Prevent early deleting of not-null assertions

Before val to var conversion applied, smart-cast can cause
dropping not-null assertion, which will be required when val will
become var

idea/src/org/jetbrains/kotlin/idea/j2k/J2kPostProcessings.kt

@@ -47,6 +47,7 @@ import org.jetbrains.kotlin.psi.psiUtil.visibilityModifierType
 import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.calls.callUtil.getType
 import org.jetbrains.kotlin.resolve.diagnostics.Diagnostics
+import org.jetbrains.kotlin.resolve.lazy.BodyResolveMode
 import org.jetbrains.kotlin.utils.mapToIndex
 import java.util.*
 
@@ -114,11 +115,6 @@ object J2KPostProcessingRegistrar {
             fix.invoke()
         }
 
-        registerDiagnosticBasedProcessing<KtSimpleNameExpression>(Errors.UNNECESSARY_NOT_NULL_ASSERTION) { element, _ ->
-            val exclExclExpr = element.parent as KtUnaryExpression
-            exclExclExpr.replace(exclExclExpr.baseExpression!!)
-        }
-
         registerDiagnosticBasedProcessingFactory(
                 Errors.VAL_REASSIGNMENT, Errors.CAPTURED_VAL_INITIALIZATION, Errors.CAPTURED_MEMBER_VAL_INITIALIZATION
         ) {
@@ -136,6 +132,15 @@ object J2KPostProcessingRegistrar {
             }
         }
 
+        registerDiagnosticBasedProcessing<KtSimpleNameExpression>(Errors.UNNECESSARY_NOT_NULL_ASSERTION) { element, _ ->
+            val exclExclExpr = element.parent as KtUnaryExpression
+            val baseExpression = exclExclExpr.baseExpression!!
+            val context = baseExpression.analyze(BodyResolveMode.PARTIAL_WITH_DIAGNOSTICS)
+            if (context.diagnostics.forElement(element).any { it.factory == Errors.UNNECESSARY_NOT_NULL_ASSERTION }) {
+                exclExclExpr.replace(baseExpression)
+            }
+        }
+
         processingsToPriorityMap.putAll(_processings.mapToIndex())
     }
 

j2k/testData/fileOrElement/nullability/LocalValReassignment.java

@@ -0,0 +1,35 @@
+import org.jetbrains.annotations.*;
+
+class A {
+
+    /* rare nullable, handle with caution */
+    public String nullableString() {
+        if (Math.random() > 0.999) {
+            return "a string";
+        }
+        return null;
+    }
+
+    public void takesNotNullString(@NotNull String s) {
+        System.out.println(s.substring(1));
+    }
+
+    public void aVoid() {
+        String aString;
+        if (nullableString() != null) {
+            aString = nullableString();
+            if (aString != null) {
+                for (int i = 0; i < 10; i++) {
+                    takesNotNullString(aString); // Bang-bang here
+                    aString = nullableString();
+                }
+            }
+            else {
+                aString = "aaa";
+            }
+        }
+        else {
+            aString = "bbbb";
+        }
+    }
+}

j2k/testData/fileOrElement/nullability/LocalValReassignment.kt

@@ -0,0 +1,32 @@
+import org.jetbrains.annotations.*
+
+internal class A {
+
+    /* rare nullable, handle with caution */
+    fun nullableString(): String? {
+        return if (Math.random() > 0.999) {
+            "a string"
+        } else null
+    }
+
+    fun takesNotNullString(s: String) {
+        println(s.substring(1))
+    }
+
+    fun aVoid() {
+        var aString: String?
+        if (nullableString() != null) {
+            aString = nullableString()
+            if (aString != null) {
+                for (i in 0..9) {
+                    takesNotNullString(aString!!) // Bang-bang here
+                    aString = nullableString()
+                }
+            } else {
+                aString = "aaa"
+            }
+        } else {
+            aString = "bbbb"
+        }
+    }
+}

j2k/tests/org/jetbrains/kotlin/j2k/JavaToKotlinConverterForWebDemoTestGenerated.java

@@ -3779,6 +3779,12 @@ public class JavaToKotlinConverterForWebDemoTestGenerated extends AbstractJavaTo
             doTest(fileName);
         }
 
+        @TestMetadata("LocalValReassignment.java")
+        public void testLocalValReassignment() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/nullability/LocalValReassignment.java");
+            doTest(fileName);
+        }
+
         @TestMetadata("MethodInvokedWithNullArg.java")
         public void testMethodInvokedWithNullArg() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/nullability/MethodInvokedWithNullArg.java");

j2k/tests/org/jetbrains/kotlin/j2k/JavaToKotlinConverterSingleFileTestGenerated.java

@@ -3779,6 +3779,12 @@ public class JavaToKotlinConverterSingleFileTestGenerated extends AbstractJavaTo
             doTest(fileName);
         }
 
+        @TestMetadata("LocalValReassignment.java")
+        public void testLocalValReassignment() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/nullability/LocalValReassignment.java");
+            doTest(fileName);
+        }
+
         @TestMetadata("MethodInvokedWithNullArg.java")
         public void testMethodInvokedWithNullArg() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/nullability/MethodInvokedWithNullArg.java");