StringBufferReplaceableByString: do not convert first operand to String if the second is String

Because implicit conversion will be applied anyway
Fixes IDEA-205019 Conversion StringBuilder -> String can be slightly improved

plugins/InspectionGadgets/src/com/siyeh/ig/style/StringBufferReplaceableByStringInspection.java

@@ -330,26 +330,31 @@ public class StringBufferReplaceableByStringInspection extends BaseInspection {
           final PsiExpression argument = arguments[0];
           final PsiType type = argument.getType();
           final String argumentText = tracker.textWithComments(argument);
-          if (result.length() != 0) {
-            addNewlineIfNeeded(argument, true, result, commentsBefore);
+          boolean needConvertToString = result.length() == 0;
+          if (needConvertToString) {
+            PsiMethodCallExpression nextCall = ExpressionUtils.getCallForQualifier(methodCallExpression);
+            if (nextCall != null && "append".equals(nextCall.getMethodExpression().getReferenceName())) {
+              PsiExpression[] args = nextCall.getArgumentList().getExpressions();
+              needConvertToString = args.length != 1 || !TypeUtils.isJavaLangString(args[0].getType());
+            }
+          }
+          addNewlineIfNeeded(argument, result.length() > 0, result, commentsBefore);
+          if (!needConvertToString) {
             if (ParenthesesUtils.getPrecedence(argument) > ParenthesesUtils.ADDITIVE_PRECEDENCE ||
                 (type instanceof PsiPrimitiveType && ParenthesesUtils.getPrecedence(argument) == ParenthesesUtils.ADDITIVE_PRECEDENCE)) {
               result.append('(').append(argumentText).append(')');
             }
+            else if (type instanceof PsiArrayType) {
+              result.append("String.valueOf(").append(argumentText).append(')');
+            }
             else {
-              if (type instanceof PsiArrayType) {
-                result.append("String.valueOf(").append(argumentText).append(")");
-              }
-              else {
-                if (StringUtil.startsWithChar(argumentText, '+')) {
-                  result.append(' ');
-                }
-                result.append(argumentText);
+              if (result.length() > 0 && StringUtil.startsWithChar(argumentText, '+')) {
+                result.append(' ');
               }
+              result.append(argumentText);
             }
           }
           else {
-            addNewlineIfNeeded(argumentList, false, result, commentsBefore);
             if (type instanceof PsiPrimitiveType) {
               if (argument instanceof PsiLiteralExpression) {
                 final PsiLiteralExpression literalExpression = (PsiLiteralExpression)argument;
@@ -369,18 +374,14 @@ public class StringBufferReplaceableByStringInspection extends BaseInspection {
                 result.append("String.valueOf(").append(argumentText).append(")");
               }
             }
+            else if (ParenthesesUtils.getPrecedence(argument) >= ParenthesesUtils.ADDITIVE_PRECEDENCE) {
+              result.append('(').append(argumentText).append(')');
+            }
+            else if (type != null && !type.equalsToText(CommonClassNames.JAVA_LANG_STRING)) {
+              result.append("String.valueOf(").append(argumentText).append(")");
+            }
             else {
-              if (ParenthesesUtils.getPrecedence(argument) >= ParenthesesUtils.ADDITIVE_PRECEDENCE) {
-                result.append('(').append(argumentText).append(')');
-              }
-              else {
-                if (type != null && !type.equalsToText(CommonClassNames.JAVA_LANG_STRING)) {
-                  result.append("String.valueOf(").append(argumentText).append(")");
-                }
-                else {
-                  result.append(argumentText);
-                }
-              }
+              result.append(argumentText);
             }
           }
         }

plugins/InspectionGadgets/test/com/siyeh/igfixes/style/replace_with_string/Escape.after.java

@@ -2,6 +2,6 @@ package com.siyeh.igfixes.style.replace_with_string;
 
 class Escape {
   {
-    String s = ("\"" + "bas");
+    String s = ("\"" + 0 + "bas");
   }
 }

plugins/InspectionGadgets/test/com/siyeh/igfixes/style/replace_with_string/Escape.java

