Make MSVC detection ludicrously robust

src/librustc_trans/back/link.rs

@@ -136,14 +136,17 @@ pub fn build_link_meta<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     return r;
 }
 
-pub fn get_linker(sess: &Session) -> (String, Command) {
+// The third parameter is for an extra path to add to PATH for MSVC
+// cross linkers for host toolchain DLL dependencies
+pub fn get_linker(sess: &Session) -> (String, Command, Option<PathBuf>) {
     if let Some(ref linker) = sess.opts.cg.linker {
-        (linker.clone(), Command::new(linker))
+        (linker.clone(), Command::new(linker), None)
     } else if sess.target.target.options.is_like_msvc {
-        ("link.exe".to_string(), msvc::link_exe_cmd(sess))
+        let (cmd, host) = msvc::link_exe_cmd(sess);
+        ("link.exe".to_string(), cmd, host)
     } else {
         (sess.target.target.options.linker.clone(),
-         Command::new(&sess.target.target.options.linker))
+         Command::new(&sess.target.target.options.linker), None)
     }
 }
 
@@ -153,17 +156,15 @@ pub fn get_ar_prog(sess: &Session) -> String {
     })
 }
 
-fn command_path(sess: &Session) -> OsString {
+fn command_path(sess: &Session, extra: Option<PathBuf>) -> OsString {
     // The compiler's sysroot often has some bundled tools, so add it to the
     // PATH for the child.
     let mut new_path = sess.host_filesearch(PathKind::All)
                            .get_tools_search_paths();
     if let Some(path) = env::var_os("PATH") {
         new_path.extend(env::split_paths(&path));
     }
-    if sess.target.target.options.is_like_msvc {
-        new_path.extend(msvc::host_dll_path());
-    }
+    new_path.extend(extra);
     env::join_paths(new_path).unwrap()
 }
 
@@ -379,7 +380,7 @@ fn archive_config<'a>(sess: &'a Session,
         src: input.map(|p| p.to_path_buf()),
         lib_search_paths: archive_search_paths(sess),
         ar_prog: get_ar_prog(sess),
-        command_path: command_path(sess),
+        command_path: command_path(sess, None),
     }
 }
 
@@ -616,8 +617,8 @@ fn link_natively(sess: &Session,
     info!("preparing {:?} from {:?} to {:?}", crate_type, objects, out_filename);
 
     // The invocations of cc share some flags across platforms
-    let (pname, mut cmd) = get_linker(sess);
-    cmd.env("PATH", command_path(sess));
+    let (pname, mut cmd, extra) = get_linker(sess);
+    cmd.env("PATH", command_path(sess, extra));
 
     let root = sess.target_filesearch(PathKind::Native).get_lib_path();
     cmd.args(&sess.target.target.options.pre_link_args);
@@ -682,10 +683,15 @@ fn link_natively(sess: &Session,
             info!("linker stdout:\n{}", escape_string(&prog.stdout[..]));
         },
         Err(e) => {
-            // Trying to diagnose https://github.com/rust-lang/rust/issues/33844
             sess.struct_err(&format!("could not exec the linker `{}`: {}", pname, e))
                 .note(&format!("{:?}", &cmd))
                 .emit();
+            if sess.target.target.options.is_like_msvc && e.kind() == io::ErrorKind::NotFound {
+                sess.note_without_error("the msvc targets depend on the msvc linker \
+                    but `link.exe` was not found");
+                sess.note_without_error("please ensure that VS 2013 or VS 2015 was installed \
+                    with the Visual C++ option");
+            }
             sess.abort_if_errors();
         }
     }

src/librustc_trans/back/msvc/arch.rs

@@ -0,0 +1,56 @@
+// Copyright 2016 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.
+
+#![allow(non_camel_case_types, non_snake_case)]
+
+use libc::c_void;
+use std::mem;
+
+type DWORD = u32;
+type WORD = u16;
+type LPVOID = *mut c_void;
+type DWORD_PTR = usize;
+
+const PROCESSOR_ARCHITECTURE_INTEL: WORD = 0;
+const PROCESSOR_ARCHITECTURE_AMD64: WORD = 9;
+
+#[repr(C)]
+struct SYSTEM_INFO {
+    wProcessorArchitecture: WORD,
+    _wReserved: WORD,
+    _dwPageSize: DWORD,
+    _lpMinimumApplicationAddress: LPVOID,
+    _lpMaximumApplicationAddress: LPVOID,
+    _dwActiveProcessorMask: DWORD_PTR,
+    _dwNumberOfProcessors: DWORD,
+    _dwProcessorType: DWORD,
+    _dwAllocationGranularity: DWORD,
+    _wProcessorLevel: WORD,
+    _wProcessorRevision: WORD,
+}
+
+extern "system" {
+    fn GetNativeSystemInfo(lpSystemInfo: *mut SYSTEM_INFO);
+}
+
+pub enum Arch {
+    X86,
+    Amd64,
+}
+
+pub fn host_arch() -> Option<Arch> {
+    let mut info = unsafe { mem::zeroed() };
+    unsafe { GetNativeSystemInfo(&mut info) };
+    match info.wProcessorArchitecture {
+        PROCESSOR_ARCHITECTURE_INTEL => Some(Arch::X86),
+        PROCESSOR_ARCHITECTURE_AMD64 => Some(Arch::Amd64),
+        _ => None,
+    }
+}