Improve remove/specify type intentions in Explicit API mode

Do not suggest to remove type for public declarations

 #KT-38915 Fixed

Do not show intention to specify type when corresponding quickfix is available

 #KT-39026 Fixed

compiler/frontend/src/org/jetbrains/kotlin/resolve/checkers/ExplicitApiDeclarationChecker.kt

@@ -7,6 +7,7 @@ package org.jetbrains.kotlin.resolve.checkers
 
 import org.jetbrains.kotlin.config.AnalysisFlags
 import org.jetbrains.kotlin.config.ExplicitApiMode
+import org.jetbrains.kotlin.config.LanguageVersionSettings
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.diagnostics.Errors
 import org.jetbrains.kotlin.diagnostics.reportDiagnosticOnce
@@ -122,5 +123,20 @@ class ExplicitApiDeclarationChecker : DeclarationChecker {
 
             return true
         }
+
+        fun publicReturnTypeShouldBePresentInApiMode(
+            element: KtCallableDeclaration,
+            languageVersionSettings: LanguageVersionSettings,
+            descriptor: DeclarationDescriptor?
+        ): Boolean {
+            val isInApiMode = languageVersionSettings.getFlag(AnalysisFlags.explicitApiMode) != ExplicitApiMode.DISABLED
+            return isInApiMode && returnTypeRequired(
+                element,
+                descriptor,
+                checkForPublicApi = true,
+                checkForInternal = false,
+                checkForPrivate = false
+            )
+        }
     }
 }

idea/src/org/jetbrains/kotlin/idea/intentions/RemoveExplicitTypeIntention.kt

@@ -10,6 +10,8 @@ import com.intellij.openapi.editor.Editor
 import com.intellij.openapi.util.TextRange
 import org.jetbrains.kotlin.descriptors.FunctionDescriptor
 import org.jetbrains.kotlin.idea.KotlinBundle
+import org.jetbrains.kotlin.idea.caches.resolve.resolveToDescriptorIfAny
+import org.jetbrains.kotlin.idea.project.languageVersionSettings
 import org.jetbrains.kotlin.idea.refactoring.addTypeArgumentsIfNeeded
 import org.jetbrains.kotlin.idea.refactoring.getQualifiedTypeArgumentList
 import org.jetbrains.kotlin.idea.references.mainReference
@@ -18,6 +20,7 @@ import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.psi.*
 import org.jetbrains.kotlin.psi.psiUtil.endOffset
 import org.jetbrains.kotlin.psi.psiUtil.startOffset
+import org.jetbrains.kotlin.resolve.checkers.ExplicitApiDeclarationChecker
 import org.jetbrains.kotlin.types.typeUtil.isUnit
 
 class RemoveExplicitTypeIntention : SelfTargetingRangeIntention<KtCallableDeclaration>(
@@ -56,6 +59,12 @@ class RemoveExplicitTypeIntention : SelfTargetingRangeIntention<KtCallableDeclar
 
             val initializer = (element as? KtDeclarationWithInitializer)?.initializer
 
+            if (ExplicitApiDeclarationChecker.publicReturnTypeShouldBePresentInApiMode(
+                    element,
+                    element.languageVersionSettings,
+                    element.resolveToDescriptorIfAny()
+                )
+            ) return null
             if (!redundantTypeSpecification(element.typeReference, initializer)) return null
 
             return when {
@@ -92,4 +101,4 @@ class RemoveExplicitTypeIntention : SelfTargetingRangeIntention<KtCallableDeclar
     }
 }
 
