[bug#53878] [PATCH v2 09/15] gnu: Add racket-vm-cgc.

[Philip McGrath <philip@philipmcgrath.com>]

* gnu/packages/patches/racket-enable-scheme-backport.patch: New patch.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/chez-and-racket-bootstrap.scm (unbundle-chez-submodules,
racket-vm-cgc): New variables.
(chez-scheme)[source]<snippet>: Use 'unbundle-chez-submodules'.
---
 gnu/local.mk                                  |   1 +
 gnu/packages/chez-and-racket-bootstrap.scm    | 315 +++++++++++-
 .../racket-enable-scheme-backport.patch       | 465 ++++++++++++++++++
 3 files changed, 772 insertions(+), 9 deletions(-)
 create mode 100644 gnu/packages/patches/racket-enable-scheme-backport.patch

diff --git a/gnu/local.mk b/gnu/local.mk
index fa3a89e7a8..aaecbc7898 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -1752,6 +1752,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/ripperx-missing-file.patch		\
   %D%/packages/patches/rpcbind-CVE-2017-8779.patch		\
   %D%/packages/patches/rtags-separate-rct.patch			\
+  %D%/packages/patches/racket-enable-scheme-backport.patch	\
   %D%/packages/patches/racket-minimal-sh-via-rktio.patch	\
   %D%/packages/patches/remake-impure-dirs.patch			\
   %D%/packages/patches/restic-0.9.6-fix-tests-for-go1.15.patch	\
diff --git a/gnu/packages/chez-and-racket-bootstrap.scm b/gnu/packages/chez-and-racket-bootstrap.scm
index 366815634d..0dd5f4bb68 100644
--- a/gnu/packages/chez-and-racket-bootstrap.scm
+++ b/gnu/packages/chez-and-racket-bootstrap.scm
@@ -34,8 +34,11 @@ (define-module (gnu packages chez-and-racket-bootstrap)
   #:use-module (guix build-system copy)
   #:use-module (guix build-system gnu)
   #:use-module (gnu packages)
+  #:use-module (gnu packages autotools)
+  #:use-module (gnu packages bash)
   #:use-module (gnu packages compression)
   #:use-module (gnu packages ghostscript)
+  #:use-module (gnu packages libffi)
   #:use-module (gnu packages linux)
   #:use-module (gnu packages ncurses)
   #:use-module (gnu packages netpbm)
@@ -62,6 +65,136 @@ (define-module (gnu packages chez-and-racket-bootstrap)
 ;; Putting the relevant definitions together in this module avoids having to
 ;; work around dependency cycles.
 ;;
+;; Anatomy of Racket:
+;; ------------------
+;;
+;; The main Racket Git repository (<https://github.com/racket/racket>) is
+;; organized broadly like this:
+;;
+;;     .
+;;     ├── Makefile
+;;     ├── pkgs/
+;;     └── racket/
+;;         ├── collects/
+;;         └── src/
+;;             ├── configure
+;;             ├── Makefile.in
+;;             ├── bc/
+;;             ├── cs/
+;;             ├── ChezScheme/
+;;             └── ...
+;;
+;; The 'racket/src/' directory contains the source of the runtime system, core
+;; compiler, and primitives for the major Racket implementations: this layer
+;; is called the ``Racket VM''. It is basically a normal autotools
+;; project. (Even when Racket VM implementations use components implemented in
+;; Racket, they are compiled in special modes to produce VM primitives.)
+;; (There are or have been experimental Racket VM implementations elsewhere,
+;; e.g. <https://github.com/pycket/pycket>.)
+;;
+;; The 'racket/collects/' directory contains ``built in'' Racket libraries
+;; that are not part of any package, including the implementation of
+;; 'racket/base': in particular, it must contain enough to implement `raco pkg
+;; install'. It is theoretically possible to use the Racket VM layer without
+;; the main collections, but it is not stable or useful.
+;;
+;; The 'pkgs/' directory contains Racket packages that are especially closely
+;; tied to the implementation of the Racket VM, including 'compiler-lib',
+;; 'racket-doc', and 'racket-test'. Some of these packages depend on Racket
+;; packages that are developed in other Git repositories, predominantly but
+;; not exclusively under the 'racket' GitHub organization. Conversely, not all
+;; of the packages developed in the main Git repository are part of the main
+;; Racket distribution.  (Additionally, components of the Racket VM that are
+;; implemented in Racket can be installed as packages, mostly for ease of
+;; development.)
+;;
+;; The top-level 'Makefile' is more like a directory of scripts: it has
+;; convienience targets for developing Racket, and it cooperates with the
+;; 'distro-build' package to assemble custom Racket distributions. It is not
+;; part of Racket source distributions: the root of a source distribution is
+;; basically 'racket/src' with some extra package sources and configuration
+;; added.
+;;
+;; A ''minimal Racket'' installation includes two packages: 'base', which is a
+;; sort of bridge between the current ``built-in'' collections and the package
+;; system's model of dependencies, and 'racket-lib', which, for installations
+;; that can not rely on a system package manager, pulls in the SQLite and
+;; OpenSSL shared libraries as platform-specific dependencies for use by the
+;; ``built-in'' collections.
+;;
+;; The main Racket distribution consists of installing the 'main-distribution'
+;; package and all of its dependencies.
+;;
+;; The default mode when building Racket (or installing it with the released
+;; installers) is an ``in-place build'', which produces a self-contained,
+;; relocatable, roughly FHS-like directory. (Racket also supports
+;; ``Unix-style'' installations, which rearrange the parts of an in-place
+;; build into Racket-specific subdirectories and generally tries to work for
+;; installation into an FHS-based system.) Certain tools, e.g. 'distro-build'
+;; and 'raco cross', are able to work with an in-place Racket build.
