d2ir: Fix for windows

Closes #1388

d2compiler/compile.go

@@ -6,7 +6,6 @@ import (
 	"io"
 	"io/fs"
 	"net/url"
-	"os"
 	"strconv"
 	"strings"
 
@@ -32,9 +31,6 @@ func Compile(p string, r io.RuneReader, opts *CompileOptions) (*d2graph.Graph, e
 	if opts == nil {
 		opts = &CompileOptions{}
 	}
-	if opts.FS == nil {
-		opts.FS = os.DirFS("/")
-	}
 
 	ast, err := d2parser.Parse(p, r, &d2parser.ParseOptions{
 		UTF16: opts.UTF16,

d2ir/import.go

@@ -2,6 +2,7 @@ package d2ir
 
 import (
 	"bufio"
+	"io/fs"
 	"os"
 	"path"
 	"strings"
@@ -85,25 +86,13 @@ func (c *compiler) __import(imp *d2ast.Import) (*Map, bool) {
 		return ir, true
 	}
 
-	p := path.Clean(impPath)
+	var f fs.File
-	if path.IsAbs(p) {
+	var err error
-		// Path cannot be absolute. DirFS does not accept absolute paths. We strip off the leading
+	if c.fs == nil {
-		// slash to make it relative to the root.
+		f, err = os.Open(impPath)
-		p = p[1:]
+	} else {
-	} else if c.fs == os.DirFS("/") {
+		f, err = c.fs.Open(impPath)
-		wd, err := os.Getwd()
-		if err != nil {
-			c.errorf(imp, "failed to import %q: %v", impPath, err)
-			return nil, false
 	}
-		p = path.Join(wd, p)
-		// See above explanation.
-		if path.IsAbs(p) {
-			p = p[1:]
-		}
-	}
-
-	f, err := c.fs.Open(p)
 	if err != nil {
 		c.errorf(imp, "failed to import %q: %v", impPath, err)
 		return nil, false