Add JS linking via a separate feature

src/librustc/middle/cstore.rs

@@ -124,6 +124,7 @@ pub enum NativeLibraryKind {
     NativeStatic,    // native static library (.a archive)
     NativeStaticNobundle, // native static library, which doesn't get bundled into .rlibs
     NativeFramework, // macOS-specific
+    NativeJS, // Emscripten-specific
     NativeUnknown,   // default way to specify a dynamic library
 }
 

src/librustc/session/config.rs

@@ -1564,11 +1564,12 @@ pub fn build_session_options_and_crate_config(matches: &getopts::Matches)
         // Parse string of the form "[KIND=]lib[:new_name]",
         // where KIND is one of "dylib", "framework", "static".
         let mut parts = s.splitn(2, '=');
-        let kind = parts.next().unwrap();
-        let (name, kind) = match (parts.next(), kind) {
+        let kind_name = parts.next().unwrap();
+        let (name, kind) = match (parts.next(), kind_name) {
             (None, name) => (name, None),
             (Some(name), "dylib") => (name, Some(cstore::NativeUnknown)),
             (Some(name), "framework") => (name, Some(cstore::NativeFramework)),
+            (Some(name), "js") => (name, Some(cstore::NativeJS)),
             (Some(name), "static") => (name, Some(cstore::NativeStatic)),
             (Some(name), "static-nobundle") => (name, Some(cstore::NativeStaticNobundle)),
             (_, s) => {
@@ -1577,9 +1578,13 @@ pub fn build_session_options_and_crate_config(matches: &getopts::Matches)
                                                  s));
             }
         };
-        if kind == Some(cstore::NativeStaticNobundle) && !nightly_options::is_nightly_build() {
-            early_error(error_format, &format!("the library kind 'static-nobundle' is only \
-                                                accepted on the nightly compiler"));
+        match kind {
+            Some(cstore::NativeStaticNobundle) | Some(cstore::NativeJS)
+            if !nightly_options::is_nightly_build() => {
+                early_error(error_format, &format!("the library kind '{}' is only \
+                                                    accepted on the nightly compiler", kind_name));
+            }
+            _ => {}
         }
         let mut name_parts = name.splitn(2, ':');
         let name = name_parts.next().unwrap();

src/librustc_metadata/creader.rs

@@ -105,6 +105,22 @@ fn register_native_lib(sess: &Session,
             None => sess.err(msg),
         }
     }
+    if lib.kind == cstore::NativeJS {
+        if !sess.target.target.options.is_like_emscripten {
+            let msg = "JavaScript libraries are only available on Emscripten targets";
+            match span {
+                Some(span) => span_err!(sess, span, E0455, "{}", msg),
+                None => sess.err(msg),
+            }
+        }
+        if !sess.features.borrow().link_js {
+            feature_gate::emit_feature_err(&sess.parse_sess,
+                                        "link_js",
+                                        span.unwrap(),
+                                        GateIssue::Language,
+                                        "kind=\"js\" is feature gated");
+        }
+    }
     if lib.cfg.is_some() && !sess.features.borrow().link_cfg {
         feature_gate::emit_feature_err(&sess.parse_sess,
                                        "link_cfg",
@@ -1026,6 +1042,7 @@ impl<'a> CrateLoader<'a> {
                 Some("static-nobundle") => cstore::NativeStaticNobundle,
                 Some("dylib") => cstore::NativeUnknown,
                 Some("framework") => cstore::NativeFramework,
+                Some("js") => cstore::NativeJS,
                 Some(k) => {
                     struct_span_err!(self.sess, m.span, E0458,
                               "unknown kind: `{}`", k)