+;;
+;; This file defines the packages 'racket-vm-cgc', 'racket-vm-bc', and
+;; 'racket-vm-cs'. All three are in-place builds of 'racket/src/' and
+;; 'racket/collects/' and are installed to 'opt/racket-vm/' in the store
+;; output. The function 'racket-vm-for-system' returns the recomended Racket
+;; VM package for a given system.
+;;
+;; The file 'racket.scm' builds on these packages to define 'racket-minimal'
+;; and 'racket' packages. These use Racket's support for ``layered
+;; installations'', which allow an immutable base layer to be extended with
+;; additional packages. They use the layer configuration directly provide
+;; ready-to-install FHS-like trees, rather than relying on the built in
+;; ``Unix-style install'' mechanism.
+;;
+;; Bootstrapping Racket:
+;; ---------------------
+;;
+;; Here's how bootstrapping Racket works:
+;;
+;;   - Racket BC [CGC] can be built with only a C compiler (except for
+;;     one caveat discussed below).
+;;   - Racket BC [3M] needs an existing Racket to run "xform",
+;;     which transforms its own C source code to add additional annotations
+;;     for the precise garbage collector.
+;;   - Racket CS needs (bootfiles for) Racket's fork of Chez Scheme.
+;;     It also needs an existing Racket to compile Racket-implemented
+;;     parts of the runtime system to R6RS libraries.
+;;   - Chez Scheme also needs bootfiles for itself, but Racket can simulate
+;;     enough of Chez Scheme to load Racket's fork of the Chez Scheme compiler
+;;     purely from source into Racket and apply the compiler to itself,
+;;     producing the needed bootfiles (albeit very slowly).
+;;     Any variant of Racket since version 7.1 can run the simulation.
+;;
+;; So, we build CGC to build 3M to build bootfiles and CS.
+;;
+;; (Note: since the CGC variant is basically only for bootstrapping, we
+;; often use "BC" to mean "3M", consistent with `(banner)` and the
+;; suffixes used on executables when more than one variant co-exists.)
+;;
+;; One remaining bootstrapping limitation is that Racket's reader, module
+;; system, and macro expander are implemented in Racket. For Racket CS,
+;; they are compiled to R6RS libraries as discussed above. This note from the
+;; README file applies to all such subsystems:
+;;
+;;     The Racket version must be practically the same as the current Racket
+;;     verson, although it can be the Racket BC implementation (instead of
+;;     the Racket CS implementation).
+;;
+;;     Unlike Chez Scheme boot files, the files generated in "schemified"
+;;     are human-readable and -editable Scheme code. That provides a way
+;;     out of bootstrapping black holes, even without BC.
+;;
+;; However, other Racket subsystems implemented in Racket for Racket CS
+;; use older C implementations for Racket BC, whereas the reader, expander,
+;; and module system were completely replaced with the Racket implementation
+;;
+;; For Racket BC, the compiled "linklet" s-expressions (primitive modules)
+;; are embeded in C as a static string constant. Eventually, they are further
+;; compiled by the C-implemented Racket BC bytecode and JIT compilers.
+;; (On platforms where Racket BC's JIT is not supported, yet another compiler
+;; instead compiles the linklets to C code, but this is not a bootstrapping
+;; issue.)
+;;
 ;; Code:
 
 (define (chez-machine->nonthreaded machine)
@@ -169,6 +302,178 @@ (define* (chez-upstream-features-for-system #:optional
    (else
     '(threads))))
 
+;;
+;; Chez auxiliary G-expressions:
+;;
+
+(define unbundle-chez-submodules
+  #~(begin
+      (use-modules (guix build utils))
+      (for-each (lambda (dir)
+                  (when (directory-exists? dir)
+                    (delete-file-recursively dir)))
+                '("stex"
+                  "nanopass"
+                  "lz4"
+                  "zlib"))))
+
+;;
+;; Racket VM:
+;;
+
+(define (racket-vm-common-configure-flags)
+  ;; under a lambda extraction to avoid evaluating bash-minimal too early
+  #~`(,@(cond
+         ((false-if-exception
+           (search-input-file %build-inputs "/bin/libtool"))
+          => (lambda (libtool)
+               (list (string-append "--enable-lt=" libtool))))
+         (else
+          '()))
+      ,@(cond
+         ((false-if-exception
+           (search-input-file %build-inputs "/opt/racket-vm/bin/racket"))
+          => (lambda (racket)
+               (list (string-append "--enable-racket=" racket))))
+         (else
+          '()))
+      ,(string-append "CPPFLAGS=-DGUIX_RKTIO_PATCH_BIN_SH="
+                      #$(file-append bash-minimal "/bin/sh"))
+      "--disable-strip"
+      "--enable-origtree"))
+
+(define-public racket-vm-cgc
+  ;; Eventually, it may make sense for some vm packages to not be hidden,
+  ;; but this one is especially likely to remain hidden.
