Don't include non-executable go_binary in dependent's runfiles

If a go_binary is built with a non-executable link mode such as
`c-archive`, its dependents currently pick up a runfile dependency on it
since its DefaultInfo specifies the resulting archive as an executable.
This is unnecessary as the dependent should be able to decide whether to
include the file (e.g. dynamic linking) or not (e.g. static linking).

With this commit, the executable field of the DefaultInfo is only
populated if the go_binary is built with an executable link mode.

Follow-up to bazel-contrib#3143

go/private/rules/binary.bzl

@@ -34,6 +34,7 @@ load(
 )
 load(
     "//go/private:mode.bzl",
+    "LINKMODES_EXECUTABLE",
     "LINKMODE_C_ARCHIVE",
     "LINKMODE_C_SHARED",
     "LINKMODE_NORMAL",
@@ -135,7 +136,7 @@ def _go_binary_impl(ctx):
         DefaultInfo(
             files = depset([executable]),
             runfiles = runfiles,
-            executable = executable,
+            executable = executable if go.mode.link in LINKMODES_EXECUTABLE else None,
         ),
     ]
 

tests/core/go_binary/non_executable_test.go

@@ -26,21 +26,51 @@ func TestMain(m *testing.M) {
 		Main: `
 -- src/BUILD.bazel --
 load("@io_bazel_rules_go//go:def.bzl", "go_binary")
+load(":rules.bzl", "no_runfiles_check")
 
 go_binary(
     name = "archive",
     srcs = ["archive.go"],
+    cgo = True,
     linkmode = "c-archive",
 )
+
+cc_binary(
+    name = "main",
+    srcs = ["main.c"],
+    deps = [":archive"],
+)
+
+no_runfiles_check(
+    name = "no_runfiles",
+    target = ":main",
+)
 -- src/archive.go --
 package main
 
+import "C"
+
 func main() {}
+-- src/main.c --
+int main() {}
+-- src/rules.bzl --
+def _no_runfiles_check_impl(ctx):
+    runfiles = ctx.attr.target[DefaultInfo].default_runfiles.files.to_list()
+    for runfile in runfiles:
+        if runfile.short_path != "src/main":
+            fail("Unexpected runfile: %s" % runfile)
+
+no_runfiles_check = rule(
+    implementation = _no_runfiles_check_impl,
+    attrs = {
+        "target": attr.label(),
+    }
+)
 `,
 	})
 }
 
-func TestNonExecutableGoBinary(t *testing.T) {
+func TestNonExecutableGoBinaryCantBeRun(t *testing.T) {
 	if err := bazel_testing.RunBazel("build", "//src:archive"); err != nil {
 		t.Fatal(err)
 	}
@@ -49,3 +79,9 @@ func TestNonExecutableGoBinary(t *testing.T) {
 		t.Errorf("Expected bazel run to fail due to //src:archive not being executable")
 	}
 }
+
+func TestNonExecutableGoBinaryNotInRunfiles(t *testing.T) {
+	if err := bazel_testing.RunBazel("build", "//src:no_runfiles"); err != nil {
+		t.Fatal(err)
+	}
+}