Link in native libraries of transitive dependencies in archive mode

When linking a go_binary in one of the native archive modes, all
native libraries of transitive dependencies should be included in the
resulting CcInfo, not just the libraries obtained from the cdeps.

This commit adds a `cc_info` field to the `GoSource` provider that
includes the result of merging the `CcInfo`s of all `deps` and `cdeps`
for all Go libraries, not just for those using cgo themselves.

go/private/common.bzl

@@ -241,6 +241,12 @@ def as_set(v):
         return depset(v)
     fail("as_tuple failed on {}".format(v))
 
+_STRUCT_TYPE = type(struct())
+
+def is_struct(v):
+    """Returns true if v is a struct."""
+    return type(v) == _STRUCT_TYPE
+
 def count_group_matches(v, prefix, suffix):
     """Counts reluctant substring matches between prefix and suffix.
 

go/private/context.bzl

@@ -50,6 +50,7 @@ load(
     "as_iterable",
     "goos_to_extension",
     "goos_to_shared_extension",
+    "is_struct",
 )
 load(
     "//go/platform:apple.bzl",
@@ -240,6 +241,7 @@ def _library_to_source(go, attr, library, coverage_instrumented):
         "clinkopts": _expand_opts(go, "clinkopts", getattr(attr, "clinkopts", [])),
         "cgo_deps": [],
         "cgo_exports": [],
+        "cc_info": None,
     }
     if coverage_instrumented:
         source["cover"] = attr_srcs
@@ -266,6 +268,7 @@ def _library_to_source(go, attr, library, coverage_instrumented):
                 fail("source {} has C/C++ extension, but cgo was not enabled (set 'cgo = True')".format(f.path))
     if library.resolve:
         library.resolve(go, attr, source, _merge_embed)
+    source["cc_info"] = _collect_cc_infos(source["deps"], source["cdeps"])
     return GoSource(**source)
 
 def _collect_runfiles(go, data, deps):
@@ -280,6 +283,19 @@ def _collect_runfiles(go, data, deps):
         runfiles = runfiles.merge(get_source(t).runfiles)
     return runfiles
 
+def _collect_cc_infos(deps, cdeps):
+    cc_infos = []
+    for dep in cdeps:
+        if CcInfo in dep:
+            cc_infos.append(dep[CcInfo])
+    for dep in deps:
+        # dep may be a struct, which doesn't support indexing by providers.
+        if is_struct(dep):
+            continue
+        if GoSource in dep:
+            cc_infos.append(dep[GoSource].cc_info)
+    return cc_common.merge_cc_infos(cc_infos = cc_infos)
+
 def _check_binary_dep(go, dep, edge):
     """Checks that this rule doesn't depend on a go_binary or go_test.
 

go/private/rules/binary.bzl

@@ -163,7 +163,7 @@ def _go_binary_impl(ctx):
             cc_import_kwargs["alwayslink"] = True
         ccinfo = new_cc_import(go, **cc_import_kwargs)
         ccinfo = cc_common.merge_cc_infos(
-            cc_infos = [ccinfo] + [d[CcInfo] for d in source.cdeps],
+            cc_infos = [ccinfo, source.cc_info],
         )
         providers.append(ccinfo)
 

go/providers.rst

@@ -204,6 +204,10 @@ method. In general, only rules_go should need to build or handle these.
 +--------------------------------+-----------------------------------------------------------------+
 | The exposed cc headers for these sources.                                                        |
 +--------------------------------+-----------------------------------------------------------------+
+| :param:`cc_info`               | :type:`CcInfo`                                                  |
++--------------------------------+-----------------------------------------------------------------+
+| The result of merging the ``CcInfo``s of all `deps` and `cdeps`                                  |
++--------------------------------+-----------------------------------------------------------------+
 
 GoArchiveData
 ~~~~~~~~~~~~~

tests/core/cgo/BUILD.bazel

@@ -434,3 +434,41 @@ go_binary(
     }),
     deps = [":use_external_symbol"],
 )
+
+cc_library(
+    name = "native_dep",
+    srcs = ["native_dep.c"],
+    hdrs = ["native_dep.h"],
+    # Force static linking to ensure that the build doesn't succeed by
+    # accidentally picking up the shared library in the search path.
+    linkstatic = True,
+)
+
+go_library(
+    name = "transitive_dep",
+    srcs = ["transitive_dep.go"],
+    cdeps = [":native_dep"],
+    cgo = True,
+    importpath = "github.com/bazelbuild/rules_go/tests/core/cgo/transitive_dep",
+)
+
+go_library(
+    name = "direct_dep",
+    srcs = ["direct_dep.go"],
+    importpath = "github.com/bazelbuild/rules_go/tests/core/cgo/direct_dep",
+    deps = [":transitive_dep"],
+)
+
+go_binary(
+    name = "use_transitive_symbol",
+    srcs = ["use_transitive_symbol.go"],
+    cgo = True,
+    linkmode = "c-archive",
+    deps = [":direct_dep"],
+)
+
+cc_binary(
+    name = "use_c_symbol_through_go",
+    srcs = ["use_c_symbol_through_go.c"],
+    deps = [":use_transitive_symbol"],
+)

tests/core/cgo/direct_dep.go

@@ -0,0 +1,9 @@
+package direct_dep
+
+import (
+	"github.com/bazelbuild/rules_go/tests/core/cgo/transitive_dep"
+)
+
+func PrintGreeting() {
+	transitive_dep.PrintGreeting()
+}

tests/core/cgo/native_dep.c

@@ -0,0 +1,5 @@
+#include <stdio.h>
+
+void native_greeting(void) {
+    printf("Hello, world!\n");
+}

tests/core/cgo/native_dep.h

@@ -0,0 +1 @@
+extern void native_greeting(void);

tests/core/cgo/transitive_dep.go

@@ -0,0 +1,10 @@
+package transitive_dep
+
+/*
+#include "tests/core/cgo/native_dep.h"
+ */
+import "C"
+
+func PrintGreeting() {
+	C.native_greeting();
+}

tests/core/cgo/use_c_symbol_through_go.c

@@ -0,0 +1,5 @@
+#include "tests/core/cgo/use_transitive_symbol.h"
+
+int main() {
+    PrintGreeting();
+}

tests/core/cgo/use_transitive_symbol.go

@@ -0,0 +1,14 @@
+package main
+
+import "C"
+
+import (
+	"github.com/bazelbuild/rules_go/tests/core/cgo/direct_dep"
+)
+
+//export PrintGreeting
+func PrintGreeting() {
+	direct_dep.PrintGreeting()
+}
+
+func main() {}