[codeInsight] IDEA-240288 Inspection for StringBuilder.toString().substring()

This patch alters the `getRedundantStringBuilderToStringProblem` method with more sophisticated algorithm to detect unnecessary freestanding `StringBuilder#toString` calls. If the call is a part of a polyadic expression it checks if there is at least one string operand (either a constant literal or a local variable or a constant variable or a method call) and based on that information it detects redundant `StringBuilder#toString` calls.

Signed-off-by: Nikita Eshkeev <nikita.eshkeev@jetbrains.com>

GitOrigin-RevId: e09ea8b8829ad9e28e8ff1bcfad34cf6b191aa6b

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/redundantStringOperation/afterStringBuilderToString.java

@@ -1,7 +1,11 @@
 // "Fix all 'Redundant String operation' problems in file" "true"
 
 class StringBuilderToString {
-  StringBuilderToString() {
+
+  private static final String CONST_STRING_VAL = "Hello";
+  static String str() { return ""; }
+
+  void stringBuilderToStringSubstring() {
     String s1 = new StringBuilder().toString();
       /* 1 */
       String s2 = new StringBuilder()/* 2 */.substring(1);
@@ -22,35 +26,8 @@ class StringBuilderToString {
       System.out.println(new StringBuilder()/* 2 */.substring(1, 3).length());
     System.out.println(new StringBuilder().substring(1, 3));
     System.out.println(new StringBuilder().substring(1, 3).length());
-
-    StringBuilder sb = new StringBuilder();
-      /* 1 */
-      String s6 = sb/* 2 */ + sb. /* 3 */toString()/* 4 */;
-      /* 1 */
-      String s7 = sb/* 2 */ + sb./* 3 */toString()/* 4 */;
-    String s8 = "Hello, World" + sb.toString();
-    String s8 = ("Hello, " + "World") + sb.toString();
-    String s9 = sb./* 1 */toString()/* 2 */ + 42;
-      /* 1 */
-      String s10 = sb/* 2 */ + "Hello, World";
-      /* 3 */
-      /* 1 */
-      String s11 = sb/* 2 */ + sb/* 4 */ + sb./* 5 */toString()/* 6 */;
-
-      /* 1 */
-      System.out.println(sb/* 2 */ + sb. /* 3 */toString()/* 4 */);
-      /* 1 */
-      System.out.println(sb/* 2 */ + sb./* 3 */toString()/* 4 */);
-      /* 3 */
-      /* 1 */
-      System.out.println(sb/* 2 */ + sb/* 4 */ + sb./* 5 */toString()/* 6 */);
-    System.out.println("Hello, World" + sb.toString());
-    System.out.println(("Hello, " + "World") + sb.toString());
-    System.out.println(sb./* 1 */toString()/* 2 */ + 42);
-      /* 1 */
-      System.out.println(sb/* 2 */ + "Hello, World");
-
   }
+
   void builder(StringBuilder sb) {
     String s1 = sb.toString();
       /* 1 */
@@ -62,11 +39,6 @@ class StringBuilderToString {
       /* 1 */
       int s5 = sb/* 2 */.substring(1, 4).length();
 
-      /* 1 */
-      String s6 = sb.append(sb)/* 2 */.substring(1);
-      /* 1 */
-      String s7 = (sb/* 2 */ + sb./* 3 */toString()/* 4 */).substring(1);
-
       /* 1 */
       System.out.println(sb/* 2 */);
       /* 1 */
@@ -77,10 +49,5 @@ class StringBuilderToString {
       System.out.println(sb/* 2 */.substring(1, 3).length());
     System.out.println(sb.substring(1, 3));
     System.out.println(sb.substring(1, 3).length());
-
-    f(sb);
-    f(sb.toString());
   }
-  void f(StringBuilder s) {}
-  void f(String s) {}
 }

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/redundantStringOperation/afterStringBuilderToStringArgs.java

