Add support for rendering Bytes values with YamlRenderer (#1276)

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

@@ -153,8 +153,7 @@ final class YamlRenderer implements ValueRenderer {
 
     @Override
     public void visitBytes(byte[] value) {
-      throw new RendererException(
-          String.format("Values of type `Bytes` cannot be rendered as YAML. Value: %s", value));
+      emitter.emit(YamlUtils.bytesScalar(value));
     }
 
     @Override

pkl-core/src/main/java/org/pkl/core/stdlib/base/YamlRendererNodes.java

@@ -180,7 +180,8 @@ public final class YamlRendererNodes {
 
     @Override
     public void visitBytes(VmBytes value) {
-      cannotRenderTypeAddConverter(value);
+      if (!builder.isEmpty()) builder.append(' ');
+      emitter.emit(value.getBytes(), currIndent, false);
     }
 
     @Override

pkl-core/src/main/java/org/pkl/core/util/yaml/YamlEmitter.java

@@ -15,6 +15,8 @@
  */
 package org.pkl.core.util.yaml;
 
+import java.util.Base64;
+
 // Useful links:
 // https://yaml-online-parser.appspot.com
 // https://github.com/FasterXML/jackson-dataformats-text/pull/201
@@ -210,6 +212,11 @@ public abstract class YamlEmitter {
     builder.append(value);
   }
 
+  public final void emit(byte[] value, StringBuilder currIndent, boolean isKey) {
+    builder.append("!!binary ");
+    emit(Base64.getEncoder().encodeToString(value), currIndent, isKey);
+  }
+
   public final void emitNull() {
     builder.append("null");
   }

pkl-core/src/main/java/org/pkl/core/util/yaml/snake/YamlUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2024-2025 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.
@@ -33,6 +33,9 @@ public final class YamlUtils {
   @SuppressWarnings("OptionalUsedAsFieldOrParameterType")
   private static final Optional<String> STRING_TAG = Optional.of(Tag.STR.toString());
 
+  @SuppressWarnings("OptionalUsedAsFieldOrParameterType")
+  private static final Optional<String> BINARY_TAG = Optional.of(Tag.BINARY.toString());
+
   private static final ImplicitTuple TUPLE = new ImplicitTuple(true, true);
 
   private YamlUtils() {}
@@ -56,6 +59,13 @@ public final class YamlUtils {
     return new ScalarEvent(Optional.empty(), STRING_TAG, tuple, value, scalarStyle);
   }
 
+  /** Constructs a {@link ScalarEvent} for emitting the given value as YAML binary. */
+  public static ScalarEvent bytesScalar(byte[] value) {
+    var encoded = Base64.getEncoder().encodeToString(value);
+    return new ScalarEvent(
+        Optional.empty(), BINARY_TAG, new ImplicitTuple(false, false), encoded, ScalarStyle.PLAIN);
+  }
+
   /** Constructs a {@link ScalarEvent} for emitting the given value in plain style. */
   public static ScalarEvent plainScalar(String value, Tag tag) {
     return new ScalarEvent(

pkl-core/src/test/files/LanguageSnippetTests/input/api/yamlRenderer2.yml.pkl

@@ -18,6 +18,9 @@ res13 = new Dynamic { name = "pigeon"; age = 30 }
 res14 = new Person { name = "pigeon" }
 res15 = null
 res16 = Pair(1, 2)
+res17 = Bytes()
+res18 = Bytes(1, 2, 3)
+res19 = IntSeq(0, 127).toList().toBytes()
 
 output {
   renderer = new YamlRenderer {

pkl-core/src/test/files/LanguageSnippetTests/input/api/yamlRenderer3.yml.pkl

@@ -18,6 +18,7 @@ res13 = new Dynamic { name = "pigeon"; age = 30 }
 res14 = new Person { name = "pigeon"; age = 30 }
 res15 = null
 res16 = Pair(1, 2)
+res17 = Bytes(1, 2, 3)
 
 output {
   renderer = new YamlRenderer {
@@ -38,6 +39,7 @@ output {
       [Null] = (it) -> "converted"
       [Pair] = (it) -> "converted"
       [IntSeq] = (it) -> "converted"
+      [Bytes] = (it) -> "converted"
     }
   }
 }

pkl-core/src/test/files/LanguageSnippetTests/output/api/yamlRenderer2.yml

@@ -37,3 +37,6 @@ res15: String
 res16:
 - 2
 - 3
+res17: !!binary ''
+res18: !!binary AQID
+res19: !!binary AAECAwQFBgcICQoLDA0ODxAREhMUFRYXGBkaGxwdHh8gISIjJCUmJygpKissLS4vMDEyMzQ1Njc4OTo7PD0+P0BBQkNERUZHSElKS0xNTk9QUVJTVFVWV1hZWltcXV5fYGFiY2RlZmdoaWprbG1ub3BxcnN0dXZ3eHl6e3x9fn8=

pkl-core/src/test/files/LanguageSnippetTests/output/api/yamlRenderer3.yml

@@ -13,3 +13,4 @@ res13: converted
 res14: converted
 res15: converted
 res16: converted
+res17: converted

pkl-core/src/test/kotlin/org/pkl/core/YamlRendererTest.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2024-2025 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.
@@ -146,4 +146,36 @@ class YamlRendererTest {
           .trimIndent()
       )
   }
+
+  @Test
+  fun `render byte array values as binary`() {
+    val evaluator = Evaluator.preconfigured()
+    val module =
+      evaluator.evaluate(
+        ModuleSource.text(
+          """
+        res1 = Bytes()
+        res2 = Bytes(1, 2, 3)
+        res3 = IntSeq(0, 127).toList().toBytes()
+        """
+            .trimIndent()
+        )
+      )
+
+    val writer = StringWriter()
+    val renderer = ValueRenderers.yaml(writer, 2, true, false)
+
+    renderer.renderDocument(module)
+    val output = writer.toString()
+
+    assertThat(output.trim())
+      .isEqualTo(
+        """
+      res1: !!binary ''
+      res2: !!binary 'AQID'
+      res3: !!binary 'AAECAwQFBgcICQoLDA0ODxAREhMUFRYXGBkaGxwdHh8gISIjJCUmJygpKissLS4vMDEyMzQ1Njc4OTo7PD0+P0BBQkNERUZHSElKS0xNTk9QUVJTVFVWV1hZWltcXV5fYGFiY2RlZmdoaWprbG1ub3BxcnN0dXZ3eHl6e3x9fn8='
+    """
+          .trimIndent()
+      )
+  }
 }