Split C and C++ compilation (#1366)

This PR splits C and C++ CGo compilation into separate steps. The main idea behind this is for specifying per language options (such as std=c++14 for C++).

For that, the pack builder has been modified to take multiple archives (C and C++) and fuse them.

This is also a required step for adding ObjC support.

I have also added a commit which tries to make relative CC options absolute (via whitelisting)

go/core.rst

@@ -90,7 +90,7 @@ Binaries that depend on this library may also set this value.
 
     go_binary(
         name = "cmd",
-        srcs = ["main.go"], 
+        srcs = ["main.go"],
         deps = ["//version:go_default_library"],
         x_defs = {"example.com/repo/version.Version", "0.9"},
     )
@@ -235,6 +235,18 @@ Attributes
 | Subject to `"Make variable"`_ substitution and `Bourne shell tokenization`_.                     |
 | Only valid if :param:`cgo` = :value:`True`.                                                      |
 +----------------------------+-----------------------------+---------------------------------------+
+| :param:`cxxopts`           | :type:`string_list`         | :value:`[]`                           |
++----------------------------+-----------------------------+---------------------------------------+
+| List of flags to add to the C++ compilation command.                                             |
+| Subject to `"Make variable"`_ substitution and `Bourne shell tokenization`_.                     |
+| Only valid if :param:`cgo` = :value:`True`.                                                      |
++----------------------------+-----------------------------+---------------------------------------+
+| :param:`cppopts`           | :type:`string_list`         | :value:`[]`                           |
++----------------------------+-----------------------------+---------------------------------------+
+| List of flags to add to the C/C++ preprocessor command.                                          |
+| Subject to `"Make variable"`_ substitution and `Bourne shell tokenization`_.                     |
+| Only valid if :param:`cgo` = :value:`True`.                                                      |
++----------------------------+-----------------------------+---------------------------------------+
 | :param:`clinkopts`         | :type:`string_list`         | :value:`[]`                           |
 +----------------------------+-----------------------------+---------------------------------------+
 | List of flags to add to the C link command.                                                      |
@@ -392,6 +404,18 @@ Attributes
 | Subject to `"Make variable"`_ substitution and `Bourne shell tokenization`_.                     |
 | Only valid if :param:`cgo` = :value:`True`.                                                      |
 +----------------------------+-----------------------------+---------------------------------------+
+| :param:`cxxopts`           | :type:`string_list`         | :value:`[]`                           |
++----------------------------+-----------------------------+---------------------------------------+
+| List of flags to add to the C++ compilation command.                                             |
+| Subject to `"Make variable"`_ substitution and `Bourne shell tokenization`_.                     |
+| Only valid if :param:`cgo` = :value:`True`.                                                      |
++----------------------------+-----------------------------+---------------------------------------+
+| :param:`cppopts`           | :type:`string_list`         | :value:`[]`                           |
++----------------------------+-----------------------------+---------------------------------------+
+| List of flags to add to the C/C++ preprocessor command.                                          |
+| Subject to `"Make variable"`_ substitution and `Bourne shell tokenization`_.                     |
+| Only valid if :param:`cgo` = :value:`True`.                                                      |
++----------------------------+-----------------------------+---------------------------------------+
 | :param:`clinkopts`         | :type:`string_list`         | :value:`[]`                           |
 +----------------------------+-----------------------------+---------------------------------------+
 | List of flags to add to the C link command.                                                      |
@@ -503,6 +527,18 @@ Attributes
 | Subject to `"Make variable"`_ substitution and `Bourne shell tokenization`_.                     |
 | Only valid if :param:`cgo` = :value:`True`.                                                      |
 +----------------------------+-----------------------------+---------------------------------------+
+| :param:`cxxopts`           | :type:`string_list`         | :value:`[]`                           |
++----------------------------+-----------------------------+---------------------------------------+
+| List of flags to add to the C++ compilation command.                                             |
+| Subject to `"Make variable"`_ substitution and `Bourne shell tokenization`_.                     |
+| Only valid if :param:`cgo` = :value:`True`.                                                      |
++----------------------------+-----------------------------+---------------------------------------+
+| :param:`cppopts`           | :type:`string_list`         | :value:`[]`                           |
++----------------------------+-----------------------------+---------------------------------------+
+| List of flags to add to the C/C++ preprocessor command.                                          |
+| Subject to `"Make variable"`_ substitution and `Bourne shell tokenization`_.                     |
+| Only valid if :param:`cgo` = :value:`True`.                                                      |
++----------------------------+-----------------------------+---------------------------------------+
 | :param:`clinkopts`         | :type:`string_list`         | :value:`[]`                           |
 +----------------------------+-----------------------------+---------------------------------------+
 | List of flags to add to the C link command.                                                      |

go/private/actions/archive.bzl

@@ -54,7 +54,7 @@ def emit_archive(go, source=None):
     runfiles = runfiles.merge(a.runfiles)
     if a.source.mode != go.mode: fail("Archive mode does not match {} is {} expected {}".format(a.data.label, mode_string(a.source.mode), mode_string(go.mode)))
 
