IG: don't suggest to replace if with switch on non-constant (IDEA-204135)

plugins/InspectionGadgets/InspectionGadgetsAnalysis/src/com/siyeh/ig/psiutils/SwitchUtils.java

@@ -230,7 +230,15 @@ public class SwitchUtils {
     }
     final PsiExpression left = check.getLeft();
     final PsiExpression right = check.getRight();
-    return PsiUtil.isConstantExpression(left) ? right : left;
+    if (PsiUtil.isConstantExpression(left)) {
+      return right;
+    }
+    else if (PsiUtil.isConstantExpression(right)) {
+      return left;
+    }
+    else {
+      return null;
+    }
   }
 
   private static boolean canBeCaseLabel(PsiExpression expression, LanguageLevel languageLevel) {

plugins/InspectionGadgets/test/com/siyeh/igtest/migration/if_switch/IfCanBeSwitch.java

@@ -92,4 +92,28 @@ class IfCanBeSwitch {
       System.out.println("-");
     }
   }
+}
+class MyText implements Comparable<MyText> {
+
+  private String name;
+
+  String getSuperType() {
+    return name.startsWith("a") ? "b" : "c";
+  }
+
+  @Override
+  public int compareTo(MyText o) {
+    String superType = getSuperType();
+    if (superType.equals(o.getSuperType())) {
+      return this.name.compareTo(o.name);
+    } else if (superType.equals("a")) {
+      return -1;
+    } else if (superType.equals("b")) {
+      return 1;
+    } else if (superType.equals("c")) {
+      return o.getSuperType().equals("a") ? 1 : -1;
+    } else {
+      return 0;
+    }
+  }
 }