-internal val KtParameter.isSetterParameter: Boolean get() = (parent.parent as? KtPropertyAccessor)?.isSetter ?: false
+internal val KtParameter.isSetterParameter: Boolean get() = (parent.parent as? KtPropertyAccessor)?.isSetter ?: false

idea/src/org/jetbrains/kotlin/idea/intentions/SpecifyTypeExplicitlyIntention.kt

@@ -23,6 +23,7 @@ import org.jetbrains.kotlin.idea.caches.resolve.resolveToDescriptorIfAny
 import org.jetbrains.kotlin.idea.core.ShortenReferences
 import org.jetbrains.kotlin.idea.core.setType
 import org.jetbrains.kotlin.idea.core.unquote
+import org.jetbrains.kotlin.idea.project.languageVersionSettings
 import org.jetbrains.kotlin.idea.util.IdeDescriptorRenderers
 import org.jetbrains.kotlin.idea.util.application.runWriteAction
 import org.jetbrains.kotlin.idea.util.getResolutionScope
@@ -42,6 +43,14 @@ class SpecifyTypeExplicitlyIntention : SelfTargetingRangeIntention<KtCallableDec
 ), HighPriorityAction {
     override fun applicabilityRange(element: KtCallableDeclaration): TextRange? {
         if (!ExplicitApiDeclarationChecker.returnTypeCheckIsApplicable(element)) return null
+        // If ApiMode is on, then this intention duplicates corresponding quickfix for compiler error
+        // and we disable it here.
+        if (ExplicitApiDeclarationChecker.publicReturnTypeShouldBePresentInApiMode(
+                element,
+                element.languageVersionSettings,
+                element.resolveToDescriptorIfAny()
+            )
+        ) return null
         setTextGetter(
             if (element is KtFunction)
                 KotlinBundle.lazyMessage("specify.return.type.explicitly")

idea/testData/intentions/removeExplicitTypeWithApiMode/.intention

@@ -0,0 +1 @@
+org.jetbrains.kotlin.idea.intentions.RemoveExplicitTypeIntention

idea/testData/intentions/removeExplicitTypeWithApiMode/nonPublicFunction.kt

@@ -0,0 +1,4 @@
+// COMPILER_ARGUMENTS: -Xexplicit-api=strict
+// IS_APPLICABLE: true
+
+internal fun foo(): <caret>Int = 42

idea/testData/intentions/removeExplicitTypeWithApiMode/nonPublicFunction.kt.after

@@ -0,0 +1,4 @@
+// COMPILER_ARGUMENTS: -Xexplicit-api=strict
+// IS_APPLICABLE: true
+
+internal fun foo() = 42

idea/testData/intentions/removeExplicitTypeWithApiMode/publicFunction.kt

@@ -0,0 +1,4 @@
+// COMPILER_ARGUMENTS: -Xexplicit-api=strict
+// IS_APPLICABLE: false
+
+public fun foo(): <caret>Int = 42

idea/tests/org/jetbrains/kotlin/idea/intentions/IntentionTestGenerated.java

@@ -14417,6 +14417,29 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
         }
     }
 
+    @TestMetadata("idea/testData/intentions/removeExplicitTypeWithApiMode")
+    @TestDataPath("$PROJECT_ROOT")
+    @RunWith(JUnit3RunnerWithInners.class)
+    public static class RemoveExplicitTypeWithApiMode extends AbstractIntentionTest {
+        private void runTest(String testDataFilePath) throws Exception {
+            KotlinTestUtils.runTest(this::doTest, this, testDataFilePath);
+        }
+
+        public void testAllFilesPresentInRemoveExplicitTypeWithApiMode() throws Exception {
+            KotlinTestUtils.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("idea/testData/intentions/removeExplicitTypeWithApiMode"), Pattern.compile("^([\\w\\-_]+)\\.(kt|kts)$"), null, true);
+        }
+
+        @TestMetadata("nonPublicFunction.kt")
+        public void testNonPublicFunction() throws Exception {
+            runTest("idea/testData/intentions/removeExplicitTypeWithApiMode/nonPublicFunction.kt");
+        }
+
+        @TestMetadata("publicFunction.kt")
+        public void testPublicFunction() throws Exception {
+            runTest("idea/testData/intentions/removeExplicitTypeWithApiMode/publicFunction.kt");
+        }
+    }
+
     @TestMetadata("idea/testData/intentions/removeForLoopIndices")
     @TestDataPath("$PROJECT_ROOT")
     @RunWith(JUnit3RunnerWithInners.class)