+  (hidden-package
+   (package
+     (name "racket-vm-cgc")
+     (version "8.4")
+     ;; ^ Remember to also update the version of
+     ;;   chez-scheme-for-racket-bootstrap-bootfiles
+     (source
+      (origin
+        (method git-fetch)
+        (uri (git-reference
+              (url "https://github.com/racket/racket")
+              (commit (string-append "v" version))))
+        (sha256
+         (base32 "1vpl66gdgc8rnldmn8rmb7ar9l057jqjvgpfn29k57i3c5skr8s6"))
+        (file-name (git-file-name "racket" version))
+        (patches (search-patches "racket-minimal-sh-via-rktio.patch"
+                                 ;; Remove by Racket 8.5:
+                                 "racket-enable-scheme-backport.patch"))
+        (modules '((guix build utils)))
+        (snippet
+         #~(begin
+             ;; Unbundle Chez submodules.
+             (with-directory-excursion "racket/src/ChezScheme"
+               #$unbundle-chez-submodules)
+             ;; Unbundle libffi.
+             (delete-file-recursively "racket/src/bc/foreign/libffi")))))
+     (inputs (list ncurses ;; <- common to all variants (for #%terminal)
+                   bash-minimal ;; <- common to all variants (for `system`)
+                   libffi)) ;; <- only for BC variants
+     (native-inputs (list libtool)) ;; <- only for BC variants
+     (outputs '("out" "debug"))
+     (build-system gnu-build-system)
+     (arguments
+      (list
+       #:configure-flags
+       #~(cons "--enable-cgcdefault"
+               #$(racket-vm-common-configure-flags))
+       ;; Tests are in packages like racket-test-core and
+       ;; main-distribution-test that aren't part of the main
+       ;; distribution.
+       #:tests? #f
+       ;; Upstream recommends #:out-of-source?, and it does
+       ;; help with debugging, but it confuses `install-license-files`.
+       #:modules '((ice-9 match)
+                   (ice-9 regex)
+                   (guix build gnu-build-system)
+                   (guix build utils))
+       #:strip-directories #~'("opt/racket-vm/bin"
+                               "opt/racket-vm/lib")
+       #:phases
+       #~(let ()
+           (define* ((wrap-racket-vm-outputs phase) . args)
+             (apply
+              phase
+              (let loop ((args args))
+                (match args
+                  ((#:outputs outputs . args)
+                   `(#:outputs
+                     ,(let loop ((outputs outputs))
+                        (match outputs
+                          ((("out" . out) . outputs)
+                           `(("out" . ,(string-append out "/opt/racket-vm/"))
+                             ,@outputs))
+                          ((other . outputs)
+                           (cons other (loop outputs)))))
+                     ,@args))
+                  ((arg . args)
+                   (cons arg (loop args)))))))
+           (modify-phases %standard-phases
+             (add-before 'configure 'initialize-config.rktd
+               (lambda* (#:key inputs #:allow-other-keys)
+                 (define (write-racket-hash alist)
+                   ;; inside must use dotted pair notation
+                   (display "#hash(")
+                   (for-each (match-lambda
+                               ((k . v)
+                                (format #t "(~s . ~s)" k v)))
+                             alist)
+                   (display ")\n"))
+                 (define maybe-release-catalog
+                   (let ((v #$(package-version this-package)))
+                     (if (string-match "^[0-9]+\\.[0-9]+($|\\.[0-8][0-9]*$)"
+                                       v)
+                         `(,(string-append
+                             "https://download.racket-lang.org/releases/"
+                             v
+                             "/catalog/"))
+                         '())))
+                 (mkdir-p "racket/etc")
+                 (with-output-to-file "racket/etc/config.rktd"
+                   (lambda ()
+                     (write-racket-hash
+                      `((build-stamp . "")
+                        (catalogs ,@maybe-release-catalog
+                                  #f)))))))
+             (add-before 'configure 'chdir
+               (lambda _
+                 (chdir "racket/src")))
+             (replace 'configure
+               (wrap-racket-vm-outputs
+                (assoc-ref %standard-phases 'configure)))
+             (replace 'patch-shebangs
+               (wrap-racket-vm-outputs
+                (assoc-ref %standard-phases 'patch-shebangs)))
+             (replace 'validate-runpath
+               (wrap-racket-vm-outputs
+                (assoc-ref %standard-phases 'validate-runpath)))
+             (replace 'make-dynamic-linker-cache
+               (wrap-racket-vm-outputs
+                (assoc-ref %standard-phases 'make-dynamic-linker-cache)))
+             (replace 'patch-dot-desktop-files
+               (wrap-racket-vm-outputs
+                (assoc-ref %standard-phases 'patch-dot-desktop-files)))))))
+     (home-page "https://racket-lang.org")
+     (synopsis "Old Racket implementation used for bootstrapping")
+     (description "This variant of the Racket BC (``before Chez'' or
+``bytecode'') implementation is not recommended for general use.  It uses
+CGC (a ``Conservative Garbage Collector''), which was succeeded as default in
+PLT Scheme version 370 (which translates to 3.7 in the current versioning
+scheme) by the 3M variant, which in turn was succeeded in version 8.0 by the
+Racket CS implementation.
+
+Racket CGC is primarily used for bootstrapping Racket BC [3M].  It may
+also be used for embedding applications without the annotations needed in C
+code to use the 3M garbage collector.")
+     ;; https://download.racket-lang.org/license.html
+     ;; The LGPL components are only used by Racket BC.
