C++: Implement Expr::mayBeFromImplicitlyDeclaredFunction

Author: calumgrant

cpp/ql/lib/semmle/code/cpp/exprs/Call.qll

@@ -300,6 +300,11 @@ class FunctionCall extends Call, @funbindexpr {
     this.isVirtual() or
     this.getTarget().getAnAttribute().getName() = "weak"
   }
+
+  override predicate mayBeFromImplicitlyDeclaredFunction() {
+    this.getType() instanceof IntType and
+    this.getTarget().getADeclarationEntry().isImplicit()
+  }
 }
 
 /** A _user-defined_ unary `operator*` function. */

cpp/ql/lib/semmle/code/cpp/exprs/Expr.qll

@@ -534,6 +534,9 @@ class Expr extends StmtParent, @expr {
 
   /** Gets the function containing this control-flow node. */
   override Function getControlFlowScope() { result = this.getEnclosingFunction() }
+
+  /** Holds if this expression could be the return value of an implicitly declared function. */
+  predicate mayBeFromImplicitlyDeclaredFunction() { none() }
 }
 
 /**

cpp/ql/src/Likely Bugs/Format/WrongTypeFormatArguments.ql

@@ -171,7 +171,7 @@ where
   not arg.isAffectedByMacro() and
   not arg.isFromUninstantiatedTemplate(_) and
   not actual.getUnspecifiedType() instanceof ErroneousType and
-  not arg.(Call).getTarget().getADeclarationEntry().isImplicit()
+  not arg.mayBeFromImplicitlyDeclaredFunction()
 select arg,
   "This format specifier for type '" + expected.getName() + "' does not match the argument type '" +
     actual.getUnspecifiedType().getName() + "'."

cpp/ql/test/library-tests/exprs/implicitly_declared/error_type.expected

@@ -0,0 +1 @@
+| file://:0:0:0:0 | <error expr> |

cpp/ql/test/library-tests/exprs/implicitly_declared/error_type.ql

@@ -0,0 +1,5 @@
+import cpp
+
+from Expr e
+where e.getType() instanceof ErroneousType
+select e

cpp/ql/test/library-tests/exprs/implicitly_declared/errors.expected

@@ -0,0 +1,2 @@
+| file://:0:0:0:0 | There was an error during this compilation |
+| implicit.cpp:5:5:5:5 | identifier 'g' is undefined |

cpp/ql/test/library-tests/exprs/implicitly_declared/errors.ql

@@ -0,0 +1,4 @@
+import cpp
+
+from Diagnostic d
+select d

cpp/ql/test/library-tests/exprs/implicitly_declared/implicit.c

@@ -0,0 +1,4 @@
+void f() {
+    f();
+    g();
+}

cpp/ql/test/library-tests/exprs/implicitly_declared/implicit.cpp

@@ -0,0 +1,6 @@
+// semmle-extractor-options: --expect_errors
+
+void f() {
+    f();
+    g();
+}

cpp/ql/test/library-tests/exprs/implicitly_declared/implicit.expected

@@ -0,0 +1 @@
+| implicit.c:3:5:3:5 | call to g |