@@ -0,0 +1,88 @@
+// "Fix all 'Redundant String operation' problems in file" "true"
+
+class StringBuilderToStringArgs {
+
+  private static final String CONST_STRING_VAL = "Hello";
+  static String str() { return ""; }
+
+  static void stringBuilderToStringArgs(StringBuilder sb) {
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      System.out.println(/* 1 */sb/* 5 */ + "Hello");
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      System.out.println("Hello" + /* 1 */sb/* 5 */);
+    System.out.println(/* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + 42);
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      System.out.println("Hello" + /* 1 */sb/* 5 */ + 42);
+
+    final String finalVal = "Hello";
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      System.out.println(/* 1 */sb/* 5 */ + finalVal);
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      System.out.println(finalVal + /* 1 */sb/* 5 */);
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      System.out.println(finalVal + /* 1 */sb/* 5 */ + 42);
+
+    String stringVal = "Hello";
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      System.out.println(stringVal + /* 1 */sb/* 5 */ + 42);
+
+    int intVal = 42;
+    System.out.println(intVal + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + 42);
+
+    final int constIntVal = 42;
+    System.out.println(/* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + constIntVal);
+    System.out.println(constIntVal + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */);
+    System.out.println(constIntVal + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + 42);
+
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      System.out.println(CONST_STRING_VAL + /* 1 */sb/* 5 */);
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      System.out.println(/* 1 */sb/* 5 */ + CONST_STRING_VAL);
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      System.out.println(CONST_STRING_VAL + /* 1 */sb/* 5 */ + 42);
+
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      System.out.println(str() + /* 1 */sb/* 5 */);
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      System.out.println(/* 1 */sb/* 5 */ + str());
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      System.out.println(str() + /* 1 */sb/* 5 */ + str());
+
+    System.out.println(/* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */);
+    System.out.println(/* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */);
+
+    System.out.println(("Hello" + sb) + sb + sb);
+    System.out.println(("Hello" + sb) + sb + sb);
+    System.out.println((("Hello" + sb) + sb) + sb);
+    System.out.println(("Hello" + sb + (sb.toString() + ((sb.toString())))));
+    System.out.println(("Hello" + sb + (sb + ((sb) + "Hello"))));
+    System.out.println(("Hello" + sb + (sb + ((sb.toString()) + 42))));
+  }
+
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/redundantStringOperation/afterStringBuilderToStringAssign.java

@@ -0,0 +1,89 @@
+// "Fix all 'Redundant String operation' problems in file" "true"
+
+class StringBuilderToStringAssign {
+
+  public static final String CONST_STRING_VAL = "Hello";
+
+  static String str() { return ""; }
+
+  static void stringBuilderToStringAssign(StringBuilder sb) {
+    String s1 = sb + "Hello";
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      String s2 = "Hello" + /* 1 */sb/* 5 */;
+    String s3 = /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + 42;
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      String s4 = "Hello" + /* 1 */sb/* 5 */ + 42;
+
+    final String finalVal = "Hello";
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      String s5 = finalVal + /* 1 */sb/* 5 */ + 42;
+
+    String stringVal = "Hello";
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      String s611 = /* 1 */sb/* 5 */ + stringVal;
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      String s621 = stringVal + /* 1 */sb/* 5 */;
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      String s631 = stringVal + /* 1 */sb/* 5 */ + 42;
+
+    int intVal = 42;
+    String s612 = /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + intVal;
+    String s622 = intVal + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */;
+    String s632 = intVal + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + 42;
+
+    final int constIntVal = 42;
+    String s61 = constIntVal + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */;
+    String s62 = /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + constIntVal;
+    String s63 = /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + constIntVal + 42;
+
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      String s71 = CONST_STRING_VAL + /* 1 */sb/* 5 */;
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      String s72 = /* 1 */sb/* 5 */ + CONST_STRING_VAL;
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      String s73 = CONST_STRING_VAL + /* 1 */sb/* 5 */ + 42;
+
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      String s81 = str() + /* 1 */sb/* 5 */;
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      String s82 = /* 1 */sb/* 5 */ + str();
+      /* 2 */
+      /* 3 */
+      /* 4 */
+      String s83 = str() + /* 1 */sb/* 5 */ + str();
+
+    String s91 = /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */;
+    String s92 = /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */;
+
+    String s101 = ("Hello" + sb) + sb + sb;
+    String s102 = ("Hello" + sb) + sb + sb;
+    String s103 = (("Hello" + sb) + sb) + sb;
+    String s104 = ("Hello" + sb + (sb.toString() + ((sb.toString()))));
+    String s105 = ("Hello" + sb + (sb + ((sb) + "Hello")));
+    String s106 = ("Hello" + sb + (sb + ((sb.toString()) + 42)));
+  }
+
+}
+

