Merge branch 'master' into core-updates

7 files changed, 288 insertions, 116 deletions

diff --git a/guix/build/go-build-system.scm b/guix/build/go-build-system.scm
index eaad9d8751..3114067aa9 100644
--- a/guix/build/go-build-system.scm
+++ b/guix/build/go-build-system.scm
@@ -37,7 +37,7 @@
 ;; process for Go libraries, so we use `go install`, which preserves the
 ;; results. [0]
 
-;; Go software is developed and built within a particular filesystem hierarchy
+;; Go software is developed and built within a particular file system hierarchy
 ;; structure called a 'workspace' [1].  This workspace is found by Go
 ;; via the GOPATH environment variable.  Typically, all Go source code
 ;; and compiled objects are kept in a single workspace, but it is
@@ -48,7 +48,7 @@
 ;; an 'import path'.  The import path is based on the URL of the
 ;; software's source.  Since most source code is provided over the
 ;; internet, the import path is typically a combination of the remote
-;; URL and the source repository's filesystem structure. For example,
+;; URL and the source repository's file system structure. For example,
 ;; the Go port of the common `du` command is hosted on github.com, at
 ;; <https://github.com/calmh/du>.  Thus, the import path is
 ;; <github.com/calmh/du>. [3]
@@ -58,12 +58,12 @@
 ;; the go-build-system.
 ;;
 ;; Modules of modular Go libraries are named uniquely with their
-;; filesystem paths.  For example, the supplemental but "standardized"
+;; file system paths.  For example, the supplemental but "standardized"
 ;; libraries developed by the Go upstream developers are available at
 ;; <https://golang.org/x/{net,text,crypto, et cetera}>.  The Go IPv4
 ;; library's import path is <golang.org/x/net/ipv4>.  The source of
 ;; such modular libraries must be unpacked at the top-level of the
-;; filesystem structure of the library.  So the IPv4 library should be
+;; file system structure of the library.  So the IPv4 library should be
 ;; unpacked to <golang.org/x/net>.  This is handled in the
 ;; go-build-system with the optional #:unpack-path key.
 ;;
@@ -72,7 +72,7 @@
 ;; that all modules of modular libraries cannot be built with a single
 ;; command.  Each module must be built individually.  This complicates
 ;; certain cases, and these issues are currently resolved by creating a
-;; filesystem union of the required modules of such libraries.  I think
+;; file system union of the required modules of such libraries.  I think
 ;; this could be improved in future revisions of the go-build-system.
 ;;
 ;; [0] `go build`:
diff --git a/guix/build/ruby-build-system.scm b/guix/build/ruby-build-system.scm
index c2d2766279..09ae2390a5 100644
--- a/guix/build/ruby-build-system.scm
+++ b/guix/build/ruby-build-system.scm
@@ -21,14 +21,15 @@
 (define-module (guix build ruby-build-system)
   #:use-module ((guix build gnu-build-system) #:prefix gnu:)
   #:use-module (guix build utils)
+  #:use-module (ice-9 ftw)
   #:use-module (ice-9 match)
   #:use-module (ice-9 popen)
+  #:use-module (ice-9 rdelim)
   #:use-module (ice-9 regex)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-26)
   #:export (%standard-phases
-            ruby-build
-            gem-home))
+            ruby-build))
 
