FIR IDE: API to determine if the given KtType is a functional interface type

idea/idea-frontend-api/src/org/jetbrains/kotlin/idea/frontend/api/components/KtTypeInfoProvider.kt

@@ -12,10 +12,17 @@ import org.jetbrains.kotlin.idea.frontend.api.types.*
 import org.jetbrains.kotlin.name.ClassId
 
 public abstract class KtTypeInfoProvider : KtAnalysisSessionComponent() {
+    public abstract fun isFunctionalInterfaceType(type: KtType): Boolean
     public abstract fun canBeNull(type: KtType): Boolean
 }
 
 public interface KtTypeInfoProviderMixIn : KtAnalysisSessionMixIn {
+    /**
+     * Returns true if this type is a functional interface type, a.k.a. SAM type, e.g., Runnable.
+     */
+    public val KtType.isFunctionalInterfaceType: Boolean
+        get() = analysisSession.typeInfoProvider.isFunctionalInterfaceType(this)
+
     /**
      * Returns true if a public value of this type can potentially be null. This means this type is not a subtype of [Any]. However, it does not
      * mean one can assign `null` to a variable of this type because it may be unknown if this type can accept `null`. For example, a public value

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/components/KtFirTypeInfoProvider.kt

@@ -5,6 +5,8 @@
 
 package org.jetbrains.kotlin.idea.frontend.api.fir.components
 
+import org.jetbrains.kotlin.fir.resolve.FirSamResolverImpl
+import org.jetbrains.kotlin.fir.resolve.ScopeSession
 import org.jetbrains.kotlin.fir.types.canBeNull
 import org.jetbrains.kotlin.idea.frontend.api.components.KtTypeInfoProvider
 import org.jetbrains.kotlin.idea.frontend.api.fir.KtFirAnalysisSession
@@ -17,5 +19,11 @@ internal class KtFirTypeInfoProvider(
     override val token: ValidityToken,
 ) : KtTypeInfoProvider(), KtFirAnalysisSessionComponent {
 
+    override fun isFunctionalInterfaceType(type: KtType): Boolean {
+        val coneType = (type as KtFirType).coneType
+        val samResolver = FirSamResolverImpl(analysisSession.rootModuleSession, ScopeSession())
+        return samResolver.getFunctionTypeForPossibleSamType(coneType) != null
+    }
+
     override fun canBeNull(type: KtType): Boolean = (type as KtFirType).coneType.canBeNull
-}
+}