gnu: rust: Bootstrap rust from 1.39.0 and optimize build time.

Only stage 1 (rather than stage 2) rustc and cargo are built and the
installation phase rewritten to not invoke the build tool, which helps to
shorten the build time to about 10 minutes per Rust on a fast machine.  The
total build time should take less than 4h30, down from the current 8 hours on
a Ryzen 3900X CPU.

* gnu/packages/patches/rust-reproducible-builds.patch: Delete file.
* gnu/packages/patches/rustc-1.39.0-src.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it, and un-register
rust-reproducible-builds.patch.
* gnu/packages/rust.scm (%mrustc-commit): New variable.
(%mrustc-source): Update to latest commit.
(rust-1.29): Morph into...
(rust-1.39): ... this.
[source]: Adjust the snippet, patches and patch-flags fields.
[inputs]: Replace llvm-7 by llvm (9).
[make-flags]: Add the RUSTC_VERSION, MRUSTC_TARGET_VER and OUTDIR_SUF make
variables.  Remove the RUSTCSRC make variable.
[phases]{copy-mrustc-and-patch}: Rename to...
{setup-mrustc-sources}: ... this.  A symbolic link is created inside the
mrustc directory, pointing to the Rust 1.39.0 sources.
{patch-makefiles}: Adjust directory.  Patch date and git definitions.  Edit
out the RUSTC_SRC_DL prerequisite.  Adjust the patching of a shebang.
{patch-cargo-checksums}: Adjust.
{configure-cargo-home}: New phase.
{configure}: Create and add a 'cc' shim to PATH.
{build}: Do not invoke make in parallel mode inside the run_rustc directory.
(rust-1.30): Morph into...
(rust-1.40): ... this, integrating the changes introduced between 1.30 and
1.40.
[modules]: Properly import (guix build cargo-utils).
[phases]{add-cc-shim-to-path}: New phase.
{configure}: Increase the codegen-units value to 256.
{build}: Only build stage 1 rustc and cargo, and group the commands into one
invocation.
{install}: Manually install the stage 1 build artifacts.
{patch-cargo-checksums}: Remove the ad-hoc use-modules, no longer needed.
[source]: Adjust.
[arguments]: Set validate-runpath? to #f.
[phases]{patch-cargo-checksums}: Remove phase.
{configure}: Repatriate the jemalloc configuration changes from 1.40.
[native-inputs]: Replace the rust-1.29 inputs by rust-1.39.  Use regular
jemalloc and llvm versions.
(rust-1.41)[phases]: Add the patch-cargo-checksums phase.
(rust-1.31, rust-1.32, rust-1.33, rust-1.34, rust-1.35, rust-1.36, rust-1.37)
(rust-1.38, rust-1.39, rust-1.40):  Delete variables.
(rust-1.46)[phases]{install}: Group build, test and install commands.
(rust-1.47)[phases]{build}: Override to adjust for the relocation of the
standard library source directory.

3 files changed, 272 insertions, 283 deletions

diff --git a/gnu/packages/patches/rust-reproducible-builds.patch b/gnu/packages/patches/rust-reproducible-builds.patch
deleted file mode 100644
index ef7bf53b5d..0000000000
--- a/gnu/packages/patches/rust-reproducible-builds.patch
+++ /dev/null
@@ -1,25 +0,0 @@
-From b9ca108fcae2b738ca3f0c88c84ae5dc5a6f843f Mon Sep 17 00:00:00 2001
-From: Tim Ryan <id@timryan.org>
-Date: Mon, 14 May 2018 06:22:21 -0400
-Subject: [PATCH] Support reproducible builds by forcing window.search to use
- stable key ordering. (#692)
-See <https://github.com/rust-lang-nursery/mdBook/pull/692>
----
- src/vendor/mdbook/src/renderer/html_handlebars/search.rs | 4 ++++
- 1 file changed, 4 insertions(+)
-
-diff --git a/src/vendor/mdbook/src/renderer/html_handlebars/search.rs b/src/vendor/mdbook/src/renderer/html_handlebars/search.rs
-index d49772f8b..1ee66a511 100644
---- a/src/vendor/mdbook/src/renderer/html_handlebars/search.rs
-+++ b/src/vendor/mdbook/src/renderer/html_handlebars/search.rs
-@@ -205,6 +205,10 @@ fn write_to_js(index: Index, search_config: &Search) -> Result<String> {
-         searchoptions,
-         index,
-     };
-+
-+    // By converting to serde_json::Value as an intermediary, we use a
-+    // BTreeMap internally and can force a stable ordering of map keys.
-+    let json_contents = serde_json::to_value(&json_contents)?;
-     let json_contents = serde_json::to_string(&json_contents)?;
- 
-     Ok(format!("window.search = {};", json_contents))
diff --git a/gnu/packages/patches/rustc-1.39.0-src.patch b/gnu/packages/patches/rustc-1.39.0-src.patch
new file mode 100644
index 0000000000..7859bd44d5
--- /dev/null
+++ b/gnu/packages/patches/rustc-1.39.0-src.patch
@@ -0,0 +1,99 @@
+# This modified patch is to disable the hunk applying to LLVM, unbundled in Guix.