 ;; Commentary:
 ;;
@@ -129,43 +130,179 @@ GEM-FLAGS are passed to the 'gem' invokation, if present."
                                          (assoc-ref inputs "ruby"))
                            1))
          (out (assoc-ref outputs "out"))
-         (gem-home (string-append out "/lib/ruby/gems/" ruby-version ".0"))
+         (vendor-dir (string-append out "/lib/ruby/vendor_ruby"))
          (gem-file (first-matching-file "\\.gem$"))
          (gem-file-basename (basename gem-file))
          (gem-name (substring gem-file-basename
                               0
-                              (- (string-length gem-file-basename) 4)))
-         (gem-directory (string-append gem-home "/gems/" gem-name)))
-    (setenv "GEM_HOME" gem-home)
-    (mkdir-p gem-home)
-    (and (apply system* "gem" "install" gem-file
-                "--local" "--ignore-dependencies"
-                ;; Executables should go into /bin, not /lib/ruby/gems.
-                "--bindir" (string-append out "/bin")
-                gem-flags)
+                              (- (string-length gem-file-basename) 4))))
+    (setenv "GEM_VENDOR" vendor-dir)
+    (and (let ((install-succeeded?
+                (zero?
+                 (apply system* "gem" "install" gem-file
+                        "--local" "--ignore-dependencies" "--vendor"
+                        ;; Executables should go into /bin, not
+                        ;; /lib/ruby/gems.
+                        "--bindir" (string-append out "/bin")
+                        gem-flags))))
+           (or install-succeeded?
+               (begin
+                 (simple-format #t "installation failed\n")
+                 (let ((failed-output-dir (string-append (getcwd) "/out")))
+                   (mkdir failed-output-dir)
+                   (copy-recursively out failed-output-dir))
+                 #f)))
          (begin
            ;; Remove the cached gem file as this is unnecessary and contains
            ;; timestamped files rendering builds not reproducible.
-           (let ((cached-gem (string-append gem-home "/cache/" gem-file)))
+           (let ((cached-gem (string-append vendor-dir "/cache/" gem-file)))
              (log-file-deletion cached-gem)
              (delete-file cached-gem))
            ;; For gems with native extensions, several Makefile-related files
            ;; are created that contain timestamps or other elements making
            ;; them not reproducible.  They are unnecessary so we remove them.
-           (if (file-exists? (string-append gem-directory "/ext"))
+           (if (file-exists? (string-append vendor-dir "/ext"))
                (begin
                  (for-each (lambda (file)
                              (log-file-deletion file)
                              (delete-file file))
                            (append
-                            (find-files (string-append gem-home "/doc")
+                            (find-files (string-append vendor-dir "/doc")
                                         "page-Makefile.ri")
-                            (find-files (string-append gem-home "/extensions")
+                            (find-files (string-append vendor-dir "/extensions")
                                         "gem_make.out")
-                            (find-files (string-append gem-directory "/ext")
+                            (find-files (string-append vendor-dir "/ext")
                                         "Makefile")))))
            #t))))
 
