[workspace] Improve qhull hidden visibility

When building C++ code, we should not use -fvisibility=hidden because
it infects all #included code, even the standard library. This causes
a lot of console spam during macOS builds, and is a typeinfo (vtable)
problem even on Ubuntu, potentially leading to ODR violation. Instead,
we should wrap the third-party C++ code in a inline hidden namespace.
That way, only the third-party code itself is hidden, not anything
that it #includes.

TODO deprecation

geometry/optimization/vpolytope.cc

@@ -6,9 +6,9 @@
 #include <memory>
 #include <numeric>
 
+#include <drake_vendor/libqhullcpp/Qhull.h>
+#include <drake_vendor/libqhullcpp/QhullVertexSet.h>
 #include <fmt/format.h>
-#include <libqhullcpp/Qhull.h>
-#include <libqhullcpp/QhullVertexSet.h>
 
 #include "drake/common/is_approx_equal_abstol.h"
 #include "drake/geometry/read_obj.h"

tools/workspace/BUILD.bazel

@@ -48,6 +48,7 @@ drake_py_binary(
     name = "vendor_cxx",
     srcs = ["vendor_cxx.py"],
     visibility = [
+        "@qhull//:__pkg__",
         "@yaml_cpp_internal//:__pkg__",
     ],
     deps = [":module_py"],

tools/workspace/qhull/package.BUILD.bazel

@@ -4,6 +4,10 @@ load(
     "@drake//tools/install:install.bzl",
     "install",
 )
+load(
+    "@drake//tools/workspace:vendor_cxx.bzl",
+    "cc_library_vendored",
+)
 
 licenses(["notice"])  # Qhull
 
@@ -53,15 +57,35 @@ _SRCS_CPP = [
 ]
 
 cc_library(
-    name = "qhull",
-    hdrs = _HDRS_C + _HDRS_CPP,
+    name = "qhull_r",
+    hdrs = _HDRS_C,
     copts = [
         "-fvisibility=hidden",
     ],
     includes = ["src"],
-    srcs = _SRCS_C + _SRCS_CPP,
+    srcs = _SRCS_C,
+    linkstatic = 1,
+)
+
+cc_library_vendored(
+    name = "qhull",
+    hdrs = _HDRS_CPP,
+    hdrs_vendored = [
+        x.replace("src/libqhullcpp/", "drake_src/drake_vendor/libqhullcpp/")
+        for x in _HDRS_CPP
+    ],
+    includes = ["drake_src"],
+    edit_include = {
+        "libqhullcpp/": "drake_vendor/libqhullcpp/",
+    },
+    srcs = _SRCS_CPP,
+    srcs_vendored = [
+        x.replace("src/", "drake_src/drake_vendor/")
+        for x in _SRCS_CPP
+    ],
     linkstatic = 1,
     visibility = ["//visibility:public"],
+    deps = [":qhull_r"],
 )
 
 # Install the license file.

tools/workspace/qhull/patches/vendor_cxx.patch

@@ -0,0 +1,27 @@
+For private access within the module, don't use out-of-namespace friendship with
+an `extern "C"` function. This doesn't work with drake's namespace vendoring.
+
+Instead, just make the fields public.
+
+--- src/libqhullcpp/QhullQh.h.orig
++++ src/libqhullcpp/QhullQh.h
+@@ -58,7 +58,7 @@
+ #//!\name Constants
+
+ #//!\name Fields
+-private:
++public:
+     int                 qhull_status;   //!< qh_ERRnone if valid
+     std::string         qhull_message;  //!< Returned messages from libqhull_r
+     std::ostream *      error_stream;   //!< overrides errorMessage, use appendQhullMessage()
+@@ -66,8 +66,9 @@
+     double              factor_epsilon; //!< Factor to increase ANGLEround and DISTround for hyperplane equality
+     bool                use_output_stream; //!< True if using output_stream
+
++private:
+     //! modified by qh_fprintf in QhullUser.cpp
+-    friend void         ::qh_fprintf(qhT *qh, FILE *fp, int msgcode, const char *fmt, ... );
++    //friend void         ::qh_fprintf(qhT *qh, FILE *fp, int msgcode, const char *fmt, ... );
+
+     static const double default_factor_epsilon;  //!< Default factor_epsilon is 1.0, never updated
+

tools/workspace/qhull/repository.bzl

@@ -13,6 +13,7 @@ def qhull_repository(
         build_file = "@drake//tools/workspace/qhull:package.BUILD.bazel",
         patches = [
             "@drake//tools/workspace/qhull:patches/disable_dead_code.patch",
+            "@drake//tools/workspace/qhull:patches/vendor_cxx.patch",
         ],
         mirrors = mirrors,
     )