Allow trailing commas in comma-separated syntax elements (#1137)

pkl-core/src/test/files/LanguageSnippetTests/input/parser/constraintsTrailingComma.pkl

@@ -0,0 +1,9 @@
+res1: Int(isEven, isNonZero, isBetween(-10, 10), ) = 6
+res2: Int(
+    isEven, isNonZero, isBetween(-10, 10),
+) = 6
+res3: Int(
+    isEven,
+    isNonZero,
+    isBetween(-10, 10),
+) = 6

pkl-core/src/test/files/LanguageSnippetTests/input/parser/lambdaTrailingCommas.pkl

@@ -0,0 +1,43 @@
+local lA1 = (a, b, c,) -> true
+local lA2 = (
+  a, b, c,
+) -> true
+local lA3 = (
+  a,
+  b,
+  c,
+) -> true
+
+local lB1 = (a: Int, b: Int, c: Int,) -> true
+local lB2 = (
+  a: Int, b: Int, c: Int,
+) -> true
+local lB3 = (
+  a: Int,
+  b: Int,
+  c: Int,
+) -> true
+
+local lC1: (Dynamic,) -> Dynamic = new Mixin { a, -> x = true }
+local lC2: (Dynamic,) -> Dynamic = new Mixin { a, ->
+  x = true
+}
+local lC3: (Dynamic,) -> Dynamic = new Mixin {
+  a, -> x = true
+}
+local lC4: (Dynamic,) -> Dynamic = new Mixin {
+  a, ->
+  x = true
+}
+
+local lD1: (Dynamic,) -> Dynamic = new Mixin { a: Dynamic, -> x = true }
+local lD2: (Dynamic,) -> Dynamic = new Mixin { a: Dynamic, ->
+  x = true
+}
+local lD3: (Dynamic,) -> Dynamic = new Mixin {
+  a: Dynamic, -> x = true
+}
+local lD4: (Dynamic,) -> Dynamic = new Mixin {
+  a: Dynamic, ->
+  x = true
+}

pkl-core/src/test/files/LanguageSnippetTests/input/parser/methodTrailingCommas.pkl

@@ -0,0 +1,157 @@
+function moduleMethodA1(a, b, c, ) = true
+function moduleMethodA2(
+  a, b, c,
+) = true
+function moduleMethodA3(
+  a,
+  b,
+  c,
+) = true
+function moduleMethodB1(a: Int, b: Int, c: Int, ) = true
+function moduleMethodB2(
+  a: Int, b: Int, c: Int,
+) = true
+function moduleMethodB3(
+  a: Int,
+  b: Int,
+  c: Int,
+) = true
+
+class A {
+  function classMethodA1(a, b, c, ) = true
+  function classMethodA2(
+    a, b, c,
+  ) = true
+  function classMethodA3(
+    a,
+    b,
+    c,
+  ) = true
+  function classMethodB1(a: Int, b: Int, c: Int, ) = true
+  function classMethodB2(
+    a: Int, b: Int, c: Int,
+  ) = true
+  function classMethodB3(
+    a: Int,
+    b: Int,
+    c: Int,
+  ) = true
+}
+
+moduleMethodA1Call1 = moduleMethodA1(1, 2, 3, )
+moduleMethodA1Call2 = moduleMethodA1(
+  1, 2, 3,
+)
+moduleMethodA1Call3 = moduleMethodA1(
+  1,
+  2,
+  3,
+)
+moduleMethodA2Call1 = moduleMethodA2(1, 2, 3, )
+moduleMethodA2Call2 = moduleMethodA2(
+  1, 2, 3,
+)
+moduleMethodA2Call3 = moduleMethodA2(
+  1,
+  2,
+  3,
+)
+
+moduleMethodA3Call1 = moduleMethodA3(1, 2, 3, )
+moduleMethodA3Call2 = moduleMethodA3(
+  1, 2, 3,
+)
+moduleMethodA3Call3 = moduleMethodA3(
+  1,
+  2,
+  3,
+)
+
+moduleMethodB1Call1 = moduleMethodB1(1, 2, 3, )
+moduleMethodB1Call2 = moduleMethodB1(
+  1, 2, 3,
+)
+moduleMethodB1Call3 = moduleMethodB1(
+  1,
+  2,
+  3,
+)
+moduleMethodB2Call1 = moduleMethodB2(1, 2, 3, )
+moduleMethodB2Call2 = moduleMethodB2(
+  1, 2, 3,
+)
+moduleMethodB2Call3 = moduleMethodB2(
+  1,
+  2,
+  3,
+)
+
+moduleMethodB3Call1 = moduleMethodB3(1, 2, 3, )
+moduleMethodB3Call2 = moduleMethodB3(
+  1, 2, 3,
+)
+moduleMethodB3Call3 = moduleMethodB3(
+  1,
+  2,
+  3,
+)
+
+local a: A = new {}
+
+classMethodA1Call1 = a.classMethodA1(1, 2, 3, )
+classMethodA1Call2 = a.classMethodA1(
+  1, 2, 3,
+)
+classMethodA1Call3 = a.classMethodA1(
+  1,
+  2,
+  3,
+)
+classMethodA2Call1 = a.classMethodA2(1, 2, 3, )
+classMethodA2Call2 = a.classMethodA2(
+  1, 2, 3,
+)
+classMethodA2Call3 = a.classMethodA2(
+  1,
+  2,
+  3,
+)
+
+classMethodA3Call1 = a.classMethodA3(1, 2, 3, )
+classMethodA3Call2 = a.classMethodA3(
+  1, 2, 3,
+)
+classMethodA3Call3 = a.classMethodA3(
+  1,
+  2,
+  3,
+)
+
+classMethodB1Call1 = a.classMethodB1(1, 2, 3, )
+classMethodB1Call2 = a.classMethodB1(
+  1, 2, 3,
+)
+classMethodB1Call3 = a.classMethodB1(
+  1,
+  2,
+  3,
+)
+classMethodB2Call1 = a.classMethodB2(1, 2, 3, )
+classMethodB2Call2 = a.classMethodB2(
+  1, 2, 3,
+)
+classMethodB2Call3 = a.classMethodB2(
+  1,
+  2,
+  3,
+)
+
+classMethodB3Call1 = a.classMethodB3(1, 2, 3, )
+classMethodB3Call2 = a.classMethodB3(
+  1, 2, 3,
+)
+classMethodB3Call3 = a.classMethodB3(
+  1,
+  2,
+  3,
+)

