Fix content dir resolution when main project is a Hugo Module

Fixes #9177

hugofs/fileinfo.go

@@ -64,6 +64,7 @@ type FileMeta struct {
 	IsOrdered  bool
 	IsSymlink  bool
 	IsRootFile bool
+	IsProject  bool
 	Watch      bool
 
 	Classifier files.ContentClass

hugofs/rootmapping_fs.go

@@ -62,6 +62,7 @@ func NewRootMappingFs(fs afero.Fs, rms ...RootMapping) (*RootMappingFs, error) {
 		rm.Meta.BaseDir = rm.ToBasedir
 		rm.Meta.MountRoot = rm.path
 		rm.Meta.Module = rm.Module
+		rm.Meta.IsProject = rm.IsProject
 
 		meta := rm.Meta.Copy()
 
@@ -118,6 +119,7 @@ type RootMapping struct {
 	To        string    // The source directory or file.
 	ToBasedir string    // The base of To. May be empty if an absolute path was provided.
 	Module    string    // The module path/ID.
+	IsProject bool      // Whether this is a mount in the main project.
 	Meta      *FileMeta // File metadata (lang etc.)
 
 	fi   FileMetaInfo

hugolib/filesystems/basefs.go

@@ -136,7 +136,7 @@ func (b *BaseFs) AbsProjectContentDir(filename string) (string, string, error) {
 	isAbs := filepath.IsAbs(filename)
 	for _, dir := range b.SourceFilesystems.Content.Dirs {
 		meta := dir.Meta()
-		if meta.Module != "project" {
+		if !meta.IsProject {
 			continue
 		}
 		if isAbs {
@@ -161,7 +161,7 @@ func (b *BaseFs) AbsProjectContentDir(filename string) (string, string, error) {
 		contentDirs := b.SourceFilesystems.Content.Dirs
 		for i := len(contentDirs) - 1; i >= 0; i-- {
 			meta := contentDirs[i].Meta()
-			if meta.Module == "project" {
+			if meta.IsProject {
 				return filename, filepath.Join(meta.Filename, filename), nil
 			}
 		}
@@ -645,6 +645,7 @@ func (b *sourceFilesystemsBuilder) createModFs(
 			To:        filename,
 			ToBasedir: base,
 			Module:    md.Module.Path(),
+			IsProject: md.isMainProject,
 			Meta: &hugofs.FileMeta{
 				Watch:           md.Watch(),
 				Weight:          mountWeight,