Introduce SpacingAroundDoubleColonRule (#722)

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

@@ -12,6 +12,7 @@ class ExperimentalRuleSetProvider : RuleSetProvider {
         MultiLineIfElseRule(),
         NoEmptyFirstLineInMethodBlockRule(),
         PackageNameRule(),
-        EnumEntryNameCaseRule()
+        EnumEntryNameCaseRule(),
+        SpacingAroundDoubleColonRule()
     )
 }

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

@@ -0,0 +1,70 @@
+package com.pinterest.ktlint.ruleset.experimental
+
+import com.pinterest.ktlint.core.Rule
+import com.pinterest.ktlint.core.ast.ElementType.CALLABLE_REFERENCE_EXPRESSION
+import com.pinterest.ktlint.core.ast.ElementType.CLASS_LITERAL_EXPRESSION
+import com.pinterest.ktlint.core.ast.ElementType.COLONCOLON
+import com.pinterest.ktlint.core.ast.isPartOf
+import com.pinterest.ktlint.core.ast.nextLeaf
+import com.pinterest.ktlint.core.ast.prevLeaf
+import org.jetbrains.kotlin.com.intellij.lang.ASTNode
+import org.jetbrains.kotlin.com.intellij.psi.PsiWhiteSpace
+import org.jetbrains.kotlin.com.intellij.psi.impl.source.tree.LeafPsiElement
+
+class SpacingAroundDoubleColonRule : Rule("double-colon-spacing") {
+
+    override fun visit(
+        node: ASTNode,
+        autoCorrect: Boolean,
+        emit: (offset: Int, errorMessage: String, canBeAutoCorrected: Boolean) -> Unit
+    ) {
+        if (node.elementType == COLONCOLON) {
+            val prevLeaf = node.prevLeaf()
+            val nextLeaf = node.nextLeaf()
+
+            var removeSingleWhiteSpace = false
+            val spacingBefore = when {
+                node.isPartOf(CLASS_LITERAL_EXPRESSION) && prevLeaf is PsiWhiteSpace -> true // Clazz::class
+                node.isPartOf(CALLABLE_REFERENCE_EXPRESSION) && prevLeaf is PsiWhiteSpace -> // String::length, ::isOdd
+                    if (node.treePrev == null) { // compose(length, ::isOdd), val predicate = ::isOdd
+                        removeSingleWhiteSpace = true
+                        !prevLeaf.textContains('\n') && prevLeaf.psi.textLength > 1
+                    } else { // String::length, List<String>::isEmpty
+                        !prevLeaf.textContains('\n')
+                    }
+                else -> false
+            }
+
+            val spacingAfter = nextLeaf is PsiWhiteSpace
+            when {
+                spacingBefore && spacingAfter -> {
+                    emit(node.startOffset, "Unexpected spacing around \"${node.text}\"", true)
+                    if (autoCorrect) {
+                        prevLeaf!!.removeSelf(removeSingleWhiteSpace)
+                        nextLeaf!!.treeParent.removeChild(nextLeaf)
+                    }
+                }
+                spacingBefore -> {
+                    emit(prevLeaf!!.startOffset, "Unexpected spacing before \"${node.text}\"", true)
+                    if (autoCorrect) {
+                        prevLeaf.removeSelf(removeSingleWhiteSpace)
+                    }
+                }
+                spacingAfter -> {
+                    emit(nextLeaf!!.startOffset, "Unexpected spacing after \"${node.text}\"", true)
+                    if (autoCorrect) {
+                        nextLeaf.treeParent.removeChild(nextLeaf)
+                    }
+                }
+            }
+        }
+    }
+
+    private fun ASTNode.removeSelf(removeSingleWhiteSpace: Boolean) {
+        if (removeSingleWhiteSpace) {
+            (this as LeafPsiElement).rawReplaceWithText(text.substring(0, textLength - 1))
+        } else {
+            treeParent.removeChild(this)
+        }
+    }
+}

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

@@ -0,0 +1,26 @@
+package com.pinterest.ktlint.ruleset.experimental
+
+import com.pinterest.ktlint.test.diffFileFormat
+import com.pinterest.ktlint.test.diffFileLint
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.Test
+
+class SpacingAroundDoubleColonRuleTest {
+
+    @Test
+    fun testLint() {
+        assertThat(
+            SpacingAroundDoubleColonRule().diffFileLint("spec/spacing-around-double-colon/lint.kt.spec")
+        ).isEmpty()
+    }
+
+    @Test
+    fun testFormat() {
+        assertThat(
+            SpacingAroundDoubleColonRule().diffFileFormat(
+                "spec/spacing-around-double-colon/format.kt.spec",
+                "spec/spacing-around-double-colon/format-expected.kt.spec"
+            )
+        ).isEmpty()
+    }
+}

ktlint-ruleset-experimental/src/test/resources/spec/spacing-around-double-colon/format-expected.kt.spec

