Support contracts in PartialBodyResolveFilter

Previously, PartialBodyResolveFilter didn't know about contracts and was
filtering out calls of such functions, leading to unstable completion in
cases like that:

fun test(x: Any?) {
    require(x is String)
    x.<caret>
}

However, PartialBodyResolveFilter works by pure PSI, while to determine
if function has a contract we have to resolve it.

To solve it, we do something very similar to what has been done with
Nothin-returning functions: introduce
KotlinProbablyContractedFunctionShortNameIndex, which collects all
function which *may* have a contract during indexing.

^KT-25275 Fixed

idea/idea-analysis/src/org/jetbrains/kotlin/idea/project/ProbablyContractedCallableNamesImpl.kt

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.idea.project
+
+import com.intellij.openapi.project.Project
+import com.intellij.psi.util.CachedValueProvider
+import com.intellij.psi.util.CachedValuesManager
+import com.intellij.psi.util.PsiModificationTracker
+import org.jetbrains.kotlin.idea.stubindex.KotlinProbablyContractedFunctionShortNameIndex
+import org.jetbrains.kotlin.resolve.lazy.ProbablyContractedCallableNames
+
+class ProbablyContractedCallableNamesImpl(project: Project) : ProbablyContractedCallableNames {
+    private val functionNames = CachedValuesManager.getManager(project).createCachedValue(
+        {
+            CachedValueProvider.Result.create(
+                KotlinProbablyContractedFunctionShortNameIndex.getInstance().getAllKeys(project),
+                PsiModificationTracker.OUT_OF_CODE_BLOCK_MODIFICATION_COUNT
+            )
+        },
+        false
+    )
+
+    override fun isProbablyContractedCallableName(name: String): Boolean = name in functionNames.value
+}

idea/idea-analysis/src/org/jetbrains/kotlin/idea/stubindex/KotlinProbablyContractedFunctionShortNameIndex.kt

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.idea.stubindex
+
+import com.intellij.openapi.project.Project
+import com.intellij.psi.search.GlobalSearchScope
+import com.intellij.psi.stubs.StringStubIndexExtension
+import com.intellij.psi.stubs.StubIndex
+import com.intellij.psi.stubs.StubIndexKey
+import org.jetbrains.kotlin.psi.KtNamedFunction
+
+class KotlinProbablyContractedFunctionShortNameIndex : StringStubIndexExtension<KtNamedFunction>() {
+    override fun getKey(): StubIndexKey<String, KtNamedFunction> = KEY
+
+    override fun get(name: String, project: Project, scope: GlobalSearchScope): MutableCollection<KtNamedFunction> =
+        StubIndex.getElements(KEY, name, project, scope, KtNamedFunction::class.java)
+
+    companion object {
+        private val KEY: StubIndexKey<String, KtNamedFunction> =
+            KotlinIndexUtil.createIndexKey(KotlinProbablyContractedFunctionShortNameIndex::class.java)
+
+        private val ourInstance = KotlinProbablyContractedFunctionShortNameIndex()
+
+        @JvmStatic
+        fun getInstance(): KotlinProbablyContractedFunctionShortNameIndex = ourInstance
+    }
+}