review feedback: find lib root path from registry

Author: mfkl

Cargo.lock

@@ -3126,6 +3126,7 @@ name = "rustc_target"
 version = "0.0.0"
 dependencies = [
  "bitflags 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc_data_structures 0.0.0",
  "serialize 0.0.0",

src/librustc_target/Cargo.toml

@@ -11,6 +11,7 @@ path = "lib.rs"
 [dependencies]
 bitflags = "1.0"
 log = "0.4"
+cc = "1.0.1"
 rustc_data_structures = { path = "../librustc_data_structures" }
 rustc_serialize = { path = "../libserialize", package = "serialize" }
 syntax_pos = { path = "../libsyntax_pos" }

src/librustc_target/spec/aarch64_uwp_windows_msvc.rs

@@ -1,5 +1,5 @@
 use crate::spec::{LinkerFlavor, Target, TargetResult, PanicStrategy};
-use std::env;
+use cc::windows_registry;
 
 pub fn target() -> TargetResult {
     let mut base = super::windows_uwp_msvc_base::opts();
@@ -9,8 +9,11 @@ pub fn target() -> TargetResult {
     // FIXME: this shouldn't be panic=abort, it should be panic=unwind
     base.panic_strategy = PanicStrategy::Abort;
 
-    let lib_root_path = env::var("VCToolsInstallDir")
-        .expect("VCToolsInstallDir not found in env");
+    let link_tool = windows_registry::find_tool("x86_64-pc-windows-msvc", "link.exe")
+        .expect("no path found for link.exe");
+
+    let original_path = link_tool.path();
+    let lib_root_path = original_path.ancestors().skip(4).next().unwrap().display();
 
     base.pre_link_args.get_mut(&LinkerFlavor::Msvc).unwrap()
         .push(format!("{}{}{}",

src/librustc_target/spec/i686_uwp_windows_msvc.rs

@@ -1,14 +1,17 @@
 use crate::spec::{LinkerFlavor, Target, TargetResult};
-use std::env;
+use cc::windows_registry;
 
 pub fn target() -> TargetResult {
     let mut base = super::windows_uwp_msvc_base::opts();
     base.cpu = "pentium4".to_string();
     base.max_atomic_width = Some(64);
     base.has_elf_tls = true;
 
-    let lib_root_path = env::var("VCToolsInstallDir")
-        .expect("VCToolsInstallDir not found in env");
+    let link_tool = windows_registry::find_tool("x86_64-pc-windows-msvc", "link.exe")
+        .expect("no path found for link.exe");
+
+    let original_path = link_tool.path();
+    let lib_root_path = original_path.ancestors().skip(4).next().unwrap().display();
 
     base.pre_link_args.get_mut(&LinkerFlavor::Msvc).unwrap()
             .push(format!("{}{}{}",

src/librustc_target/spec/x86_64_uwp_windows_msvc.rs

@@ -1,14 +1,17 @@
 use crate::spec::{LinkerFlavor, Target, TargetResult};
-use std::env;
+use cc::windows_registry;
 
 pub fn target() -> TargetResult {
     let mut base = super::windows_uwp_msvc_base::opts();
     base.cpu = "x86-64".to_string();
     base.max_atomic_width = Some(64);
     base.has_elf_tls = true;
 
-    let lib_root_path = env::var("VCToolsInstallDir")
-        .expect("VCToolsInstallDir not found in env");
+    let link_tool = windows_registry::find_tool("x86_64-pc-windows-msvc", "link.exe")
+        .expect("no path found for link.exe");
+
+    let original_path = link_tool.path();
+    let lib_root_path = original_path.ancestors().skip(4).next().unwrap().display();
 
     base.pre_link_args.get_mut(&LinkerFlavor::Msvc).unwrap()
             .push(format!("{}{}{}",