+
+# Add mrustc slice length intrinsics
+--- src/libcore/intrinsics.rs
++++ src/libcore/intrinsics.rs
+@@ -685,4 +685,8 @@
+     pub fn min_align_of_val<T: ?Sized>(_: &T) -> usize;
+ 
++    /// Obtain the length of a slice pointer
++    #[cfg(rust_compiler="mrustc")]
++    pub fn mrustc_slice_len<T>(pointer: *const [T]) -> usize;
++
+     /// Gets a static string slice containing the name of a type.
+     pub fn type_name<T: ?Sized>() -> &'static str;
+
+--- src/libcore/slice/mod.rs
++++ src/libcore/slice/mod.rs
+@@ -68,5 +68,8 @@
+     pub const fn len(&self) -> usize {
+-        unsafe {
+-            crate::ptr::Repr { rust: self }.raw.len
+-        }
++        #[cfg(not(rust_compiler="mrustc"))]
++        #[cfg_attr(not(bootstrap), allow_internal_unstable(const_fn_union))]
++        const fn len_inner<T>(s: &[T]) -> usize { unsafe { crate::ptr::Repr { rust: s }.raw.len } };
++        #[cfg(rust_compiler="mrustc")]
++        const fn len_inner<T>(s: &[T]) -> usize { unsafe { crate::intrinsics::mrustc_slice_len(s) } }
++        len_inner(self)
+     }
+#
+# Static-link rustc_codegen_llvm so the generated rustc is standalone
+# > Note: Interacts with `rustc-1.39.0-overrides.toml`
+#
+--- src/librustc_interface/util.rs
++++ src/librustc_interface/util.rs
+@@ -421,2 +421,4 @@
+ pub fn get_codegen_sysroot(backend_name: &str) -> fn() -> Box<dyn CodegenBackend> {
++    #[cfg(rust_compiler="mrustc")]
++    { if(backend_name == "llvm") { extern "Rust" { fn __rustc_codegen_backend() -> Box<dyn CodegenBackend>; } return || unsafe { __rustc_codegen_backend() } } }
+     // For now we only allow this function to be called once as it'll dlopen a
+# Disable most architecture intrinsics
+--- src/stdarch/crates/std_detect/src/detect/mod.rs
++++ src/stdarch/crates/std_detect/src/detect/mod.rs
+@@ -74,4 +74,7 @@
+         // this run-time detection logic is never called.
+         #[path = "os/other.rs"]
+         mod os;
++    } else if #[cfg(rust_compiler="mrustc")] {
++        #[path = "os/other.rs"]
++        mod os;
+     } else if #[cfg(any(target_arch = "x86", target_arch = "x86_64"))] {
+--- vendor/ppv-lite86/src/lib.rs
++++ vendor/ppv-lite86/src/lib.rs
+@@ -12,10 +12,10 @@
+-#[cfg(all(feature = "simd", target_arch = "x86_64", not(miri)))]
++#[cfg(all(feature = "simd", target_arch = "x86_64", not(miri), not(rust_compiler="mrustc")))]
+ pub mod x86_64;
+-#[cfg(all(feature = "simd", target_arch = "x86_64", not(miri)))]
++#[cfg(all(feature = "simd", target_arch = "x86_64", not(miri), not(rust_compiler="mrustc")))]
+ use self::x86_64 as arch;
+
+-#[cfg(any(miri, not(all(feature = "simd", any(target_arch = "x86_64")))))]
++#[cfg(any(miri, rust_compiler="mrustc", not(all(feature = "simd", any(target_arch = "x86_64")))))]
+ pub mod generic;
+-#[cfg(any(miri, not(all(feature = "simd", any(target_arch = "x86_64")))))]
++#[cfg(any(miri, rust_compiler="mrustc", not(all(feature = "simd", any(target_arch = "x86_64")))))]
+ use self::generic as arch;
+
+# diff --git a/llvm/include/llvm/Demangle/MicrosoftDemangleNodes.h b/llvm/include/llvm/Demangle/MicrosoftDemangleNodes.h
+# index da9d9d5bfdc0..3d47471f0ef0 100644
+# --- src/llvm-project/llvm/include/llvm/Demangle/MicrosoftDemangleNodes.h
+# +++ src/llvm-project/llvm/include/llvm/Demangle/MicrosoftDemangleNodes.h
+# @@ -16,6 +16,8 @@
+#  #include "llvm/Demangle/DemangleConfig.h"
+#  #include "llvm/Demangle/StringView.h"
+#  #include <array>
+# +#include <cstdint>
+# +#include <string>
+
+#  namespace llvm {
+#  namespace itanium_demangle {
+##
+## gcc (used by mrustc) has 16-byte uint128_t alignment, while rustc uses 8
+##
+#--- src/libsyntax/ast.rs
+#+++ src/libsyntax/ast.rs
+#@@ -986,2 +986,2 @@
+#-#[cfg(target_arch = "x86_64")]
+#-static_assert_size!(Expr, 96);
+#+//#[cfg(target_arch = "x86_64")]
+#+//static_assert_size!(Expr, 96);
+#--- src/librustc/ty/sty.rs
+#+++ src/librustc/ty/sty.rs
+#@@ -2258,2 +2258,2 @@
+#-#[cfg(target_arch = "x86_64")]
+#-static_assert_size!(Const<'_>, 40);
+#+//#[cfg(target_arch = "x86_64")]
+#+//static_assert_size!(Const<'_>, 40);
+
diff --git a/gnu/packages/rust.scm b/gnu/packages/rust.scm
index 72991aea72..ea5bcaf198 100644
--- a/gnu/packages/rust.scm
+++ b/gnu/packages/rust.scm
@@ -118,37 +118,43 @@
                                    (package-native-inputs base-rust))))))
 
 ;;; Note: mrustc's only purpose is to be able to bootstap Rust; it's designed
-;;; to be used in source form.
