(basePath, modulePath); err != nil {
+	if err := CheckPathWithoutVersion(basePath); err != nil {
 		return err
 	}
-	i := strings.Index(basePath, "/")
-	if i < 0 {
-		i = len(basePath)
-	}
-	if i == 0 {
-		return fmt.Errorf("leading slash")
-	}
-	if !strings.Contains(basePath[:i], ".") {
-		return fmt.Errorf("missing dot in first path element")
-	}
-	if basePath[0] == '-' {
-		return fmt.Errorf("leading dash in first path element")
-	}
-	for _, r := range basePath[:i] {
-		if !firstPathOK(r) {
-			return fmt.Errorf("invalid char %q in first path element", r)
-		}
-	}
-	// Sanity check agreement with OCI specs.
-	if !basePathPat.MatchString(basePath) {
-		return fmt.Errorf("non-conforming path %q", basePath)
-	}
 	if !tagPat.MatchString(vers) {
 		return fmt.Errorf("non-conforming version %q", vers)
 	}