[FIR] Do not set must-use status for a local function unconditionally

Use corresponding AnalysisFlag instead, to avoid unwanted warnings on local functions usages — CHECKER mode usually means that user wanted to see reports only on stdlib/libraries functions.

#KT-78112 Fixed

Author: sandwwraith

analysis/low-level-api-fir/tests-gen/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLDiagnosticsFe10TestGenerated.java

@@ -124,9 +124,10 @@ abstract class FirMustUseReturnValueStatusComponent : FirSessionComponent {
             containingProperty: FirPropertySymbol?,
             overriddenStatuses: List<FirResolvedDeclarationStatus>,
         ): ReturnValueStatus {
+            val analysisMode = session.languageVersionSettings.getFlag(AnalysisFlags.returnValueCheckerMode)
             if (isLocal) {
-                // FIXME (KT-78112): pass through outer declaration through BodyResolveTransformer when we compute status for local functions
-                return if (declaration is FirFunctionSymbol) ReturnValueStatus.MustUse else ReturnValueStatus.Unspecified
+                // To compute status using annotations, getFirCallableContainerFile/getContainingDeclaration should work correctly for local declarations (KT-80564)
+                return if (declaration is FirFunctionSymbol && analysisMode == ReturnValueCheckerMode.FULL) ReturnValueStatus.MustUse else ReturnValueStatus.Unspecified
             }
             // Implementation note: just with intersection overrides, in case we have more than one immediate parent, we take first from the list
             // See inheritanceChainIgnorability.kt test.
@@ -138,7 +139,7 @@ abstract class FirMustUseReturnValueStatusComponent : FirSessionComponent {
             // In the case of inheriting from Ignorable or Unspecified, global FULL setting has lesser priority than annotations/parent
             // but we want to check it here first to avoid looking through the containers
             val overridesIgnorableOrUnspecified = overriddenFlag == ReturnValueStatus.ExplicitlyIgnorable || overriddenFlag == ReturnValueStatus.Unspecified
-            if (session.languageVersionSettings.getFlag(AnalysisFlags.returnValueCheckerMode) == ReturnValueCheckerMode.FULL && !overridesIgnorableOrUnspecified)
+            if (analysisMode == ReturnValueCheckerMode.FULL && !overridesIgnorableOrUnspecified)
                 return ReturnValueStatus.MustUse
 
             if (findMustUseAmongContainers(

analysis/low-level-api-fir/tests-gen/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLPartialDiagnosticsFe10TestGenerated.java

@@ -5,14 +5,32 @@
 
 fun localFun() {
     fun local(): Int = 123
-    <!RETURN_VALUE_NOT_USED!>local()<!>     //unused
+    @IgnorableReturnValue fun localIgnorable() = ""
+    local()
+    localIgnorable()
 }
 
-class A {
-    fun foo(): Int = 123
-    fun test() {
-        <!RETURN_VALUE_NOT_USED!>foo()<!>               //unused
+class Outer {
+    fun foo(): String {
+        class Inner {
+            @IgnorableReturnValue fun bar() {
+                fun local() = ""
+                local()
+            }
+            fun inner() = ""
+        }
+        Inner()
+        Inner().inner()
+        Inner().bar()
+        return ""
     }
+
+    fun bar(): String = ""
+}
+
+fun main() {
+    <!RETURN_VALUE_NOT_USED!>Outer().foo()<!>
+    <!RETURN_VALUE_NOT_USED!>Outer().bar()<!>
 }
 
 /* GENERATED_FIR_TAGS: annotationUseSiteTargetFile, classDeclaration, functionDeclaration, integerLiteral, localFunction */

analysis/low-level-api-fir/tests-gen/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLReversedDiagnosticsFe10TestGenerated.java

@@ -5,14 +5,32 @@
 
 fun localFun() {
     fun local(): Int = 123
-    local()     //unused
+    @IgnorableReturnValue fun localIgnorable() = ""
+    local()
+    localIgnorable()
 }
 
-class A {
-    fun foo(): Int = 123
-    fun test() {
-        foo()               //unused
+class Outer {
+    fun foo(): String {
+        class Inner {
+            @IgnorableReturnValue fun bar() {
+                fun local() = ""
+                local()
+            }
+            fun inner() = ""
+        }
+        Inner()
+        Inner().inner()
+        Inner().bar()
+        return ""
     }
+
+    fun bar(): String = ""
+}
+
+fun main() {
+    Outer().foo()
+    Outer().bar()
 }
 
 /* GENERATED_FIR_TAGS: annotationUseSiteTargetFile, classDeclaration, functionDeclaration, integerLiteral, localFunction */

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeOldFrontendDiagnosticsWithLatestLanguageVersionTestGenerated.java

@@ -0,0 +1,34 @@
+// RUN_PIPELINE_TILL: BACKEND
+// WITH_STDLIB
+
+fun localFun() {
+    fun local(): Int = 123
+    @IgnorableReturnValue fun localIgnorable() = ""
+    <!RETURN_VALUE_NOT_USED!>local()<!>
+    localIgnorable()
+}
+
+class Outer {
+    fun foo(): String {
+        class Inner {
+            @IgnorableReturnValue fun bar() {
+                fun local() = ""
+                <!RETURN_VALUE_NOT_USED!>local()<!>
+            }
+            fun inner() = ""
+        }
+        <!RETURN_VALUE_NOT_USED!>Inner()<!>
+        <!RETURN_VALUE_NOT_USED!>Inner().inner()<!>
+        Inner().bar()
+        return ""
+    }
+
+    fun bar(): String = ""
+}
+
+fun main() {
+    <!RETURN_VALUE_NOT_USED!>Outer().foo()<!>
+    <!RETURN_VALUE_NOT_USED!>Outer().bar()<!>
+}
+
+/* GENERATED_FIR_TAGS: annotationUseSiteTargetFile, classDeclaration, functionDeclaration, integerLiteral, localFunction */