+;;; to be used in source form.  The latest support for bootstrapping from
+;;; 1.39.0 is not yet released so use the latest commit (see:
+;;; https://github.com/thepowersgang/mrustc/issues/185).
+(define %mrustc-commit "474bec9cfd7862a20e7288cecd7fcf5e18648b9a")
 (define %mrustc-source
-  (let ((name "mrustc")
-        (version "0.9"))
+  (let* ((version "0.9")
+         (commit %mrustc-commit)
+         (revision "1")
+         (name "mrustc"))
     (origin
       (method git-fetch)
       (uri (git-reference
             (url "https://github.com/thepowersgang/mrustc")
-            (commit (string-append "v" version))))
-      (file-name (git-file-name name version))
+            (commit commit)))
+      (file-name (git-file-name name (git-version version revision commit)))
       (sha256
        (base32
-        "194ny7vsks5ygiw7d8yxjmp1qwigd71ilchis6xjl6bb2sj97rd2")))))
+        "1zacz5qia0r457mv74wvrvznnv4az5g2w9j8ji9ssy727wljhvz7")))))
 
-;;; Rust 1.29 is special in that it is built with mrustc, which shortens the
-;;; bootstrap path.  Note: the build is non-deterministic.
-(define-public rust-1.29
+;;; Rust 1.39 is special in that it is built with mrustc, which shortens the
+;;; bootstrap path.
+(define rust-1.39
   (package
     (name "rust")
-    (version "1.29.2")
+    (version "1.39.0")
     (source
      (origin
        (method url-fetch)
        (uri (rust-uri version))
-       (sha256 (base32 "1jb787080z754caa2w3w1amsygs4qlzj9rs1vy64firfmabfg22h"))
+       (sha256 (base32 "0mwkc1bnil2cfyf6nglpvbn2y0zfbv44zfhsd5qg4c9rm6vgd8dl"))
        (modules '((guix build utils)))
        (snippet '(for-each delete-file-recursively
-                           '("src/jemalloc"
-                             "src/llvm"
-                             "src/llvm-emscripten")))
-       (patches (search-patches "rust-reproducible-builds.patch"))))
+                           '("src/llvm-emscripten"
+                             "src/llvm-project"
+                             "vendor/jemalloc-sys/jemalloc")))
+       (patches (search-patches "rustc-1.39.0-src.patch"))
+       (patch-flags '("-p0"))))         ;default is -p1
     (outputs '("out" "cargo"))
     (properties '((timeout . 72000)           ;20 hours
                   (max-silent-time . 18000))) ;5 hours (for armel)
@@ -156,9 +162,7 @@
     (inputs
      `(("libcurl" ,curl)
        ("libssh2" ,libssh2)
-       ;; Use llvm-7, which enables rust to be built reproducibly.
-       ;; Versions newer than 7 fail to compile.
-       ("llvm" ,llvm-7)
+       ("llvm" ,llvm)
        ("openssl" ,openssl)
        ("zlib" ,zlib)))
     (native-inputs
@@ -180,7 +184,10 @@
        (list ,(string-append "RUSTC_TARGET="
                              (or (%current-target-system)
                                  (nix-system->gnu-triplet-for-rust)))
-             ,(string-append "RUSTCSRC=../"))
+             ,(string-append "RUSTC_VERSION=" version)
+             ,(string-append "MRUSTC_TARGET_VER="
+                             (version-major+minor version))
+             "OUTDIR_SUF=")           ;do not add version suffix to output dir
        #:phases
        (modify-phases %standard-phases
          (add-after 'unpack 'patch-reference-to-cc
@@ -191,11 +198,15 @@
                (substitute* (find-files "." "^link.rs$")
                  (("\"cc\".as_ref")
                   (format #f "~s.as_ref" (string-append gcc "/bin/gcc")))))))
-         (add-after 'unpack 'copy-mrustc-and-patch
+         (add-after 'unpack 'setup-mrustc-sources
            (lambda* (#:key inputs #:allow-other-keys)
-             (copy-recursively (assoc-ref inputs "mrustc-source") "mrustc")
-             (invoke "patch" "-p0" "-i" "mrustc/rustc-1.29.0-src.patch")))
-         (add-after 'copy-mrustc-and-patch 'patch-makefiles
+             (copy-recursively (assoc-ref inputs "mrustc-source") "../mrustc")
+             ;; The Makefile of mrustc expects the sources directory of rustc
+             ;; to be at this location, and it simplifies things to make it
+             ;; so.
+             (symlink (getcwd)
+                      (string-append "../mrustc/rustc-" ,version "-src"))))
+         (add-after 'setup-mrustc-sources 'patch-makefiles
            ;; This disables building the (unbundled) LLVM.
