Add custom fs implementation

compiler/fs.go

@@ -0,0 +1,57 @@
+package compiler
+
+import "os"
+import "io/fs"
+import "runtime"
+import "strings"
+import "path/filepath"
+
+// OsFS returns an fs.FS that represents the operating system's filesystem. In
+// Windows, volume names (A:, B:, C:, etc.) are treated as subdirectories within
+// the root.
+type OsFS struct { }
+
+// win
+// C:/Something -> C:\Something
+// "" -> ""
+
+// unix
+// C:/Something -> /C:/Something
+// "" -> /
+
+func (this OsFS) Open (name string) (fs.File, error) {
+	fullname, err := this.nativize(name)
+	if err != nil {
+		return nil, this.err("open", name, err)
+	}
+	file, err := os.Open(fullname)
+	if err != nil {
+		return nil, this.err("open", name, err.(*os.PathError).Err)
+	}
+	return file, nil
+}
+
+func (this OsFS) nativize (name string) (string, error) {
+	if !fs.ValidPath(name) {
+		return "", fs.ErrInvalid
+	}
+	if filepath.Separator != '/' {
+		if strings.Contains(name, string(filepath.Separator)) {
+			return "", fs.ErrInvalid
+		}
+	}
+	if runtime.GOOS != "windows" {
+		// TODO is this correct for all non-windows systems?
+		name = "/" + name
+	}
+	name = filepath.FromSlash(name)
+	return name, nil
+}
+
+func (this OsFS) err (op, path string, err error) error {
+	return &fs.PathError {
+		Op:   "open",
+		Path: path,
+		Err:  err,
+	}
+}

compiler/resolver.go

@@ -20,10 +20,10 @@ type Resolver struct {
 	Path []string
 }
 
-// NewResolver creates a new resolver with os.DirFS("/").
+// NewResolver creates a new resolver with OsFS.
 func NewResolver (path ...string) *Resolver {
 	return &Resolver {
-		FS:   os.DirFS("/"),
+		FS:   OsFS { },
 		Path: path,
 	}
 }
@@ -108,13 +108,6 @@ func (resolver *Resolver) ResolveCwd (address entity.Address) (string, error) {
 // paths, which the FSPL compiler runs on. It converts an absolute path to a
 // slash path relative to "/" and opens the file.
 func openAbsolute (filesystem fs.FS, path string) (fs.File, error) {
-	rootName := "/"
-	// FIXME: this does not distinguish between volumes on windows. this is
-	// a limitation of os.DirFS, we might want our own DirFS implementation
-	// that has volumes as subdirs of /.
-	if volumeName := filepath.VolumeName(path); volumeName != "" {
-		rootName = volumeName
-	}
-	path = strings.TrimPrefix(filepath.ToSlash(path), rootName)
+	path = strings.TrimPrefix(filepath.ToSlash(path), "/")
 	return filesystem.Open(path)
 }