From c3661c4bca0e71dbbe2fff0a1ee247ddd82fcce4 Mon Sep 17 00:00:00 2001
From: Jeremy Nimmer <jeremy.nimmer@tri.global>
Date: Wed, 14 Sep 2022 11:34:15 -0700
Subject: [PATCH] link as hidden, vendor the include path

---
 perception/point_cloud.cc                     |  2 +-
 .../nanoflann_internal/package.BUILD.bazel    |  4 ++--
 .../patches/namespace.patch                   | 21 +++++++++++++++++++
 .../nanoflann_internal/repository.bzl         |  3 +++
 4 files changed, 27 insertions(+), 3 deletions(-)
 create mode 100644 tools/workspace/nanoflann_internal/patches/namespace.patch

diff --git a/perception/point_cloud.cc b/perception/point_cloud.cc
index b31823216131..772e421eff24 100644
--- a/perception/point_cloud.cc
+++ b/perception/point_cloud.cc
@@ -6,9 +6,9 @@
 #include <vector>
 
 #include "absl/container/flat_hash_map.h"
+#include <drake_vendor/nanoflann.hpp>
 #include <fmt/format.h>
 #include <fmt/ostream.h>
-#include <nanoflann.hpp>
 
 #include "drake/common/drake_assert.h"
 #include "drake/common/drake_throw.h"
diff --git a/tools/workspace/nanoflann_internal/package.BUILD.bazel b/tools/workspace/nanoflann_internal/package.BUILD.bazel
index 3f98490cb4f0..5d7b8eca81ef 100644
--- a/tools/workspace/nanoflann_internal/package.BUILD.bazel
+++ b/tools/workspace/nanoflann_internal/package.BUILD.bazel
@@ -12,8 +12,8 @@ package(default_visibility = ["//visibility:public"])
 cc_library(
     name = "nanoflann",
     hdrs = ["include/nanoflann.hpp"],
-    includes = ["include"],
-    deps = [],
+    include_prefix = "drake_vendor",
+    strip_include_prefix = "include",
     linkstatic = 1,
 )
 
diff --git a/tools/workspace/nanoflann_internal/patches/namespace.patch b/tools/workspace/nanoflann_internal/patches/namespace.patch
new file mode 100644
index 000000000000..f471a526d45f
--- /dev/null
+++ b/tools/workspace/nanoflann_internal/patches/namespace.patch
@@ -0,0 +1,21 @@
+Add a drake_vendor namespace ala tools/workspace/vendor_cxx
+
+This prevents link-time symbol conflicts in case code downstream of
+Drake wants to use a different build of nanoflann.
+
+--- include/nanoflann.hpp.orig
++++ include/nanoflann.hpp
+@@ -70,6 +70,7 @@
+ #endif
+ #endif
+ 
++inline namespace drake_vendor __attribute__ ((visibility ("hidden"))) {
+ namespace nanoflann
+ {
+ /** @addtogroup nanoflann_grp nanoflann C++ library for ANN
+@@ -2414,3 +2415,4 @@
+ 
+ /** @} */  // end of grouping
+ }  // namespace nanoflann
++}  // namespace drake_vendor
+\ No newline at end of file
diff --git a/tools/workspace/nanoflann_internal/repository.bzl b/tools/workspace/nanoflann_internal/repository.bzl
index 2bf8e9467cd4..c7ec1f138668 100644
--- a/tools/workspace/nanoflann_internal/repository.bzl
+++ b/tools/workspace/nanoflann_internal/repository.bzl
@@ -11,5 +11,8 @@ def nanoflann_internal_repository(
         commit = "v1.4.3",
         sha256 = "cbcecf22bec528a8673a113ee9b0e134f91f1f96be57e913fa1f74e98e4449fa",  # noqa
         build_file = ":package.BUILD.bazel",
+        patches = [
+            ":patches/namespace.patch",
+        ],
         mirrors = mirrors,
     )