gnu: rust: Update to 1.27.0.

* gnu/packages/rust.scm (rust): Rename to...
(rust-1.26): ...this.
(rust): New variable.
* gnu/packages/patches/rust-bootstrap-stage0-test.patch: New file.

gnu/packages/patches/rust-bootstrap-stage0-test.patch

@@ -0,0 +1,55 @@
+Bootstrap tests failed with local stage0 cargo and rustc
+Backported changes from https://github.com/rust-lang/rust/pull/51977
+
+From 0834d9d771e912f51deca6c25699e44734624546 Mon Sep 17 00:00:00 2001
+From: Nikolai Merinov <nikolai.merinov@member.fsf.org>
+Date: Mon, 2 Jul 2018 01:45:35 +0500
+Subject: [PATCH] bootstrap: tests should use rustc from config.toml
+
+Tests should always use "rustc" and "cargo" from config.toml instead
+of assuming that stage0 binaries was downloaded to build directory.
+---
+ src/bootstrap/bootstrap.py | 2 ++
+ src/bootstrap/config.rs    | 6 ++----
+ 2 files changed, 4 insertions(+), 4 deletions(-)
+
+diff --git a/src/bootstrap/bootstrap.py b/src/bootstrap/bootstrap.py
+index 487440becf..1701f7b83a 100644
+--- a/src/bootstrap/bootstrap.py
++++ b/src/bootstrap/bootstrap.py
+@@ -788,6 +788,8 @@ def bootstrap(help_triggered):
+     env["BOOTSTRAP_PARENT_ID"] = str(os.getpid())
+     env["BOOTSTRAP_PYTHON"] = sys.executable
+     env["BUILD_DIR"] = build.build_dir
++    env["CARGO"] = build.cargo()
++    env["RUSTC"] = build.rustc()
+     run(args, env=env, verbose=build.verbose)
+ 
+ 
+diff --git a/src/bootstrap/config.rs b/src/bootstrap/config.rs
+index 6dd6291be2..d1a0deb583 100644
+--- a/src/bootstrap/config.rs
++++ b/src/bootstrap/config.rs
+@@ -23,7 +23,6 @@ use std::cmp;
+ 
+ use num_cpus;
+ use toml;
+-use util::exe;
+ use cache::{INTERNER, Interned};
+ use flags::Flags;
+ pub use flags::Subcommand;
+@@ -362,9 +361,8 @@ impl Config {
+         config.src = Config::path_from_python("SRC");
+         config.out = Config::path_from_python("BUILD_DIR");
+ 
+-        let stage0_root = config.out.join(&config.build).join("stage0/bin");
+-        config.initial_rustc = stage0_root.join(exe("rustc", &config.build));
+-        config.initial_cargo = stage0_root.join(exe("cargo", &config.build));
++        config.initial_rustc = Config::path_from_python("RUSTC");
++        config.initial_cargo = Config::path_from_python("CARGO");
+ 
+         config
+     }
+-- 
+2.17.1
+

gnu/packages/rust.scm

@@ -564,7 +564,7 @@ jemalloc = \"" jemalloc "/lib/libjemalloc_pic.a" "\"
                    (("codegen-tests = false") ""))))
              (delete 'ignore-glibc-2.27-incompatible-test))))))))
 
-(define-public rust
+(define-public rust-1.26
   (let ((base-rust
          (rust-bootstrapped-package rust-1.25 "1.26.2"
                                     "0047ais0fvmqvngqkdsxgrzhb0kljg8wy85b01kbbjc88hqcz7pv"
@@ -611,3 +611,24 @@ jemalloc = \"" jemalloc "/lib/libjemalloc_pic.a" "\"
                    ;; This test wants to update the crate index.
                    (("fn no_index_update") "#[ignore]\nfn no_index_update"))
                  #t)))))))))
+
+(define-public rust
+  (let ((base-rust
+         (rust-bootstrapped-package rust-1.26 "1.27.0"
+                                    "089d7rhw55zpvnw71dj8vil6qrylvl4xjr4m8bywjj83d4zq1f9c"
+                                    #:patches
+                                    '("rust-coresimd-doctest.patch"
+                                      "rust-bootstrap-stage0-test.patch"))))
+    (package
+      (inherit base-rust)
+      (arguments
+       (substitute-keyword-arguments (package-arguments base-rust)
+         ((#:phases phases)
+          `(modify-phases ,phases
+             (add-before 'install 'mkdir-prefix-paths
+               (lambda* (#:key outputs #:allow-other-keys)
+                 ;; As result of https://github.com/rust-lang/rust/issues/36989
+                 ;; `prefix' directory should exist before `install' call
+                 (mkdir-p (assoc-ref outputs "out"))
+                 (mkdir-p (assoc-ref outputs "cargo"))
+                 #t)))))))))