+     (license (list license:lgpl3+ license:asl2.0 license:expat)))))
+
 ;;
 ;; Chez Scheme:
 ;;
@@ -188,15 +493,7 @@ (define-public chez-scheme
                (base32
                 "07s433hn1z2slfc026sidrpzxv3a8narcd40qqr1xrpb9012xdky"))
               (file-name (git-file-name "chez-scheme" version))
-              (snippet #~(begin
-                           (use-modules (guix build utils))
-                           (for-each (lambda (dir)
-                                       (when (directory-exists? dir)
-                                         (delete-file-recursively dir)))
-                                     '("stex"
-                                       "nanopass"
-                                       "lz4"
-                                       "zlib"))))))
+              (snippet unbundle-chez-submodules)))
     (build-system gnu-build-system)
     (inputs
      (list
diff --git a/gnu/packages/patches/racket-enable-scheme-backport.patch b/gnu/packages/patches/racket-enable-scheme-backport.patch
new file mode 100644
index 0000000000..3a5a4a3d82
--- /dev/null
+++ b/gnu/packages/patches/racket-enable-scheme-backport.patch
@@ -0,0 +1,465 @@
+From 8d7687842f099e3e7e60d3a83fed58b2c6a92863 Mon Sep 17 00:00:00 2001
+From: Matthew Flatt <mflatt@racket-lang.org>
+Date: Sun, 6 Feb 2022 10:36:09 -0700
+Subject: [PATCH 1/2] Chez Scheme: adapt bootfile build for supplied `Scheme=`
+
+(cherry picked from commit fca1e02349664060e10278ca2ce6577a949bebf5)
+
+(Fixed conflicts by dropping pbchunks and pbarch changes.)
+---
+ racket/src/ChezScheme/configure  | 15 ++++++++++++++-
+ racket/src/ChezScheme/s/Mf-base  |  4 ++--
+ racket/src/ChezScheme/s/Mf-cross |  4 +++-
+ 3 files changed, 19 insertions(+), 4 deletions(-)
+
+diff --git a/racket/src/ChezScheme/configure b/racket/src/ChezScheme/configure
+index 4515ffc105..0098829091 100755
+--- a/racket/src/ChezScheme/configure
++++ b/racket/src/ChezScheme/configure
+@@ -45,6 +45,7 @@ threads=yes
+ nothreads=no
+ temproot=""
+ help=no
++forceworkarea=no
+ gzipmanpages=yes
+ installowner=""
+ installgroup=""
+@@ -205,6 +206,9 @@ while [ $# != 0 ] ; do
+     --pb)
+       pb=yes
+       ;;
++    --force)
++      forceworkarea=yes
++      ;;
+     --installprefix=*)
+       installprefix=`echo $1 | sed -e 's/^--installprefix=//'`
+       ;;
+@@ -439,6 +443,7 @@ if [ "$help" = "yes" ]; then
+   echo "  --toolprefix=<prefix>             prefix tool (compiler, linker, ...) names"
+   echo "  --[no]gzip-man-pages              compress manual pages ($gzipmanpages)"
+   echo "  --workarea=<pathname>             build directory ($w)"
++  echo "  --force                           configure even without boot files"
+   echo "  CC=<C compiler>                   C compiler"
+   echo "  CPPFLAGS=<C preprocessor flags>   C preprocessor flags"
+   echo "  CFLAGS=<C compiler flags>         C compiler flags"
+@@ -721,8 +726,16 @@ case "${flagsmuni}" in
+         ;;
+ esac
+ 
++if [ "$w" = "$m" ] ; then
++    configuringin=""
++else
++    configuringin=" in $w"
++fi
++
+ if [ -f boot/$m/scheme.boot -o -f "$srcdir"/boot/$m/scheme.boot ] ; then
+-  echo "Configuring for $m"
++    echo "Configuring for $m$configuringin"
++elif [ "$forceworkarea" = yes ] ; then
++    echo "Configuring for $m$configuringin despite missing boot files"
+ else
+   if [ "$m" = "" ] ; then
+       maybem="<machine type>"
+diff --git a/racket/src/ChezScheme/s/Mf-base b/racket/src/ChezScheme/s/Mf-base
+index cc6178c973..1f4a967998 100644
+--- a/racket/src/ChezScheme/s/Mf-base
++++ b/racket/src/ChezScheme/s/Mf-base
+@@ -94,7 +94,7 @@ endif
+ # that Scheme and SCHEMEHEAPDIRS are set by Mf-cross to point to the host Scheme
+ # implementation
+ Scheme = ../bin/$m/scheme${ExeSuffix}
+-export SCHEMEHEAPDIRS=../boot/%m
++export SCHEMEHEAPDIRS=../boot/$m
+ export CHEZSCHEMELIBDIRS=.
+ 
+ # Define the libdirs separator character
+@@ -691,4 +691,4 @@ reset-one:
+ 
+ .PHONY: run
+ run:
+-	env SCHEMEHEAPDIRS=../boot/$m/ ../bin/$m/scheme $(ARGS)
++	env SCHEMEHEAPDIRS=${SCHEMEHEAPDIRS} ${Scheme} $(ARGS)
+diff --git a/racket/src/ChezScheme/s/Mf-cross b/racket/src/ChezScheme/s/Mf-cross
+index d796cbb459..397af59a28 100644
+--- a/racket/src/ChezScheme/s/Mf-cross
++++ b/racket/src/ChezScheme/s/Mf-cross
+@@ -43,5 +43,7 @@ x$(xm).$(m):
+ 	$(MAKE) -f Mf-cross m=$(m) xm=$(xm) i=f o=3 d=0 xpatch
+ 	mv xpatch x$(xm).$(m)
+ 
++ifneq ($(SCHEMEHEAPDIRS),:)
+ # Ensure that cross-compiling "nanopass.so" is rebuilt if the host compiler changed
+-nanopass.so: ${SCHEME} ${SCHEMEHEAPDIRS}/petite.boot ${SCHEMEHEAPDIRS}/scheme.boot
++nanopass.so: ${Scheme} ${SCHEMEHEAPDIRS}/petite.boot ${SCHEMEHEAPDIRS}/scheme.boot
++endif
+-- 
+2.32.0
+
+
+From 26c8e2c1d9b02ad85acef8bda40d92154cf0b699 Mon Sep 17 00:00:00 2001
+From: Matthew Flatt <mflatt@racket-lang.org>
+Date: Sun, 6 Feb 2022 11:03:30 -0700
+Subject: [PATCH 2/2] configure: make `--enable-scheme` work with an executable
+
+When the same Chez Scheme version as used by Racket is already
+available, then `--enable-scheme=...` can supply an executable. For
+cross builds, `--enable-scheme=...` can still supply a build
+directory, instead, as before.
