If e1 Then s1 'Else skip' adaptation (#21)

## Description
Simulated an "Else { skip; }" when no else expression is present in the
original code.

## Related Issue
Closes #11 

## Type of change
- [ ] Bug fix
- [x] New feature
- [ ] Documentation update
- [ ] Code refactoring

## How Has This Been Tested?
Some simple feature tests were ran locally, with no found bugs

Author: Pichers

latte/src/main/java/typechecking/LatteTypeChecker.java

@@ -534,11 +534,21 @@ public void visitCtIf(CtIf ifElement) {
 		PermissionEnvironment thenPermEnv = permEnv.cloneLast();
 		exitScopes();
 
-		enterScopes();
-		super.visitCtBlock(ifElement.getElseStatement());
-		SymbolicEnvironment elseSymbEnv = symbEnv.cloneLast();
-		PermissionEnvironment elsePermEnv = permEnv.cloneLast();
-		exitScopes();
+		SymbolicEnvironment elseSymbEnv;
+    	PermissionEnvironment elsePermEnv;
+
+		if (ifElement.getElseStatement() != null) {
+			//Else statement
+			enterScopes();
+			super.visitCtBlock(ifElement.getElseStatement());
+			elseSymbEnv = symbEnv.cloneLast();
+			elsePermEnv = permEnv.cloneLast();
+			exitScopes();
+		} else {
+			//No Else statement
+			elseSymbEnv = symbEnv.cloneLast();
+			elsePermEnv = permEnv.cloneLast();
+		}
 
 		joining(thenSymbEnv, thenPermEnv, elseSymbEnv, elsePermEnv);
 	}

latte/src/test/examples/MyNodeAllKindsIfs.java

@@ -0,0 +1,43 @@
+package latte;
+
+import specification.Free;
+import specification.Unique;
+
+/*
+ * This file is part of the Latte test suite.
+ */
+class MyNode {
+
+    @Unique Object value;
+    @Unique Node next;
+
+    /**
+     * Constructor for the Node class using @Free value and next nodes
+     * @param value
+     * @param next
+     */
+    public MyNode (@Free Object value, @Free Node next) {
+        this.value = value;
+        this.next = next;
+    }
+
+    public Object test(@Free Object v1, @Free Object v2, boolean c1, boolean c2){
+        if (c1) {
+            this.value = v1;
+        } else if (c2) {
+            this.value = v2;
+        } else {
+            this.value = v1;
+        }
+
+        if (c2 || this.value == null) {
+            this.value = v1;
+        } else {
+            this.value = v2;
+        }
+        if (c1 && this.value == v1) {
+            this.value = v2;
+        }
+        return this.value;
+    }
+}

latte/src/test/examples/MyNodeIfNoElse.java

@@ -0,0 +1,30 @@
+package latte;
+
+import specification.Free;
+import specification.Unique;
+
+/*
+ * This file is part of the Latte test suite.
+ */
+class MyNode {
+
+    @Unique Object value;
+    @Unique Node next;
+
+    /**
+     * Constructor for the Node class using @Free value and next nodes
+     * @param value
+     * @param next
+     */
+    public MyNode (@Free Object value, @Free Node next) {
+        this.value = value;
+        this.next = next;
+    }
+
+    public Object test(@Free Object v1, boolean c1){
+        if (c1) {
+            this.value = v1;
+        }
+        return this.value;
+    }
+}

latte/src/test/examples/MyNodeIfPermissionCheck.java

@@ -0,0 +1,20 @@
+package latte;
+
+import specification.Free;
+import specification.Unique;
+
+class MyNodeIfNoElse {
+
+    @Unique Object value;
+
+    public @Unique Object test(@Free Object v1, boolean cond) {
+        Object n;
+        n = new Object();
+
+        this.value = n;
+        if (cond) {
+            this.value = v1;
+        }
+        return this.value; // should still be @Unique
+    }
+}

latte/src/test/examples/MyNodeIncorrectIfPermission.java

@@ -0,0 +1,23 @@
+package latte;
+
+import specification.Free;
+import specification.Unique;
+import specification.Shared;
+import specification.Borrowed;
+
+class MyNodeIfNoElse {
+
+    @Unique Object value;
+
+    public @Unique Object test(@Shared Object v1, boolean cond) {
+        Object n;
+        n = new Object();
+
+        this.value = n;
+        if (cond) {
+            this.value = v1;
+        }
+
+        return this.value;
+    }
+}

latte/src/test/java/AppTest.java

@@ -41,6 +41,9 @@ private static Stream<Arguments> provideCorrectTestCases() {
             Arguments.of("src/test/examples/searching_state_space/ResultSetNoNext.java"),
             Arguments.of("src/test/examples/searching_state_space/ResultSetForwardOnly.java"),
             Arguments.of("src/test/examples/stack_overflow/MediaRecord.java"),
+            Arguments.of("src/test/examples/MyNodeAllKindsIfs.java"),
+            Arguments.of("src/test/examples/MyNodeIfNoElse.java"),
+            Arguments.of("src/test/examples/MyNodeIfPermissionCheck.java"),
             Arguments.of("src/test/examples/MyNodeInvocationIf.java"),
             Arguments.of("src/test/examples/MyNodeIfInvocationPermission.java")
         );
@@ -62,7 +65,8 @@ private static Stream<Arguments> provideIncorrectTestCases() {
             Arguments.of("src/test/examples/SmallestIncorrectExample.java", "UNIQUE but got BORROWED"),
             Arguments.of("src/test/examples/MyStackFieldAssignMethod.java", "UNIQUE but got SHARED"),
             Arguments.of("src/test/examples/FieldAccessNoThis.java", "UNIQUE but got SHARED"),
-            Arguments.of("src/test/examples/FieldAccessRightNoThis.java", "FREE but got UNIQUE")
+            Arguments.of("src/test/examples/FieldAccessRightNoThis.java", "FREE but got UNIQUE"),
+            Arguments.of("src/test/examples/MyNodeIncorrectIfPermission.java", "Expected UNIQUE but got SHARED")
         );
     }