+(define* (wrap-ruby-program prog #:key (gem-clear-paths #t) #:rest vars)
+  "Make a wrapper for PROG.  VARS should look like this:
+
+  '(VARIABLE DELIMITER POSITION LIST-OF-DIRECTORIES)
+
+where DELIMITER is optional.  ':' will be used if DELIMITER is not given.
+
+For example, this command:
+
+  (wrap-ruby-program \"foo\"
+                '(\"PATH\" \":\" = (\"/gnu/.../bar/bin\"))
+                '(\"CERT_PATH\" suffix (\"/gnu/.../baz/certs\"
+                                        \"/qux/certs\")))
+
+will copy 'foo' to '.real/fool' and create the file 'foo' with the following
+contents:
+
+  #!location/of/bin/ruby
+  ENV['PATH'] = \"/gnu/.../bar/bin\"
+  ENV['CERT_PATH'] = (ENV.key?('CERT_PATH') ? (ENV['CERT_PATH'] + ':') : '') + '/gnu/.../baz/certs:/qux/certs'
+  load location/of/.real/foo
+
+This is useful for scripts that expect particular programs to be in $PATH, for
+programs that expect particular gems to be in the GEM_PATH.
+
+This is preferable to wrap-program, which uses a bash script, as this prevents
+ruby scripts from being executed with @command{ruby -S ...}.
+
+If PROG has previously been wrapped by 'wrap-ruby-program', the wrapper is
+extended with definitions for VARS."
+  (define wrapped-file
+    (string-append (dirname prog) "/.real/" (basename prog)))
+
+  (define already-wrapped?
+    (file-exists? wrapped-file))
+
+  (define (last-line port)
+    ;; Return the last line read from PORT and leave PORT's cursor right
+    ;; before it.
+    (let loop ((previous-line-offset 0)
+               (previous-line "")
+               (position (seek port 0 SEEK_CUR)))
+      (match (read-line port 'concat)
+        ((? eof-object?)
+         (seek port previous-line-offset SEEK_SET)
+         previous-line)
+        ((? string? line)
+         (loop position line (+ (string-length line) position))))))
+
+  (define (export-variable lst)
+    ;; Return a string that exports an environment variable.
+    (match lst
+      ((var sep '= rest)
+       (format #f "ENV['~a'] = '~a'"
+               var (string-join rest sep)))
+      ((var sep 'prefix rest)
+       (format #f "ENV['~a'] = '~a' + (ENV.key?('~a') ? ('~a' + ENV['~a']) : '')"
+               var (string-join rest sep) var sep var))
+      ((var sep 'suffix rest)
+       (format #f "ENV['~a'] = (ENV.key?('~a') ? (ENV['~a'] + '~a') : '') + '~a'"
+               var var var sep (string-join rest sep)))
+      ((var '= rest)
+       (format #f "ENV['~a'] = '~a'"
+               var (string-join rest ":")))
+      ((var 'prefix rest)
+       (format #f "ENV['~a'] = '~a' + (ENV.key?('~a') ? (':' + ENV['~a']) : '')"
+               var (string-join rest ":") var var))
+      ((var 'suffix rest)
+       (format #f "ENV['~a'] = (ENV.key?('~a') ? (ENV['~a'] + ':') : '') + '~a'"
+               var var var (string-join rest ":")))))
+
+  (if already-wrapped?
+
+      ;; PROG is already a wrapper: add the new "export VAR=VALUE" lines just
+      ;; before the last line.
+      (let* ((port (open-file prog "r+"))
+             (last (last-line port)))
+        (for-each (lambda (var)
+                    (display (export-variable var) port)
+                    (newline port))
+                  vars)
+        (display last port)
+        (close-port port))
+
+      ;; PROG is not wrapped yet: create a shell script that sets VARS.
+      (let ((prog-tmp (string-append wrapped-file "-tmp")))
+        (mkdir-p (dirname prog-tmp))
+        (link prog wrapped-file)
+
+        (call-with-output-file prog-tmp
+          (lambda (port)
+            (format port
+                    "#!~a~%~a~%~a~%load '~a'~%"
+                    (which "ruby")
+                    (string-join (map export-variable vars) "\n")
+                    ;; This ensures that if the GEM_PATH has been changed,
+                    ;; then that change will be noticed.
+                    (if gem-clear-paths "Gem.clear_paths" "")
+                    (canonicalize-path wrapped-file))))
+
+        (chmod prog-tmp #o755)
+        (rename-file prog-tmp prog))))
+
+(define* (wrap #:key inputs outputs #:allow-other-keys)
+  (define (list-of-files dir)
+    (map (cut string-append dir "/" <>)
+         (or (scandir dir (lambda (f)
+                            (let ((s (stat (string-append dir "/" f))))
+                              (eq? 'regular (stat:type s)))))
+             '())))
+
+  (define bindirs
+    (append-map (match-lambda
+                 ((_ . dir)
+                  (list (string-append dir "/bin")
+                        (string-append dir "/sbin"))))
+                outputs))
+
+  (let* ((out  (assoc-ref outputs "out"))
+         (var `("GEM_PATH" prefix
+                (,(string-append out "/lib/ruby/vendor_ruby")
+                 ,(getenv "GEM_PATH")))))
+    (for-each (lambda (dir)
+                (let ((files (list-of-files dir)))
+                  (for-each (cut wrap-ruby-program <> var)
+                            files)))
+              bindirs)))
+
 (define (log-file-deletion file)
   (display (string-append "deleting '" file "' for reproducibility\n")))
 