+
+(cherry picked from commit 4f0e76855ce7e86107de495292a553469daf0b3f)
+---
+ racket/src/ChezScheme/makefiles/Makefile.in |  3 ++
+ racket/src/README.txt                       | 30 +++++++++++---
+ racket/src/configure                        |  8 +++-
+ racket/src/cs/README.txt                    |  6 ++-
+ racket/src/cs/c/Makefile.in                 | 44 ++++++++++++++++-----
+ racket/src/cs/c/configure                   | 24 +++++++++--
+ racket/src/cs/c/configure.ac                | 21 ++++++++--
+ 7 files changed, 112 insertions(+), 24 deletions(-)
+
+diff --git a/racket/src/ChezScheme/makefiles/Makefile.in b/racket/src/ChezScheme/makefiles/Makefile.in
+index c396efc851..3998ef9ccd 100644
+--- a/racket/src/ChezScheme/makefiles/Makefile.in
++++ b/racket/src/ChezScheme/makefiles/Makefile.in
+@@ -59,6 +59,9 @@ reset:
+ %.boot:
+ 	(cd $(workarea) && $(MAKE) $*.boot)
+ 
++auto.boot:
++	(cd $(workarea) && $(MAKE) $(defaultm).boot)
++
+ # <machine>.bootquick to build boot files for <machine>
+ # with o=3 d=0 for the cross compiler, and only after
+ # building the kernel for the configured machine
+diff --git a/racket/src/README.txt b/racket/src/README.txt
+index 98647aebce..d77310b4a4 100644
+--- a/racket/src/README.txt
++++ b/racket/src/README.txt
+@@ -354,6 +354,10 @@ variant of MinGW without "libdelayimp.a", get the implementation of
+ ========================================================================
+ 
+ Cross-compilation requires at least two flags to `configure`:
++`--host=OS` and either `--enable-racket=RACKET` or (for Racket CS)
++`--enable-scheme-SCHEME`.
++
++More information:
+ 
+  * `--host=OS`, where OS is something like `i386-gnu-linux` to
+    indicate the target platform.
+@@ -374,11 +378,27 @@ Cross-compilation requires at least two flags to `configure`:
+    run `configure` again (with no arguments) in a "local" subdirectory
+    to create a build for the current platform.
+ 
+-An additional flag is needed for building Racket CS, unless the flag
+-`--enable-racket=auto` is used:
+-
+- * `--enable-scheme=DIR`, where DIR is a path that has a "ChezScheme"
+-   directory where Chez Scheme is built for the host system.
++ * `--enable-scheme=SCHEME`, where SCHEME is a Chez Scheme executable
++   executable that runs on the build platform; the executable must be
++   the same version as used in Racket built for the target platform.
++ 
++   Supplying `--enable-scheme=DIR` is also supported in cross-build
++   mode, where DIR is a path that has a "ChezScheme" directory where
++   Chez Scheme is built for the host system.
++
++The `--enable-racket=RACKET` and `--enable-scheme=SCHEME` flags are
++allowed for non-cross builds, too:
++
++ * For Racket CS, supplying either selects a Racket or Chez Scheme
++   implementation used to create boot files to the build platform.
++   Suppling Chez Scheme is a much more direct path, but when Racket is
++   supplied, its version does not have to match the version being
++   built.
++
++ * For Racket BC, `--enable-racket=RACKET` selects a Racket for
++   prepare C sources to cooperate with garbage collection. Its version
++   needs to be close to the one being built, and potentially exactly
++   the same version.
+ 
+ Some less commonly needed `configure` flags are for Racket BC:
+ 
+diff --git a/racket/src/configure b/racket/src/configure
+index c9f3ba4419..1b53ec7ce2 100755
+--- a/racket/src/configure
++++ b/racket/src/configure
+@@ -9,6 +9,7 @@ pb_dir="$dir/ChezScheme/boot/pb"
+ use_cs=maybe
+ use_bc=maybe
+ supplied_racket=no
++supplied_scheme=no
+ enable_boothelp=
+ 
+ # We don't have to detect conflicts like `--enable-csdefault --enable-bcdefault`,
+@@ -34,6 +35,9 @@ for arg in $*; do
+         --enable-racket=*)
+             supplied_racket=yes
+             ;;
++        --enable-scheme=*)
++            supplied_scheme=yes
++            ;;
+         --help | -h)
+             echo $0:
+             echo see --help-bc or --help-cs, since the Racket CS build and the
+@@ -70,8 +74,8 @@ elif test "$use_cs" = "maybe" ; then
+ fi
+ 
+ if test "$use_cs" = "yes" ; then
+-    if test $use_bc = no  -a $supplied_racket = no -a ! -d "$pb_dir" ; then
+-        echo $0: must have $pb_dir or --enable-racket=... for --enable-csonly
++    if test $use_bc = no  -a $supplied_racket = no  -a $supplied_scheme = no  -a ! -d "$pb_dir" ; then
++        echo $0: must have $pb_dir, --enable-racket=... or --enable-scheme=... for --enable-csonly
+         exit 1
+     fi
+ 
+diff --git a/racket/src/cs/README.txt b/racket/src/cs/README.txt
+index 2ece417b78..8e6fc57b74 100644
+--- a/racket/src/cs/README.txt
++++ b/racket/src/cs/README.txt
+@@ -39,6 +39,11 @@ build:
+    installed in the "../ChezScheme/boot/pb" directory as described by
+    "../ChezScheme/BUILDING".