@@ -2,6 +2,6 @@ package com.siyeh.igfixes.style.replace_with_string;
 
 class Escape {
   {
-    String s = (((((new <caret>StringBuilder()).append('"')).append("bas"))).toString());
+    String s = (((((new <caret>StringBuilder()).append('"')).append(0).append("bas"))).toString());
   }
 }

plugins/InspectionGadgets/test/com/siyeh/igfixes/style/replace_with_string/StartsWithPrimitive2.after.java

@@ -0,0 +1,6 @@
+class StartsWithPrimitive2 {
+
+  String foo(String str) {
+    return 'L' + str + '<caret>;';
+  }
+}

plugins/InspectionGadgets/test/com/siyeh/igfixes/style/replace_with_string/StartsWithPrimitive2.java

@@ -0,0 +1,6 @@
+class StartsWithPrimitive2 {
+
+  String foo(String str) {
+    return new Strin<caret>gBuilder().append('L').append(str).append(';').toString();
+  }
+}

plugins/InspectionGadgets/test/com/siyeh/igfixes/style/replace_with_string/StartsWithPrimitive3.after.java

@@ -0,0 +1,6 @@
+class StartsWithPrimitive2 {
+
+  String foo(String str) {
+    return +1 + str + ';<caret>';
+  }
+}

plugins/InspectionGadgets/test/com/siyeh/igfixes/style/replace_with_string/StartsWithPrimitive3.java

@@ -0,0 +1,6 @@
+class StartsWithPrimitive2 {
+
+  String foo(String str) {
+    return new Strin<caret>gBuilder().append(+1).append(str).append(';').toString();
+  }
+}

plugins/InspectionGadgets/test/com/siyeh/igfixes/style/replace_with_string/StartsWithPrimitive4.after.java

@@ -0,0 +1,6 @@
+class StartsWithPrimitive2 {
+
+  String foo(String str) {
+    return String.va<caret>lueOf(+1) + 0 + str + ';';
+  }
+}

plugins/InspectionGadgets/test/com/siyeh/igfixes/style/replace_with_string/StartsWithPrimitive4.java

@@ -0,0 +1,6 @@
+class StartsWithPrimitive2 {
+
+  String foo(String str) {
+    return new Strin<caret>gBuilder().append(+1).append(0).append(str).append(';').toString();
+  }
+}

plugins/InspectionGadgets/test/com/siyeh/igfixes/style/replace_with_string/Unescape.after.java

@@ -2,6 +2,6 @@ package com.siyeh.igfixes.style.replace_with_string;
 
 class Escape {
   {
-    String s = "'" + "bas";
+    String s = "'" + 0 + "bas";
   }
 }

plugins/InspectionGadgets/test/com/siyeh/igfixes/style/replace_with_string/Unescape.java

@@ -2,6 +2,6 @@ package com.siyeh.igfixes.style.replace_with_string;
 
 class Escape {
   {
-    String s = new StringBuilder<caret>().append('\'').append("bas").toString();
+    String s = new StringBuilder<caret>().append('\'').append(0).append("bas").toString();
   }
 }

plugins/InspectionGadgets/testsrc/com/siyeh/ig/fixes/style/StringBufferReplaceableByStringFixTest.java

@@ -33,6 +33,9 @@ public class StringBufferReplaceableByStringFixTest extends IGQuickFixesTestCase
   public void testStringBufferVariable() { doTestFor("StringBuffer"); }
   public void testStringBufferVariable2() { doTestFor("StringBuffer"); }
   public void testStartsWithPrimitive() { doTestFor("StringBuffer"); }
+  public void testStartsWithPrimitive2() { doTestFor("StringBuilder"); }
+  public void testStartsWithPrimitive3() { doTestFor("StringBuilder"); }
+  public void testStartsWithPrimitive4() { doTestFor("StringBuilder"); }
   public void testPrecedence() { doTestFor("StringBuilder"); }
   public void testPrecedence2() { doTestFor("StringBuilder"); }
   public void testPrecedence3() { doTestFor("StringBuilder"); }