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.

18 files changed, 18 insertions, 44 deletions

diff --git a/src/librustc_back/lib.rs b/src/librustc_back/lib.rs
index 141c8954a33..9de56cca339 100644
--- a/src/librustc_back/lib.rs
+++ b/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)]
diff --git a/src/librustc_back/target/aarch64_unknown_cloudabi.rs b/src/librustc_back/target/aarch64_unknown_cloudabi.rs
index 59c82e06a67..a5d0e5bf166 100644
--- a/src/librustc_back/target/aarch64_unknown_cloudabi.rs
+++ b/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(),
diff --git a/src/librustc_back/target/armv7_unknown_cloudabi_eabihf.rs b/src/librustc_back/target/armv7_unknown_cloudabi_eabihf.rs
index faa2c4fdceb..fa66a35abbf 100644
--- a/src/librustc_back/target/armv7_unknown_cloudabi_eabihf.rs
+++ b/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(),
diff --git a/src/librustc_back/target/asmjs_unknown_emscripten.rs b/src/librustc_back/target/asmjs_unknown_emscripten.rs
index 5d9f0f6012b..f114926740a 100644
--- a/src/librustc_back/target/asmjs_unknown_emscripten.rs
+++ b/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(),
diff --git a/src/librustc_back/target/emscripten_base.rs b/src/librustc_back/target/emscripten_base.rs
deleted file mode 100644
index bacada3f5ab..00000000000
--- a/src/librustc_back/target/emscripten_base.rs
+++ /dev/null
@@ -1,17 +0,0 @@
-// Copyright 2014-2015 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.
-
-pub fn cmd(name: &str) -> String {
-    if cfg!(windows) {
-        format!("{}.bat", name)
-    } else {
-        name.to_string()
-    }
-}
diff --git a/src/librustc_back/target/haiku_base.rs b/src/librustc_back/target/haiku_base.rs
index 112f424f7a8..a1ccb632cab 100644
--- a/src/librustc_back/target/haiku_base.rs
+++ b/src/librustc_back/target/haiku_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,
diff --git a/src/librustc_back/target/i686_unknown_cloudabi.rs b/src/librustc_back/target/i686_unknown_cloudabi.rs
index e244f443d3e..69c3b298cab 100644
--- a/src/librustc_back/target/i686_unknown_cloudabi.rs
+++ b/src/librustc_back/target/i686_unknown_cloudabi.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;
 
diff --git a/src/librustc_back/target/l4re_base.rs b/src/librustc_back/target/l4re_base.rs
index 31d428d2668..7cb7f8d613d 100644
--- a/src/librustc_back/target/l4re_base.rs
+++ b/src/librustc_back/target/l4re_base.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()),
diff --git a/src/librustc_back/target/mod.rs b/src/librustc_back/target/mod.rs
index be69127d8f2..0a3e1826f3a 100644
--- a/src/librustc_back/target/mod.rs
+++ b/src/librustc_back/target/mod.rs
@@ -58,7 +58,6 @@ mod arm_base;
 mod bitrig_base;
 mod cloudabi_base;
 mod dragonfly_base;
-mod emscripten_base;
 mod freebsd_base;
 mod haiku_base;
 mod linux_base;
@@ -279,8 +278,8 @@ pub struct TargetOptions {
     /// Whether the target is built-in or loaded from a custom target specification.
     pub is_builtin: bool,
 
-    /// Linker to invoke. Defaults to "cc".
-    pub linker: String,
+    /// Linker to invoke
+    pub linker: Option<String>,
 
     /// Linker arguments that are unconditionally passed *before* any
     /// user-defined libraries.
@@ -482,7 +481,7 @@ impl Default for TargetOptions {
     fn default() -> TargetOptions {
         TargetOptions {
             is_builtin: false,
-            linker: option_env!("CFG_DEFAULT_LINKER").unwrap_or("cc").to_string(),
+            linker: option_env!("CFG_DEFAULT_LINKER").map(|s| s.to_string()),
             pre_link_args: LinkArgs::new(),
             post_link_args: LinkArgs::new(),
             asm_args: Vec::new(),
@@ -732,7 +731,7 @@ impl Target {
         }
 
         key!(is_builtin, bool);
-        key!(linker);
+        key!(linker, optional);
         key!(pre_link_args, link_args);
         key!(pre_link_objects_exe, list);
         key!(pre_link_objects_dll, list);
diff --git a/src/librustc_back/target/msp430_none_elf.rs b/src/librustc_back/target/msp430_none_elf.rs
index 966df897f01..d0f512ae47c 100644
--- a/src/librustc_back/target/msp430_none_elf.rs
+++ b/src/librustc_back/target/msp430_none_elf.rs
@@ -32,7 +32,7 @@ pub fn target() -> TargetResult {
             // to gcc to get object files. For this reason we have a hard
             // dependency on this specific gcc.
             asm_args: vec!["-mcpu=msp430".to_string()],
-            linker: "msp430-elf-gcc".to_string(),
+            linker: Some("msp430-elf-gcc".to_string()),
             no_integrated_as: true,
 
