diff --git a/src/bootstrap/check.rs b/src/bootstrap/check.rs
index dd2a64402b46f..8838cdeed8687 100644
--- a/src/bootstrap/check.rs
+++ b/src/bootstrap/check.rs
@@ -12,7 +12,7 @@
 
 use compile::{run_cargo, std_cargo, test_cargo, rustc_cargo, rustc_cargo_env, add_to_sysroot};
 use builder::{RunConfig, Builder, ShouldRun, Step};
-use tool::{self, prepare_tool_cargo};
+use tool::{self, prepare_tool_cargo, SourceType};
 use {Compiler, Mode};
 use cache::{INTERNER, Interned};
 use std::path::PathBuf;
@@ -223,7 +223,7 @@ impl Step for Rustdoc {
                                            target,
                                            "check",
                                            "src/tools/rustdoc",
-                                           false);
+                                           SourceType::InTree);
 
         let _folder = builder.fold_output(|| format!("stage{}-rustdoc", compiler.stage));
         println!("Checking rustdoc artifacts ({} -> {})", &compiler.host, target);
diff --git a/src/bootstrap/doc.rs b/src/bootstrap/doc.rs
index 913b8162a44bf..fd3730ffc78de 100644
--- a/src/bootstrap/doc.rs
+++ b/src/bootstrap/doc.rs
@@ -28,7 +28,7 @@ use build_helper::up_to_date;
 
 use util::symlink_dir;
 use builder::{Builder, Compiler, RunConfig, ShouldRun, Step};
-use tool::{self, prepare_tool_cargo, Tool};
+use tool::{self, prepare_tool_cargo, Tool, SourceType};
 use compile;
 use cache::{INTERNER, Interned};
 use config::Config;
@@ -814,7 +814,7 @@ impl Step for Rustdoc {
             target,
             "doc",
             "src/tools/rustdoc",
-            false
+            SourceType::InTree,
         );
 
         cargo.env("RUSTDOCFLAGS", "--document-private-items");
diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index 6cb70deb86c74..7c69197885cf2 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -30,7 +30,7 @@ use compile;
 use dist;
 use flags::Subcommand;
 use native;
-use tool::{self, Tool};
+use tool::{self, Tool, SourceType};
 use toolstate::ToolState;
 use util::{self, dylib_path, dylib_path_var};
 use Crate as CargoCrate;
@@ -228,7 +228,7 @@ impl Step for Cargo {
                                                  self.host,
                                                  "test",
                                                  "src/tools/cargo",
-                                                 true);
+                                                 SourceType::Submodule);
 
         if !builder.fail_fast {
             cargo.arg("--no-fail-fast");
@@ -288,7 +288,7 @@ impl Step for Rls {
                                                  host,
                                                  "test",
                                                  "src/tools/rls",
-                                                 true);
+                                                 SourceType::Submodule);
 
         builder.add_rustc_lib_path(compiler, &mut cargo);
 
@@ -341,7 +341,7 @@ impl Step for Rustfmt {
                                                  host,
                                                  "test",
                                                  "src/tools/rustfmt",
-                                                 true);
+                                                 SourceType::Submodule);
 
         let dir = testdir(builder, compiler.host);
         t!(fs::create_dir_all(&dir));
@@ -396,7 +396,7 @@ impl Step for Miri {
                                                  host,
                                                  "test",
                                                  "src/tools/miri",
-                                                 true);
+                                                 SourceType::Submodule);
 
             // miri tests need to know about the stage sysroot
             cargo.env("MIRI_SYSROOT", builder.sysroot(compiler));
@@ -455,7 +455,7 @@ impl Step for Clippy {
                                                  host,
                                                  "test",
                                                  "src/tools/clippy",
-                                                 true);
+                                                 SourceType::Submodule);
 
             // clippy tests need to know about the stage sysroot
             cargo.env("SYSROOT", builder.sysroot(compiler));
@@ -1740,7 +1740,7 @@ impl Step for CrateRustdoc {
                                                  target,
                                                  test_kind.subcommand(),
                                                  "src/tools/rustdoc",
-                                                 false);
+                                                 SourceType::InTree);
         if test_kind.subcommand() == "test" && !builder.fail_fast {
             cargo.arg("--no-fail-fast");
         }
diff --git a/src/bootstrap/tool.rs b/src/bootstrap/tool.rs
index 7301c59b0fae1..5e68b797b3d54 100644
--- a/src/bootstrap/tool.rs
+++ b/src/bootstrap/tool.rs
@@ -75,6 +75,12 @@ impl Step for CleanTools {
     }
 }
 
