FIR: Report UNSAFE_INFIX_CALL for all infix-style calls, even if the

candidate is not an infix function.

This mirrors FE 1.0 (see
`AbstractTracingStrategy.reportUnsafeCallOnBinaryExpression()`) and
allows consistent handling for quickfixes on infix calls.

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/coneDiagnosticToFirDiagnostic.kt

@@ -26,7 +26,6 @@ import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.resolve.calls.inference.model.*
 import org.jetbrains.kotlin.resolve.calls.tower.CandidateApplicability
 import org.jetbrains.kotlin.resolve.calls.tower.isSuccess
-import org.jetbrains.kotlin.types.AbstractTypeChecker
 import org.jetbrains.kotlin.utils.addIfNotNull
 import org.jetbrains.kotlin.utils.addToStdlib.firstIsInstance
 import org.jetbrains.kotlin.utils.addToStdlib.safeAs
@@ -105,16 +104,15 @@ private fun mapUnsafeCallError(
         (candidateFunction?.isOperator == true || candidateFunction?.isInfix == true)
     ) {
         val operationToken = source.getChild(KtTokens.IDENTIFIER)
-        if (candidateFunction.isInfix && operationToken?.elementType == KtTokens.IDENTIFIER) {
-            return FirErrors.UNSAFE_INFIX_CALL.on(
+        return if (operationToken != null) {
+            FirErrors.UNSAFE_INFIX_CALL.on(
                 source,
                 receiverExpression,
                 candidateFunctionName!!.asString(),
                 singleArgument,
             )
-        }
-        if (candidateFunction.isOperator && operationToken == null) {
-            return FirErrors.UNSAFE_OPERATOR_CALL.on(
+        } else {
+            FirErrors.UNSAFE_OPERATOR_CALL.on(
                 source,
                 receiverExpression,
                 candidateFunctionName!!.asString(),

compiler/testData/diagnostics/tests/BinaryCallsOnNullableValues.fir.kt

@@ -6,7 +6,7 @@ fun f(): Unit {
     var x: Int? = 1
     x = null
     x <!UNSAFE_OPERATOR_CALL!>+<!> 1
-    x <!UNSAFE_CALL!>plus<!> 1
+    x <!UNSAFE_INFIX_CALL!>plus<!> 1
     x <!UNSAFE_OPERATOR_CALL!><<!> 1
     x <!UNRESOLVED_REFERENCE!>+=<!> 1
 

idea/testData/quickfix/nullables/unsafeInfixCall/unsafeInfixCall.kt

@@ -1,6 +1,4 @@
 // "Replace with safe (?.) call" "true"
 fun test(a : Int?) : Int? {
     return a <caret>compareTo 6;
-}
-
-/* IGNORE_FIR */
+}

idea/testData/quickfix/nullables/unsafeInfixCall/unsafeInfixCall.kt.after

@@ -1,6 +1,4 @@
 // "Replace with safe (?.) call" "true"
 fun test(a : Int?) : Int? {
     return a?.compareTo(6);
-}
-
-/* IGNORE_FIR */
+}