rustc: Tweak default linker selection

This commit refactors how the path to the linker that we're going to invoke is
selected. Previously all targets listed *both* a `LinkerFlavor` and a `linker`
(path) option, but this meant that whenever you changed one you had to change
the other. The purpose of this commit is to avoid coupling these where possible.

Target specifications now only unconditionally define the *flavor* of the linker
that they're using by default. If not otherwise specified each flavor now
implies a particular default linker to run. As a result, this means that if
you'd like to test out `ld` for example you should be able to do:

    rustc -Z linker-flavor=ld foo.rs

whereas previously you had to do

    rustc -Z linker-flavor=ld -C linker=ld foo.rs

This will hopefully make it a bit easier to tinker around with variants that
should otherwise be well known to work, for example with LLD, `ld` on OSX, etc.

Author: alexcrichton

src/bootstrap/dist.rs

@@ -606,8 +606,10 @@ impl Step for Std {
         let mut src = builder.sysroot_libdir(compiler, target).to_path_buf();
         src.pop(); // Remove the trailing /lib folder from the sysroot_libdir
         cp_filtered(&src, &dst, &|path| {
-            path.file_name().and_then(|s| s.to_str()) !=
-                Some(build.config.rust_codegen_backends_dir.as_str())
+            let name = path.file_name().and_then(|s| s.to_str());
+            name != Some(build.config.rust_codegen_backends_dir.as_str()) &&
+                name != Some("bin")
+
         });
 
         let mut cmd = rust_installer(builder);

src/bootstrap/native.rs

@@ -208,7 +208,7 @@ impl Step for Llvm {
             cfg.define("LLVM_NATIVE_BUILD", build.llvm_out(build.build).join("build"));
         }
 
-        configure_cmake(build, target, &mut cfg);
+        configure_cmake(build, target, &mut cfg, false);
 
         // FIXME: we don't actually need to build all LLVM tools and all LLVM
         //        libraries here, e.g. we just want a few components and a few
@@ -241,7 +241,8 @@ fn check_llvm_version(build: &Build, llvm_config: &Path) {
 
 fn configure_cmake(build: &Build,
                    target: Interned<String>,
-                   cfg: &mut cmake::Config) {
+                   cfg: &mut cmake::Config,
+                   building_dist_binaries: bool) {
     if build.config.ninja {
         cfg.generator("Ninja");
     }
@@ -294,8 +295,10 @@ fn configure_cmake(build: &Build,
     cfg.build_arg("-j").build_arg(build.jobs().to_string());
     cfg.define("CMAKE_C_FLAGS", build.cflags(target).join(" "));
     let mut cxxflags = build.cflags(target).join(" ");
-    if build.config.llvm_static_stdcpp && !target.contains("windows") {
-        cxxflags.push_str(" -static-libstdc++");
+    if building_dist_binaries {
+        if build.config.llvm_static_stdcpp && !target.contains("windows") {
+            cxxflags.push_str(" -static-libstdc++");
+        }
     }
     cfg.define("CMAKE_CXX_FLAGS", cxxflags);
     if let Some(ar) = build.ar(target) {
@@ -350,7 +353,7 @@ impl Step for Lld {
         t!(fs::create_dir_all(&out_dir));
 
         let mut cfg = cmake::Config::new(build.src.join("src/tools/lld"));
-        configure_cmake(build, target, &mut cfg);
+        configure_cmake(build, target, &mut cfg, true);
 
         cfg.out_dir(&out_dir)
            .profile("Release")

src/librustc_back/lib.rs

@@ -57,6 +57,9 @@ pub enum LinkerFlavor {
          RustcEncodable, RustcDecodable)]
 pub enum LldFlavor {
     Wasm,
+    Ld64,
+    Ld,
+    Link,
 }
 
 impl ToJson for LinkerFlavor {
@@ -94,6 +97,9 @@ flavor_mappings! {
     ((LinkerFlavor::Ld), "ld"),
     ((LinkerFlavor::Msvc), "msvc"),
     ((LinkerFlavor::Lld(LldFlavor::Wasm)), "wasm-ld"),
+    ((LinkerFlavor::Lld(LldFlavor::Ld64)), "ld64.lld"),
+    ((LinkerFlavor::Lld(LldFlavor::Ld)), "ld.lld"),
+    ((LinkerFlavor::Lld(LldFlavor::Link)), "lld-link"),
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Hash, RustcEncodable, RustcDecodable)]

src/librustc_back/target/aarch64_unknown_cloudabi.rs

@@ -15,7 +15,7 @@ pub fn target() -> TargetResult {
     let mut base = super::cloudabi_base::opts();
     base.max_atomic_width = Some(128);
     base.abi_blacklist = super::arm_base::abi_blacklist();
-    base.linker = "aarch64-unknown-cloudabi-cc".to_string();
+    base.linker = Some("aarch64-unknown-cloudabi-cc".to_string());
 
     Ok(Target {
         llvm_target: "aarch64-unknown-cloudabi".to_string(),

src/librustc_back/target/armv7_unknown_cloudabi_eabihf.rs

@@ -17,7 +17,7 @@ pub fn target() -> TargetResult {
     base.max_atomic_width = Some(64);
     base.features = "+v7,+vfp3,+neon".to_string();
     base.abi_blacklist = super::arm_base::abi_blacklist();
-    base.linker = "armv7-unknown-cloudabi-eabihf-cc".to_string();
+    base.linker = Some("armv7-unknown-cloudabi-eabihf-cc".to_string());
 
     Ok(Target {
         llvm_target: "armv7-unknown-cloudabi-eabihf".to_string(),

src/librustc_back/target/asmjs_unknown_emscripten.rs

@@ -10,7 +10,6 @@
 
 use LinkerFlavor;
 use super::{LinkArgs, Target, TargetOptions};
-use super::emscripten_base::{cmd};
 
 pub fn target() -> Result<Target, String> {
     let mut args = LinkArgs::new();
@@ -19,8 +18,6 @@ pub fn target() -> Result<Target, String> {
                      "ERROR_ON_UNDEFINED_SYMBOLS=1".to_string()]);
 
     let opts = TargetOptions {
-        linker: cmd("emcc"),
-
         dynamic_linking: false,
         executables: true,
         exe_suffix: ".js".to_string(),

src/librustc_back/target/emscripten_base.rs

@@ -13,7 +13,6 @@ use std::default::Default;
 
 pub fn opts() -> TargetOptions {
     TargetOptions {
-        linker: "cc".to_string(),
         dynamic_linking: true,
         executables: true,
         has_rpath: false,

src/librustc_back/target/haiku_base.rs

@@ -15,7 +15,7 @@ pub fn target() -> TargetResult {
     let mut base = super::cloudabi_base::opts();
     base.cpu = "pentium4".to_string();
     base.max_atomic_width = Some(64);
-    base.linker = "i686-unknown-cloudabi-cc".to_string();
+    base.linker = Some("i686-unknown-cloudabi-cc".to_string());
     base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-m32".to_string());
     base.stack_probes = true;
 

src/librustc_back/target/i686_unknown_cloudabi.rs

@@ -73,7 +73,6 @@ pub fn opts() -> Result<TargetOptions, String> {
         has_elf_tls: false,
         exe_allocation_crate: None,
         panic_strategy: PanicStrategy::Abort,
-        linker: "ld".to_string(),
         pre_link_args,
         post_link_args,
         target_family: Some("unix".to_string()),