+#[derive(Debug, Clone, Hash, PartialEq, Eq)]
+pub enum SourceType {
+    InTree,
+    Submodule,
+}
+
 #[derive(Debug, Clone, Hash, PartialEq, Eq)]
 struct ToolBuild {
     compiler: Compiler,
@@ -83,7 +89,7 @@ struct ToolBuild {
     path: &'static str,
     mode: Mode,
     is_optional_tool: bool,
-    is_external_tool: bool,
+    source_type: SourceType,
     extra_features: Vec<String>,
 }
 
@@ -123,7 +129,7 @@ impl Step for ToolBuild {
             target,
             "build",
             path,
-            self.is_external_tool,
+            self.source_type,
         );
         cargo.arg("--features").arg(self.extra_features.join(" "));
 
@@ -247,7 +253,7 @@ pub fn prepare_tool_cargo(
     target: Interned<String>,
     command: &'static str,
     path: &'static str,
-    is_external_tool: bool,
+    source_type: SourceType,
 ) -> Command {
     let mut cargo = builder.cargo(compiler, mode, target, command);
     let dir = builder.src.join(path);
@@ -257,7 +263,7 @@ pub fn prepare_tool_cargo(
     // stages and such and it's just easier if they're not dynamically linked.
     cargo.env("RUSTC_NO_PREFER_DYNAMIC", "1");
 
-    if is_external_tool {
+    if source_type == SourceType::Submodule {
         cargo.env("RUSTC_EXTERNAL_TOOL", "1");
     }
 
@@ -289,7 +295,7 @@ pub fn prepare_tool_cargo(
 
 macro_rules! tool {
     ($($name:ident, $path:expr, $tool_name:expr, $mode:expr
-        $(,llvm_tools = $llvm:expr)* $(,external_tool = $external:expr)*;)+) => {
+        $(,llvm_tools = $llvm:expr)* $(,is_external_tool = $external:expr)*;)+) => {
         #[derive(Copy, PartialEq, Eq, Clone)]
         pub enum Tool {
             $(
@@ -367,7 +373,11 @@ macro_rules! tool {
                     mode: $mode,
                     path: $path,
                     is_optional_tool: false,
-                    is_external_tool: false $(|| $external)*,
+                    source_type: if false $(|| $external)* {
+                        SourceType::Submodule
+                    } else {
+                        SourceType::InTree
+                    },
                     extra_features: Vec::new(),
                 }).expect("expected to build -- essential tool")
             }
@@ -387,7 +397,7 @@ tool!(
     BuildManifest, "src/tools/build-manifest", "build-manifest", Mode::ToolBootstrap;
     RemoteTestClient, "src/tools/remote-test-client", "remote-test-client", Mode::ToolBootstrap;
     RustInstaller, "src/tools/rust-installer", "fabricate", Mode::ToolBootstrap,
-        external_tool = true;
+        is_external_tool = true;
     RustdocTheme, "src/tools/rustdoc-themes", "rustdoc-themes", Mode::ToolBootstrap;
 );
 
@@ -419,7 +429,7 @@ impl Step for RemoteTestServer {
             mode: Mode::ToolStd,
             path: "src/tools/remote-test-server",
             is_optional_tool: false,
-            is_external_tool: false,
+            source_type: SourceType::InTree,
             extra_features: Vec::new(),
         }).expect("expected to build -- essential tool")
     }
@@ -474,7 +484,7 @@ impl Step for Rustdoc {
             target,
             "build",
             "src/tools/rustdoc",
-            false,
+            SourceType::InTree,
         );
 
         // Most tools don't get debuginfo, but rustdoc should.
@@ -547,7 +557,7 @@ impl Step for Cargo {
             mode: Mode::ToolRustc,
             path: "src/tools/cargo",
             is_optional_tool: false,
-            is_external_tool: true,
+            source_type: SourceType::Submodule,
             extra_features: Vec::new(),
         }).expect("expected to build -- essential tool")
     }
@@ -597,7 +607,7 @@ macro_rules! tool_extended {
                     path: $path,
                     extra_features: $sel.extra_features,
                     is_optional_tool: true,
-                    is_external_tool: true,
+                    source_type: SourceType::Submodule,
                 })
             }
         }