[groovy] add api for determining whether some expression is not really an expression

plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/GroovyExpressionFilter.kt

@@ -0,0 +1,15 @@
+// Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+package org.jetbrains.plugins.groovy.lang
+
+import org.jetbrains.annotations.ApiStatus.Experimental
+import org.jetbrains.plugins.groovy.lang.psi.api.statements.expressions.GrExpression
+
+@Experimental
+interface GroovyExpressionFilter {
+
+  /**
+   * @return `true` if [expression] is not really an expression,
+   * meaning it would be transformed into something else
+   */
+  fun isFake(expression: GrExpression): Boolean
+}

plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/util/expressionUtil.kt

@@ -0,0 +1,16 @@
+// Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+@file:JvmName("GroovyExpressionUtil")
+
+package org.jetbrains.plugins.groovy.lang.psi.util
+
+import com.intellij.openapi.extensions.ExtensionPointName
+import org.jetbrains.plugins.groovy.lang.GroovyExpressionFilter
+import org.jetbrains.plugins.groovy.lang.psi.api.statements.expressions.GrExpression
+
+private val EP_NAME = ExtensionPointName.create<GroovyExpressionFilter>("org.intellij.groovy.expressionFilter")
+
+fun GrExpression.isFake(): Boolean {
+  return EP_NAME.extensions.any {
+    it.isFake(this)
+  }
+}

plugins/groovy/src/META-INF/plugin.xml

@@ -82,6 +82,7 @@
     <extensionPoint name="gdslScriptProvider" interface="org.jetbrains.plugins.groovy.dsl.GdslScriptProvider"/>
     <extensionPoint name="expectedPackageNameProvider" interface="org.jetbrains.plugins.groovy.lang.resolve.ExpectedPackageNameProvider"/>
     <extensionPoint name="delegatesToProvider" interface="org.jetbrains.plugins.groovy.lang.resolve.delegatesTo.GrDelegatesToProvider"/>
+    <extensionPoint name="expressionFilter" interface="org.jetbrains.plugins.groovy.lang.GroovyExpressionFilter"/>
   </extensionPoints>
 
   <extensions defaultExtensionNs="org.intellij.groovy">