Playing around with a dynamic type

cpg-core/src/main/kotlin/de/fraunhofer/aisec/cpg/frontends/Language.kt

@@ -217,6 +217,10 @@ abstract class Language<T : LanguageFrontend<*, *>> : Node() {
     open fun shouldPropagateType(hasType: HasType, srcType: Type): Boolean {
         val nodeType = hasType.type
 
+        if (srcType is DynamicType) {
+            return false
+        }
+
         // We only want to add certain types, in case we have a numeric type
         if (nodeType is NumericType) {
             // We do not allow to propagate non-numeric types into numeric types

cpg-core/src/main/kotlin/de/fraunhofer/aisec/cpg/graph/TypeBuilder.kt

@@ -41,6 +41,10 @@ fun MetadataProvider?.unknownType(): Type {
     }
 }
 
+fun LanguageProvider.dynamicType(): Type {
+    return DynamicType(this.language)
+}
+
 fun LanguageProvider.autoType(): Type {
     return AutoType(this.language)
 }

cpg-core/src/main/kotlin/de/fraunhofer/aisec/cpg/graph/statements/expressions/AssignExpression.kt

@@ -33,6 +33,7 @@ import de.fraunhofer.aisec.cpg.graph.edges.unwrapping
 import de.fraunhofer.aisec.cpg.graph.types.HasType
 import de.fraunhofer.aisec.cpg.graph.types.TupleType
 import de.fraunhofer.aisec.cpg.graph.types.Type
+import de.fraunhofer.aisec.cpg.graph.types.UnknownType
 import org.neo4j.ogm.annotation.Relationship
 import org.slf4j.Logger
 import org.slf4j.LoggerFactory
@@ -208,10 +209,19 @@ class AssignExpression :
             val targets = findTargets(src)
             if (targets.size == newType.types.size) {
                 // Set the corresponding type on the left-side
-                newType.types.forEachIndexed { idx, t -> lhs.getOrNull(idx)?.addAssignedType(t) }
+                newType.types.forEachIndexed { idx, t ->
+                    var lhs = lhs.getOrNull(idx) ?: return
+                    lhs.addAssignedType(t)
+                }
             }
         } else {
-            findTargets(src).forEach { it.addAssignedType(newType) }
+            findTargets(src).forEach {
+                // If the type is unknown, we can also set it
+                if (it.type is UnknownType) {
+                    it.type = newType
+                }
+                it.addAssignedType(newType)
+            }
         }
 
         // If this is used as an expression, we also set the type accordingly

cpg-core/src/main/kotlin/de/fraunhofer/aisec/cpg/graph/types/DynamicType.kt

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2024, Fraunhofer AISEC. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ *                    $$$$$$\  $$$$$$$\   $$$$$$\
+ *                   $$  __$$\ $$  __$$\ $$  __$$\
+ *                   $$ /  \__|$$ |  $$ |$$ /  \__|
+ *                   $$ |      $$$$$$$  |$$ |$$$$\
+ *                   $$ |      $$  ____/ $$ |\_$$ |
+ *                   $$ |  $$\ $$ |      $$ |  $$ |
+ *                   \$$$$$   |$$ |      \$$$$$   |
+ *                    \______/ \__|       \______/
+ *
+ */
+package de.fraunhofer.aisec.cpg.graph.types
+
+import de.fraunhofer.aisec.cpg.frontends.Language
+
+/**
+ * This type represents a [Type] that is dynamically determined at run-time. This is used for a
+ * [Language]. which has dynamic runtime typing, such as Python or Java/TypeScript.
+ */
+class DynamicType(override var language: Language<*>?) : Type("dynamic", language) {
+    override fun reference(pointer: PointerType.PointerOrigin?): Type {
+        TODO("Not yet implemented")
+    }
+
+    override fun dereference(): Type {
+        TODO("Not yet implemented")
+    }
+}

cpg-core/src/main/kotlin/de/fraunhofer/aisec/cpg/graph/types/HasType.kt

@@ -179,7 +179,7 @@ interface HasType : ContextProvider, LanguageProvider {
 
         // If we would only propagate the unknown type, we can also skip it
         val newType = this.type
-        if (newType !is UnknownType) {
+        if (newType !is UnknownType && newType !is DynamicType) {
             // Immediately inform about changes
             typeObserver.typeChanged(newType, this)
         }
@@ -207,6 +207,12 @@ interface HasType : ContextProvider, LanguageProvider {
 class InitializerTypePropagation(private var decl: HasType, private var tupleIdx: Int = -1) :
     HasType.TypeObserver {
     override fun typeChanged(newType: Type, src: HasType) {
+        // We do not want to change the type of a "dynamic type" declaration, since the "type" will
+        // always be dynamic.
+        if (decl.type is DynamicType) {
+            return
+        }
+
         if (newType is TupleType && tupleIdx != -1) {
             decl.type = newType.types.getOrElse(tupleIdx) { decl.unknownType() }
         } else {

cpg-language-python/src/main/kotlin/de/fraunhofer/aisec/cpg/passes/PythonAddDeclarationsPass.kt

@@ -123,6 +123,7 @@ class PythonAddDeclarationsPass(ctx: TranslationContext) : ComponentPass(ctx) {
                 newVariableDeclaration(node.name)
             }
 
+        decl.type = node.dynamicType()
         decl.code = node.code
         decl.location = node.location
         decl.isImplicit = true

cpg-language-python/src/test/kotlin/de/fraunhofer/aisec/cpg/frontends/python/PythonFrontendTest.kt

@@ -1256,6 +1256,27 @@ class PythonFrontendTest : BaseTest() {
         assertInvokes(call, cCompletelyDifferentFunc)
     }
 
+    @Test
+    fun testTypePropagation() {
+        val topLevel = Path.of("src", "test", "resources", "python")
+        val tu =
+            analyzeAndGetFirstTU(
+                listOf(topLevel.resolve("type_propagation.py").toFile()),
+                topLevel,
+                true
+            ) {
+                it.registerLanguage<PythonLanguage>()
+            }
+        assertNotNull(tu)
+
+        var a = tu.variables["a"]
+        assertNotNull(a)
+        println("type: {${a.type}, assigned: {${a.assignedTypes}")
+
+        var refs = tu.refs("a")
+        refs.forEach { println("type: {${it.type}, assigned: {${it.assignedTypes}") }
+    }
+
     class PythonValueEvaluator : ValueEvaluator() {
         override fun computeBinaryOpEffect(
             lhsValue: Any?,

cpg-language-python/src/test/resources/python/type_propagation.py

@@ -0,0 +1,2 @@
+a = "test"
+a = 2