@@ -0,0 +1,32 @@
+fun main() {
+    val a = AClass::class
+    val b = BClass::class
+    val c = CClass::class
+    val d = DClass::class
+    val e = EClass::class
+    val f = FClass::class
+
+    fun isOdd(s: String) = s == "brillig" || s == "slithy" || s == "tove"
+    val predicateA: (String) -> Boolean = ::isOdd
+    val predicateB: (String) -> Boolean = ::isOdd
+    val predicateC: (String) -> Boolean = ::isOdd
+    val predicateD: (String) -> Boolean = ::isOdd
+    val predicateE: (String) -> Boolean =
+        ::isOdd
+    val predicateF: (String) -> Boolean = ::isOdd
+
+    if (true == ::isOdd.invoke("")) {
+        // do stuff
+    }
+
+    val isEmptyStringList: List<String>.() -> Boolean = List<String>::isEmpty
+    val isNotEmptyStringList: List<String>.() -> Boolean = List<String>::isNotEmpty
+
+    function(::Foo)
+    function(
+        ::Foo
+    )
+
+    items.filter(::isEven)
+        .map(String::length)
+}

ktlint-ruleset-experimental/src/test/resources/spec/spacing-around-double-colon/format.kt.spec

@@ -0,0 +1,35 @@
+fun main() {
+    val a = AClass::class
+    val b = BClass ::class
+    val c = CClass:: class
+    val d = DClass :: class
+    val e = EClass::
+        class
+    val f = FClass  ::  class
+
+    fun isOdd(s: String) = s == "brillig" || s == "slithy" || s == "tove"
+    val predicateA: (String) -> Boolean = :: isOdd
+    val predicateB: (String) -> Boolean =  ::isOdd
+    val predicateC: (String) -> Boolean =  :: isOdd
+    val predicateD: (String) -> Boolean = ::isOdd
+    val predicateE: (String) -> Boolean =
+        ::isOdd
+    val predicateF: (String) -> Boolean = ::
+        isOdd
+
+    if (true == ::isOdd.invoke("")) {
+        // do stuff
+    }
+
+    val isEmptyStringList: List<String>.() -> Boolean = List<String> :: isEmpty
+    val isNotEmptyStringList: List<String>.() -> Boolean = List<String>::isNotEmpty
+
+    function(::Foo)
+    function(
+        ::
+        Foo
+    )
+
+    items.filter(::isEven)
+        .map(String ::length)
+}

ktlint-ruleset-experimental/src/test/resources/spec/spacing-around-double-colon/lint.kt.spec

@@ -0,0 +1,47 @@
+fun main() {
+    val a = AClass::class
+    val b = BClass ::class
+    val c = CClass:: class
+    val d = DClass :: class
+    val e = EClass::
+        class
+
+    fun isOdd(s: String) = s == "brillig" || s == "slithy" || s == "tove"
+    val predicateA: (String) -> Boolean = :: isOdd
+    val predicateB: (String) -> Boolean =  ::isOdd
+    val predicateC: (String) -> Boolean =  :: isOdd
+    val predicateD: (String) -> Boolean = ::isOdd
+    val predicateE: (String) -> Boolean =
+        ::isOdd
+    val predicateF: (String) -> Boolean = ::
+        isOdd
+
+    if (true == ::isOdd.invoke("")) {
+        // do stuff
+    }
+
+    val isEmptyStringList: List<String>.() -> Boolean = List<String> :: isEmpty
+    val isNotEmptyStringList: List<String>.() -> Boolean = List<String>::isNotEmpty
+
+    function(::Foo)
+    function(
+        ::
+        Foo
+    )
+
+    items.filter(::isEven)
+        .map(String ::length)
+}
+
+// expect
+// 3:19:Unexpected spacing before "::"
+// 4:21:Unexpected spacing after "::"
+// 5:20:Unexpected spacing around "::"
+// 6:21:Unexpected spacing after "::"
+// 10:45:Unexpected spacing after "::"
+// 11:42:Unexpected spacing before "::"
+// 12:44:Unexpected spacing around "::"
+// 16:45:Unexpected spacing after "::"
+// 23:70:Unexpected spacing around "::"
+// 28:11:Unexpected spacing after "::"
+// 33:20:Unexpected spacing before "::"