C++: Resolve functions using complete mangled names

cpp/ql/lib/semmle/code/cpp/Element.qll

@@ -7,6 +7,7 @@ import semmle.code.cpp.Location
 private import semmle.code.cpp.Enclosing
 private import semmle.code.cpp.internal.ResolveClass
 private import semmle.code.cpp.internal.ResolveGlobalVariable
+private import semmle.code.cpp.internal.ResolveFunction
 
 /**
  * Get the `Element` that represents this `@element`.
@@ -30,11 +31,14 @@ pragma[inline]
 @element unresolveElement(Element e) {
   not result instanceof @usertype and
   not result instanceof @variable and
+  not result instanceof @function and
   result = e
   or
   e = resolveClass(result)
   or
   e = resolveGlobalVariable(result)
+  or
+  e = resolveFunction(result)
 }
 
 /**

cpp/ql/lib/semmle/code/cpp/Function.qll

@@ -9,6 +9,7 @@ import semmle.code.cpp.exprs.Call
 import semmle.code.cpp.metrics.MetricFunction
 import semmle.code.cpp.Linkage
 private import semmle.code.cpp.internal.ResolveClass
+private import semmle.code.cpp.internal.ResolveFunction
 
 /**
  * A C/C++ function [N4140 8.3.5]. Both member functions and non-member
@@ -25,6 +26,8 @@ private import semmle.code.cpp.internal.ResolveClass
  * in more detail in `Declaration.qll`.
  */
 class Function extends Declaration, ControlFlowNode, AccessHolder, @function {
+  Function() { isFunction(underlyingElement(this)) }
+
   override string getName() { functions(underlyingElement(this), result, _) }
 
   /**

cpp/ql/lib/semmle/code/cpp/internal/ResolveFunction.qll

@@ -0,0 +1,57 @@
+private predicate hasDefinition(@function f) {
+  exists(@fun_decl fd | fun_decls(fd, f, _, _, _) | fun_def(fd))
+}
+
+private predicate onlyOneCompleteFunctionExistsWithMangledName(@mangledname name) {
+  strictcount(@function f | hasDefinition(f) and mangled_name(f, name, true)) = 1
+}
+
+/** Holds if `f` is a unique function with a definition named `name`. */
+private predicate isFunctionWithMangledNameAndWithDefinition(@mangledname name, @function f) {
+  hasDefinition(f) and
+  mangled_name(f, name, true) and
+  onlyOneCompleteFunctionExistsWithMangledName(name)
+}
+
+/** Holds if `f` is a function without a definition named `name`. */
+private predicate isFunctionWithMangledNameAndWithoutDefinition(@mangledname name, @function f) {
+  not hasDefinition(f) and
+  mangled_name(f, name, true)
+}
+
+/**
+ * Holds if `incomplete` is a function without a definition, and there exists
+ * a unique function `complete` with the same name that does have a definition.
+ */
+private predicate hasTwinWithDefinition(@function incomplete, @function complete) {
+  not function_instantiation(incomplete, complete) and
+  (
+    not compgenerated(incomplete) or
+    not compgenerated(complete)
+  ) and
+  exists(@mangledname name |
+    isFunctionWithMangledNameAndWithoutDefinition(name, incomplete) and
+    isFunctionWithMangledNameAndWithDefinition(name, complete)
+  )
+}
+
+import Cached
+
+cached
+private module Cached {
+  /**
+   * If `f` is a function without a definition, and there exists a unique
+   * function with the same name that does have a definition, then the
+   * result is that unique function. Otherwise, the result is `f`.
+   */
+  cached
+  @function resolveFunction(@function f) {
+    hasTwinWithDefinition(f, result)
+    or
+    not hasTwinWithDefinition(f, _) and
+    result = f
+  }
+
+  cached
+  predicate isFunction(@function f) { f = resolveFunction(_) }
+}