C++: Allow querying for "C" language linkage on routine types.

Author: sashabu

cpp/change-notes/2021-08-17-has-c-linkage.md

@@ -0,0 +1,2 @@
+lgtm,codescanning
+* Added `RoutineType.hasCLinkage` predicate to check whether a function type has "C" language linkage.

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

@@ -1621,6 +1621,19 @@ class RoutineType extends Type, @routinetype {
    */
   Type getReturnType() { routinetypes(underlyingElement(this), unresolveElement(result)) }
 
+  /**
+   * Holds if this function type has "C" language linkage.
+   *
+   * This includes any function declared in a C source file, or explicitly marked as having "C" linkage:
+   * ```
+   * extern "C" void f();
+   * extern "C" {
+   * void g();
+   * }
+   * ```
+   */
+  predicate hasCLinkage() { this.hasSpecifier("c_linkage") }
+
   override string explain() {
     result =
       "function returning {" + this.getReturnType().explain() + "} with arguments (" +

cpp/ql/test/library-tests/clang_ms/element.expected

@@ -66,6 +66,7 @@
 | file://:0:0:0:0 | auto |
 | file://:0:0:0:0 | auto |
 | file://:0:0:0:0 | bool |
+| file://:0:0:0:0 | c_linkage |
 | file://:0:0:0:0 | char |
 | file://:0:0:0:0 | char8_t |
 | file://:0:0:0:0 | char16_t |

cpp/ql/test/library-tests/conditions/elements.expected

@@ -40,6 +40,7 @@
 | file://:0:0:0:0 | auto |
 | file://:0:0:0:0 | auto |
 | file://:0:0:0:0 | bool |
+| file://:0:0:0:0 | c_linkage |
 | file://:0:0:0:0 | char |
 | file://:0:0:0:0 | char8_t |
 | file://:0:0:0:0 | char16_t |

cpp/ql/test/library-tests/specifiers2/specifiers2.expected

@@ -17,12 +17,19 @@
 | Function | cpp20.cpp:7:19:7:40 | member_const_constexpr | member_const_constexpr | inline |
 | Function | cpp20.cpp:7:19:7:40 | member_const_constexpr | member_const_constexpr | is_constexpr |
 | Function | cpp20.cpp:7:19:7:40 | member_const_constexpr | member_const_constexpr | private |
+| Function | specifiers2.c:11:6:11:6 | f | f | c_linkage |
 | Function | specifiers2.c:11:6:11:6 | f | f | extern |
+| Function | specifiers2.c:12:13:12:13 | f | f | c_linkage |
 | Function | specifiers2.c:12:13:12:13 | f | f | extern |
+| Function | specifiers2.c:13:13:13:13 | f | f | c_linkage |
 | Function | specifiers2.c:13:13:13:13 | f | f | extern |
+| Function | specifiers2.c:15:13:15:13 | g | g | c_linkage |
 | Function | specifiers2.c:15:13:15:13 | g | g | extern |
+| Function | specifiers2.c:16:13:16:13 | g | g | c_linkage |
 | Function | specifiers2.c:16:13:16:13 | g | g | extern |
+| Function | specifiers2.c:21:6:21:12 | somefun | somefun | c_linkage |
 | Function | specifiers2.c:21:6:21:12 | somefun | somefun | extern |
+| Function | specifiers2.c:25:12:25:14 | add | add | c_linkage |
 | Function | specifiers2.c:25:12:25:14 | add | add | inline |
 | Function | specifiers2pp.cpp:8:7:8:7 | MyClass | MyClass | extern |
 | Function | specifiers2pp.cpp:8:7:8:7 | MyClass | MyClass | extern |
@@ -96,8 +103,11 @@
 | Function | specifiers2pp.cpp:35:7:35:7 | operator= | operator= | public |
 | Function | specifiers2pp.cpp:35:7:35:7 | operator= | operator= | public |
 | Function | specifiers2pp.cpp:40:12:40:18 | someFun | someFun | extern |
+| Function | specifiers2pp.cpp:41:16:41:23 | someFun2 | someFun2 | c_linkage |
 | Function | specifiers2pp.cpp:41:16:41:23 | someFun2 | someFun2 | extern |
+| Function | specifiers2pp.cpp:43:9:43:16 | someFun3 | someFun3 | c_linkage |
 | Function | specifiers2pp.cpp:43:9:43:16 | someFun3 | someFun3 | extern |
+| Function | specifiers2pp.cpp:44:16:44:23 | someFun4 | someFun4 | c_linkage |
 | Function | specifiers2pp.cpp:44:16:44:23 | someFun4 | someFun4 | static |
 | Function | specifiers2pp.cpp:62:7:62:7 | operator= | operator= | extern |
 | Function | specifiers2pp.cpp:62:7:62:7 | operator= | operator= | extern |

cpp/ql/test/library-tests/templates/instantiations_functions/elements.expected

@@ -70,6 +70,7 @@
 | file://:0:0:0:0 | auto |
 | file://:0:0:0:0 | auto |
 | file://:0:0:0:0 | bool |
+| file://:0:0:0:0 | c_linkage |
 | file://:0:0:0:0 | char |
 | file://:0:0:0:0 | char8_t |
 | file://:0:0:0:0 | char16_t |

cpp/ql/test/library-tests/unnamed/elements.expected

@@ -34,6 +34,7 @@
 | file://:0:0:0:0 | auto | Other |
 | file://:0:0:0:0 | auto | Other |
 | file://:0:0:0:0 | bool | Other |
+| file://:0:0:0:0 | c_linkage | Other |
 | file://:0:0:0:0 | char | Other |
 | file://:0:0:0:0 | char8_t | Other |
 | file://:0:0:0:0 | char16_t | Other |