src/librustc_trans/back/link.rs

@@ -485,6 +485,7 @@ fn link_rlib<'a>(sess: &'a Session,
             NativeLibraryKind::NativeStatic => {}
             NativeLibraryKind::NativeStaticNobundle |
             NativeLibraryKind::NativeFramework |
+            NativeLibraryKind::NativeJS |
             NativeLibraryKind::NativeUnknown => continue,
         }
         ab.add_native_library(&lib.name.as_str());
@@ -683,6 +684,7 @@ fn link_staticlib(sess: &Session, objects: &[PathBuf], out_filename: &Path,
     for lib in all_native_libs.iter().filter(|l| relevant_lib(sess, l)) {
         let name = match lib.kind {
             NativeLibraryKind::NativeStaticNobundle |
+            NativeLibraryKind::NativeJS |
             NativeLibraryKind::NativeUnknown => "library",
             NativeLibraryKind::NativeFramework => "framework",
             // These are included, no need to print them
@@ -1035,6 +1037,7 @@ fn add_local_native_libraries(cmd: &mut Linker, sess: &Session) {
         match lib.kind {
             NativeLibraryKind::NativeUnknown => cmd.link_dylib(&lib.name.as_str()),
             NativeLibraryKind::NativeFramework => cmd.link_framework(&lib.name.as_str()),
+            NativeLibraryKind::NativeJS => cmd.link_js(&lib.name.as_str()),
             NativeLibraryKind::NativeStaticNobundle => cmd.link_staticlib(&lib.name.as_str()),
             NativeLibraryKind::NativeStatic => cmd.link_whole_staticlib(&lib.name.as_str(),
                                                                         &search_path)
@@ -1329,6 +1332,7 @@ fn add_upstream_native_libraries(cmd: &mut Linker, sess: &Session, crate_type: c
             }
             match lib.kind {
                 NativeLibraryKind::NativeUnknown => cmd.link_dylib(&lib.name.as_str()),
+                NativeLibraryKind::NativeJS => cmd.link_js(&lib.name.as_str()),
                 NativeLibraryKind::NativeFramework => cmd.link_framework(&lib.name.as_str()),
                 NativeLibraryKind::NativeStaticNobundle => {
                     // Link "static-nobundle" native libs only if the crate they originate from

src/librustc_trans/back/linker.rs

@@ -94,6 +94,7 @@ pub trait Linker {
     fn link_dylib(&mut self, lib: &str);
     fn link_rust_dylib(&mut self, lib: &str, path: &Path);
     fn link_framework(&mut self, framework: &str);
+    fn link_js(&mut self, lib: &str);
     fn link_staticlib(&mut self, lib: &str);
     fn link_rlib(&mut self, lib: &Path);
     fn link_whole_rlib(&mut self, lib: &Path);
@@ -187,6 +188,10 @@ impl<'a> Linker for GccLinker<'a> {
         self.cmd.arg("-framework").arg(framework);
     }
 
+    fn link_js(&mut self, _lib: &str) {
+        bug!("JS libraries are not supported on macOS")
+    }
+
     // Here we explicitly ask that the entire archive is included into the
     // result artifact. For more details see #15460, but the gist is that
     // the linker will strip away any unused objects in the archive if we
@@ -455,10 +460,15 @@ impl<'a> Linker for MsvcLinker<'a> {
     fn framework_path(&mut self, _path: &Path) {
         bug!("frameworks are not supported on windows")
     }
+
     fn link_framework(&mut self, _framework: &str) {
         bug!("frameworks are not supported on windows")
     }
 
+    fn link_js(&mut self, _lib: &str) {
+        bug!("JS libraries are not supported on windows")
+    }
+
     fn link_whole_staticlib(&mut self, lib: &str, _search_path: &[PathBuf]) {
         // not supported?
         self.link_staticlib(lib);
@@ -607,6 +617,10 @@ impl<'a> Linker for EmLinker<'a> {
         bug!("frameworks are not supported on Emscripten")
     }
 
+    fn link_js(&mut self, lib: &str) {
+        self.cmd.args(&["--js-library", lib]);
+    }
+
     fn gc_sections(&mut self, _keep_metadata: bool) {
         // noop
     }

src/libsyntax/feature_gate.rs

@@ -321,6 +321,9 @@ declare_features! (
     // Allows #[link(kind="static-nobundle"...]
     (active, static_nobundle, "1.16.0", Some(37403)),
 
+    // Allows #[link(kind="js"...)]
+    (active, link_js, "1.18.0", None),
+
     // `extern "msp430-interrupt" fn()`
     (active, abi_msp430_interrupt, "1.16.0", Some(38487)),
 

src/test/compile-fail/emscripten-libraries.rs

@@ -0,0 +1,20 @@
+// Copyright 2013-2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// ignore-asmjs
+// ignore-wasm32
+// ignore-wasm64
+
+#[link(name = "foo", kind = "js")]
+extern {}
+//~^^ ERROR: JavaScript libraries are only available on Emscripten
+
+fn main() {
+}