KTIJ-650 [Code completion]: no "sealed" for classes with modifiers

annotation, data, enum, inner, open - classes supplied with these
modifiers cannot be sealed.

Commit fixes code completion - "sealed" is no longer suggested in
the mentioned case.

idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/KeywordCompletion.kt

@@ -66,17 +66,32 @@ object KeywordCompletion {
     private val KEYWORDS_TO_IGNORE_PREFIX =
         TokenSet.create(OVERRIDE_KEYWORD /* it's needed to complete overrides that should be work by member name too */)
 
+    private val INCOMPATIBLE_KEYWORDS_AROUND_SEALED = setOf(
+        SEALED_KEYWORD,
+        ANNOTATION_KEYWORD,
+        DATA_KEYWORD,
+        ENUM_KEYWORD,
+        OPEN_KEYWORD,
+        INNER_KEYWORD,
+        ABSTRACT_KEYWORD
+    ).mapTo(HashSet()) { it.value }
+
     private val COMPOUND_KEYWORDS = mapOf<KtKeywordToken, Set<KtKeywordToken>>(
         COMPANION_KEYWORD to setOf(OBJECT_KEYWORD),
         DATA_KEYWORD to setOf(CLASS_KEYWORD),
         ENUM_KEYWORD to setOf(CLASS_KEYWORD),
         ANNOTATION_KEYWORD to setOf(CLASS_KEYWORD),
-        SEALED_KEYWORD to setOf(CLASS_KEYWORD, INTERFACE_KEYWORD),
+        SEALED_KEYWORD to setOf(CLASS_KEYWORD, INTERFACE_KEYWORD, FUN_KEYWORD),
         LATEINIT_KEYWORD to setOf(VAR_KEYWORD),
         CONST_KEYWORD to setOf(VAL_KEYWORD),
         SUSPEND_KEYWORD to setOf(FUN_KEYWORD)
     )
 
+    private val COMPOUND_KEYWORDS_NOT_SUGGEST_TOGETHER = mapOf<KtKeywordToken, Set<KtKeywordToken>>(
+        // 'fun' can follow 'sealed', e.g. "sealed fun interface". But "sealed fun" looks irrelevant differ to "sealed interface/class".
+        SEALED_KEYWORD to setOf(FUN_KEYWORD),
+    )
+
     private val KEYWORD_CONSTRUCTS = mapOf<KtKeywordToken, String>(
         IF_KEYWORD to "fun foo() { if (caret)",
         WHILE_KEYWORD to "fun foo() { while(caret)",
@@ -105,7 +120,6 @@ object KeywordCompletion {
         SET_KEYWORD
     ).map { it.value } + "companion object"
 
-
     fun complete(position: PsiElement, prefixMatcher: PrefixMatcher, isJvmModule: Boolean, consumer: (LookupElement) -> Unit) {
         if (!GENERAL_FILTER.isAcceptable(position, position)) return
 
@@ -125,6 +139,11 @@ object KeywordCompletion {
         }
     }
 
+    private fun KtKeywordToken.avoidSuggestingWith(keywordToken: KtKeywordToken): Boolean {
+        val nextKeywords = COMPOUND_KEYWORDS_NOT_SUGGEST_TOGETHER[this] ?: return false
+        return keywordToken in nextKeywords
+    }
+
     private fun handleCompoundKeyword(
         position: PsiElement,
         keywordToken: KtKeywordToken,
@@ -143,7 +162,15 @@ object KeywordCompletion {
             var next = position.nextLeaf { !(it.isSpace() || it.text == "$") }?.text
             next = next?.removePrefix("$")
 
+            if (keywordToken == SEALED_KEYWORD) {
+                if (next in INCOMPATIBLE_KEYWORDS_AROUND_SEALED) return
+                val prev = position.prevLeaf { !(it.isSpace() || it is PsiErrorElement) }?.text
+                if (prev in INCOMPATIBLE_KEYWORDS_AROUND_SEALED) return
+            }
+
             val nextIsNotYetPresent = keywordToken.getNextPossibleKeywords(position)?.none { it.value == next } == true
+            if (nextIsNotYetPresent && keywordToken.avoidSuggestingWith(nextKeyword)) return
+
             if (nextIsNotYetPresent)
                 keyword += " " + nextKeyword.value
             else
@@ -609,4 +636,4 @@ object KeywordCompletion {
             else -> it.parent
         }
     }
-}
+}