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/redundantStringOperation/beforeStringBuilderToString.java

@@ -1,9 +1,13 @@
 // "Fix all 'Redundant String operation' problems in file" "true"
 
 class StringBuilderToString {
-  StringBuilderToString() {
+
+  private static final String CONST_STRING_VAL = "Hello";
+  static String str() { return ""; }
+
+  void stringBuilderToStringSubstring() {
     String s1 = new StringBuilder().toString();
-    String s2 = new StringBuilder()./* 1 */<caret>toString()/* 2 */.substring(1);
+    String s2 = new StringBuilder()./* 1 */to<caret>String()/* 2 */.substring(1);
     String s3 = new StringBuilder()./* 1 */toString()/* 2 */.substring(1, 4);
     String s4 = new StringBuilder()./* 1 */toString()/* 2 */.substring(1, 4);
     int s5 = new StringBuilder()./* 1 */toString()/* 2 */.substring(1, 4).length();
@@ -14,25 +18,8 @@ class StringBuilderToString {
     System.out.println(new StringBuilder()./* 1 */toString()/* 2 */.substring(1, 3).length());
     System.out.println(new StringBuilder().substring(1, 3));
     System.out.println(new StringBuilder().substring(1, 3).length());
-
-    StringBuilder sb = new StringBuilder();
-    String s6 = sb./* 1 */toString()/* 2 */ + sb. /* 3 */toString()/* 4 */;
-    String s7 = sb./* 1 */toString()/* 2 */ + sb./* 3 */toString()/* 4 */;
-    String s8 = "Hello, World" + sb.toString();
-    String s8 = ("Hello, " + "World") + sb.toString();
-    String s9 = sb./* 1 */toString()/* 2 */ + 42;
-    String s10 = sb./* 1 */toString()/* 2 */ + "Hello, World";
-    String s11 = sb./* 1 */toString()/* 2 */ + sb./* 3 */toString()/* 4 */ + sb./* 5 */toString()/* 6 */;
-
-    System.out.println(sb./* 1 */toString()/* 2 */ + sb. /* 3 */toString()/* 4 */);
-    System.out.println(sb./* 1 */toString()/* 2 */ + sb./* 3 */toString()/* 4 */);
-    System.out.println(sb./* 1 */toString()/* 2 */ + sb./* 3 */toString()/* 4 */ + sb./* 5 */toString()/* 6 */);
-    System.out.println("Hello, World" + sb.toString());
-    System.out.println(("Hello, " + "World") + sb.toString());
-    System.out.println(sb./* 1 */toString()/* 2 */ + 42);
-    System.out.println(sb./* 1 */toString()/* 2 */ + "Hello, World");
-
   }
+
   void builder(StringBuilder sb) {
     String s1 = sb.toString();
     String s2 = sb./* 1 */toString()/* 2 */.substring(1);
@@ -40,19 +27,11 @@ class StringBuilderToString {
     String s4 = sb./* 1 */toString()/* 2 */.substring(1, 4);
     int s5 = sb./* 1 */toString()/* 2 */.substring(1, 4).length();
 
-    String s6 = sb.append(sb)./* 1 */toString()/* 2 */.substring(1);
-    String s7 = (sb./* 1 */toString()/* 2 */ + sb./* 3 */toString()/* 4 */).substring(1);
-
     System.out.println(sb./* 1 */toString()/* 2 */);
     System.out.println(sb./* 1 */toString()/* 2 */.substring(1));
     System.out.println(sb./* 1 */toString()/* 2 */.substring(1, 3));
     System.out.println(sb./* 1 */toString()/* 2 */.substring(1, 3).length());
     System.out.println(sb.substring(1, 3));
     System.out.println(sb.substring(1, 3).length());
-
-    f(sb);
-    f(sb.toString());
   }
-  void f(StringBuilder s) {}
-  void f(String s) {}
 }

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/redundantStringOperation/beforeStringBuilderToStringArgs.java

