bindgen::Builder::extern_fn_block_attrs does not apply to static variables

[alejnp]

The extern_fn_block_attrs (introduced in commit d5fc49c) option is not part of the public API of bindgen::Builder (not accessible through methods nor directly).

For context, I am using the programmatic Builder API through lib.rs to create -sys style crates but I'm running into issue similar to #2548. A key distinction is that my origin source code is correctly marked with __declspec and doesn't require a separate .def file.

What I want to achieve is to add #[link(name = LIBRARY)] to my extern "C" blocks, for largely two reasons:

1. Ensure that the generated symbols can be verified to exist during compilation and
2. Ensure that Windows-style DllImport and DllExport works with extern static variables.

What are my options here? Should I open a PR?
I've looked at builder_from_flags but this is also not part of the public API.

[alejnp]

Well, after writing this and reasoning with myself with some coffee, I think this flag would not help me whatsoever, because my extern "C" blocks are for extern static variables. I think there's simply not been a release yet. I'll be pinning my dependency as a git#commit to workaround this.

[alejnp]

I've actually gone back on my words after giving this a test run.

While the extern_fn_block_attrs can cover the first point (1: Ensure that the generated symbols can be verified to exist during compilation), it cannot work for the second point (2: Ensure that Windows-style DllImport and DllExport works with extern static variables).

The reasoning is simply that extern_fn_block_attrs is only used in the CodeGenerator impl for Function but not for Var. I've created a local fork and reused the pattern (and source) used in commit d5fc49c, and this has solved my issue.

diff --git a/bindgen-tests/tests/expectations/tests/extern-fn-block-attrs-static.rs b/bindgen-tests/tests/expectations/tests/extern-fn-block-attrs-static.rs
new file mode 100644
index 00000000..6d99f488
--- /dev/null
+++ b/bindgen-tests/tests/expectations/tests/extern-fn-block-attrs-static.rs
@@ -0,0 +1,9 @@
+#![allow(dead_code, non_snake_case, non_camel_case_types, non_upper_case_globals)]
+#[allow(dead_code)]
+unsafe extern "C" {
+    pub static mut test_var: ::std::os::raw::c_int;
+}
+#[allow(dead_code)]
+unsafe extern "C" {
+    pub static test_const_var: ::std::os::raw::c_int;
+}
diff --git a/bindgen-tests/tests/headers/extern-fn-block-attrs-static.h b/bindgen-tests/tests/headers/extern-fn-block-attrs-static.h
new file mode 100644
index 00000000..ec74d47b
--- /dev/null
+++ b/bindgen-tests/tests/headers/extern-fn-block-attrs-static.h
@@ -0,0 +1,4 @@
+// bindgen-flags: --extern-fn-block-attrs '#[allow(dead_code)]'
+
+extern int test_var;
+extern const int test_const_var;
diff --git a/bindgen/codegen/mod.rs b/bindgen/codegen/mod.rs
index 7a998c8f..de4ee4e7 100644
--- a/bindgen/codegen/mod.rs
+++ b/bindgen/codegen/mod.rs
@@ -844,6 +844,21 @@ impl CodeGenerator for Var {
                 }
             });
 
+            let mut block_attributes = quote! {};
+            // TODO: Use a new `extern_var_block_attrs`?
+            for attr in &ctx.options().extern_fn_block_attrs {
+                let parsed_attr = proc_macro2::TokenStream::from_str(attr).unwrap_or_else(
+                    |err| {
+                        panic!(
+                            "Error parsing extern static block attribute `{attr}`: {err}"
+                        )
+                    },
+                );
+                block_attributes.extend(quote! {
+                    #parsed_attr
+                });
+            }
+
             let maybe_mut = if self.is_const() {
                 quote! {}
             } else {
@@ -857,6 +872,7 @@ impl CodeGenerator for Var {
                 .then(|| quote!(unsafe));
 
             let tokens = quote!(
+                #block_attributes
                 #safety extern "C" {
                     #(#attrs)*
                     pub static #maybe_mut #canonical_ident: #ty;

@emilio Apologies for pinging you (moreso on May 1st, a national holiday in Spain) as I think you're a maintainer of this repository. Should I open a PR on this? Should we reuse the same BindgenOptions field or use a dedicated one? If choosing the former, should we rename the field itself? Fortunately, no tagged version has this symbol present at the moment.