Extend loplugin:external to warn about classes

...following up on 314f15bff08b76bf96acf99141776ef64d2f1355 "Extend
loplugin:external to warn about enums".

Cases where free functions were moved into an unnamed namespace along with a
class, to not break ADL, are in:

filter/source/svg/svgexport.cxx
sc/source/filter/excel/xelink.cxx
sc/source/filter/excel/xilink.cxx
svx/source/sdr/contact/viewobjectcontactofunocontrol.cxx

All other free functions mentioning moved classes appear to be harmless and not
give rise to (silent, even) ADL breakage.  (One remaining TODO in
compilerplugins/clang/external.cxx is that derived classes are not covered by
computeAffectedTypes, even though they could also be affected by ADL-breakage---
but don't seem to be in any acutal case across the code base.)

For friend declarations using elaborate type specifiers, like

class C1 {};
class C2 { friend class C1; };

* If C2 (but not C1) is moved into an unnamed namespace, the friend declaration
must be changed to not use an elaborate type specifier (i.e., "friend C1;"; see
C++17 [namespace.memdef]/3: "If the name in a friend declaration is neither
qualified nor a template-id and the declaration is a function or an
elaborated-type-specifier, the lookup to determine whether the entity has been
previously declared shall not consider any scopes outside the innermost
enclosing namespace.")

* If C1 (but not C2) is moved into an unnamed namespace, the friend declaration
must be changed too, see <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71882>
"elaborated-type-specifier friend not looked up in unnamed namespace".

Apart from that, to keep changes simple and mostly mechanical (which should help
avoid regressions), out-of-line definitions of class members have been left in
the enclosing (named) namespace.  But explicit specializations of class
templates had to be moved into the unnamed namespace to appease
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92598> "explicit specialization of
template from unnamed namespace using unqualified-id in enclosing namespace".

Also, accompanying declarations (of e.g. typedefs or static variables) that
could arguably be moved into the unnamed namespace too have been left alone.

And in some cases, mention of affected types in blacklists in other loplugins
needed to be adapted.

And sc/qa/unit/mark_test.cxx uses a hack of including other .cxx, one of which
is sc/source/core/data/segmenttree.cxx where e.g. ScFlatUInt16SegmentsImpl is
not moved into an unnamed namespace (because it is declared in
sc/inc/segmenttree.hxx), but its base ScFlatSegmentsImpl is.  GCC warns about
such combinations with enabled-by-default -Wsubobject-linkage, but "The compiler
doesn’t give this warning for types defined in the main .C file, as those are
unlikely to have multiple definitions."
(<https://gcc.gnu.org/onlinedocs/gcc-9.2.0/gcc/Warning-Options.html>)  The
warned-about classes also don't have multiple definitions in the given test, so
disable the warning when including the .cxx.

Change-Id: Ib694094c0d8168be68f8fe90dfd0acbb66a3f1e4
Reviewed-on: https://gerrit.libreoffice.org/83239
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

4 files changed, 24 insertions, 0 deletions

diff --git a/basegfx/source/polygon/b2dpolygon.cxx b/basegfx/source/polygon/b2dpolygon.cxx
index 87343028ecfe..4cf280cd5b91 100644
--- a/basegfx/source/polygon/b2dpolygon.cxx
+++ b/basegfx/source/polygon/b2dpolygon.cxx
@@ -29,6 +29,8 @@
 #include <memory>
 #include <vector>
 
+namespace {
+
 struct CoordinateData2D : public basegfx::B2DPoint
 {
 public:
@@ -552,6 +554,8 @@ public:
     }
 };
 
+}
+
 class ImplB2DPolygon
 {
 private:
diff --git a/basegfx/source/polygon/b2dpolygonclipper.cxx b/basegfx/source/polygon/b2dpolygonclipper.cxx
index 9d672b4397c0..043f2c9bdfe3 100644
--- a/basegfx/source/polygon/b2dpolygonclipper.cxx
+++ b/basegfx/source/polygon/b2dpolygonclipper.cxx
@@ -510,6 +510,8 @@ namespace basegfx
             return aRetval;
         }
 
+        namespace {
+
         /*
         * let a plane be defined as
         *
@@ -536,6 +538,8 @@ namespace basegfx
             sal_uInt32 clipmask;    // clipping mask, e.g. 1000 1000
         };
 
+        }
+
         /*
         *
         * polygon clipping rules  (straight out of Foley and Van Dam)
diff --git a/basegfx/source/polygon/b2dtrapezoid.cxx b/basegfx/source/polygon/b2dtrapezoid.cxx
index ec3d037e6aa8..8bba58f8106e 100644
--- a/basegfx/source/polygon/b2dtrapezoid.cxx
+++ b/basegfx/source/polygon/b2dtrapezoid.cxx
@@ -36,6 +36,8 @@ namespace basegfx
         // class for this since holding the pointers is more effective and also can be
         // used as baseclass for the traversing edges
 
+        namespace {
+
         class TrDeSimpleEdge
         {
         protected:
@@ -58,6 +60,8 @@ namespace basegfx
             const B2DPoint& getEnd() const { return *mpEnd; }
         };
 
+        }
+
         // define vector of simple edges
 
         typedef std::vector< TrDeSimpleEdge > TrDeSimpleEdges;
@@ -67,6 +71,8 @@ namespace basegfx
         // hold and used in SortValue to allow sorting traversing edges by Y, X and slope
         // (in that order)
 
+        namespace {
+
         class TrDeEdgeEntry : public TrDeSimpleEdge
         {
         private:
@@ -179,6 +185,8 @@ namespace basegfx
             }
         };
 
+        }
+
         // define double linked list of edges (for fast random insert)
 
         typedef std::list< TrDeEdgeEntry > TrDeEdgeEntries;
@@ -192,6 +200,8 @@ namespace basegfx
     {
         // FIXME: templatize this and use it for TrDeEdgeEntries too ...
 
+        namespace {
+
         /// Class to allow efficient allocation and release of B2DPoints
         class PointBlockAllocator
         {
@@ -883,6 +893,8 @@ namespace basegfx
                 }
             }
         };
+
+        }
     } // end of anonymous namespace
 } // end of namespace basegfx
 
diff --git a/basegfx/source/polygon/b3dpolygon.cxx b/basegfx/source/polygon/b3dpolygon.cxx
index 5d23be90562c..422353fba8ad 100644
--- a/basegfx/source/polygon/b3dpolygon.cxx
+++ b/basegfx/source/polygon/b3dpolygon.cxx
@@ -27,6 +27,8 @@
 #include <vector>
 #include <algorithm>
 
+namespace {
+
 class CoordinateData3D
 {
     basegfx::B3DPoint                               maPoint;
@@ -672,6 +674,8 @@ public:
     }
 };
 
+}
+
 class ImplB3DPolygon
 {
     // The point vector. This vector exists always and defines the