Add flann dependency to fix kdtree, segmentation, and search

Previously, these libraries would appear to build, but would fail to
link when actually used in the deps of a cc_binary.

This commit also adds all the examples to the pcl build file. This will
help ensure the pcl libraries actually link properly in the future.

The examples that depend on visualization are added, but commented out
with a TODO.

bzl/repositories.bzl

@@ -1,15 +1,16 @@
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+load("@bazel_tools//tools/build_defs/repo:utils.bzl", "maybe")
 
 def pcl_repositories():
-    _maybe_repo(
+    maybe(
         http_archive,
         name = "com_github_nelhage_rules_boost",
         sha256 = "b64e6f7e96c5b0d7ebcb74c5ee29ab879b8ef8c37581ed0be5ff6c23168da985",
         strip_prefix = "rules_boost-ed844db5990d21b75dc3553c057069f324b3916b",
         urls = ["https://github.com/nelhage/rules_boost/archive/ed844db5990d21b75dc3553c057069f324b3916b.tar.gz"],
     )
 
-    _maybe_repo(
+    maybe(
         http_archive,
         name = "eigen",
         build_file = "@rules_pcl//third_party:eigen.BUILD",
@@ -24,7 +25,26 @@ def pcl_repositories():
         urls = ["https://github.com/eigenteam/eigen-git-mirror/archive/3.3.7.tar.gz"],
     )
 
-    _maybe_repo(
+    # Latest commit as of April 6, 2019
+    maybe(
+        http_archive,
+        name = "flann",
+        build_file = "@rules_pcl//third_party:flann.BUILD",
+        sha256 = "9080a91be5759a0b4ef41f62e58896a714ec85d37c2567341a0503039655b1eb",
+        strip_prefix = "flann-1d04523268c388dabf1c0865d69e1b638c8c7d9d",
+        urls = ["https://github.com/flann-lib/flann/archive/1d04523268c388dabf1c0865d69e1b638c8c7d9d.tar.gz"],
+    )
+
+    maybe(
+        http_archive,
+        name = "lz4",
+        build_file = "@rules_pcl//third_party:lz4.BUILD",
+        sha256 = "030644df4611007ff7dc962d981f390361e6c97a34e5cbc393ddfbe019ffe2c1",
+        strip_prefix = "lz4-1.9.3",
+        urls = ["https://github.com/lz4/lz4/archive/refs/tags/v1.9.3.tar.gz"],
+    )
+
+    maybe(
         http_archive,
         name = "net_zlib_zlib",
         sha256 = "6d4d6640ca3121620995ee255945161821218752b551a1a180f4215f7d124d45",
@@ -36,7 +56,7 @@ def pcl_repositories():
         ],
     )
 
-    _maybe_repo(
+    maybe(
         http_archive,
         name = "org_libpng_libpng",
         build_file = "@rules_pcl//third_party:libpng.BUILD",
@@ -48,7 +68,7 @@ def pcl_repositories():
         ],
     )
 
-    _maybe_repo(
+    maybe(
         http_archive,
         name = "pcl",
         build_file = "@rules_pcl//third_party:pcl.BUILD",
@@ -57,18 +77,11 @@ def pcl_repositories():
         urls = ["https://github.com/PointCloudLibrary/pcl/archive/1d3622c1e624994bc013e3e66bc5d98fbb807a89.tar.gz"],
     )
 
-    _maybe_repo(
+    maybe(
         http_archive,
         name = "qhull",
         build_file = "@rules_pcl//third_party:qhull.BUILD",
         sha256 = "cf7235b76244595a86b9407b906e3259502b744528318f2178155e5899d6cf9f",
         strip_prefix = "qhull-2019.1",
         urls = ["https://github.com/qhull/qhull/archive/2019.1.tar.gz"],
     )
-
-def _maybe_repo(repo_rule, name, **kwargs):
-    """A wrapper around repo rules to prevent adding a rule if it already exists, e.g. if it was
-        already added to a user's WORKSPACE file by other dependencies.
-    """
-    if name not in native.existing_rules():
-        repo_rule(name = name, **kwargs)

third_party/flann.BUILD

@@ -0,0 +1,25 @@
+licenses(["notice"])  # BSD 3-Clause
+
+# Do not support cuda for now.
+FLANN_CUDA_HDRS = [
+    "cpp/flann/algorithms/all_indices.h",
+    "cpp/flann/algorithms/kdtree_cuda_builder.h",
+    "cpp/flann/util/cutil_math.h",
+]
+
+cc_library(
+    name = "flann",
+    hdrs = glob(
+        [
+            "src/cpp/flann/*.h",
+            "src/cpp/flann/*.hpp",
+            "src/cpp/flann/algorithms/*.h",
+            "src/cpp/flann/nn/*.h",
+            "src/cpp/flann/util/*.h",
+        ],
+        exclude = FLANN_CUDA_HDRS,
+    ),
+    includes = ["src/cpp"],
+    visibility = ["//visibility:public"],
+    deps = ["@lz4"],
+)

third_party/lz4.BUILD

@@ -0,0 +1,24 @@
+licenses(["notice"])  # BSD 2-Clause
+
+cc_library(
+    name = "lz4",
+    srcs = [
+        "lib/lz4.c",
+        "lib/lz4frame.c",
+        "lib/lz4hc.c",
+        "lib/xxhash.c",
+    ],
+    hdrs = [
+        "lib/lz4.h",
+        "lib/lz4frame.h",
+        "lib/lz4frame_static.h",
+        "lib/lz4hc.h",
+        "lib/xxhash.h",
+    ],
+    include_prefix = "lz4",
+    includes = ["lib"],
+    strip_include_prefix = "lib",
+    # This c file is included by lib/lz4hc.c
+    textual_hdrs = ["lib/lz4.c"],
+    visibility = ["//visibility:public"],
+)