+ 
++   Supplying `--enable-scheme=...` is also an option if you alerady
++   have the same version of Chez Scheme built on the current platform.
++   Another build will be created, anyway, but more quickly than
++   without Chez Scheme.
++
+  * Racket is needed to generate the files in the "schemified"
+    directory from the sources in sibling directories like "../io". The
+    Racket version must be practically the same as the current Racket
+@@ -48,7 +53,6 @@ build:
+    Unlike Chez Scheme boot files, the files generated in "schemified"
+    are human-readable and -editable Scheme code. That provides a way
+    out of bootstrapping black holes, even without BC.
+-   
+ 
+ 
+ ========================================================================
+diff --git a/racket/src/cs/c/Makefile.in b/racket/src/cs/c/Makefile.in
+index 54a644a1d9..d73993f0fc 100644
+--- a/racket/src/cs/c/Makefile.in
++++ b/racket/src/cs/c/Makefile.in
+@@ -12,7 +12,9 @@ CS_HOST_WORKAREA_PREFIX = @CS_HOST_WORKAREA_PREFIX@
+ SCHEME_HOST_WORKAREA = $(CS_HOST_WORKAREA_PREFIX)$(SCHEME_WORKAREA)
+ SCHEME_BIN = $(SCHEME_HOST_WORKAREA)/$(MACH)/bin/$(MACH)/scheme
+ SCHEME_INC = $(SCHEME_HOST_WORKAREA)/$(MACH)/boot/$(MACH)
+-SCHEME = $(SCHEME_BIN) -B $(SCHEME_INC)/petite.boot -B $(SCHEME_INC)/scheme.boot
++SCHEME_built = $(SCHEME_BIN) -B $(SCHEME_INC)/petite.boot -B $(SCHEME_INC)/scheme.boot
++SCHEME_existing = @MAKE_SCHEME_SCHEME@
++SCHEME = $(SCHEME@USE_SCHEME_MODE@)
+ 
+ TARGET_MACH = @TARGET_MACH@
+ SCHEME_TARGET_INC = $(SCHEME_WORKAREA)/$(TARGET_MACH)/boot/$(TARGET_MACH)
+@@ -88,7 +90,7 @@ mainsrcdir = @srcdir@/../..
+ @INCLUDEDEP@ @srcdir@/../../version/version.mak
+ 
+ cs:
+-	$(MAKE) scheme@T_CROSS_MODE@
++	$(MAKE) scheme@MAKE_SCHEME_MODE@
+ 	$(MAKE) racket-so
+ 	cd rktio; $(MAKE)
+ 	$(MAKE) racketcs
+@@ -121,9 +123,13 @@ racket-so:
+ 
+ RACKET_SO_ENV = @CONFIGURE_RACKET_SO_COMPILE@
+ 
++TARGET_MACH_built = $(TARGET_MACH)
++TARGET_MACH_existing = xc-$(TARGET_MACH)
++XPATCH_FILE = $(SCHEME_WORKAREA)/$(TARGET_MACH@USE_SCHEME_MODE@)/s/xpatch
++
+ CS_PROGS = SCHEME="$(SCHEME)"
+ CS_OPTS = COMPRESS_COMP=@COMPRESS_COMP@ @ENABLE_OR_DISABLE_WPO@
+-CS_OPTScross = $(CS_OPTS) CSO=$(MACH) CROSS_COMP="--xpatch $(SCHEME_WORKAREA)/$(TARGET_MACH)/s/xpatch"
++CS_OPTScross = $(CS_OPTS) CSO=$(MACH) CROSS_COMP="--xpatch $(XPATCH_FILE)"
+ PASS_COMPILE_DEPS = EXTRA_COMPILE_DEPS="$(SCHEME_INC)/petite.boot $(SCHEME_INC)/scheme.boot"
+ 
+ build-racket-so:
+@@ -163,6 +169,15 @@ pb-bootquick:
+ 	cd $(SCHEME_WORKAREA) && $(MAKE) reset
+ 	$(SHELL) $(srcdir)/ready_boot.sh $(MACH) $(SCHEME_WORKAREA)
+ 
++scheme-via-scheme:
++	$(MAKE) $(SCHEME_WORKAREA)/boot/$(MACH)/scheme.boot
++	$(MAKE) mach-make
++
++$(SCHEME_WORKAREA)/boot/$(MACH)/scheme.boot:
++	mkdir -p $(SCHEME_WORKAREA)
++	$(MAKE) config-scheme CONFIG_SCHEME_MODE="$(CONFIG_SCHEME_MODE) --force"
++	cd $(SCHEME_WORKAREA) && $(MAKE) $(MACH).boot Scheme="$(SCHEME)" SCHEMEHEAPDIRS=: o=3 d=0 what=all
++
+ mach-make:
+ 	$(MAKE) config-scheme
+ 	cd $(SCHEME_WORKAREA) && $(MAKE)
+@@ -182,24 +197,33 @@ config-scheme:
+ 
+ scheme-cross:
+ 	env MAKE_BOOT_FOR_CROSS=yes SCHEME_SRC="$(SCHEME_DIR)" SCHEME_WORKAREA=$(SCHEME_WORKAREA) MACH="$(TARGET_MACH)" $(BOOTSTRAP_RACKET) "$(SCHEME_DIR)"/rktboot/make-boot.rkt
++	$(MAKE) finish-scheme-cross
++
++finish-scheme-cross:
+ 	$(SHELL) $(srcdir)/reset_boot.sh $(TARGET_MACH) $(SCHEME_WORKAREA)
+ 	cd $(SCHEME_WORKAREA) && "$(UP_SCHEME_DIR)"/configure @SCHEME_CROSS_CONFIG_ARGS@ $(SCHEME_CONFIG_VARS)
