Improved guessCastExpressions in C++ frontend (#1357)

There were more ambiguities when guesssing cast expressions, so I added them.
Fixes #1347

cpg-language-cxx/src/main/kotlin/de/fraunhofer/aisec/cpg/frontends/cxx/ExpressionHandler.kt

@@ -345,9 +345,10 @@ class ExpressionHandler(lang: CXXLanguageFrontend) :
                     val typeName = (ctx.operand as IASTIdExpression).name.toString()
                     if (frontend.typeManager.typeExists(typeName)) {
                         val cast = newCastExpression(frontend.codeOf(ctx))
+                        cast.setCastOperator(0)
                         cast.castType = frontend.typeOf((ctx.operand as IASTIdExpression).name)
                         // The expression member can only be filled by the parent call
-                        // (handleFunctionCallExpression)
+                        // (handleFunctionCallExpression and handleBinaryExpression)
                         cast.location = frontend.locationOf(ctx)
                         return cast
                     }
@@ -429,7 +430,8 @@ class ExpressionHandler(lang: CXXLanguageFrontend) :
                     )
                     .forEach { callExpression.addTemplateParameter(it) }
             }
-            reference is CastExpression -> {
+            reference is CastExpression &&
+                frontend.config.inferenceConfiguration.guessCastExpressions -> {
                 // this really is a cast expression in disguise
                 reference.expression =
                     ctx.arguments.firstOrNull()?.let { handle(it) }
@@ -501,6 +503,22 @@ class ExpressionHandler(lang: CXXLanguageFrontend) :
                 handle(ctx.initOperand2)
             }
                 ?: newProblemExpression("could not parse rhs")
+
+        if (lhs is CastExpression && frontend.config.inferenceConfiguration.guessCastExpressions) {
+            // this really is a combination of a cast and a unary operator
+            val op =
+                newUnaryOperator(
+                    operatorCode,
+                    postfix = true,
+                    prefix = false,
+                    code = ctx.rawSignature
+                )
+            op.input = rhs
+            op.location = frontend.locationOf(ctx.operand2)
+            lhs.expression = op
+            return lhs
+        }
+
         binaryOperator.lhs = lhs
         binaryOperator.rhs = rhs
 

cpg-language-cxx/src/test/kotlin/de/fraunhofer/aisec/cpg/frontends/cxx/CXXLanguageFrontendTest.kt

@@ -1320,21 +1320,43 @@ internal class CXXLanguageFrontendTest : BaseTest() {
                 it.inferenceConfiguration(builder().guessCastExpressions(true).build())
                 it.registerLanguage<CPPLanguage>()
             }
-        val main =
-            tu.getDeclarationsByName("main", FunctionDeclaration::class.java).iterator().next()
+        val main = tu.functions["main"]
         assertNotNull(main)
 
-        val declStatement = main.getBodyStatementAs(0, DeclarationStatement::class.java)
-        assertNotNull(declStatement)
+        val count = tu.variables["count"]
+        assertNotNull(count)
 
-        val decl = declStatement.singleDeclaration as VariableDeclaration
-        assertNotNull(decl)
+        var cast = count.initializer
+        assertIs<CastExpression>(cast)
+        assertLocalName("size_t", cast.castType)
+        assertLiteralValue(42, cast.expression)
 
-        val initializer = decl.initializer
-        assertNotNull(initializer)
-        assertTrue(initializer is CastExpression)
-        assertLocalName("size_t", initializer.castType)
-        assertLiteralValue(42, initializer.expression)
+        val addr = tu.variables["addr"]
+        assertNotNull(addr)
+
+        cast = addr.initializer
+        assertIs<CastExpression>(cast)
+        assertLocalName("int64_t", cast.castType)
+
+        val unary = cast.expression
+        assertIs<UnaryOperator>(unary)
+
+        val refCount = unary.input
+        assertIs<Reference>(refCount)
+        assertRefersTo(refCount, count)
+
+        var paths = addr.followPrevDFGEdgesUntilHit { it == refCount }
+        assertTrue(paths.fulfilled.isNotEmpty())
+        assertTrue(paths.failed.isEmpty())
+
+        val refKey = tu.refs["key"]
+        assertNotNull(refKey)
+
+        val assign = tu.assignments.firstOrNull { it.value is UnaryOperator }
+        assertNotNull(assign)
+        paths = assign.value.followPrevDFGEdgesUntilHit { it == refKey }
+        assertTrue(paths.fulfilled.isNotEmpty())
+        assertTrue(paths.failed.isEmpty())
     }
 
     @Test

cpg-language-cxx/src/test/resources/cxx/parenthesis.cpp

@@ -1,4 +1,18 @@
+// These headers are just here so that we could compile it, if we want it,
+// to check for errors with clang. We will not parse them.
+#include <cstddef>
+#include <cstdint>
+
 int main() {
+	// this cast could be mistaken for a call expression
 	size_t count = (size_t)(42);
+
+	// this cast could be mistaken for a binary operation
+	int64_t addr = (int64_t) &count;
+
+	// finally, a more complex example of unary operators and casts
+	char* outptr, key;
+	*(int64_t *)outptr = *(int64_t *)&key;
+
 	return 0;
 }