Require global settings file to use pkl:settings (#477)

This is technically a breaking change, but follows the intended use-case
and documentation of settings.

* Require that the global settings file at `~/.pkl/settings.pkl`
amends stdlib module `pkl:settings`, or otherwise sets `output.value`
to an instance of `pkl.Settings`.
* Simplify the object mapping of `PklSettings.java`

pkl-core/src/main/java/org/pkl/core/PClassInfo.java

@@ -37,6 +37,7 @@ public final class PClassInfo<T> implements Serializable {
 
   public static final URI pklBaseUri = URI.create("pkl:base");
   public static final URI pklSemverUri = URI.create("pkl:semver");
+  public static final URI pklSettingsUri = URI.create("pkl:settings");
   public static final URI pklProjectUri = URI.create("pkl:Project");
 
   public static final PClassInfo<Void> Any = pklBaseClassInfo("Any", Void.class);
@@ -79,6 +80,8 @@ public final class PClassInfo<T> implements Serializable {
       new PClassInfo<>("pkl.semver", "Version", PObject.class, pklSemverUri);
   public static final PClassInfo<PObject> Project =
       new PClassInfo<>("pkl.Project", "ModuleClass", PObject.class, pklProjectUri);
+  public static final PClassInfo<PObject> Settings =
+      new PClassInfo<>("pkl.settings", "ModuleClass", PObject.class, pklSettingsUri);
 
   public static final PClassInfo<Object> Unavailable =
       new PClassInfo<>("unavailable", "unavailable", Object.class, URI.create("pkl:unavailable"));

pkl-core/src/main/java/org/pkl/core/runtime/SettingsModule.java

@@ -15,13 +15,13 @@
  */
 package org.pkl.core.runtime;
 
-import java.net.URI;
+import static org.pkl.core.PClassInfo.pklSettingsUri;
 
 public final class SettingsModule extends StdLibModule {
   private static final VmTyped instance = VmUtils.createEmptyModule();
 
   static {
-    loadModule(URI.create("pkl:settings"), instance);
+    loadModule(pklSettingsUri, instance);
   }
 
   private SettingsModule() {}

pkl-core/src/main/java/org/pkl/core/settings/PklSettings.java

@@ -23,7 +23,6 @@ import org.pkl.core.*;
 import org.pkl.core.module.ModuleKeyFactories;
 import org.pkl.core.resource.ResourceReaders;
 import org.pkl.core.runtime.VmEvalException;
-import org.pkl.core.runtime.VmExceptionBuilder;
 import org.pkl.core.util.IoUtils;
 import org.pkl.core.util.Nullable;
 
@@ -73,23 +72,16 @@ public final class PklSettings {
             .addResourceReader(ResourceReaders.environmentVariable())
             .addEnvironmentVariables(System.getenv())
             .build()) {
-      var module = evaluator.evaluate(moduleSource);
-      return parseSettings(module, moduleSource);
+      var module = evaluator.evaluateOutputValueAs(moduleSource, PClassInfo.Settings);
+      return parseSettings(module);
     }
   }
 
-  private static PklSettings parseSettings(PModule module, ModuleSource location)
-      throws VmEvalException {
+  private static PklSettings parseSettings(PObject module) throws VmEvalException {
     // can't use object mapping in pkl-core, so map manually
-    var editor = module.getPropertyOrNull("editor");
-    if (!(editor instanceof PObject pObject)) {
-      throw new VmExceptionBuilder().evalError("invalidSettingsFile", location.getUri()).build();
-    }
-    var urlScheme = pObject.getPropertyOrNull("urlScheme");
-    if (!(urlScheme instanceof String string)) {
-      throw new VmExceptionBuilder().evalError("invalidSettingsFile", location.getUri()).build();
-    }
-    return new PklSettings(new Editor(string));
+    var editor = (PObject) module.getProperty("editor");
+    var urlScheme = (String) editor.getProperty("urlScheme");
+    return new PklSettings(new Editor(urlScheme));
   }
 
   /** Returns the editor for viewing and editing Pkl files. */

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

@@ -700,9 +700,6 @@ Refusing to load module `{0}` because it does not match any entry in the module
 insufficientModuleTrustLevel=\
 Refusing to import module `{0}` because importing module `{1}` has an insufficient trust level.
 
-invalidSettingsFile=\
-Pkl settings file `{0}` must start with `amends "pkl:settings"`.
-
 invalidRegexSyntax=\
 Syntax error in regex `{0}`: {1}
 

pkl-core/src/test/kotlin/org/pkl/core/settings/PklSettingsTest.kt

@@ -2,6 +2,7 @@ package org.pkl.core.settings
 
 import java.nio.file.Path
 import org.assertj.core.api.Assertions.assertThat
+import org.assertj.core.api.Assertions.assertThatCode
 import org.junit.jupiter.api.Test
 import org.junit.jupiter.api.io.TempDir
 import org.pkl.commons.createParentDirectories
@@ -67,6 +68,13 @@ class PklSettingsTest {
     checkEquals(Editor.VS_CODE, module.getProperty("vsCode") as PObject)
   }
 
+  @Test
+  fun `invalid settings file`(@TempDir tempDir: Path) {
+    val settingsFile = tempDir.resolve("settings.pkl").apply { writeString("foo = 1") }
+    assertThatCode { PklSettings.loadFromPklHomeDir(tempDir) }
+      .hasMessageContaining("Expected `output.value` of module `${settingsFile.toUri()}` to be of type `pkl.settings`, but got type `settings`.")
+  }
+
   private fun checkEquals(expected: Editor, actual: PObject) {
     assertThat(actual.getProperty("urlScheme") as String).isEqualTo(expected.urlScheme)
   }