Merge branch 'master' into core-updates

ui: Replace the global 'symlink' binding.

* guix/ui.scm (symlink): Set! the global symlink.

ui: Do not call 'display-error' for SRFI-34 exceptions.

* guix/ui.scm (report-load-error, warn-about-load-error, read/eval): Add
  clause for SRFI-34 exceptions.

ui: Improve error reporting for 'read/eval'.

The effect is visible on commands like:

  guix build -e '(+ 2 "foo")'
  guix build -e '()'

* guix/ui.scm (read/eval): Change handler to properly report syntax errors and
  use 'display-error' for other errors.

guix system: Add '--on-error'.

* guix/ui.scm (load*): Add #:on-error parameter.
  [tag, error-string]: New variables.
  Wrap 'load' call in 'call-with-prompt'.  Pass TAG to 'make-stack'.  Honor
  ON-ERROR after 'report-load-error' call.
  (report-load-error): Change to not exit on error.  Make private.
* guix/scripts/system.scm (show-help, %options): Add --on-error.
  (guix-system): Use 'load*' and pass it #:on-error.

ui: Auto-compile user code, and improve error reporting.

Reported by Christian Grothoff.

* guix/ui.scm (load*): Add 'frame-with-source'.  Set
  %load-should-auto-compile.  Change error handle to just (exit 1).  Add
  pre-unwind handler to capture the stack and call 'report-load-error'.
  (report-load-error): Add optional 'frame' parameter and pass it to
  'display-error'.
* tests/guix-system.sh: Add "unbound variable" test.

ui: Make 'symlink' replacement more future-proof.

* guix/ui.scm (symlink): Change next-to-last 'throw' argument to explicitly
  ignore ARGS; change last argument to (list errno).

ui: Add 'copy-file' replacement with better error reporting.

* guix/ui.scm (copy-file): New procedure.

Merge branch 'master' into gtk-rebuild

Conflicts:
	gnu/packages/gtk.scm

ui: Deduplicate 'show-what-to-build*'.

* guix/ui.scm (show-what-to-build*): New procedure.
* guix/scripts/environment.scm (show-what-to-build*): Delete.
* guix/scripts/system.scm (show-what-to-build*): Likewise.
* build-aux/make-binary-tarball.scm (show-what-to-build*): Likewise.

ui: Factorize user-provided Scheme file loading.

* guix/ui.scm (make-user-module, load*): New procedures.
* guix/scripts/system.scm (%user-module): Define in terms of
  'make-user-module'.
  (read-operating-system): Define in terms of load*'.

Remove assorted Guile 2.0.5 workarounds.

* guix/scripts/authenticate.scm (%default-port-conversion-strategy):
  Remove.
* guix/scripts/substitute.scm (fetch): Remove 2.0.5 special cases.
* guix/serialization.scm (write-file): Remove 'scandir' workaround.
* guix/ui.scm (command-files): Likewise.

ui: Add 'symlink' replacement with better error reporting.

* guix/ui.scm (symlink): New procedure.

guix package: -A and -s take supported systems into account.

* guix/scripts/package.scm (guix-package)[process-query]
  <list-available>: Restrict results to packages matching
  'supported-package?".
* guix/ui.scm (package->recutils): Print "systems:".
* tests/guix-package.sh: Add tests.
* doc/guix.texi (Invoking guix package): Adjust description of
  '--list-available' accordingly.

Merge branch 'core-updates'

Merge branch 'master' into core-updates

gnu: Emit a warning when a package module cannot be loaded.

* guix/ui.scm (warn-about-load-error): New procedure.
* gnu/packages.scm (package-modules): Wrap 'resolve-interface' call in
  'catch #t', and call 'warn-about-load-error' in handler.

ui: Add 'report-load-error'.

* guix/scripts/system.scm (read-operating-system): Replace error
  handling code by a call to 'report-load-error'.
* guix/ui.scm (report-load-error): New procedure.

ui: Recognize 'guix help'.

Suggested by Andy Wingo.

* guix/ui.scm (guix-main): Add "help" case.

Merge branch 'master' into core-updates