Add flatbuffer_cc library support (#5061)

* Add flatbuffer_cc library support

* Update flags so all the tests pass

Tests now all pass!

* Modify the tests to use the generated code

This should be a simple serialize/deserialize test of the new generated
code to make sure the bazel rules are doing something sane.

* Use generated monster_test.fb in testing/test.cpp

cmake drops it's generated code in tests/monster_test_generated.h
Instead of checking that in, let's generate it with bazel.

* Make grpc tests depend on monster_test_generated.h

* Remove redundant cmake dependency

This should address @aardappel's feedback.

* Run flatc for Android as well

This will fix the last travis.ci failure

* Add generated output folder and fix flags

* Move flatbuffers_header_build_rules to the library that uses it

* Use --cpp-ptr-type to fix android

Android was the only target using the STL emulation layer.  It needed
the --cpp-ptr-type flatbuffers::unique_ptr flag to work.  Add it!

* Roll back changes to use autogenerated monster_test_generated.

Flip tests/test.cpp to use the autogenerated file as well.

1 files changed, 230 insertions, 0 deletions

diff --git a/build_defs.bzl b/build_defs.bzl
new file mode 100644
index 00000000..707371ff
--- /dev/null
+++ b/build_defs.bzl
@@ -0,0 +1,230 @@
+# Description:
+#   BUILD rules for generating flatbuffer files in various languages.
+
+flatc_path = "//:flatc"
+
+DEFAULT_INCLUDE_PATHS = [
+    "./",
+    "$(GENDIR)",
+    "$(BINDIR)",
+]
+
+DEFAULT_FLATC_ARGS = [
+    "--gen-object-api",
+    "--gen-compare",
+    "--no-includes",
+    "--gen-mutable",
+    "--reflect-names",
+    "--cpp-ptr-type flatbuffers::unique_ptr",
+]
+
+def flatbuffer_library_public(
+        name,
+        srcs,
+        outs,
+        language_flag,
+        out_prefix = "",
+        includes = [],
+        include_paths = DEFAULT_INCLUDE_PATHS,
+        flatc_args = DEFAULT_FLATC_ARGS,
+        reflection_name = "",
+        reflection_visiblity = None,
+        output_to_bindir = False):
+    """Generates code files for reading/writing the given flatbuffers in the requested language using the public compiler.
+
+    Args:
+      name: Rule name.
+      srcs: Source .fbs files. Sent in order to the compiler.
+      outs: Output files from flatc.
+      language_flag: Target language flag. One of [-c, -j, -js].
+      out_prefix: Prepend this path to the front of all generated files except on
+          single source targets. Usually is a directory name.
+      includes: Optional, list of filegroups of schemas that the srcs depend on.
+      include_paths: Optional, list of paths the includes files can be found in.
+      flatc_args: Optional, list of additional arguments to pass to flatc.
+      reflection_name: Optional, if set this will generate the flatbuffer
+        reflection binaries for the schemas.
+      reflection_visiblity: The visibility of the generated reflection Fileset.
+      output_to_bindir: Passed to genrule for output to bin directory.
+    Outs:
+      filegroup(name): all generated source files.
+      Fileset([reflection_name]): (Optional) all generated reflection binaries.
+    """
+    include_paths_cmd = ["-I %s" % (s) for s in include_paths]
+
+    # '$(@D)' when given a single source target will give the appropriate
+    # directory. Appending 'out_prefix' is only necessary when given a build
+    # target with multiple sources.
+    output_directory = (
+        ("-o $(@D)/%s" % (out_prefix)) if len(srcs) > 1 else ("-o $(@D)")
+    )
+    genrule_cmd = " ".join([
+        "SRCS=($(SRCS));",
+        "for f in $${SRCS[@]:0:%s}; do" % len(srcs),
+        "$(location %s)" % (flatc_path),
+        " ".join(include_paths_cmd),
+        " ".join(flatc_args),
+        language_flag,
+        output_directory,
+        "$$f;",
+        "done",
+    ])
+    native.genrule(
+        name = name,
+        srcs = srcs + includes,
+        outs = outs,
+        output_to_bindir = output_to_bindir,
+        tools = [flatc_path],
+        cmd = genrule_cmd,
+        message = "Generating flatbuffer files for %s:" % (name),
+    )
+    if reflection_name:
+        reflection_genrule_cmd = " ".join([
+            "SRCS=($(SRCS));",
+            "for f in $${SRCS[@]:0:%s}; do" % len(srcs),
+            "$(location %s)" % (flatc_path),
+            "-b --schema",
+            " ".join(flatc_args),
+            " ".join(include_paths_cmd),
+            language_flag,
+            output_directory,
+            "$$f;",
+            "done",
+        ])
+        reflection_outs = [
+            (out_prefix + "%s.bfbs") % (s.replace(".fbs", "").split("/")[-1])
+            for s in srcs
+        ]
+        native.genrule(
+            name = "%s_srcs" % reflection_name,
+            srcs = srcs + includes,
+            outs = reflection_outs,
+            output_to_bindir = output_to_bindir,
+            tools = [flatc_path],
+            cmd = reflection_genrule_cmd,