@@ -0,0 +1,49 @@
+// "Fix all 'Redundant String operation' problems in file" "true"
+
+class StringBuilderToStringArgs {
+
+  private static final String CONST_STRING_VAL = "Hello";
+  static String str() { return ""; }
+
+  static void stringBuilderToStringArgs(StringBuilder sb) {
+    System.out.println(/* 1 */sb./* 2 */to<caret>String/* 3 */(/* 4 */)/* 5 */ + "Hello");
+    System.out.println("Hello" + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */);
+    System.out.println(/* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + 42);
+    System.out.println("Hello" + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + 42);
+
+    final String finalVal = "Hello";
+    System.out.println(/* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + finalVal);
+    System.out.println(finalVal + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */);
+    System.out.println(finalVal + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + 42);
+
+    String stringVal = "Hello";
+    System.out.println(stringVal + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + 42);
+
+    int intVal = 42;
+    System.out.println(intVal + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + 42);
+
+    final int constIntVal = 42;
+    System.out.println(/* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + constIntVal);
+    System.out.println(constIntVal + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */);
+    System.out.println(constIntVal + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + 42);
+
+    System.out.println(CONST_STRING_VAL + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */);
+    System.out.println(/* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + CONST_STRING_VAL);
+    System.out.println(CONST_STRING_VAL + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + 42);
+
+    System.out.println(str() + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */);
+    System.out.println(/* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + str());
+    System.out.println(str() + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + str());
+
+    System.out.println(/* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */);
+    System.out.println(/* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */);
+
+    System.out.println(("Hello" + sb.toString()) + sb + sb.toString());
+    System.out.println(("Hello" + sb.toString()) + sb.toString() + sb.toString());
+    System.out.println((("Hello" + sb.toString()) + sb.toString()) + sb.toString());
+    System.out.println(("Hello" + sb.toString() + (sb.toString() + ((sb.toString())))));
+    System.out.println(("Hello" + sb.toString() + (sb.toString() + ((sb.toString()) + "Hello"))));
+    System.out.println(("Hello" + sb.toString() + (sb.toString() + ((sb.toString()) + 42))));
+  }
+
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/redundantStringOperation/beforeStringBuilderToStringAssign.java

@@ -0,0 +1,53 @@
+// "Fix all 'Redundant String operation' problems in file" "true"
+
+class StringBuilderToStringAssign {
+
+  public static final String CONST_STRING_VAL = "Hello";
+
+  static String str() { return ""; }
+
+  static void stringBuilderToStringAssign(StringBuilder sb) {
+    String s1 = sb.<caret>toString() + "Hello";
+    String s2 = "Hello" + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */;
+    String s3 = /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + 42;
+    String s4 = "Hello" + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + 42;
+
+    final String finalVal = "Hello";
+    String s5 = finalVal + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + 42;
+
+    String stringVal = "Hello";
+    String s611 = /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + stringVal;
+    String s621 = stringVal + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */;
+    String s631 = stringVal + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + 42;
+
+    int intVal = 42;
+    String s612 = /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + intVal;
+    String s622 = intVal + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */;
+    String s632 = intVal + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + 42;
+
+    final int constIntVal = 42;
+    String s61 = constIntVal + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */;
+    String s62 = /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + constIntVal;
+    String s63 = /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + constIntVal + 42;
+
+    String s71 = CONST_STRING_VAL + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */;
+    String s72 = /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + CONST_STRING_VAL;
+    String s73 = CONST_STRING_VAL + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + 42;
+
+    String s81 = str() + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */;
+    String s82 = /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + str();
+    String s83 = str() + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + str();
+
+    String s91 = /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */;
+    String s92 = /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */ + /* 1 */sb./* 2 */toString/* 3 */(/* 4 */)/* 5 */;
+
+    String s101 = ("Hello" + sb.toString()) + sb + sb.toString();
+    String s102 = ("Hello" + sb.toString()) + sb.toString() + sb.toString();
+    String s103 = (("Hello" + sb.toString()) + sb.toString()) + sb.toString();
+    String s104 = ("Hello" + sb.toString() + (sb.toString() + ((sb.toString()))));
+    String s105 = ("Hello" + sb.toString() + (sb.toString() + ((sb.toString()) + "Hello")));
+    String s106 = ("Hello" + sb.toString() + (sb.toString() + ((sb.toString()) + 42)));
+  }
+
+}
+

plugins/InspectionGadgets/src/com/siyeh/ig/redundancy/RedundantStringOperationInspection.java

