[fix] Add support for handling remote file URIs. (#629)

Co-authored-by: Jen Basch <jbasch@apple.com>

pkl-core/src/main/java/org/pkl/core/util/IoUtils.java

@@ -892,6 +892,9 @@ public final class IoUtils {
     if (!uri.getSchemeSpecificPart().startsWith("/")) {
       throw new URISyntaxException(uri.toString(), ErrorMessages.create("invalidOpaqueFileUri"));
     }
+    if (uri.getRawAuthority() != null) {
+      throw new URISyntaxException(uri.toString(), ErrorMessages.create("invalidRemoteFileUri"));
+    }
   }
 
   public static void validateRewriteRule(URI rewrite) {

pkl-core/src/main/resources/org/pkl/core/errorMessages.properties

@@ -1130,6 +1130,9 @@ invalidOpaqueFileUri=\
 File URIs must have a path that starts with `/` (e.g. file:/path/to/my_module.pkl).\n\
 To resolve relative paths, remove the scheme prefix (remove "file:").
 
+invalidRemoteFileUri=\
+File URIs may not include an authority.
+
 invalidStringBase64=\
 `{0}` is not in base64 encoding.
 

pkl-core/src/test/kotlin/org/pkl/core/util/IoUtilsTest.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2024-2026 Apple Inc. and the Pkl project authors. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -400,6 +400,13 @@ class IoUtilsTest {
     assertThrows<IllegalArgumentException> { IoUtils.readString(URI("http://example.com").toURL()) }
   }
 
+  @Test
+  fun `toUrl() throws UnsupportedOperationException for file URIs with remote hostnames`() {
+    val uri = URI("file://example.com/bar/baz.pkl")
+    val exception = assertThrows<URISyntaxException> { IoUtils.validateFileUri(uri) }
+    assertThat(exception.message).contains("File URIs may not include an authority.")
+  }
+
   @Test
   fun `encodePath encodes characters reserved on windows`() {
     assertThat(IoUtils.encodePath("foo:bar")).isEqualTo("foo(3a)bar")