pkl-core/src/test/files/LanguageSnippetTests/input/parser/trailingCommas.pkl

@@ -0,0 +1,3 @@
+res1: Mapping<String, String,>(!isEmpty) = new Mapping<String, String,> {
+  ["hello"] = "world"
+}

pkl-core/src/test/files/LanguageSnippetTests/output/parser/constraintsTrailingComma.pcf

@@ -0,0 +1,3 @@
+res1 = 6
+res2 = 6
+res3 = 6

pkl-core/src/test/files/LanguageSnippetTests/output/parser/methodTrailingCommas.pcf

@@ -0,0 +1,36 @@
+moduleMethodA1Call1 = true
+moduleMethodA1Call2 = true
+moduleMethodA1Call3 = true
+moduleMethodA2Call1 = true
+moduleMethodA2Call2 = true
+moduleMethodA2Call3 = true
+moduleMethodA3Call1 = true
+moduleMethodA3Call2 = true
+moduleMethodA3Call3 = true
+moduleMethodB1Call1 = true
+moduleMethodB1Call2 = true
+moduleMethodB1Call3 = true
+moduleMethodB2Call1 = true
+moduleMethodB2Call2 = true
+moduleMethodB2Call3 = true
+moduleMethodB3Call1 = true
+moduleMethodB3Call2 = true
+moduleMethodB3Call3 = true
+classMethodA1Call1 = true
+classMethodA1Call2 = true
+classMethodA1Call3 = true
+classMethodA2Call1 = true
+classMethodA2Call2 = true
+classMethodA2Call3 = true
+classMethodA3Call1 = true
+classMethodA3Call2 = true
+classMethodA3Call3 = true
+classMethodB1Call1 = true
+classMethodB1Call2 = true
+classMethodB1Call3 = true
+classMethodB2Call1 = true
+classMethodB2Call2 = true
+classMethodB2Call3 = true
+classMethodB3Call1 = true
+classMethodB3Call2 = true
+classMethodB3Call3 = true

pkl-core/src/test/files/LanguageSnippetTests/output/parser/trailingCommas.pcf

@@ -0,0 +1,3 @@
+res1 {
+  ["hello"] = "world"
+}

pkl-core/src/test/kotlin/org/pkl/core/parser/TrailingCommasTest.kt

@@ -0,0 +1,82 @@
+/*
+ * Copyright © 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.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.parser
+
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.Test
+import org.pkl.core.Evaluator
+import org.pkl.parser.Parser
+
+// tests type argument and parameter parsing with trailing commas that cannot be tested with
+// snippets because these constructs are currently only allowed in the stdlib
+class TrailingCommasTest {
+  private val evaluator = Evaluator.preconfigured()
+
+  @Test
+  fun `class type parameter lists parse correctly`() {
+    val module =
+      Parser()
+        .parseModule(
+          """
+        class Foo<
+          Key,
+          Value,
+        >
+        
+        class Bar<
+          Key,
+          Value,
+        > {
+          baz: Key
+          buzz: Value
+        }
+      """
+            .trimIndent()
+        )
+
+    val fooClass = module.classes.find { it.name.value == "Foo" }
+    assertThat(fooClass).isNotNull
+    assertThat(fooClass!!.typeParameterList?.parameters?.first()?.identifier?.value)
+      .isEqualTo("Key")
+    assertThat(fooClass.typeParameterList?.parameters?.last()?.identifier?.value).isEqualTo("Value")
+
+    val barClass = module.classes.find { it.name.value == "Bar" }
+    assertThat(barClass).isNotNull
+    assertThat(barClass!!.typeParameterList?.parameters?.first()?.identifier?.value)
+      .isEqualTo("Key")
+    assertThat(barClass.typeParameterList?.parameters?.last()?.identifier?.value).isEqualTo("Value")
+  }
+
+  @Test
+  fun `method type parameter lists parse correctly`() {
+    val module =
+      Parser()
+        .parseModule(
+          """
+        function foo<
+          A,
+          B,
+        >(a: A, b: B,): Value? = "\(a):\(b)"
+      """
+            .trimIndent()
+        )
+
+    val fooMethod = module.methods.find { it.name.value == "foo" }
+    assertThat(fooMethod).isNotNull
+    assertThat(fooMethod!!.typeParameterList?.parameters?.first()?.identifier?.value).isEqualTo("A")
+    assertThat(fooMethod.typeParameterList?.parameters?.last()?.identifier?.value).isEqualTo("B")
+  }
+}