            (lambda* (#:key inputs parallel-build? #:allow-other-keys)
              (let ((llvm (assoc-ref inputs "llvm"))
@@ -203,7 +214,7 @@
                                      (if parallel-build?
                                          (number->string (parallel-job-count))
                                          "1"))))
-               (with-directory-excursion "mrustc"
+               (with-directory-excursion "../mrustc"
                  (substitute* '("minicargo.mk"
                                 "run_rustc/Makefile")
                    ;; Use the system-provided LLVM.
@@ -213,27 +224,40 @@
                     "$(LLVM_CONFIG):\n")
                    (("\\$Vcd \\$\\(RUSTCSRC\\)build && \\$\\(MAKE\\).*")
                     "true\n"))
-                 ;; Patch date.
                  (substitute* "Makefile"
-                   (("shell date")
-                    "shell date -d @1"))
+                   ;; Patch date and git obtained version information.
+                   ((" -D VERSION_GIT_FULLHASH=.*")
+                    (string-append
+                     " -D VERSION_GIT_FULLHASH=\\\"" ,%mrustc-commit "\\\""
+                     " -D VERSION_GIT_BRANCH=\\\"master\\\""
+                     " -D VERSION_GIT_SHORTHASH=\\\""
+                     ,(string-take %mrustc-commit 7) "\\\""
+                     " -D VERSION_BUILDTIME="
+                     "\"\\\"Thu, 01 Jan 1970 00:00:01 +0000\\\"\""
+                     " -D VERSION_GIT_ISDIRTY=0\n"))
+                   ;; Do not try to fetch sources from the Internet.
+                   ((": \\$\\(RUSTC_SRC_DL\\)")
+                    ":"))
                  (substitute* "run_rustc/Makefile"
                    (("[$]Vtime ")
                     "$V ")
                    ;; Unlock the number of parallel jobs for cargo.
                    (("-j [[:digit:]]+ ")
                     "")
-                   ;; Patch the shebang of a generated wrapper for rustc, and
-                   ;; make sure that \n newline escapes get interpreted
-                   ;; correctly, specifying the '-e' option of echo.
-                   (("echo '#!/bin/sh")
-                    (string-append "echo -e '#!" (which "sh"))))))))
-         (add-after 'patch-source-shebangs 'patch-cargo-checksums
+                   ;; Patch the shebang of a generated wrapper for rustc
+                   (("#!/bin/sh")
+                    (string-append "#!" (which "sh"))))))))
+         (add-after 'patch-generated-file-shebangs 'patch-cargo-checksums
            (lambda* _
-             (substitute* "src/Cargo.lock"
-               (("(\"checksum .* = )\".*\"" all name)
+             (substitute* "Cargo.lock"
+               (("(checksum = )\".*\"" all name)
                 (string-append name "\"" ,%cargo-reference-hash "\"")))
-             (generate-all-checksums "src/vendor")))
+             (generate-all-checksums "vendor")))
+         (add-before 'configure 'configure-cargo-home
+           (lambda _
+             (let ((cargo-home (string-append (getcwd) "/.cargo")))
+               (mkdir-p cargo-home)
+               (setenv "CARGO_HOME" cargo-home))))
          (replace 'configure
            (lambda _
              (setenv "CC" "gcc")
@@ -242,29 +266,35 @@
              (setenv "LLVM_LINK_SHARED" "1")
              ;; This is a workaround for
              ;; https://github.com/thepowersgang/mrustc/issues/138.
-             (setenv "LIBSSH2_SYS_USE_PKG_CONFIG" "yes")))
+             (setenv "LIBSSH2_SYS_USE_PKG_CONFIG" "yes")
+             ;; rustc still insists on having 'cc' on PATH in some places
+             ;; (e.g. when building the 'test' library crate).
+             (mkdir-p "/tmp/bin")
+             (symlink (which "gcc") "/tmp/bin/cc")
+             (setenv "PATH" (string-append "/tmp/bin:" (getenv "PATH")))))
          (delete 'patch-generated-file-shebangs)
          (replace 'build
            (lambda* (#:key make-flags parallel-build? #:allow-other-keys)
-             (let* ((job-count (if parallel-build?
+             (let* ((src-root (getcwd))
+                    (job-count (if parallel-build?
                                    (parallel-job-count)
                                    1))
-                    (job-spec (string-append "-j" (number->string job-count)))
-                    (make-flags* (cons job-spec make-flags)))
+                    (job-spec (string-append "-j" (number->string job-count))))
                ;; Adapted from:
                ;; https://github.com/dtolnay/bootstrap/blob/master/build.sh.
-               (chdir "mrustc")
+               (chdir "../mrustc")
                (setenv "MINICARGO_FLAGS" job-spec)
                (setenv "CARGO_BUILD_JOBS" (number->string job-count))
                (display "Building rustc...\n")
                (apply invoke "make" "-f" "minicargo.mk" "output/rustc"
-                      make-flags*)
+                      job-spec make-flags)
                (display "Building cargo...\n")
                (apply invoke "make" "-f" "minicargo.mk" "output/cargo"
-                      make-flags*)
+                      job-spec make-flags)
                (display "Rebuilding stdlib with rustc...\n")
-               (with-directory-excursion "run_rustc"
-                 (apply invoke "make" "RUST_SRC=../../src/" make-flags*)))))
+               ;; Note: invoking make with -j would cause a compiler error
+               ;; (unexpected panic).
