Use find_cpp_toolchain instead of ctx.fragments.cpp

ctx.fragments.cpp is deprecated.

This doesn't fully get us away from deprecated APIs. We should use
cc_common for flags and C/C++ compilation command lines.

Related bazel-contrib#1744

go/platform/apple.bzl

@@ -29,14 +29,13 @@ PLATFORMS = {
 def _apple_version_min(platform, version):
     return "-m" + platform.name_in_plist.lower() + "-version-min=" + version
 
-def apple_ensure_options(ctx, env, tags, compiler_options, linker_options):
+def apple_ensure_options(ctx, env, tags, compiler_options, linker_options, target_gnu_system_name):
     """apple_ensure_options ensures that, when building an Apple target, the
     proper environment, compiler flags and Go tags are correctly set."""
-    system_name = ctx.fragments.cpp.target_gnu_system_name
-    platform = PLATFORMS.get(system_name)
+    platform = PLATFORMS.get(target_gnu_system_name)
     if platform == None:
         return
-    if system_name.endswith("-ios"):
+    if target_gnu_system_name.endswith("-ios"):
         tags.append("ios")  # needed for stdlib building
     if platform in [apple_common.platform.ios_device, apple_common.platform.ios_simulator]:
         min_version = _apple_version_min(platform, "7.0")

go/private/context.bzl

@@ -12,6 +12,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+load(
+    "@bazel_tools//tools/cpp:toolchain_utils.bzl",
+    "find_cpp_toolchain",
+)
 load(
     "@io_bazel_rules_go//go/private:providers.bzl",
     "EXPLICIT_PATH",
@@ -326,26 +330,26 @@ def go_context(ctx, attr = None):
     )
 
 def _go_context_data(ctx):
-    cpp = ctx.fragments.cpp
+    cpp = find_cpp_toolchain(ctx)
     features = ctx.features
     compiler_options = _filter_options(
-        cpp.compiler_options(features) + cpp.unfiltered_compiler_options(features),
+        cpp.compiler_options() + cpp.unfiltered_compiler_options(features),
         _COMPILER_OPTIONS_BLACKLIST,
     )
     linker_options = _filter_options(
-        cpp.link_options + cpp.mostly_static_link_options(features, False),
+        cpp.mostly_static_link_options(False),
         _LINKER_OPTIONS_BLACKLIST,
     )
 
     env = {}
     tags = []
     if "gotags" in ctx.var:
         tags = ctx.var["gotags"].split(",")
-    apple_ensure_options(ctx, env, tags, compiler_options, linker_options)
+    apple_ensure_options(ctx, env, tags, compiler_options, linker_options, cpp.target_gnu_system_name)
     compiler_path, _ = cpp.ld_executable.rsplit("/", 1)
     return struct(
         strip = ctx.attr.strip,
-        crosstool = ctx.files._crosstool,
+        crosstool = ctx.files._cc_toolchain,
         tags = tags,
         env = env,
         cgo_tools = struct(
@@ -355,18 +359,18 @@ def _go_context_data(ctx):
             compiler_options = compiler_options,
             linker_options = linker_options,
             options = compiler_options + linker_options,
-            c_options = cpp.c_options,
+            c_options = cpp.c_options(),
         ),
     )
 
 go_context_data = rule(
     _go_context_data,
     attrs = {
         "strip": attr.string(mandatory = True),
-        "_crosstool": attr.label(default = "@bazel_tools//tools/cpp:current_cc_toolchain"),
+        "_cc_toolchain": attr.label(default = "@bazel_tools//tools/cpp:current_cc_toolchain"),
         "_xcode_config": attr.label(
             default = "@bazel_tools//tools/osx:current_xcode_config",
         ),
     },
-    fragments = ["cpp", "apple"],
+    fragments = ["apple"],
 )

tests/bazel_tests.bzl

@@ -230,10 +230,7 @@ _bazel_test_script = go_rule(
         "check": attr.string(),
         "config": attr.string(default = "isolate"),
         "extra_files": attr.label_list(allow_files = True),
-        "data": attr.label_list(
-            allow_files = True,
-            cfg = "data",
-        ),
+        "data": attr.label_list(allow_files = True),
         "clean_build": attr.bool(default = False),
         "bazelrc": attr.label(
             allow_single_file = True,