@@ -177,18 +314,9 @@ GEM-FLAGS are passed to the 'gem' invokation, if present."
     (add-after 'extract-gemspec 'replace-git-ls-files replace-git-ls-files)
     (replace 'build build)
     (replace 'check check)
-    (replace 'install install)))
+    (replace 'install install)
+    (add-after 'install 'wrap wrap)))
 
 (define* (ruby-build #:key inputs (phases %standard-phases)
                      #:allow-other-keys #:rest args)
   (apply gnu:gnu-build #:inputs inputs #:phases phases args))
-
-(define (gem-home store-path ruby-version)
-  "Return a string to the gem home directory in the store given a STORE-PATH
-and the RUBY-VERSION used to build that ruby package"
-  (string-append
-   store-path
-   "/lib/ruby/gems/"
-   (regexp-substitute #f
-                      (string-match "^[0-9]+\\.[0-9]+" ruby-version)
-                      0 ".0")))
diff --git a/guix/packages.scm b/guix/packages.scm
index be0a5eeedb..b5c0b60440 100644
--- a/guix/packages.scm
+++ b/guix/packages.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017, 2018 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2014, 2015, 2017 Mark H Weaver <mhw@netris.org>
 ;;; Copyright © 2015 Eric Bavier <bavier@member.fsf.org>
 ;;; Copyright © 2016 Alex Kost <alezost@gmail.com>
@@ -789,7 +789,8 @@ when CUT? returns true for a given package."
           (location (package-location p))
           (inputs (map rewrite (package-inputs p)))
           (native-inputs (map rewrite (package-native-inputs p)))
-          (propagated-inputs (map rewrite (package-propagated-inputs p)))))))
+          (propagated-inputs (map rewrite (package-propagated-inputs p)))
+          (replacement (and=> (package-replacement p) proc))))))
 
   replace)
 
diff --git a/guix/scripts/offload.scm b/guix/scripts/offload.scm
index 7e114fa2c9..56d6de6308 100644
--- a/guix/scripts/offload.scm
+++ b/guix/scripts/offload.scm
@@ -358,26 +358,19 @@ MACHINE."
     (parameterize ((current-build-output-port (build-log-port)))
       (build-derivations store (list drv))))
 
-  (retrieve-files* outputs store)
+  (retrieve-files* outputs store
+
+                   ;; We cannot use the 'import-paths' RPC here because we
+                   ;; already hold the locks for FILES.
+                   #:import
+                   (lambda (port)
+                     (restore-file-set port
+                                       #:log-port (current-error-port)
+                                       #:lock? #f)))
+
   (format (current-error-port) "done with offloaded '~a'~%"
           (derivation-file-name drv)))
 
-(define (retrieve-files* files remote)
-  "Retrieve FILES from REMOTE and import them using 'restore-file-set'."
-  (let-values (((port count)
-                (file-retrieval-port files remote)))
-    (format #t (N_ "retrieving ~a store item from '~a'...~%"
-                   "retrieving ~a store items from '~a'...~%" count)
-            count (remote-store-host remote))
-
-    ;; We cannot use the 'import-paths' RPC here because we already
-    ;; hold the locks for FILES.
-    (let ((result (restore-file-set port
-                                    #:log-port (current-error-port)
-                                    #:lock? #f)))
-      (close-port port)
-      result)))
-
 
