Fix cdeps propagation through embed chains

go/private/context.bzl

@@ -225,11 +225,17 @@ def _merge_embed(source, embed):
         if source["cgo"]:
             fail("multiple libraries with cgo enabled")
         source["cgo"] = s.cgo
-        source["cdeps"] = s.cdeps
-        source["cppopts"] = s.cppopts
-        source["copts"] = s.copts
-        source["cxxopts"] = s.cxxopts
-        source["clinkopts"] = s.clinkopts
+
+    # Merge cgo-related attributes if the embedded library has them,
+    # even if it doesn't have cgo=True itself. This is necessary because
+    # a library can have cdeps without cgo=True if it embeds another library
+    # that has cgo=True. The cdeps must propagate through the embed chain.
+    if s.cdeps or s.cppopts or s.copts or s.cxxopts or s.clinkopts:
+        source["cdeps"] = source["cdeps"] or s.cdeps
+        source["cppopts"] = source["cppopts"] or s.cppopts
+        source["copts"] = source["copts"] or s.copts
+        source["cxxopts"] = source["cxxopts"] or s.cxxopts
+        source["clinkopts"] = source["clinkopts"] or s.clinkopts
 
 def _dedup_archives(archives):
     """Returns a list of archives without duplicate import paths.

tests/core/cgo/BUILD.bazel

@@ -507,6 +507,7 @@ cc_library(
     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.
+    alwayslink = True,
     linkstatic = True,
 )
 
@@ -556,3 +557,30 @@ go_bazel_test(
         "//conditions:default": ["@platforms//:incompatible"],
     }),
 )
+
+# Regression test for cdeps propagation through embed chains.
+# Tests that when a go_library with cdeps embeds another go_library with cgo=True,
+# and a go_test embeds the library with cdeps, the cdeps are properly propagated.
+# This was broken in rules_go v0.51.0+ and fixed in this commit.
+go_library(
+    name = "cdeps_embed_base",
+    srcs = [
+        "cdeps_embed_base.go",
+        "cdeps_embed.h",
+    ],
+    cgo = True,
+    importpath = "github.com/bazelbuild/rules_go/tests/core/cgo/cdeps_embed",
+)
+
+go_library(
+    name = "cdeps_embed_with_cdeps",
+    cdeps = [":native_dep"],
+    embed = [":cdeps_embed_base"],
+    importpath = "github.com/bazelbuild/rules_go/tests/core/cgo/cdeps_embed",
+)
+
+go_test(
+    name = "cdeps_embed_test",
+    srcs = ["cdeps_embed_test.go"],
+    embed = [":cdeps_embed_with_cdeps"],
+)

tests/core/cgo/cdeps_embed.h

@@ -0,0 +1,6 @@
+#ifndef CDEPS_EMBED_H
+#define CDEPS_EMBED_H
+
+void native_greeting(void);
+
+#endif

tests/core/cgo/cdeps_embed_base.go

@@ -0,0 +1,8 @@
+package cdeps_embed
+
+// #include "cdeps_embed.h"
+import "C"
+
+func CallNative() {
+	C.native_greeting()
+}

tests/core/cgo/cdeps_embed_test.go

@@ -0,0 +1,15 @@
+package cdeps_embed
+
+import "testing"
+
+// TestCdepsEmbedPropagation tests that cdeps are properly propagated
+// when a go_library with cdeps embeds another go_library with cgo=True,
+// and a go_test embeds the library with cdeps.
+//
+// This is a regression test for the issue where cdeps were not being
+// propagated through embed chains in rules_go v0.51.0+.
+func TestCdepsEmbedPropagation(t *testing.T) {
+	// If cdeps are properly propagated, this will link successfully
+	// and call the C function from native_dep.
+	CallNative()
+}