[kotlin] "Convert concatenation to template" (K2): fix false negative when first variable is nullable

^KTIJ-25483 Fixed

closes https://github.com/JetBrains/intellij-community/pull/2444

GitOrigin-RevId: d94d73bc79c1e683bcb72c991dd73e8e72167c1a

plugins/kotlin/code-insight/impl-base/src/org/jetbrains/kotlin/idea/codeinsights/impl/base/StringTemplateUtils.kt

@@ -50,10 +50,11 @@ fun isStringPlusExpressionWithoutNewLineInOperands(expression: KtBinaryExpressio
     if (expression.getKtType()?.isString != true) return false
     val plusOperation = expression.operationReference.mainReference.resolveToSymbol() as? KtCallableSymbol
     val classContainingPlus = plusOperation?.getContainingSymbol() as? KtNamedClassOrObjectSymbol
-    if (classContainingPlus == null) {
-        return plusOperation?.callableIdIfNonLocal?.asSingleFqName()?.asString() == "kotlin.text.plus"
+    return if (classContainingPlus != null) {
+        classContainingPlus.classIdIfNonLocal?.asSingleFqName() == StandardNames.FqNames.string.toSafe()
+    } else {
+        plusOperation?.callableIdIfNonLocal?.asSingleFqName()?.asString() in listOf("kotlin.text.plus", "kotlin.plus")
     }
-    return classContainingPlus.classIdIfNonLocal?.asSingleFqName() == StandardNames.FqNames.string.toSafe()
 }
 
 /**

plugins/kotlin/code-insight/intentions-k2/tests/test/org/jetbrains/kotlin/idea/k2/intentions/tests/K2IntentionTestGenerated.java

@@ -2067,6 +2067,11 @@ public abstract class K2IntentionTestGenerated extends AbstractK2IntentionTest {
             runTest("../../../idea/tests/testData/intentions/convertToStringTemplate/specialCharsInCharLiteral.kt");
         }
 
+        @TestMetadata("startsWithNullableVariable.kt")
+        public void testStartsWithNullableVariable() throws Exception {
+            runTest("../../../idea/tests/testData/intentions/convertToStringTemplate/startsWithNullableVariable.kt");
+        }
+
         @TestMetadata("stringPlusStringLiteral.kt")
         public void testStringPlusStringLiteral() throws Exception {
             runTest("../../../idea/tests/testData/intentions/convertToStringTemplate/stringPlusStringLiteral.kt");

plugins/kotlin/idea/tests/test/org/jetbrains/kotlin/idea/intentions/K1IntentionTestGenerated.java

@@ -9608,6 +9608,11 @@ public abstract class K1IntentionTestGenerated extends AbstractK1IntentionTest {
             runTest("testData/intentions/convertToStringTemplate/specialCharsInCharLiteral.kt");
         }
 
+        @TestMetadata("startsWithNullableVariable.kt")
+        public void testStartsWithNullableVariable() throws Exception {
+            runTest("testData/intentions/convertToStringTemplate/startsWithNullableVariable.kt");
+        }
+
         @TestMetadata("stringPlusStringLiteral.kt")
         public void testStringPlusStringLiteral() throws Exception {
             runTest("testData/intentions/convertToStringTemplate/stringPlusStringLiteral.kt");

plugins/kotlin/idea/tests/testData/intentions/convertToStringTemplate/startsWithNullableVariable.kt

@@ -0,0 +1,2 @@
+val foo: String? = "text"
+val bar = <caret>foo + "bar"

plugins/kotlin/idea/tests/testData/intentions/convertToStringTemplate/startsWithNullableVariable.kt.after

@@ -0,0 +1,2 @@
+val foo: String? = "text"
+val bar = "${foo}bar"

plugins/kotlin/k2-fe10-bindings/test/org/jetbrains/kotlin/idea/k2/fe10bindings/inspections/Fe10BindingIntentionTestGenerated.java

@@ -686,6 +686,11 @@ public abstract class Fe10BindingIntentionTestGenerated extends AbstractFe10Bind
             runTest("../idea/tests/testData/intentions/convertToStringTemplate/specialCharsInCharLiteral.kt");
         }
 
+        @TestMetadata("startsWithNullableVariable.kt")
+        public void testStartsWithNullableVariable() throws Exception {
+            runTest("../idea/tests/testData/intentions/convertToStringTemplate/startsWithNullableVariable.kt");
+        }
+
         @TestMetadata("stringPlusStringLiteral.kt")
         public void testStringPlusStringLiteral() throws Exception {
             runTest("../idea/tests/testData/intentions/convertToStringTemplate/stringPlusStringLiteral.kt");