Emit correct header in CGo c-archive

CONTRIBUTORS

@@ -14,6 +14,7 @@ Brian Silverman <bsilver16384@gmail.com>
 Damien Martin-Guillerez <dmarting@google.com>
 David Chen <dzc@google.com>
 David Santiago <david.santiago@gmail.com>
+Fabian Meumertzheim <fabian@meumertzhe.im>
 Han-Wen Nienhuys <hanwen@google.com>
 Ian Cottrell <iancottrell@google.com>
 Jake Voytko <jake@reviewninja.com>

go/private/actions/archive.bzl

@@ -176,9 +176,13 @@ def emit_archive(go, source = None, _recompile_suffix = ""):
     for a in direct:
         x_defs.update(a.x_defs)
     cgo_exports_direct = list(source.cgo_exports)
+
+    # Ensure that the _cgo_export.h of the current target comes first when cgo_exports is iterated
+    # by prepending it and specifying the order explicitly. This is required as the CcInfo attached
+    # to the archive only exposes a single header rather than combining all headers.
     if out_cgo_export_h:
-        cgo_exports_direct.append(out_cgo_export_h)
-    cgo_exports = depset(direct = cgo_exports_direct, transitive = [a.cgo_exports for a in direct])
+        cgo_exports_direct.insert(0, out_cgo_export_h)
+    cgo_exports = depset(direct = cgo_exports_direct, transitive = [a.cgo_exports for a in direct], order = "preorder")
     return GoArchive(
         source = source,
         data = data,

tests/core/c_linkmodes/BUILD.bazel

@@ -93,16 +93,16 @@ cc_library(
     name = "adder_sandwich_cc",
     srcs = ["add_sandwich.c"],
     hdrs = ["add_sandwich.h"],
-    alwayslink = True,
     linkstatic = True,
+    alwayslink = True,
 )
 
 go_binary(
     name = "adder_sandwich_archive",
     srcs = ["add_sandwich.go"],
+    cdeps = [":adder_sandwich_cc"],
     cgo = True,
     linkmode = "c-archive",
-    cdeps = [":adder_sandwich_cc"],
     tags = ["manual"],
 )
 
@@ -117,3 +117,23 @@ cc_test(
         "//conditions:default": [":adder_sandwich_archive"],
     }),
 )
+
+go_binary(
+    name = "go_with_cgo_dep",
+    srcs = select({
+        "@io_bazel_rules_go//go/platform:windows": ["empty.go"],
+        "//conditions:default": ["go_with_cgo_dep.go"],
+    }),
+    cgo = True,
+    linkmode = "c-archive",
+    deps = ["@org_golang_x_sys//unix"],
+)
+
+cc_binary(
+    name = "go_with_cgo_dep_caller",
+    srcs = select({
+        "@io_bazel_rules_go//go/platform:windows": ["skip.c"],
+        "//conditions:default": ["go_with_cgo_dep_caller.cc"],
+    }),
+    deps = [":go_with_cgo_dep"],
+)

tests/core/c_linkmodes/go_with_cgo_dep.go

@@ -0,0 +1,29 @@
+// Copyright 2021 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import "C"
+import (
+	"fmt"
+
+	"golang.org/x/sys/unix"
+)
+
+//export UnixHello
+func UnixHello() {
+	fmt.Printf("Hello, %d\n", unix.Getuid())
+}
+
+func main() {}

tests/core/c_linkmodes/go_with_cgo_dep_caller.cc

@@ -0,0 +1,20 @@
+// Copyright 2021 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "tests/core/c_linkmodes/go_with_cgo_dep.h"
+
+int main() {
+    UnixHello();
+    return 0;
+}