shell: Detect --symlink spec problems early.

* guix/scripts/pack.scm (symlink-spec-option-parser): Remove extraneous
char-set.  Raise an exception when the target is an absolute file name.
(guix-pack): Move with-error-handler earlier.
* guix/scripts/shell.scm (guix-shell): Likewise.
* guix/scripts/environment.scm (guix-environment): Wrap the whole
guix-environment* call with the with-error-handling handler.
* tests/guix-environment-container.sh: Add tests.
* tests/guix-pack.sh: Adjust symlink spec.

guix/scripts/environment.scm

@@ -980,12 +980,12 @@ message if any test fails."
   (category development)
   (synopsis "spawn one-off software environments (deprecated)")
 
-  (guix-environment* (parse-args args)))
+  (with-error-handling
+    (guix-environment* (parse-args args))))
 
 (define (guix-environment* opts)
   "Run the 'guix environment' command on OPTS, an alist resulting for
 command-line option processing with 'parse-command-line'."
-  (with-error-handling
   (let* ((pure?        (assoc-ref opts 'pure))
          (container?   (assoc-ref opts 'container?))
          (link-prof?   (assoc-ref opts 'link-profile?))
@@ -1131,7 +1131,7 @@ when using '--container'; doing nothing~%"))
                    (exit/status
                     (launch-environment/fork command profile manifest
                                              #:white-list white-list
-                                               #:pure? pure?))))))))))))))
+                                             #:pure? pure?)))))))))))))
 
 ;;; Local Variables:
 ;;; eval: (put 'with-store/maybe 'scheme-indent-function 1)

guix/scripts/pack.scm

@@ -42,6 +42,7 @@
   #:use-module (guix profiles)
   #:use-module (guix describe)
   #:use-module (guix derivations)
+  #:use-module (guix diagnostics)
   #:use-module (guix search-paths)
   #:use-module (guix build-system gnu)
   #:use-module (guix scripts build)
@@ -59,6 +60,7 @@
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-9)
   #:use-module (srfi srfi-26)
+  #:use-module (srfi srfi-35)
   #:use-module (srfi srfi-37)
   #:use-module (ice-9 match)
   #:export (symlink-spec-option-parser
@@ -163,12 +165,27 @@ its source property."
           ((names ... _) (loop names))))))
 
 (define (symlink-spec-option-parser opt name arg result)
-  "A SRFI-37 option parser for the --symlink option."
+  "A SRFI-37 option parser for the --symlink option.  The symlink spec accepts
+the link file name as its left-hand side value and its target as its
+right-hand side value.  The target must be a relative link."
   ;; Note: Using 'string-split' allows us to handle empty
   ;; TARGET (as in "/opt/guile=", meaning that /opt/guile is
   ;; a symlink to the profile) correctly.
-  (match (string-split arg (char-set #\=))
+  (match (string-split arg #\=)
     ((source target)
+     (when (string-prefix? "/" target)
+       (raise-exception
+        (make-compound-condition
+         (formatted-message (G_ "symlink target is absolute: '~a'~%") target)
+         (condition
+          (&fix-hint (hint (format #f (G_ "The target of the symlink must be
+relative rather than absolute, as it is relative to the profile created.
+Perhaps the source and target components of the symlink spec were inverted?
+Below is a valid example, where the @file{/usr/bin/env} symbolic link is to
+target the profile's @file{bin/env} file:
+@example
+--symlink=/usr/bin/env=bin/env
+@end example"))))))))
      (let ((symlinks (assoc-ref result 'symlinks)))
        (alist-cons 'symlinks
                    `((,source -> ,target) ,@symlinks)
@@ -1326,6 +1343,7 @@ Create a bundle of PACKAGE.\n"))
   (category development)
   (synopsis "create application bundles")
 
+  (with-error-handling
     (define opts
       (parse-command-line args %options (list %default-options)))
 
@@ -1393,7 +1411,6 @@ Create a bundle of PACKAGE.\n"))
            (local-file value))
           (#f #f))))
 
-  (with-error-handling
     (with-store store
       (with-status-verbosity (assoc-ref opts 'verbosity)
         ;; Set the build options before we do anything else.

guix/scripts/shell.scm

@@ -534,6 +534,7 @@ concatenates MANIFESTS, a list of expressions."
   (category development)
   (synopsis "spawn one-off software environments")
 
+  (with-error-handling
     (define (cache-entries directory)
       (filter-map (match-lambda
                     ((or "." "..") #f)
@@ -573,4 +574,4 @@ to make sure your shell does not clobber environment variables."))) )
 
     (if (assoc-ref opts 'export-manifest?)
         (export-manifest opts (current-output-port))
-      (guix-environment* opts)))
+        (guix-environment* opts))))

tests/guix-environment-container.sh

@@ -250,3 +250,6 @@ guix shell --bootstrap guile-bootstrap --container \
 
 # A dangling symlink causes the command to fail.
 ! guix shell --bootstrap -CS /usr/bin/python=bin/python guile-bootstrap -- exit
+
+# An invalid symlink spec causes the command to fail.
+! guix shell --bootstrap -CS bin/guile=/usr/bin/guile guile-bootstrap -- exit

tests/guix-pack.sh

@@ -103,7 +103,7 @@ fi
 guix pack --dry-run --bootstrap -f docker guile-bootstrap
 
 # Build a Docker image with a symlink.
-guix pack --dry-run --bootstrap -f docker -S /opt/gnu=/ guile-bootstrap
+guix pack --dry-run --bootstrap -f docker -S /opt/gnu= guile-bootstrap
 
 # Build a tarball pack of cross-compiled software.  Use coreutils because
 # guile-bootstrap is not intended to be cross-compiled.