@@ -20,12 +20,10 @@ import com.siyeh.ig.PsiReplacementUtil;
 import com.siyeh.ig.callMatcher.CallMapper;
 import com.siyeh.ig.callMatcher.CallMatcher;
 import com.siyeh.ig.psiutils.*;
-import org.jetbrains.annotations.Nls;
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
-import org.jetbrains.annotations.PropertyKey;
+import org.jetbrains.annotations.*;
 
 import javax.swing.*;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import java.util.Objects;
@@ -282,15 +280,17 @@ public class RedundantStringOperationInspection extends AbstractBaseJavaLocalIns
       if (!ExpressionUtils.isConversionToStringNecessary(call, false)) {
         // report naked `new StringBuilder().toString()`
         final PsiElement parent = PsiUtil.skipParenthesizedExprUp(call.getParent());
-        if (parent instanceof PsiPolyadicExpression && ((PsiPolyadicExpression)parent).getOperationTokenType() == JavaTokenType.PLUS) {
-          // if there is a polyadic expression where all the operands are `new StringBuilder().toString()`
-          // then it is wrong to report all the `toString` calls as redundant: at least one of them should call
-          // `toString()`, let's choose the last one to remain with `toString()`
+        if (parent instanceof PsiPolyadicExpression) {
+          if (((PsiPolyadicExpression)parent).getOperationTokenType() != JavaTokenType.PLUS) return null;
+
           final PsiPolyadicExpression polyadicExpression = (PsiPolyadicExpression)parent;
-          final PsiExpression lastChild = PsiUtil.skipParenthesizedExprDown(polyadicExpression.getOperands()[polyadicExpression.getOperands().length - 1]);
-          if (lastChild == call) {
-            return null;
-          }
+          final PsiExpression[] operands = polyadicExpression.getOperands();
+
+          final boolean hasStringOperand = Arrays.stream(operands)
+            .filter(operand -> operand != call)
+            .anyMatch(RedundantStringOperationVisitor::isOperandOfStringType);
+
+          if (!hasStringOperand) return null;
         }
         return getProblem(call, "inspection.redundant.string.call.message");
       }
@@ -301,6 +301,56 @@ public class RedundantStringOperationInspection extends AbstractBaseJavaLocalIns
       return getProblem(call, "inspection.redundant.string.call.message");
     }
 
+    @Contract("null -> false")
+    private static boolean isOperandOfStringType(final PsiExpression op) {
+      final PsiExpression operand = PsiUtil.skipParenthesizedExprDown(op);
+
+      if (operand == null) return false;
+
+      if (operand instanceof PsiReferenceExpression) {
+        final PsiReferenceExpression referenceExpression = (PsiReferenceExpression)operand;
+        final PsiElement resolve = referenceExpression.resolve();
+        final PsiType type;
+        if (resolve instanceof PsiVariable) {
+          type = ((PsiVariable)resolve).getType();
+        }
+        else if (resolve instanceof PsiMethod && ((PsiMethod)resolve).getReturnType() != null) {
+          type = ((PsiMethod)resolve).getReturnType();
+        }
+        else if (resolve instanceof PsiExpression && ((PsiExpression)resolve).getType() != null) {
+          type = ((PsiExpression)resolve).getType();
+        }
+        else {
+          return false;
+        }
+        if (type != null && type.equalsToText(String.class.getName())) {
+          return true;
+        }
+      }
+      else if (operand instanceof PsiMethodCallExpression) {
+        if (STRING_BUILDER_TO_STRING.matches(operand)) return false;
+
+        final PsiMethodCallExpression methodCallExpression = (PsiMethodCallExpression)operand;
+        final PsiMethod method = methodCallExpression.resolveMethod();
+        if (method != null && method.getReturnType() != null && method.getReturnType().equalsToText(String.class.getName())) {
+          return true;
+        }
+      }
+      else if (operand instanceof PsiPolyadicExpression) {
+        final PsiPolyadicExpression expression = (PsiPolyadicExpression)operand;
+        if (expression.getType() != null && expression.getType().equalsToText(String.class.getName())) {
+          return true;
+        }
+      }
+      else {
+        final String value = tryCast(ExpressionUtils.computeConstantExpression(operand), String.class);
+        if (value != null) {
+          return true;
+        }
+      }
+      return false;
+    }
+
     @Nullable
     private ProblemDescriptor getInternProblem(PsiMethodCallExpression call) {
       return PsiUtil.isConstantExpression(call.getMethodExpression().getQualifierExpression())