+               (apply invoke "make" "-C" "run_rustc" make-flags))))
          (replace 'install
            (lambda* (#:key inputs outputs #:allow-other-keys)
              (let* ((out (assoc-ref outputs "out"))
@@ -291,31 +321,43 @@ safety and thread safety guarantees.")
     ;; Dual licensed.
     (license (list license:asl2.0 license:expat))))
 
-(define-public rust-1.30
+(define-public rust-1.40
   (package
     (name "rust")
-    (version "1.30.1")
-    (source (origin
-              (inherit (package-source rust-1.29))
-              (uri (rust-uri version))
-              (sha256
-               (base32 "0aavdc1lqv0cjzbqwl5n59yd0bqdlhn0zas61ljf38yrvc18k8rn"))
-              (snippet '(for-each delete-file-recursively
-                                  '("src/jemalloc"
-                                    "src/llvm"
-                                    "src/llvm-emscripten"
-                                    "src/tools/clang"
-                                    "src/tools/lldb")))))
+    (version "1.40.0")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (rust-uri version))
+       (sha256 (base32 "1ba9llwhqm49w7sz3z0gqscj039m53ky9wxzhaj11z6yg1ah15yx"))
+       (modules '((guix build utils)))
+       ;; llvm-emscripten is no longer bundled, as that codegen backend got
+       ;; removed.
+       (snippet '(for-each delete-file-recursively
+                           '("src/llvm-project"
+                             "vendor/jemalloc-sys/jemalloc")))))
     (outputs '("out" "cargo"))
     (properties '((timeout . 72000)           ;20 hours
                   (max-silent-time . 18000))) ;5 hours (for armel)
     (build-system gnu-build-system)
+    ;; Rust 1.40 does not ship rustc-internal libraries by default (see
+    ;; rustc-dev-split). This means that librustc_driver.so is no longer
+    ;; available in lib/rustlib/$target/lib, which is the directory
+    ;; included in the runpath of librustc_codegen_llvm-llvm.so.  This is
+    ;; detected by our validate-runpath phase as an error, but it is
+    ;; harmless as the codegen backend is loaded by librustc_driver.so
+    ;; itself, which must at that point have been already loaded.  As such,
+    ;; we skip validating the runpath for Rust 1.40.  Rust 1.41 stopped
+    ;; putting the codegen backend in a separate library, which makes this
+    ;; workaround only necessary for this release.
     (arguments
-     ;; Only the final Rust is tested, not the intermediate bootstrap ones,
-     ;; for performance and simplicity.
-     `(#:tests? #f
+     `(#:validate-runpath? #f
+       ;; Only the final Rust is tested, not the intermediate bootstrap ones,
+       ;; for performance and simplicity.
+       #:tests? #f
        #:imported-modules ,%cargo-utils-modules ;for `generate-all-checksums'
-       #:modules ((guix build utils)
+       #:modules ((guix build cargo-utils)
+                  (guix build utils)
                   (guix build gnu-build-system)
                   (ice-9 match)
                   (srfi srfi-1))
@@ -328,6 +370,11 @@ safety and thread safety guarantees.")
              (setenv "CC" (search-input-file inputs "/bin/gcc"))
              ;; The Guix LLVM package installs only shared libraries.
              (setenv "LLVM_LINK_SHARED" "1")))
+         (add-after 'unpack 'add-cc-shim-to-path
+           (lambda _
+             (mkdir-p "/tmp/bin")
+             (symlink (which "gcc") "/tmp/bin/cc")
+             (setenv "PATH" (string-append "/tmp/bin:" (getenv "PATH")))))
          (add-after 'unpack 'neuter-tidy
            ;; We often need to patch tests with various Guix-specific paths.
            ;; This often increases the line length and makes tidy, rustc's
@@ -341,13 +388,6 @@ safety and thread safety guarantees.")
              (substitute* "src/bootstrap/builder.rs"
                ((".*::Tidy,.*")
                 ""))))
-         (add-after 'patch-generated-file-shebangs 'patch-cargo-checksums
-           (lambda* _
-             (use-modules (guix build cargo-utils))
-             (substitute* "src/Cargo.lock"
-               (("(\"checksum .* = )\".*\"" all name)
-                (string-append name "\"" ,%cargo-reference-hash "\"")))
-             (generate-all-checksums "src/vendor")))
          (replace 'configure
            (lambda* (#:key inputs outputs #:allow-other-keys)
              (let* ((out (assoc-ref outputs "out"))
@@ -358,6 +398,14 @@ safety and thread safety guarantees.")
                     (cargo (assoc-ref inputs "cargo-bootstrap"))
                     (llvm (assoc-ref inputs "llvm"))
                     (jemalloc (assoc-ref inputs "jemalloc")))
+               ;; The compiler is no longer directly built against jemalloc, but
+               ;; rather via the jemalloc-sys crate (which vendors the jemalloc
+               ;; source). To use jemalloc we must enable linking to it (otherwise
+               ;; it would use the system allocator), and set an environment
+               ;; variable pointing to the compiled jemalloc.
