Allow writing metadata without llvm

src/librustc_trans_utils/Cargo.toml

@@ -10,6 +10,8 @@ crate-type = ["dylib"]
 test = false
 
 [dependencies]
+log = "0.3"
 rustc = { path = "../librustc" }
+rustc_incremental = { path = "../librustc_incremental" }
 syntax = { path = "../libsyntax" }
 syntax_pos = { path = "../libsyntax_pos" }

src/librustc_trans_utils/lib.rs

@@ -29,8 +29,68 @@
 
 #![cfg_attr(stage0, feature(const_fn))]
 
+#[macro_use]
+extern crate log;
 extern crate rustc;
+extern crate rustc_incremental;
 extern crate syntax;
 extern crate syntax_pos;
 
+use rustc::ty::TyCtxt;
+use rustc::hir;
+use rustc::hir::map as hir_map;
+use rustc::util::nodemap::NodeSet;
+
+use syntax::attr;
+
 pub mod link;
+
+/// The context provided lists a set of reachable ids as calculated by
+/// middle::reachable, but this contains far more ids and symbols than we're
+/// actually exposing from the object file. This function will filter the set in
+/// the context to the set of ids which correspond to symbols that are exposed
+/// from the object file being generated.
+///
+/// This list is later used by linkers to determine the set of symbols needed to
+/// be exposed from a dynamic library and it's also encoded into the metadata.
+pub fn find_exported_symbols(tcx: TyCtxt, reachable: &NodeSet) -> NodeSet {
+    reachable.iter().cloned().filter(|&id| {
+        // Next, we want to ignore some FFI functions that are not exposed from
+        // this crate. Reachable FFI functions can be lumped into two
+        // categories:
+        //
+        // 1. Those that are included statically via a static library
+        // 2. Those included otherwise (e.g. dynamically or via a framework)
+        //
+        // Although our LLVM module is not literally emitting code for the
+        // statically included symbols, it's an export of our library which
+        // needs to be passed on to the linker and encoded in the metadata.
+        //
+        // As a result, if this id is an FFI item (foreign item) then we only
+        // let it through if it's included statically.
+        match tcx.hir.get(id) {
+            hir_map::NodeForeignItem(..) => {
+                let def_id = tcx.hir.local_def_id(id);
+                tcx.sess.cstore.is_statically_included_foreign_item(def_id)
+            }
+
+            // Only consider nodes that actually have exported symbols.
+            hir_map::NodeItem(&hir::Item {
+                node: hir::ItemStatic(..), .. }) |
+            hir_map::NodeItem(&hir::Item {
+                node: hir::ItemFn(..), .. }) |
+            hir_map::NodeImplItem(&hir::ImplItem {
+                node: hir::ImplItemKind::Method(..), .. }) => {
+                let def_id = tcx.hir.local_def_id(id);
+                let generics = tcx.generics_of(def_id);
+                let attributes = tcx.get_attrs(def_id);
+                (generics.parent_types == 0 && generics.types.is_empty()) &&
+                // Functions marked with #[inline] are only ever translated
+                // with "internal" linkage and are never exported.
+                !attr::requests_inline(&attributes)
+            }
+
+            _ => false
+        }
+    }).collect()
+}

src/librustc_trans_utils/link.rs

@@ -10,11 +10,23 @@
 
 use rustc::session::config::{self, OutputFilenames, Input, OutputType};
 use rustc::session::Session;
-use rustc::middle::cstore;
+use rustc::middle::cstore::{self, LinkMeta};
+use rustc::dep_graph::{DepKind, DepNode};
+use rustc::hir::svh::Svh;
+use rustc_incremental::IncrementalHashesMap;
 use std::path::PathBuf;
 use syntax::ast;
 use syntax_pos::Span;
 
+pub fn build_link_meta(incremental_hashes_map: &IncrementalHashesMap) -> LinkMeta {
+    let krate_dep_node = &DepNode::new_no_params(DepKind::Krate);
+    let r = LinkMeta {
+        crate_hash: Svh::new(incremental_hashes_map[krate_dep_node].to_smaller_hash()),
+    };
+    info!("{:?}", r);
+    return r;
+}
+
 pub fn find_crate_name(sess: Option<&Session>,
                        attrs: &[ast::Attribute],
                        input: &Input) -> String {