-  if len(extra_objects) == 0 and source.cgo_archive == None:
+  if len(extra_objects) == 0 and not source.cgo_archives:
     go.compile(go,
         sources = split.go,
         importpath = source.library.importmap,
@@ -77,7 +77,7 @@ def emit_archive(go, source=None):
         in_lib = partial_lib,
         out_lib = out_lib,
         objects = extra_objects,
-        archive = source.cgo_archive,
+        archives = source.cgo_archives,
     )
   data = GoArchiveData(
       name = source.library.name,

go/private/actions/pack.bzl

@@ -16,7 +16,7 @@ def emit_pack(go,
     in_lib = None,
     out_lib = None,
     objects = [],
-    archive = None):
+    archives = []):
   """See go/toolchains.rst#pack for full documentation."""
 
   if in_lib == None: fail("in_lib is a required parameter")
@@ -32,9 +32,8 @@ def emit_pack(go,
   inputs.extend(objects)
   arguments.add(objects, before_each="-obj")
 
-  if archive:
-    inputs.append(archive)
-    arguments.add(["-arc", archive])
+  inputs.extend(archives)
+  arguments.add(archives, before_each="-arc")
 
   go.actions.run(
       inputs = inputs,

go/private/common.bzl

@@ -41,6 +41,10 @@ hdr_exts = [
 
 c_exts = [
     ".c",
+    ".h",
+]
+
+cxx_exts = [
     ".cc",
     ".cxx",
     ".cpp",
@@ -56,7 +60,7 @@ cc_hdr_filetype = FileType(hdr_exts)
 
 # Extensions of files we can build with the Go compiler or with cc_library.
 # This is a subset of the extensions recognized by go/build.
-cgo_filetype = FileType(go_exts + asm_exts + c_exts)
+cgo_filetype = FileType(go_exts + asm_exts + c_exts + cxx_exts)
 
 def pkg_dir(workspace_root, package_name):
   """Returns a relative path to a package directory from the root of the
@@ -75,12 +79,14 @@ def split_srcs(srcs):
     asm = [],
     headers = [],
     c = [],
+    cxx = [],
   )
   ext_pairs = (
     (sources.go, go_exts),
     (sources.headers, hdr_exts),
     (sources.asm, asm_exts),
     (sources.c, c_exts),
+    (sources.cxx, cxx_exts),
   )
   extmap = {}
   for outs, exts in ext_pairs:
@@ -97,7 +103,7 @@ def split_srcs(srcs):
   return sources
 
 def join_srcs(source):
-  return source.go + source.headers + source.asm + source.c
+  return source.go + source.headers + source.asm + source.c + source.cxx
 
 def env_execute(ctx, arguments, environment = {}, **kwargs):
   """env_executes a command in a repository context. It prepends "env -i"

go/private/context.bzl

@@ -97,6 +97,8 @@ def _new_args(go):
       "-compiler_path", go.cgo_tools.compiler_path,
       "-cc", go.cgo_tools.compiler_executable,
     ])
+    args.add(go.cgo_tools.compiler_options, before_each = "-c_flag")
+    args.add(go.cgo_tools.compiler_options, before_each = "-cxx_flag")
     args.add(go.cgo_tools.compiler_options, before_each = "-cpp_flag")
     args.add(go.cgo_tools.linker_options, before_each = "-ld_flag")
   return args
@@ -129,10 +131,10 @@ def _merge_embed(source, embed):
   source["runfiles"] = source["runfiles"].merge(s.runfiles)
   source["cgo_deps"] = source["cgo_deps"] + s.cgo_deps
   source["cgo_exports"] = source["cgo_exports"] + s.cgo_exports
-  if s.cgo_archive:
-    if source["cgo_archive"]:
-      fail("multiple libraries with cgo_archive embedded")
-    source["cgo_archive"] = s.cgo_archive
+  if s.cgo_archives:
+    if source["cgo_archives"]:
+      fail("multiple libraries with cgo_archives embedded")
+    source["cgo_archives"] = s.cgo_archives
 
 def _library_to_source(go, attr, library, coverage_instrumented):
   #TODO: stop collapsing a depset in this line...
@@ -149,7 +151,7 @@ def _library_to_source(go, attr, library, coverage_instrumented):
       "deps" : getattr(attr, "deps", []),
       "gc_goopts" : getattr(attr, "gc_goopts", []),
       "runfiles" : go._ctx.runfiles(collect_data = True),
-      "cgo_archive" : None,
+      "cgo_archives" : [],
       "cgo_deps" : [],
       "cgo_exports" : [],
   }