Remove env vars instead of setting them to an empty string

src/librustc_codegen_ssa/back/command.rs

@@ -14,6 +14,7 @@ pub struct Command {
     program: Program,
     args: Vec<OsString>,
     env: Vec<(OsString, OsString)>,
+    env_remove: Vec<OsString>,
 }
 
 #[derive(Clone)]
@@ -41,6 +42,7 @@ impl Command {
             program,
             args: Vec::new(),
             env: Vec::new(),
+            env_remove: Vec::new(),
         }
     }
 
@@ -75,6 +77,17 @@ impl Command {
         self.env.push((key.to_owned(), value.to_owned()));
     }
 
+    pub fn env_remove<K>(&mut self, key: K) -> &mut Command
+        where K: AsRef<OsStr>,
+    {
+        self._env_remove(key.as_ref());
+        self
+    }
+
+    fn _env_remove(&mut self, key: &OsStr) {
+        self.env_remove.push(key.to_owned());
+    }
+
     pub fn output(&mut self) -> io::Result<Output> {
         self.command().output()
     }
@@ -100,6 +113,9 @@ impl Command {
         };
         ret.args(&self.args);
         ret.envs(self.env.clone());
+        for k in &self.env_remove {
+            ret.env_remove(k);
+        }
         return ret
     }
 

src/librustc_codegen_ssa/back/link.rs

@@ -532,6 +532,9 @@ fn link_natively<'a, B: ArchiveBuilder<'a>>(sess: &'a Session,
     for &(ref k, ref v) in &sess.target.target.options.link_env {
         cmd.env(k, v);
     }
+    for k in &sess.target.target.options.link_env_remove {
+        cmd.env_remove(k);
+    }
 
     if sess.opts.debugging_opts.print_link_args {
         println!("{:?}", &cmd);

src/librustc_target/spec/apple_base.rs

@@ -52,18 +52,18 @@ pub fn macos_llvm_target(arch: &str) -> String {
     format!("{}-apple-macosx{}.{}.0", arch, major, minor)
 }
 
-pub fn macos_link_env() -> Vec<(String, String)> {
-    let mut env = Vec::with_capacity(2);
-    // Ignore the `SDKROOT` environment variable if it's clearly set for the wrong platform, which
+pub fn macos_link_env_remove() -> Vec<String> {
+    let mut env_remove = Vec::with_capacity(2);
+    // Remove the `SDKROOT` environment variable if it's clearly set for the wrong platform, which
     // may occur when we're linking a custom build script while targeting iOS for example.
     if let Some(sdkroot) = env::var("SDKROOT").ok() {
         if sdkroot.contains("iPhoneOS.platform") || sdkroot.contains("iPhoneSimulator.platform") {
-            env.push(("SDKROOT".to_string(), String::new()))
+            env_remove.push("SDKROOT".to_string())
         }
     }
     // Additionally, `IPHONEOS_DEPLOYMENT_TARGET` must not be set when using the Xcode linker at
     // "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld",
     // although this is apparently ignored when using the linker at "/usr/bin/ld".
-    env.push(("IPHONEOS_DEPLOYMENT_TARGET".to_string(), String::new()));
-    env
+    env_remove.push("IPHONEOS_DEPLOYMENT_TARGET".to_string());
+    env_remove
 }

src/librustc_target/spec/i686_apple_darwin.rs

@@ -5,7 +5,7 @@ pub fn target() -> TargetResult {
     base.cpu = "yonah".to_string();
     base.max_atomic_width = Some(64);
     base.pre_link_args.insert(LinkerFlavor::Gcc, vec!["-m32".to_string()]);
-    base.link_env.extend(super::apple_base::macos_link_env());
+    base.link_env_remove.extend(super::apple_base::macos_link_env_remove());
     base.stack_probes = true;
     base.eliminate_frame_pointer = false;
 

src/librustc_target/spec/mod.rs

@@ -580,8 +580,10 @@ pub struct TargetOptions {
     /// user-defined libraries.
     pub post_link_args: LinkArgs,
 
-    /// Environment variables to be set before invoking the linker.
+    /// Environment variables to be set for the linker invocation.
     pub link_env: Vec<(String, String)>,
+    /// Environment variables to be removed for the linker invocation.
+    pub link_env_remove: Vec<String>,
 
     /// Extra arguments to pass to the external assembler (when used)
     pub asm_args: Vec<String>,
@@ -843,6 +845,7 @@ impl Default for TargetOptions {
             post_link_objects_crt: Vec::new(),
             late_link_args: LinkArgs::new(),
             link_env: Vec::new(),
+            link_env_remove: Vec::new(),
             archive_format: "gnu".to_string(),
             custom_unwind_resume: false,
             allow_asm: true,
@@ -1118,6 +1121,7 @@ impl Target {
         key!(post_link_objects_crt, list);
         key!(post_link_args, link_args);
         key!(link_env, env);
+        key!(link_env_remove, list);
         key!(asm_args, list);
         key!(cpu);
         key!(features);
@@ -1334,6 +1338,7 @@ impl ToJson for Target {
         target_option_val!(post_link_objects_crt);
         target_option_val!(link_args - post_link_args);
         target_option_val!(env - link_env);
+        target_option_val!(link_env_remove);
         target_option_val!(asm_args);
         target_option_val!(cpu);
         target_option_val!(features);

src/librustc_target/spec/x86_64_apple_darwin.rs

@@ -6,7 +6,7 @@ pub fn target() -> TargetResult {
     base.max_atomic_width = Some(128); // core2 support cmpxchg16b
     base.eliminate_frame_pointer = false;
     base.pre_link_args.insert(LinkerFlavor::Gcc, vec!["-m64".to_string()]);
-    base.link_env.extend(super::apple_base::macos_link_env());
+    base.link_env_remove.extend(super::apple_base::macos_link_env_remove());
     base.stack_probes = true;
 
     // Clang automatically chooses a more specific target based on