+ 	cd $(SCHEME_WORKAREA)/$(TARGET_MACH)/c && $(CHOST_HACK@T_CROSS_MODE@) $(MAKE) o=o cross=t
+-	$(MAKE) $(SCHEME_WORKAREA)/$(TARGET_MACH)/s/xpatch
++	$(MAKE) $(XPATCH_FILE)
++
++scheme-cross-via-scheme:
++	$(MAKE) $(SCHEME_WORKAREA)/boot/$(TARGET_MACH)/scheme.boot MACH=$(TARGET_MACH)
++	$(MAKE) finish-scheme-cross
+ 
+ # Rebuild patch file and cross "petite.boot" and "scheme.boot" when older
+-# than the build-host "scheme.boot" or when "make-boot.rkt" touchs dummy boot files
+-XPATCH_DEPS = $(SCHEME_HOST_WORKAREA)/$(MACH)/boot/$(MACH)/scheme.boot \
+-              $(SCHEME_WORKAREA)/boot/$(TARGET_MACH)/scheme.boot
++# than the build-<host "scheme.boot" or when "make-boot.rkt" touchs dummy boot files
++XPATCH_DEPS_built = $(SCHEME_HOST_WORKAREA)/$(MACH)/boot/$(MACH)/scheme.boot \
++                    $(SCHEME_WORKAREA)/boot/$(TARGET_MACH)/scheme.boot
++XPATCH_DEPS_existing = 
++XPATCH_DEPS = $(XPATCH_DEPS@USE_SCHEME_MODE@)
+ 
+-$(SCHEME_WORKAREA)/$(TARGET_MACH)/s/xpatch: $(XPATCH_DEPS)
++$(XPATCH_FILE): $(XPATCH_DEPS)
+ 	$(MAKE) bounce TARGET=build-xpatch-using-host
+ 
+ build-xpatch-using-host:
+ 	cd $(SCHEME_WORKAREA)/$(TARGET_MACH)/s && $(MAKE) -f Mf-cross m=$(MACH) xm=$(TARGET_MACH) Scheme="$(SCHEME_BIN)" SCHEMEHEAPDIRS="$(SCHEME_INC)"
+ 
+ XPATCH =
+-XPATCHcross = --xpatch $(SCHEME_WORKAREA)/$(TARGET_MACH)/s/xpatch
++XPATCHcross = --xpatch $(XPATCH_FILE)
+ 
+ racket.boot: racket.so
+ 	$(SCHEME) --script $(srcdir)/convert-to-boot.ss @BOOT_COMPRESS_COMP@ $(XPATCH@CROSS_MODE@) racket.so racket.boot $(TARGET_MACH)
+@@ -410,7 +434,7 @@ install-cross:
+ 	$(MAKE) compile-xpatch.$(TARGET_MACH)
+ 	$(MAKE) library-xpatch.$(TARGET_MACH)
+ 
+-SCHEME_XPATCH = $(SCHEME_WORKAREA)/$(TARGET_MACH)/s/xpatch
++SCHEME_XPATCH = $(XPATCH_FILE)
+ 
+ CROSS_SERVE_DEPS = $(srcdir)/mk-cross-serve.ss $(srcdir)/cross-serve.ss \
+                    $(srcdir)/../expander/env.ss $(srcdir)/../linklet/config.ss
+diff --git a/racket/src/cs/c/configure b/racket/src/cs/c/configure
+index 21695a431a..1eeef57753 100755
+--- a/racket/src/cs/c/configure
++++ b/racket/src/cs/c/configure
+@@ -654,6 +654,9 @@ MINGW
+ NOT_OSX
+ OSX
+ SETUP_BOOT_MODE
++USE_SCHEME_MODE
++MAKE_SCHEME_SCHEME
++MAKE_SCHEME_MODE
+ TT_CROSS_MODE
+ T_CROSS_MODE
+ CROSS_MODE
+@@ -1448,7 +1451,7 @@ Optional Features:
+   --enable-docs           build docs on install (enabled by default)
+   --enable-usersetup      setup user-specific files on install
+   --enable-racket=<path>  use <path> as Racket for build; or "auto" to create
+-  --enable-scheme=<path>  use <path> as host's build directory for cross
++  --enable-scheme=<path>  use <path> as host build for cross
+   --enable-mach=<mach>    use Chez Scheme machine type <mach>
+   --enable-target=<mach>  cross-build for Chez Scheme machine type <mach>
+   --enable-portable       prefer portable to host-specific
+@@ -2867,7 +2870,7 @@ show_explicitly_enabled "${enable_xonx}" "Unix style"
+ show_explicitly_enabled "${enable_libzo}" 'Compiled ".zo" files moved to lib'
+ 
+ show_explicitly_set "${enable_racket}" "Racket"
+-show_explicitly_set "${enable_scheme}" "Chez Scheme build directory"
++show_explicitly_set "${enable_scheme}" "Chez Scheme for build"
+ show_explicitly_set "${enable_mach}" "machine type"
+ show_explicitly_set "${enable_target}" "cross-build machine type"
+ show_explicitly_enabled "${enable_portable}" "portable"
+@@ -4745,9 +4748,21 @@ esac