+            message = "Generating flatbuffer reflection binary for %s:" % (name),
+        )
+        native.Fileset(
+            name = reflection_name,
+            out = "%s_out" % reflection_name,
+            entries = [
+                native.FilesetEntry(files = reflection_outs),
+            ],
+            visibility = reflection_visiblity,
+        )
+
+def flatbuffer_cc_library(
+        name,
+        srcs,
+        srcs_filegroup_name = "",
+        out_prefix = "",
+        includes = [],
+        include_paths = DEFAULT_INCLUDE_PATHS,
+        flatc_args = DEFAULT_FLATC_ARGS,
+        visibility = None,
+        srcs_filegroup_visibility = None,
+        gen_reflections = False):
+    '''A cc_library with the generated reader/writers for the given flatbuffer definitions.
+
+    Args:
+      name: Rule name.
+      srcs: Source .fbs files. Sent in order to the compiler.
+      srcs_filegroup_name: Name of the output filegroup that holds srcs. Pass this
+          filegroup into the `includes` parameter of any other
+          flatbuffer_cc_library that depends on this one's schemas.
+      out_prefix: Prepend this path to the front of all generated files. Usually
+          is a directory name.
+      includes: Optional, list of filegroups of schemas that the srcs depend on.
+          ** SEE REMARKS BELOW **
+      include_paths: Optional, list of paths the includes files can be found in.
+      flatc_args: Optional list of additional arguments to pass to flatc
+          (e.g. --gen-mutable).
+      visibility: The visibility of the generated cc_library. By default, use the
+          default visibility of the project.
+      srcs_filegroup_visibility: The visibility of the generated srcs filegroup.
+          By default, use the value of the visibility parameter above.
+      gen_reflections: Optional, if true this will generate the flatbuffer
+        reflection binaries for the schemas.
+    Outs:
+      filegroup([name]_srcs): all generated .h files.
+      filegroup(srcs_filegroup_name if specified, or [name]_includes if not):
+          Other flatbuffer_cc_library's can pass this in for their `includes`
+          parameter, if they depend on the schemas in this library.
+      Fileset([name]_reflection): (Optional) all generated reflection binaries.
+      cc_library([name]): library with sources and flatbuffers deps.
+
+    Remarks:
+      ** Because the genrule used to call flatc does not have any trivial way of
+        computing the output list of files transitively generated by includes and
+        --gen-includes (the default) being defined for flatc, the --gen-includes
+        flag will not work as expected. The way around this is to add a dependency
+        to the flatbuffer_cc_library defined alongside the flatc included Fileset.
+        For example you might define:
+
+        flatbuffer_cc_library(
+            name = "my_fbs",
+            srcs = [ "schemas/foo.fbs" ],
+            includes = [ "//third_party/bazz:bazz_fbs_includes" ],
+        )
+
+        In which foo.fbs includes a few files from the Fileset defined at
+        //third_party/bazz:bazz_fbs_includes. When compiling the library that
+        includes foo_generated.h, and therefore has my_fbs as a dependency, it
+        will fail to find any of the bazz *_generated.h files unless you also
+        add bazz's flatbuffer_cc_library to your own dependency list, e.g.:
+
+        cc_library(
+            name = "my_lib",
+            deps = [
+                ":my_fbs",
+                "//third_party/bazz:bazz_fbs"
+            ],
+        )
+
+        Happy dependent Flatbuffering!
+    '''
+    output_headers = [
+        (out_prefix + "%s_generated.h") % (s.replace(".fbs", "").split("/")[-1])
+        for s in srcs
+    ]
+    reflection_name = "%s_reflection" % name if gen_reflections else ""
+
+    srcs_lib = "%s_srcs" % (name)
+    flatbuffer_library_public(
+        name = srcs_lib,
+        srcs = srcs,
+        outs = output_headers,
+        language_flag = "-c",
+        out_prefix = out_prefix,
+        includes = includes,
+        include_paths = include_paths,
+        flatc_args = flatc_args,
+        reflection_name = reflection_name,
+        reflection_visiblity = visibility,
+    )
+    native.cc_library(
+        name = name,
+        hdrs = [
+            ":" + srcs_lib,
+        ],
+        srcs = [
+            ":" + srcs_lib,
+        ],
+        features = [
+            "-parse_headers",
+        ],
+        deps = [
+            "//:runtime_cc",
+        ],
+        includes = [],
+        linkstatic = 1,
+        visibility = visibility,
+    )
+
+    # A filegroup for the `srcs`. That is, all the schema files for this
+    # Flatbuffer set.
+    native.filegroup(
+        name = srcs_filegroup_name if srcs_filegroup_name else "%s_includes" % (name),
+        srcs = srcs,
+        visibility = srcs_filegroup_visibility if srcs_filegroup_visibility != None else visibility,
+    )