+               (setenv "JEMALLOC_OVERRIDE"
+                       (search-input-file inputs
+                                          "/lib/libjemalloc_pic.a"))
                (call-with-output-file "config.toml"
                  (lambda (port)
                    (display (string-append "
@@ -373,6 +421,7 @@ submodules = false
 prefix = \"" out "\"
 sysconfdir = \"etc\"
 [rust]
+jemalloc=true
 default-linker = \"" gcc "/bin/gcc" "\"
 channel = \"stable\"
 rpath = true
@@ -381,7 +430,6 @@ llvm-config = \"" llvm "/bin/llvm-config" "\"
 cc = \"" gcc "/bin/gcc" "\"
 cxx = \"" gcc "/bin/g++" "\"
 ar = \"" binutils "/bin/ar" "\"
-jemalloc = \"" jemalloc "/lib/libjemalloc_pic.a" "\"
 [dist]
 ") port))))))
          (replace 'build
@@ -390,20 +438,25 @@ jemalloc = \"" jemalloc "/lib/libjemalloc_pic.a" "\"
                               "-j" (if parallel-build?
                                        (number->string (parallel-job-count))
                                        "1"))))
-               (invoke "./x.py" job-spec "build")
-               (invoke "./x.py" job-spec "build" "src/tools/cargo"))))
+               (invoke "./x.py" job-spec "build" "--stage=1"
+                       "src/libstd"
+                       "src/tools/cargo"))))
          (replace 'install
            (lambda* (#:key outputs #:allow-other-keys)
-             (let ((out (assoc-ref outputs "out"))
-                   (cargo-out (assoc-ref outputs "cargo")))
-               (mkdir-p out)
-               (invoke "./x.py" "install")
-               (substitute* "config.toml"
-                 ;; Adjust the prefix to the 'cargo' output.
-                 (("prefix = \"[^\"]*\"")
-                  (format #f "prefix = ~s" cargo-out)))
-               (mkdir-p cargo-out)
-               (invoke "./x.py" "install" "cargo"))))
+             (let* ((out (assoc-ref outputs "out"))
+                    (cargo-out (assoc-ref outputs "cargo"))
+                    (gnu-triplet ,(or (%current-target-system)
+                                      (nix-system->gnu-triplet-for-rust)))
+                    (build (string-append "build/" gnu-triplet)))
+               ;; Manually do the installation instead of calling './x.py
+               ;; install', as that is slow and needlessly rebuilds some
+               ;; things.
+               (install-file (string-append build "/stage1/bin/rustc")
+                             (string-append out "/bin"))
+               (copy-recursively (string-append build "/stage1/lib")
+                                 (string-append out "/lib"))
+               (install-file (string-append build "/stage1-tools-bin/cargo")
+                             (string-append cargo-out "/bin")))))
          (add-after 'install 'delete-install-logs
            (lambda* (#:key outputs #:allow-other-keys)
              (for-each (lambda (f)
@@ -427,12 +480,12 @@ jemalloc = \"" jemalloc "/lib/libjemalloc_pic.a" "\"
      `(("cmake" ,cmake-minimal)
        ("pkg-config" ,pkg-config)       ; For "cargo"
        ("python" ,python-wrapper)
-       ("rustc-bootstrap" ,rust-1.29)
-       ("cargo-bootstrap" ,rust-1.29 "cargo")
+       ("rustc-bootstrap" ,rust-1.39)
+       ("cargo-bootstrap" ,rust-1.39 "cargo")
        ("which" ,which)))
     (inputs
-     `(("jemalloc" ,jemalloc-4.5.0)
-       ("llvm" ,llvm-7)
+     `(("jemalloc" ,jemalloc)
+       ("llvm" ,llvm)
        ("openssl" ,openssl)
        ("libssh2" ,libssh2)             ; For "cargo"
        ("libcurl" ,curl)))              ; For "cargo"
@@ -450,7 +503,7 @@ jemalloc = \"" jemalloc "/lib/libjemalloc_pic.a" "\"
             (variable "LIBRARY_PATH")
             (files '("lib" "lib64")))))
     (supported-systems
-     (delete "i686-linux"  ; fails to build, see bug #35519
+     (delete "i686-linux"               ; fails to build, see bug #35519
              %supported-systems))
     (synopsis "Compiler for the Rust progamming language")
     (description "Rust is a systems programming language that provides memory
@@ -459,182 +512,26 @@ safety and thread safety guarantees.")
     ;; Dual licensed.
     (license (list license:asl2.0 license:expat))))
 
-(define-public rust-1.31
-  (rust-bootstrapped-package
-   rust-1.30 "1.31.1" "0sk84ff0cklybcp0jbbxcw7lk7mrm6kb6km5nzd6m64dy0igrlli"))
-
-(define-public rust-1.32
-  (let ((base-rust (rust-bootstrapped-package
-                    rust-1.31 "1.32.0"
-                    "0ji2l9xv53y27xy72qagggvq47gayr5lcv2jwvmfirx029vlqnac")))
-    (package
-      (inherit base-rust)
-      (source
-       (origin
-         (inherit (package-source base-rust))
-         (snippet '(for-each delete-file-recursively
-                             '("src/llvm"
-                               "src/llvm-emscripten"
-                               "src/tools/clang"
-                               "src/tools/lldb"
-                               "vendor/jemalloc-sys/jemalloc")))
-          ;; the vendor directory has moved to the root of
-          ;; the tarball, so we have to strip an extra prefix
-         (patch-flags '("-p2"))))
-      (arguments
-       (substitute-keyword-arguments (package-arguments base-rust)
-         ;; The test suite fails due to LLVM 7, required for the build to be
-         ;; reproducible.
