Fix Permalink for resource, baseURL with path and canonifyURLs set

Fixes #5226

hugolib/paths/paths.go

@@ -34,7 +34,6 @@ type Paths struct {
 	BaseURL
 
 	// If the baseURL contains a base path, e.g. https://example.com/docs, then "/docs" will be the BasePath.
-	// This will not be set if canonifyURLs is enabled.
 	BasePath string
 
 	// Directories
@@ -192,6 +191,15 @@ func New(fs *hugofs.Fs, cfg config.Provider) (*Paths, error) {
 	return p, nil
 }
 
+// GetBasePath returns any path element in baseURL if needed.
+func (p *Paths) GetBasePath(isRelativeURL bool) string {
+	if isRelativeURL && p.CanonifyURLs {
+		// The baseURL will be prepended later.
+		return ""
+	}
+	return p.BasePath
+}
+
 func (p *Paths) Lang() string {
 	if p == nil || p.Language == nil {
 		return ""