Add array-to-Stream-to-List.ql

Author: Marcono1234

codeql-custom-queries-java/queries/performance/array-to-Stream-to-List.ql

@@ -0,0 +1,51 @@
+/**
+ * Finds code which first creates a `Stream` for an array (or varargs arguments) just to
+ * directly afterwards call `collect(Collectors.toList())` on it. Such code should be
+ * simplified by using `java.util.Arrays.asList(...)` instead, especially because
+ * `Collectors.toList()` makes no guarantees about the type of the created list, so there
+ * is really no advantage of using it over `Arrays.asList`.
+ * 
+ * @kind problem
+ */
+
+import java
+
+class StreamFromArrayMethod extends Method {
+    StreamFromArrayMethod() {
+        (
+            getDeclaringType().hasQualifiedName("java.util", "Arrays")
+            // Only consider method which accepts object array (ignore primitive ones), and only
+            // the one without start and end index
+            and hasStringSignature("stream(T[])")
+        )
+        or (
+            getDeclaringType().hasQualifiedName("java.util.stream", "Stream")
+            // Only consider method which accepts an array (respectively varargs)
+            and hasStringSignature("of(T[])") 
+        )
+    }
+}
+
+class StreamCollectMethod extends Method {
+    StreamCollectMethod() {
+        getDeclaringType().hasQualifiedName("java.util.stream", "Stream")
+        and hasName("collect")
+        and getNumberOfParameters() = 1
+    }
+}
+
+class CollectorsToListMethod extends Method {
+    CollectorsToListMethod() {
+        getDeclaringType().hasQualifiedName("java.util.stream", "Collectors")
+        and hasStringSignature("toList()")
+    }
+}
+
+from MethodAccess streamCreationCall, MethodAccess collectCall
+where
+    streamCreationCall.getMethod() instanceof StreamFromArrayMethod
+    and streamCreationCall = collectCall.getQualifier()
+    and collectCall.getMethod().getSourceDeclaration().getASourceOverriddenMethod*() instanceof StreamCollectMethod
+    // Note: Don't cover `Stream.toList()` because that makes guarantees about the list, such as it being unmodifiable
+    and collectCall.getArgument(0).(MethodAccess).getMethod() instanceof CollectorsToListMethod
+select collectCall, "Should use `Arrays.asList(...)` instead"