-         ((#:tests? _ #t)
-          #f)
-         ((#:phases phases)
-          `(modify-phases ,phases
-             ;; Cargo.lock and the vendor/ directory have been moved to the
-             ;; root of the rust tarball
-             (replace 'patch-cargo-checksums
-               (lambda* _
-                 (use-modules (guix build cargo-utils))
-                 (substitute* "Cargo.lock"
-                   (("(\"checksum .* = )\".*\"" all name)
-                    (string-append name "\"" ,%cargo-reference-hash "\"")))
-                 (generate-all-checksums "vendor")))
-             (add-after 'configure 'override-jemalloc
-               (lambda* (#:key inputs #:allow-other-keys)
-                 ;; The compiler is no longer directly built against jemalloc,
-                 ;; but rather via the jemalloc-sys crate (which vendors the
-                 ;; jemalloc source). To use jemalloc we must enable linking to
-                 ;; it (otherwise it would use the system allocator), and set
-                 ;; an environment variable pointing to the compiled jemalloc.
-                 (substitute* "config.toml"
-                   (("^jemalloc =.*$") "")
-                   (("[[]rust[]]") "\n[rust]\njemalloc=true\n"))
-                 (setenv "JEMALLOC_OVERRIDE"
-                         (search-input-file inputs
-                                            "/lib/libjemalloc_pic.a")))))))))))
-
-(define-public rust-1.33
-  (let ((base-rust (rust-bootstrapped-package
-                    rust-1.32 "1.33.0"
-                    "152x91mg7bz4ygligwjb05fgm1blwy2i70s2j03zc9jiwvbsh0as")))
-    (package
-      (inherit base-rust)
-      (source
-       (origin
-         (inherit (package-source base-rust))
-         (patches '())
-         (patch-flags '("-p1"))))
-      (inputs
-       ;; Upgrade jemalloc.
-       (alist-replace "jemalloc" (list jemalloc) (package-inputs base-rust))))))
-
-(define-public rust-1.34
-  (let ((base-rust (rust-bootstrapped-package
-                    rust-1.33 "1.34.1"
-                    "19s09k7y5j6g3y4d2rk6kg9pvq6ml94c49w6b72dmq8p9lk8bixh")))
-    (package
-      (inherit base-rust)
-      (source
-       (origin
-         (inherit (package-source base-rust))
-         (snippet '(for-each delete-file-recursively
-                             '("src/llvm-emscripten"
-                               "src/llvm-project"
-                               "vendor/jemalloc-sys/jemalloc"))))))))
-
-(define-public rust-1.35
-  (let ((base-rust (rust-bootstrapped-package
-                    rust-1.34 "1.35.0"
-                    "0bbizy6b7002v1rdhrxrf5gijclbyizdhkglhp81ib3bf5x66kas")))
-    (package
-      (inherit base-rust)
-      (arguments
-       (substitute-keyword-arguments (package-arguments base-rust)
-         ((#:phases phases)
-          `(modify-phases ,phases
-             (delete 'disable-codegen-tests))))))))
-
-(define-public rust-1.36
-  (rust-bootstrapped-package
-   rust-1.35 "1.36.0" "06xv2p6zq03lidr0yaf029ii8wnjjqa894nkmrm6s0rx47by9i04"))
-
-(define-public rust-1.37
-  (let ((base-rust (rust-bootstrapped-package
-                    rust-1.36 "1.37.0"
-                    "1hrqprybhkhs6d9b5pjskfnc5z9v2l2gync7nb39qjb5s0h703hj")))
-    (package
-      (inherit base-rust)
-      (arguments
-       (substitute-keyword-arguments (package-arguments base-rust)
-         ((#:phases phases)
-          `(modify-phases ,phases
-             (add-before 'configure 'configure-cargo-home
-               (lambda _
-                 (let ((cargo-home (string-append (getcwd) "/.cargo")))
-                   (mkdir-p cargo-home)
-                   (setenv "CARGO_HOME" cargo-home)))))))))))
-
-(define-public rust-1.38
-  (rust-bootstrapped-package
-    rust-1.37 "1.38.0" "101dlpsfkq67p0hbwx4acqq6n90dj4bbprndizpgh1kigk566hk4"))
-
-(define-public rust-1.39
+(define-public rust-1.41
   (let ((base-rust (rust-bootstrapped-package
-                    rust-1.38 "1.39.0"
-                    "0mwkc1bnil2cfyf6nglpvbn2y0zfbv44zfhsd5qg4c9rm6vgd8dl")))
+                    rust-1.40 "1.41.1"
+                    "0ws5x0fxv57fyllsa6025h3q6j9v3m8nb3syl4x0hgkddq0kvj9q")))
     (package
       (inherit base-rust)
       (arguments
        (substitute-keyword-arguments (package-arguments base-rust)
+         ((#:validate-runpath? _ #t)
+          #t)
          ((#:phases phases)
           `(modify-phases ,phases
-             (replace 'patch-cargo-checksums
-               ;; The Cargo.lock format changed.