 ;;;
 ;;; Scheduling.
@@ -407,7 +400,7 @@ allowed on MACHINE.  Return +∞ if MACHINE is unreachable."
            +inf.0 ;MACHINE does not respond, so assume it is infinitely loaded
            (match (string-tokenize line)
              ((one five fifteen . x)
-              (let* ((raw        (string->number five))
+              (let* ((raw        (string->number one))
                      (jobs       (build-machine-parallel-builds machine))
                      (normalized (/ raw jobs)))
                 (format (current-error-port) "load on machine '~a' is ~s\
@@ -549,8 +542,7 @@ slot (which must later be released with 'release-build-slot'), or #f and #f."
   "Bail out if NODE is not running Guile."
   (match (node-guile-version node)
     (#f
-     (leave (G_ "Guile could not be started on '~a'~%")
-            name))
+     (report-guile-error name))
     ((? string? version)
      ;; Note: The version string already contains the word "Guile".
      (info (G_ "'~a' is running ~a~%")
@@ -558,18 +550,34 @@ slot (which must later be released with 'release-build-slot'), or #f and #f."
 
 (define (assert-node-has-guix node name)
   "Bail out if NODE lacks the (guix) module, or if its daemon is not running."
-  (match (node-eval node
-                    '(begin
-                       (use-modules (guix))
-                       (with-store store
-                         (add-text-to-store store "test"
-                                            "Hello, build machine!"))))
-    ((? string? str)
-     (info (G_ "Guix is usable on '~a' (test returned ~s)~%")
-           name str))
-    (x
-     (leave (G_ "failed to use Guix module on '~a' (test returned ~s)~%")
-            name x))))
+  (catch 'node-repl-error
+    (lambda ()
+      (match (node-eval node
+                        '(begin
+                           (use-modules (guix))
+                           (and add-text-to-store 'alright)))
+        ('alright #t)
+        (_ (report-module-error name))))
+    (lambda (key . args)
+      (report-module-error name)))
+
+  (catch 'node-repl-error
+    (lambda ()
+      (match (node-eval node
+                        '(begin
+                           (use-modules (guix))
+                           (with-store store
+                             (add-text-to-store store "test"
+                                                "Hello, build machine!"))))
+        ((? string? str)
+         (info (G_ "Guix is usable on '~a' (test returned ~s)~%")
+               name str))
+        (x
+         (leave (G_ "failed to talk to guix-daemon on '~a' (test returned ~s)~%")
+                name x))))
+    (lambda (key . args)
+      (leave (G_ "remove evaluation on '~a' failed:~{ ~s~}~%")
+             args))))
 
 (define %random-state
   (delay
diff --git a/guix/scripts/system.scm b/guix/scripts/system.scm
index ebcf3e4f3b..55a02fb96d 100644
--- a/guix/scripts/system.scm
+++ b/guix/scripts/system.scm
@@ -709,8 +709,8 @@ and TARGET arguments."
   "Perform ACTION for OS.  INSTALL-BOOTLOADER? specifies whether to install
 bootloader; BOOTLOADER-TAGET is the target for the bootloader; TARGET is the
 target root directory; IMAGE-SIZE is the size of the image to be built, for
-the 'vm-image' and 'disk-image' actions.  The root filesystem is created as a
-FILE-SYSTEM-TYPE filesystem.  FULL-BOOT? is used for the 'vm' action; it
+the 'vm-image' and 'disk-image' actions.  The root file system is created as a
+FILE-SYSTEM-TYPE file system.  FULL-BOOT? is used for the 'vm' action; it
 determines whether to boot directly to the kernel or to the bootloader.
 
 When DERIVATIONS-ONLY? is true, print the derivation file name(s) without
diff --git a/guix/ssh.scm b/guix/ssh.scm
index cb560c0e9c..5e442024bc 100644
--- a/guix/ssh.scm
+++ b/guix/ssh.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2016, 2017 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2016, 2017, 2018 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -28,7 +28,9 @@
   #:use-module (ssh session)
   #:use-module (ssh dist)
   #:use-module (ssh dist node)
+  #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-11)
+  #:use-module (srfi srfi-26)
   #:use-module (srfi srfi-34)
   #:use-module (srfi srfi-35)
   #:use-module (ice-9 match)
@@ -38,9 +40,11 @@
             connect-to-remote-daemon
             send-files
             retrieve-files
+            retrieve-files*
             remote-store-host
 
