Fix pic default for musl

[keith]

Previously since this defaulted to on, linking cgo with musl would fail
because cgo assumes pic is off by default

[keith]

the second commit here shows the issue with this approach. this breaks if you try to enable --force_pic unless you also set that for rules_go. this makes it pass:

diff --git a/tests/cgo/defs.bzl b/tests/cgo/defs.bzl
index 665010b..811a622 100644
--- a/tests/cgo/defs.bzl
+++ b/tests/cgo/defs.bzl
@@ -7,4 +7,7 @@ force_pic_go_binary, _force_pic_go_binary_internal = with_cfg(
 ).set(
     "force_pic",
     True,
+).set(
+    Label("@rules_go//go/config:linkmode"),
+    "pie",
 ).build()

we could maybe make rules_go read the cc* stuff for this, but I'm not sure if it's worth it. the nice thing about this change is that it works by default. we could also continue supporting //constraints/pie by making a new default of unset or something, and only respecting it when it was unset

[keith]

like this works to maintain override behavior:

diff --git a/constraints/pie/BUILD.bazel b/constraints/pie/BUILD.bazel
new file mode 100644
index 0000000..2542880
--- /dev/null
+++ b/constraints/pie/BUILD.bazel
@@ -0,0 +1,21 @@
+package(default_visibility = ["//visibility:public"])
+
+constraint_setting(
+    name = "pie",
+    default_constraint_value = "unset",
+)
+
+constraint_value(
+    name = "unset",
+    constraint_setting = "pie",
+)
+
+constraint_value(
+    name = "on",
+    constraint_setting = "pie",
+)
+
+constraint_value(
+    name = "off",
+    constraint_setting = "pie",
+)
diff --git a/toolchain/args/BUILD.bazel b/toolchain/args/BUILD.bazel
index c358fff..f05b12f 100644
--- a/toolchain/args/BUILD.bazel
+++ b/toolchain/args/BUILD.bazel
@@ -153,6 +153,20 @@ cc_args(
     },
 )
 
+cc_args(
+    name = "static_link_executable_custom_pic",
+    actions = [
+        "@rules_cc//cc/toolchains/actions:cpp_link_executable",
+        "@rules_cc//cc/toolchains/actions:lto_index_for_executable",
+        "@rules_cc//cc/toolchains/actions:lto_index_for_dynamic_library",
+        "@rules_cc//cc/toolchains/actions:lto_index_for_nodeps_dynamic_library",
+    ],
+    args = select({
+        "//constraints/pie:on": ["-static-pie"],
+        "//constraints/pie:off": ["-static"],
+    }),
+)
+
 cc_args(
     name = "static_link_executable_pic",
     actions = [
@@ -179,10 +193,13 @@ cc_args(
 
 cc_args_list(
     name = "static_link_executable",
-    args = [
-        ":static_link_executable_pic",
-        ":static_link_executable_no_pic",
-    ],
+    args = select({
+        "//constraints/pie:unset": [
+            ":static_link_executable_pic",
+            ":static_link_executable_no_pic",
+        ],
+        "//conditions:default": [":static_link_executable_custom_pic"],
+    }),
 )
 
 cc_args(

[keith]

rules_go stuff would be fixed by bazel-contrib/rules_go#4648

[dzbarsky]

should we factor out an action_set for these?

[dzbarsky]

should we keep these around as no-op with deprecation warning for a bit? give rules_rs and anyone else using them a chance to upgrade?

[keith]

i will rebase once rules_go is released with that fix