fix: reorg attaching MultiReadFS

Author: nedpals

errgoengine.go

@@ -17,14 +17,13 @@ type ErrgoEngine struct {
 }
 
 func New() *ErrgoEngine {
-	filesystems := make([]fs.ReadFileFS, 2)
-	filesystems[0] = &RawFS{}
-
 	return &ErrgoEngine{
 		SharedStore:    NewEmptyStore(),
 		ErrorTemplates: ErrorTemplates{},
 		FS: &MultiReadFileFS{
-			FSs: filesystems,
+			FSs: []fs.ReadFileFS{
+				&RawFS{},
+			},
 		},
 		OutputGen: &OutputGenerator{},
 	}
@@ -39,7 +38,7 @@ func (e *ErrgoEngine) Analyze(workingPath, msg string) (*CompiledErrorTemplate,
 	// initial context data extraction
 	contextData := NewContextData(e.SharedStore, workingPath)
 	contextData.Analyzer = template.Language.AnalyzerFactory(contextData)
-	e.FS.FSs[1] = template.Language.stubFs
+	e.FS.Attach(template.Language.stubFs, 1)
 
 	groupNames := template.Pattern.SubexpNames()
 	for _, submatches := range template.Pattern.FindAllStringSubmatch(msg, -1) {

fs.go

@@ -11,6 +11,30 @@ type MultiReadFileFS struct {
 	FSs []fs.ReadFileFS
 }
 
+func (mfs *MultiReadFileFS) LastAttachedIdx() int {
+	return len(mfs.FSs) - 1
+}
+
+func (mfs *MultiReadFileFS) Attach(fs fs.ReadFileFS, idx int) {
+	if idx < len(mfs.FSs) && idx >= 0 {
+		if mfs.FSs[idx] == fs {
+			return
+		}
+
+		mfs.FSs[idx] = fs
+		return
+	}
+
+	// check first if the fs is already attached
+	for _, f := range mfs.FSs {
+		if f == fs {
+			return
+		}
+	}
+
+	mfs.FSs = append(mfs.FSs, fs)
+}
+
 func (mfs *MultiReadFileFS) Open(name string) (fs.File, error) {
 	for _, fs := range mfs.FSs {
 		if fs == nil {