+ 
+ SCHEME_DIR=${srcdir}/../../ChezScheme
+ MAKE_BUILD_SCHEME=checkout
++USE_SCHEME_MODE="_built"
++MAKE_SCHEME_MODE="${T_CROSS_MODE}"
+ 
+ if test "${enable_scheme}" != "" ; then
+-  CS_HOST_WORKAREA_PREFIX="${enable_scheme}/"
++   if test -d "${enable_scheme}" ; then
++     # Directory exists, so use it as a build directory
++     echo "Using supplied Scheme path as a build directory"
++     CS_HOST_WORKAREA_PREFIX="${enable_scheme}/"
++   else
++     # Directory does not exist, so assume it's an executable
++     echo "Using supplied Scheme path as an executable"
++     MAKE_SCHEME_MODE="${T_CROSS_MODE}-via-scheme"
++     MAKE_SCHEME_SCHEME="${enable_scheme}"
++     USE_SCHEME_MODE="_existing"
++   fi
+ fi
+ 
+ if test "${enable_racket}" != "" ; then
+@@ -6012,6 +6027,9 @@ SCHEME_CROSS_CONFIG_ARGS="--machine=${TARGET_MACH} --disable-x11 ${cs_auto_flags
+ 
+ 
+ 
++
++
++
+ 
+ 
+ 
+diff --git a/racket/src/cs/c/configure.ac b/racket/src/cs/c/configure.ac
+index 464ebe1760..aaee88156d 100644
+--- a/racket/src/cs/c/configure.ac
++++ b/racket/src/cs/c/configure.ac
+@@ -23,7 +23,7 @@ AC_ARG_ENABLE(compressmore, [  --enable-compressmore   compress compiled code ev
+ AC_ARG_ENABLE(compressboot, [  --enable-compressboot   compress boot files])
+ m4_include(../ac/path_arg.m4)
+ AC_ARG_ENABLE(racket,     [  --enable-racket=<path>  use <path> as Racket for build; or "auto" to create])
+-AC_ARG_ENABLE(scheme,     [  --enable-scheme=<path>  use <path> as host's build directory for cross])
++AC_ARG_ENABLE(scheme,     [  --enable-scheme=<path>  use <path> as host build for cross])
+ AC_ARG_ENABLE(mach,       [  --enable-mach=<mach>    use Chez Scheme machine type <mach>])
+ AC_ARG_ENABLE(target,     [  --enable-target=<mach>  cross-build for Chez Scheme machine type <mach>])
+ m4_include(../ac/portable_arg.m4)
+@@ -81,7 +81,7 @@ show_explicitly_disabled "${enable_compressboot}" "Compressed boot files"
+ show_explicitly_enabled "${enable_xonx}" "Unix style"
+ m4_include(../ac/path_show.m4)
+ show_explicitly_set "${enable_racket}" "Racket"
+-show_explicitly_set "${enable_scheme}" "Chez Scheme build directory"
++show_explicitly_set "${enable_scheme}" "Chez Scheme for build"
+ show_explicitly_set "${enable_mach}" "machine type"
+ show_explicitly_set "${enable_target}" "cross-build machine type"
+ m4_include(../ac/portable_show.m4)
+@@ -504,9 +504,21 @@ esac
+ 
+ SCHEME_DIR=${srcdir}/../../ChezScheme
+ MAKE_BUILD_SCHEME=checkout
++USE_SCHEME_MODE="_built"
++MAKE_SCHEME_MODE="${T_CROSS_MODE}"
+ 
+ if test "${enable_scheme}" != "" ; then
+-  CS_HOST_WORKAREA_PREFIX="${enable_scheme}/"
++   if test -d "${enable_scheme}" ; then
++     # Directory exists, so use it as a build directory
++     echo "Using supplied Scheme path as a build directory"
++     CS_HOST_WORKAREA_PREFIX="${enable_scheme}/"
++   else
++     # Directory does not exist, so assume it's an executable
++     echo "Using supplied Scheme path as an executable"
++     MAKE_SCHEME_MODE="${T_CROSS_MODE}-via-scheme"
++     MAKE_SCHEME_SCHEME="${enable_scheme}"
++     USE_SCHEME_MODE="_existing"
++   fi     
+ fi
+ 
+ if test "${enable_racket}" != "" ; then
+@@ -821,6 +833,9 @@ AC_SUBST(DIFF_MACH)
+ AC_SUBST(CROSS_MODE)
+ AC_SUBST(T_CROSS_MODE)
+ AC_SUBST(TT_CROSS_MODE)
++AC_SUBST(MAKE_SCHEME_MODE)
++AC_SUBST(MAKE_SCHEME_SCHEME)
++AC_SUBST(USE_SCHEME_MODE)
+ AC_SUBST(SETUP_BOOT_MODE)
+ AC_SUBST(OSX)
+ AC_SUBST(NOT_OSX)
+-- 
+2.32.0
+
-- 
2.32.0