-            file-retrieval-port))
+            report-guile-error
+            report-module-error))
 
 ;;; Commentary:
 ;;;
@@ -102,42 +106,36 @@ Throw an error on failure."
     ;; hack.
     `(begin
        (use-modules (ice-9 match) (rnrs io ports)
-                    (rnrs bytevectors) (system foreign))
-
-       (define read!
-         ;; XXX: We would use 'get-bytevector-some' but it always returns a
-         ;; single byte in Guile <= 2.2.3---see <https://bugs.gnu.org/30066>.
-         ;; This procedure works around it.
-         (let ((proc (pointer->procedure int
-                                         (dynamic-func "read" (dynamic-link))
-                                         (list int '* size_t))))
-           (lambda (port bv)
-             (proc (fileno port) (bytevector->pointer bv)
-                   (bytevector-length bv)))))
+                    (rnrs bytevectors))
 
        (let ((sock   (socket AF_UNIX SOCK_STREAM 0))
              (stdin  (current-input-port))
-             (stdout (current-output-port))
-             (buffer (make-bytevector 65536)))
-         (setvbuf stdin _IONBF)
+             (stdout (current-output-port)))
          (setvbuf stdout _IONBF)
+
+         ;; Use buffered ports so that 'get-bytevector-some' returns up to the
+         ;; whole buffer like read(2) would--see <https://bugs.gnu.org/30066>.
+         (setvbuf stdin _IOFBF 65536)
+         (setvbuf sock _IOFBF 65536)
+
          (connect sock AF_UNIX ,socket-name)
 
          (let loop ()
            (match (select (list stdin sock) '() '())
              ((reads () ())
               (when (memq stdin reads)
-                (match (read! stdin buffer)
-                  ((? zero?)                      ;EOF
+                (match (get-bytevector-some stdin)
+                  ((? eof-object?)
                    (primitive-exit 0))
-                  (count
-                   (put-bytevector sock buffer 0 count))))
+                  (bv
+                   (put-bytevector sock bv)
+                   (force-output sock))))
               (when (memq sock reads)
-                (match (read! sock buffer)
-                  ((? zero?)                      ;EOF
+                (match (get-bytevector-some sock)
+                  ((? eof-object?)
                    (primitive-exit 0))
-                  (count
-                   (put-bytevector stdout buffer 0 count))))
+                  (bv
+                   (put-bytevector stdout bv))))
               (loop))
              (_
               (primitive-exit 1)))))))
@@ -235,6 +233,10 @@ be read.  When RECURSIVE? is true, the closure of FILES is exported."
                (write `(invalid-items ,invalid))
                (exit 1))
 
+             ;; TODO: When RECURSIVE? is true, we could send the list of store
+             ;; items in the closure so that the other end can filter out
+             ;; those it already has.
+
              (write '(exporting))                 ;we're ready
              (force-output)
 
@@ -339,10 +341,11 @@ to the length of FILES.)"
              (&message
               (message (format #f fmt args ...))))))))
 
-(define* (retrieve-files local files remote
-                         #:key recursive? (log-port (current-error-port)))
-  "Retrieve FILES from REMOTE and import them using the 'import-paths' RPC on
-LOCAL.  When RECURSIVE? is true, retrieve the closure of FILES."
+(define* (retrieve-files* files remote
+                          #:key recursive? (log-port (current-error-port))
+                          (import (const #f)))
+  "Pass IMPORT an input port from which to read the sequence of FILES coming
+from REMOTE.  When RECURSIVE? is true, retrieve the closure of FILES."
   (let-values (((port count)
                 (file-retrieval-port files remote
                                      #:recursive? recursive?)))
@@ -352,25 +355,16 @@ LOCAL.  When RECURSIVE? is true, retrieve the closure of FILES."
                       "retrieving ~a store items from '~a'...~%" count)
                count (remote-store-host remote))
 
