FIR: Fix smartcast case after equals on class from different module

^KT-50534 Relates

compiler/fir/analysis-tests/testData/resolve/smartcasts/smartcastsFromEquals_differentModule.fir.txt

@@ -33,7 +33,7 @@ FILE: module_main_smartcastsFromEquals_differentModule.kt
     public final fun testFinal(x: R|Final<*>|, y: R|Final<kotlin/Int>|): R|kotlin/Unit| {
         when () {
             ==(R|<local>/x|, R|<local>/y|) ->  {
-                <Inapplicable(INAPPLICABLE): /takeIntFinal>#(R|<local>/x|)
+                R|/takeIntFinal|(R|<local>/x|)
             }
         }
 
@@ -61,7 +61,7 @@ FILE: module_main_smartcastsFromEquals_differentModule.kt
     public final fun testDerived(x: R|Derived<*>|, y: R|Derived<kotlin/Int>|): R|kotlin/Unit| {
         when () {
             ==(R|<local>/x|, R|<local>/y|) ->  {
-                <Inapplicable(INAPPLICABLE): /takeIntDerived>#(R|<local>/x|)
+                R|/takeIntDerived|(R|<local>/x|)
             }
         }
 

compiler/fir/analysis-tests/testData/resolve/smartcasts/smartcastsFromEquals_differentModule.kt

@@ -20,7 +20,10 @@ class FinalWithOverride<T> {
 // MODULE: main(lib)
 fun testFinal(x: Final<*>, y: Final<Int>) {
     if (x == y) {
-        takeIntFinal(<!ARGUMENT_TYPE_MISMATCH!>x<!>) // Error
+        // No error, even while `Final` belongs to a different module and "equals" contract might be changed without re-compilation
+        // But since we had such behavior in FE1.0, it might be too strict to prohibit it now, especially once there's a lot of cases
+        // when different modules belong to a single project, so they're totally safe (see KT-50534)
+        takeIntFinal(x)
     }
     if (x === y) {
         takeIntFinal(x) // OK
@@ -38,7 +41,10 @@ fun testBase(x: Base<*>, y: Base<Int>) {
 
 fun testDerived(x: Derived<*>, y: Derived<Int>) {
     if (x == y) {
-        takeIntDerived(<!ARGUMENT_TYPE_MISMATCH!>x<!>) // Error
+        // No error, even while `Final` belongs to a different module and "equals" contract might be changed without re-compilation
+        // But since we had such behavior in FE1.0, it might be too strict to prohibit it now, especially once there's a lot of cases
+        // when different modules belong to a single project, so they're totally safe (see KT-50534)
+        takeIntDerived(x)
     }
     if (x === y) {
         takeIntDerived(x) // OK

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/dfa/FirDataFlowAnalyzer.kt

@@ -15,7 +15,6 @@ import org.jetbrains.kotlin.fir.contracts.description.ConeConstantReference
 import org.jetbrains.kotlin.fir.contracts.description.ConeReturnsEffectDeclaration
 import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.declarations.impl.FirDefaultPropertyAccessor
-import org.jetbrains.kotlin.fir.declarations.utils.isFinal
 import org.jetbrains.kotlin.fir.declarations.utils.isLocal
 import org.jetbrains.kotlin.fir.expressions.*
 import org.jetbrains.kotlin.fir.references.FirControlFlowGraphReference
@@ -30,7 +29,10 @@ import org.jetbrains.kotlin.fir.resolve.transformers.body.resolve.resultType
 import org.jetbrains.kotlin.fir.scopes.getFunctions
 import org.jetbrains.kotlin.fir.scopes.impl.declaredMemberScope
 import org.jetbrains.kotlin.fir.symbols.FirBasedSymbol
-import org.jetbrains.kotlin.fir.symbols.impl.*
+import org.jetbrains.kotlin.fir.symbols.impl.FirClassSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirRegularClassSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirTypeParameterSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirVariableSymbol
 import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.fir.visitors.transformSingle
 import org.jetbrains.kotlin.name.StandardClassIds
@@ -710,10 +712,17 @@ abstract class FirDataFlowAnalyzer<FLOW : Flow>(
         if (status.isExpect) return true
         when (classId) {
             StandardClassIds.Any, StandardClassIds.String -> return false
+            // Float and Double effectively had non-trivial `equals` semantics while they don't have explicit overrides (see KT-50535)
+            StandardClassIds.Float, StandardClassIds.Double -> return true
         }
-        if (moduleData != session.moduleData) {
+
-            return true
+        // When the class belongs to a different module, "equals" contract might be changed without re-compilation
-        }
+        // But since we had such behavior in FE1.0, it might be too strict to prohibit it now, especially once there's a lot of cases
+        // when different modules belong to a single project, so they're totally safe (see KT-50534)
+        // if (moduleData != session.moduleData) {
+        //     return true
+        // }
+
         return session.declaredMemberScope(this)
             .getFunctions(OperatorNameConventions.EQUALS)
             .any { it.fir.isEquals() }