             // There are no atomic instructions available in the MSP430
diff --git a/src/librustc_back/target/thumb_base.rs b/src/librustc_back/target/thumb_base.rs
index 6bb496649a8..6a8f52f5093 100644
--- a/src/librustc_back/target/thumb_base.rs
+++ b/src/librustc_back/target/thumb_base.rs
@@ -45,7 +45,7 @@ pub fn opts() -> TargetOptions {
         executables: true,
         // In 99%+ of cases, we want to use the `arm-none-eabi-gcc` compiler (there aren't many
         // options around)
-        linker: "arm-none-eabi-gcc".to_string(),
+        linker: Some("arm-none-eabi-gcc".to_string()),
         // Because these devices have very little resources having an unwinder is too onerous so we
         // default to "abort" because the "unwind" strategy is very rare.
         panic_strategy: PanicStrategy::Abort,
diff --git a/src/librustc_back/target/wasm32_experimental_emscripten.rs b/src/librustc_back/target/wasm32_experimental_emscripten.rs
index a261c982b3f..13dee3a5768 100644
--- a/src/librustc_back/target/wasm32_experimental_emscripten.rs
+++ b/src/librustc_back/target/wasm32_experimental_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 post_link_args = LinkArgs::new();
@@ -24,8 +23,6 @@ pub fn target() -> Result<Target, String> {
                                "-g3".to_string()]);
 
     let opts = TargetOptions {
-        linker: cmd("emcc"),
-
         dynamic_linking: false,
         executables: true,
         // Today emcc emits two files - a .js file to bootstrap and
diff --git a/src/librustc_back/target/wasm32_unknown_emscripten.rs b/src/librustc_back/target/wasm32_unknown_emscripten.rs
index 4823541f226..2770e67e30a 100644
--- a/src/librustc_back/target/wasm32_unknown_emscripten.rs
+++ b/src/librustc_back/target/wasm32_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 post_link_args = LinkArgs::new();
@@ -21,8 +20,6 @@ pub fn target() -> Result<Target, String> {
                                "ERROR_ON_UNDEFINED_SYMBOLS=1".to_string()]);
 
     let opts = TargetOptions {
-        linker: cmd("emcc"),
-
         dynamic_linking: false,
         executables: true,
         // Today emcc emits two files - a .js file to bootstrap and
diff --git a/src/librustc_back/target/wasm32_unknown_unknown.rs b/src/librustc_back/target/wasm32_unknown_unknown.rs
index c771762cfc8..1d84e137517 100644
--- a/src/librustc_back/target/wasm32_unknown_unknown.rs
+++ b/src/librustc_back/target/wasm32_unknown_unknown.rs
@@ -22,8 +22,6 @@ use super::{Target, TargetOptions, PanicStrategy};
 
 pub fn target() -> Result<Target, String> {
     let opts = TargetOptions {
-        linker: "lld".to_string(),
-
         // we allow dynamic linking, but only cdylibs. Basically we allow a
         // final library artifact that exports some symbols (a wasm module) but
         // we don't allow intermediate `dylib` crate types
diff --git a/src/librustc_back/target/windows_base.rs b/src/librustc_back/target/windows_base.rs
index 30038400f6c..05b6247c951 100644
--- a/src/librustc_back/target/windows_base.rs
+++ b/src/librustc_back/target/windows_base.rs
@@ -75,7 +75,7 @@ pub fn opts() -> TargetOptions {
     TargetOptions {
         // FIXME(#13846) this should be enabled for windows
         function_sections: false,
-        linker: "gcc".to_string(),
+        linker: Some("gcc".to_string()),
         dynamic_linking: true,
         executables: true,
         dll_prefix: "".to_string(),
diff --git a/src/librustc_back/target/windows_msvc_base.rs b/src/librustc_back/target/windows_msvc_base.rs
index e0bf36ee407..34aa17267f8 100644
--- a/src/librustc_back/target/windows_msvc_base.rs
+++ b/src/librustc_back/target/windows_msvc_base.rs
@@ -20,7 +20,6 @@ pub fn opts() -> TargetOptions {
 
     TargetOptions {
         function_sections: true,
-        linker: "link.exe".to_string(),
         dynamic_linking: true,
         executables: true,
         dll_prefix: "".to_string(),
diff --git a/src/librustc_back/target/x86_64_rumprun_netbsd.rs b/src/librustc_back/target/x86_64_rumprun_netbsd.rs
index 18f6380b6ee..3158665a2e2 100644
--- a/src/librustc_back/target/x86_64_rumprun_netbsd.rs
+++ b/src/librustc_back/target/x86_64_rumprun_netbsd.rs
@@ -15,7 +15,7 @@ pub fn target() -> TargetResult {
     let mut base = super::netbsd_base::opts();
     base.cpu = "x86-64".to_string();
     base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-m64".to_string());
-    base.linker = "x86_64-rumprun-netbsd-gcc".to_string();
+    base.linker = Some("x86_64-rumprun-netbsd-gcc".to_string());
     base.max_atomic_width = Some(64);
 
     base.dynamic_linking = false;
diff --git a/src/librustc_back/target/x86_64_unknown_cloudabi.rs b/src/librustc_back/target/x86_64_unknown_cloudabi.rs
index 1ce3c6444f1..d1a9cb1cd7e 100644
--- a/src/librustc_back/target/x86_64_unknown_cloudabi.rs
+++ b/src/librustc_back/target/x86_64_unknown_cloudabi.rs
@@ -15,7 +15,7 @@ pub fn target() -> TargetResult {
     let mut base = super::cloudabi_base::opts();
     base.cpu = "x86-64".to_string();
     base.max_atomic_width = Some(64);
-    base.linker = "x86_64-unknown-cloudabi-cc".to_string();
+    base.linker = Some("x86_64-unknown-cloudabi-cc".to_string());
     base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-m64".to_string());
     base.stack_probes = true;