Add new experimental rule to remove trailing comma's from argument an…

…d values lists (pinterest#709)

ktlint-ruleset-experimental/src/main/kotlin/com/pinterest/ktlint/ruleset/experimental/ExperimentalRuleSetProvider.kt

@@ -11,6 +11,7 @@ public class ExperimentalRuleSetProvider : RuleSetProvider {
         ArgumentListWrappingRule(),
         MultiLineIfElseRule(),
         NoEmptyFirstLineInMethodBlockRule(),
+        NoTrailingCommaRule(),
         PackageNameRule(),
         EnumEntryNameCaseRule(),
         SpacingAroundDoubleColonRule(),

ktlint-ruleset-experimental/src/main/kotlin/com/pinterest/ktlint/ruleset/experimental/NoTrailingCommaRule.kt

@@ -0,0 +1,31 @@
+package com.pinterest.ktlint.ruleset.experimental
+
+import com.pinterest.ktlint.core.Rule
+import com.pinterest.ktlint.core.ast.ElementType
+import com.pinterest.ktlint.core.ast.children
+import org.jetbrains.kotlin.com.intellij.lang.ASTNode
+import org.jetbrains.kotlin.psi.psiUtil.endOffset
+
+class NoTrailingCommaRule : Rule("no-trailing-comma") {
+
+    override fun visit(
+        node: ASTNode,
+        autoCorrect: Boolean,
+        emit: (offset: Int, errorMessage: String, canBeAutoCorrected: Boolean) -> Unit
+    ) {
+        if (node.elementType == ElementType.VALUE_ARGUMENT_LIST || node.elementType == ElementType.VALUE_PARAMETER_LIST) {
+            val lastNode = node
+                .children()
+                .filter { it.elementType != ElementType.WHITE_SPACE }
+                .filter { it.elementType != ElementType.EOL_COMMENT }
+                .filter { it.elementType != ElementType.RPAR }
+                .last()
+            if (lastNode.elementType == ElementType.COMMA) {
+                emit(lastNode.psi.endOffset - 1, "Trailing command in argument list is redundant", true)
+                if (autoCorrect) {
+                    node.removeChild(lastNode)
+                }
+            }
+        }
+    }
+}

ktlint-ruleset-experimental/src/test/kotlin/com/pinterest/ktlint/ruleset/experimental/NoTrailingCommaRuleTest.kt

@@ -0,0 +1,65 @@
+package com.pinterest.ktlint.ruleset.experimental
+
+import com.pinterest.ktlint.core.LintError
+import com.pinterest.ktlint.test.format
+import com.pinterest.ktlint.test.lint
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.Test
+
+class NoTrailingCommaRuleTest {
+    @Test
+    fun testFormatIsCorrectWithArgumentList() {
+        val code =
+            """
+            val list1 = listOf("a", "b",)
+            val list2 = listOf(
+                "a",
+                "b", // The comma before the comment should be removed without removing the comment itself
+            )
+            """.trimIndent()
+        val autoCorrectedCode =
+            """
+            val list1 = listOf("a", "b")
+            val list2 = listOf(
+                "a",
+                "b" // The comma before the comment should be removed without removing the comment itself
+            )
+            """.trimIndent()
+
+        assertThat(NoTrailingCommaRule().lint(code)).isEqualTo(
+            listOf(
+                LintError(line = 1, col = 28, ruleId = "no-trailing-comma", detail = "Trailing command in argument list is redundant"),
+                LintError(line = 4, col = 8, ruleId = "no-trailing-comma", detail = "Trailing command in argument list is redundant"),
+            )
+        )
+        assertThat(NoTrailingCommaRule().format(code))
+            .isEqualTo(autoCorrectedCode)
+    }
+
+    @Test
+    fun testFormatIsCorrectWithValueList() {
+        val code =
+            """
+            data class Foo1(
+               val bar: Int, // The comma before the comment should be removed without removing the comment itself
+            )
+            data class Foo2(val bar: Int,)
+            """.trimIndent()
+        val autoCorrectedCode =
+            """
+            data class Foo1(
+               val bar: Int // The comma before the comment should be removed without removing the comment itself
+            )
+            data class Foo2(val bar: Int)
+            """.trimIndent()
+
+        assertThat(NoTrailingCommaRule().lint(code)).isEqualTo(
+            listOf(
+                LintError(line = 2, col = 16, ruleId = "no-trailing-comma", detail = "Trailing command in argument list is redundant"),
+                LintError(line = 4, col = 29, ruleId = "no-trailing-comma", detail = "Trailing command in argument list is redundant"),
+            )
+        )
+        assertThat(NoTrailingCommaRule().format(code))
+            .isEqualTo(autoCorrectedCode)
+    }
+}