-       (let ((result (import-paths local port)))
-         (close-port port)
-         result))
+       (dynamic-wind
+         (const #t)
+         (lambda ()
+           (import port))
+         (lambda ()
+           (close-port port))))
       ((? eof-object?)
-       (raise-error (G_ "failed to start Guile on remote host '~A': exit code ~A")
-                    (remote-store-host remote)
-                    (channel-get-exit-status port)
-                    (=> (G_ "Make sure @command{guile} can be found in
-@code{$PATH} on the remote host.  Run @command{ssh ~A guile --version} to
-check.")
-                        (remote-store-host remote))))
+       (report-guile-error (remote-store-host remote)))
       (('module-error . _)
-       ;; TRANSLATORS: Leave "Guile" untranslated.
-       (raise-error (G_ "Guile modules not found on remote host '~A'")
-                    (remote-store-host remote)
-                    (=> (G_ "Make sure @code{GUILE_LOAD_PATH} includes Guix'
-own module directory.  Run @command{ssh ~A env | grep GUILE_LOAD_PATH} to
-check.")
-                        (remote-store-host remote))))
+       (report-module-error (remote-store-host remote)))
       (('connection-error file code . _)
        (raise-error (G_ "failed to connect to '~A' on remote host '~A': ~a")
                     file (remote-store-host remote) (strerror code)))
@@ -386,4 +380,36 @@ check.")
        (raise-error (G_ "failed to retrieve store items from '~a'")
                     (remote-store-host remote))))))
 
+(define* (retrieve-files local files remote
+                         #:key recursive? (log-port (current-error-port)))
+  "Retrieve FILES from REMOTE and import them using the 'import-paths' RPC on
+LOCAL.  When RECURSIVE? is true, retrieve the closure of FILES."
+  (retrieve-files* (remove (cut valid-path? local <>) files)
+                   remote
+                   #:recursive? recursive?
+                   #:log-port log-port
+                   #:import (lambda (port)
+                              (import-paths local port))))
+
+
+;;;
+;;; Error reporting.
+;;;
+
+(define (report-guile-error host)
+  (raise-error (G_ "failed to start Guile on remote host '~A'") host
+               (=> (G_ "Make sure @command{guile} can be found in
+@code{$PATH} on the remote host.  Run @command{ssh ~A guile --version} to
+check.")
+                   host)))
+
+(define (report-module-error host)
+  "Report an error about missing Guix modules on HOST."
+  ;; TRANSLATORS: Leave "Guile" untranslated.
+  (raise-error (G_ "Guile modules not found on remote host '~A'") host
+               (=> (G_ "Make sure @code{GUILE_LOAD_PATH} includes Guix'
+own module directory.  Run @command{ssh ~A env | grep GUILE_LOAD_PATH} to
+check.")
+                   host)))
+
 ;;; ssh.scm ends here
diff --git a/guix/ui.scm b/guix/ui.scm
index 895179744b..fb2380b68a 100644
--- a/guix/ui.scm
+++ b/guix/ui.scm
@@ -195,7 +195,16 @@ messages."
   (catch #t
     (lambda ()
       ;; XXX: Force a recompilation to avoid ABI issues.
-      ;; (set! %fresh-auto-compile #t)
+      ;;
+      ;; In 2.2.3, the bogus answer to <https://bugs.gnu.org/29226> was to
+      ;; ignore all available .go, not just those from ~/.cache, which in turn
+      ;; meant that we had to rebuild *everything*.  Since this is too costly,
+      ;; we have to turn auto '%fresh-auto-compile' with that version, at the
+      ;; risk of getting ABI breakage in the user's config file.  See
+      ;; <https://bugs.gnu.org/29881>.
+      (unless (string=? (version) "2.2.3")
+        (set! %fresh-auto-compile #t))
+
       (set! %load-should-auto-compile #t)
 
       (save-module-excursion