+             (delete 'add-cc-shim-to-path)
+             (add-after 'patch-generated-file-shebangs 'patch-cargo-checksums
                (lambda* _
-                 (use-modules (guix build cargo-utils))
                  (substitute* "Cargo.lock"
                    (("(checksum = )\".*\"" all name)
                     (string-append name "\"" ,%cargo-reference-hash "\"")))
                  (generate-all-checksums "vendor"))))))))))
 
-(define-public rust-1.40
-  (let ((base-rust (rust-bootstrapped-package
-                    rust-1.39 "1.40.0"
-                    "1ba9llwhqm49w7sz3z0gqscj039m53ky9wxzhaj11z6yg1ah15yx")))
-    (package
-      (inherit base-rust)
-      (source
-       (origin
-         (inherit (package-source base-rust))
-         ;; llvm-emscripten is no longer bundled, as that codegen backend
-         ;; got removed.
-         (snippet '(for-each delete-file-recursively
-                             '("src/llvm-project"
-                               "vendor/jemalloc-sys/jemalloc")))))
-       ;; Rust 1.40 does not ship rustc-internal libraries by default (see
-       ;; rustc-dev-split). This means that librustc_driver.so is no longer
-       ;; available in lib/rustlib/$target/lib, which is the directory
-       ;; included in the runpath of librustc_codegen_llvm-llvm.so.  This is
-       ;; detected by our validate-runpath phase as an error, but it is
-       ;; harmless as the codegen backend is loaded by librustc_driver.so
-       ;; itself, which must at that point have been already loaded.  As such,
-       ;; we skip validating the runpath for Rust 1.40.  Rust 1.41 stopped
-       ;; putting the codegen backend in a separate library, which makes this
-       ;; workaround only necessary for this release.
-      (arguments (substitute-keyword-arguments (package-arguments base-rust)
-         ((#:validate-runpath? _ #f)
-          #f))))))
-
-(define-public rust-1.41
-  (let ((base-rust (rust-bootstrapped-package
-                    rust-1.40 "1.41.1"
-                    "0ws5x0fxv57fyllsa6025h3q6j9v3m8nb3syl4x0hgkddq0kvj9q")))
-    (package
-      (inherit base-rust)
-      (arguments
-       (substitute-keyword-arguments (package-arguments base-rust)
-         ((#:validate-runpath? _ #t)
-          #t))))))
-
 (define-public rust-1.42
   (rust-bootstrapped-package
    rust-1.41 "1.42.0" "0x9lxs82may6c0iln0b908cxyn1cv7h03n5cmbx3j1bas4qzks6j"))
@@ -687,9 +584,10 @@ safety and thread safety guarantees.")
                                   "-j" (if parallel-build?
                                            (number->string (parallel-job-count))
                                            "1"))))
-                   (invoke "./x.py" job-spec "build")
-                   (invoke "./x.py" job-spec "build" "src/tools/cargo")
-                   (invoke "./x.py" job-spec "build" "src/tools/rustfmt"))))
+                   (invoke "./x.py" job-spec "build"
+                           "library/std" ;rustc
+                           "src/tools/cargo"
+                           "src/tools/rustfmt"))))
              (replace 'check
                ;; Phase overridden to also test rustfmt.
                (lambda* (#:key tests? parallel-build? #:allow-other-keys)
@@ -698,9 +596,10 @@ safety and thread safety guarantees.")
                                     "-j" (if parallel-build?
                                              (number->string (parallel-job-count))
                                              "1"))))
-                     (invoke "./x.py" job-spec "test" "-vv")
-                     (invoke "./x.py" job-spec "test" "src/tools/cargo")
-                     (invoke "./x.py" job-spec "test" "src/tools/rustfmt")))))
+                     (invoke "./x.py" job-spec "test" "-vv"
+                             "library/std"
+                             "src/tools/cargo"
+                             "src/tools/rustfmt")))))
              (replace 'install
                ;; Phase overridden to also install rustfmt.
                (lambda* (#:key outputs #:allow-other-keys)
@@ -717,8 +616,24 @@ safety and thread safety guarantees.")
                  (invoke "./x.py" "install" "rustfmt"))))))))))
 
 (define-public rust-1.47
-  (rust-bootstrapped-package
-    rust-1.46 "1.47.0" "07fqd2vp7cf1ka3hr207dnnz93ymxml4935vp74g4is79h3dz19i"))
+  (let ((base-rust (rust-bootstrapped-package
+                    rust-1.46 "1.47.0"
+                    "07fqd2vp7cf1ka3hr207dnnz93ymxml4935vp74g4is79h3dz19i")))
+    (package/inherit base-rust
+      (arguments
+       (substitute-keyword-arguments (package-arguments base-rust)
+         ((#:phases phases)
+          `(modify-phases ,phases
+             (replace 'build
+               ;; The standard library source location moved in this release.
+               (lambda* (#:key parallel-build? #:allow-other-keys)
+                 (let ((job-spec (string-append
+                                  "-j" (if parallel-build?
+                                           (number->string (parallel-job-count))
+                                           "1"))))
+                   (invoke "./x.py" job-spec "build" "--stage=1"
+                           "library/std"
+                           "src/tools/cargo")))))))))))
 
 (define-public rust-1.48
   (rust-bootstrapped-package