idea/idea-completion/testData/keywords/SealedForAlreadySealed.kt

@@ -0,0 +1,4 @@
+seal<caret> sealed class A
+// ABSENT: "sealed"
+// ABSENT: "sealed class"
+// ABSENT: "sealed interface"

idea/idea-completion/testData/keywords/SealedForAnnotationClass.kt

@@ -0,0 +1,4 @@
+seal<caret> annotation class A
+// ABSENT: "sealed"
+// ABSENT: "sealed class"
+// ABSENT: "sealed interface"

idea/idea-completion/testData/keywords/SealedForDataClass.kt

@@ -0,0 +1,2 @@
+seal<caret> data class A(val f: Int)
+// ABSENT: "sealed"

idea/idea-completion/testData/keywords/SealedForEnumClass.kt

@@ -0,0 +1,2 @@
+seal<caret> enum class A
+// ABSENT: "sealed"

idea/idea-completion/testData/keywords/SealedForFunInterface.kt

@@ -0,0 +1,6 @@
+seal<caret> fun interface A {
+    fun aFunction()
+}
+
+// EXIST: "sealed"
+// NOTHING_ELSE

idea/idea-completion/testData/keywords/SealedForInnerClass.kt

@@ -0,0 +1,4 @@
+class A {
+    seal<caret>inner class B
+}
+// ABSENT: "sealed"

idea/idea-completion/testData/keywords/SealedForOpenClass.kt

@@ -0,0 +1,2 @@
+seal<caret> open class A
+// ABSENT: "sealed"

idea/idea-completion/tests/org/jetbrains/kotlin/idea/completion/test/KeywordCompletionTestGenerated.java

@@ -503,6 +503,21 @@ public class KeywordCompletionTestGenerated extends AbstractKeywordCompletionTes
         runTest("idea/idea-completion/testData/keywords/ReturnSet.kt");
     }
 
+    @TestMetadata("SealedForAlreadySealed.kt")
+    public void testSealedForAlreadySealed() throws Exception {
+        runTest("idea/idea-completion/testData/keywords/SealedForAlreadySealed.kt");
+    }
+
+    @TestMetadata("SealedForAnnotationClass.kt")
+    public void testSealedForAnnotationClass() throws Exception {
+        runTest("idea/idea-completion/testData/keywords/SealedForAnnotationClass.kt");
+    }
+
+    @TestMetadata("SealedForDataClass.kt")
+    public void testSealedForDataClass() throws Exception {
+        runTest("idea/idea-completion/testData/keywords/SealedForDataClass.kt");
+    }
+
     @TestMetadata("SealedForDeclaredClass.kt")
     public void testSealedForDeclaredClass() throws Exception {
         runTest("idea/idea-completion/testData/keywords/SealedForDeclaredClass.kt");
@@ -513,6 +528,26 @@ public class KeywordCompletionTestGenerated extends AbstractKeywordCompletionTes
         runTest("idea/idea-completion/testData/keywords/SealedForDeclaredInterface.kt");
     }
 
+    @TestMetadata("SealedForEnumClass.kt")
+    public void testSealedForEnumClass() throws Exception {
+        runTest("idea/idea-completion/testData/keywords/SealedForEnumClass.kt");
+    }
+
+    @TestMetadata("SealedForFunInterface.kt")
+    public void testSealedForFunInterface() throws Exception {
+        runTest("idea/idea-completion/testData/keywords/SealedForFunInterface.kt");
+    }
+
+    @TestMetadata("SealedForInnerClass.kt")
+    public void testSealedForInnerClass() throws Exception {
+        runTest("idea/idea-completion/testData/keywords/SealedForInnerClass.kt");
+    }
+
+    @TestMetadata("SealedForOpenClass.kt")
+    public void testSealedForOpenClass() throws Exception {
+        runTest("idea/idea-completion/testData/keywords/SealedForOpenClass.kt");
+    }
+
     @TestMetadata("SealedWithName.kt")
     public void testSealedWithName() throws Exception {
         runTest("idea/idea-completion/testData/keywords/SealedWithName.kt");