gexp: Add 'with-imported-modules' macro.

* guix/gexp.scm (<gexp>)[modules]: New field.
(gexp-modules): New procedure.
(gexp->derivation): Use it and append the result to %MODULES.
Update docstring to mark #:modules as deprecated.
(current-imported-modules, with-imported-modules): New macros.
(gexp): Pass CURRENT-IMPORTED-MODULES as second argument to 'gexp'.
(gexp->script): Use and honor 'gexp-modules'; define '%modules'.
* tests/gexp.scm ("gexp->derivation & with-imported-modules")
("gexp->derivation & nested with-imported-modules")
("gexp-modules & ungexp", "gexp-modules & ungexp-splicing"):
New tests.
("program-file"): Use 'with-imported-modules'.  Remove #:modules
argument to 'program-file'.
* doc/guix.texi (G-Expressions): Document 'with-imported-modules'.
Mark #:modules of 'gexp->derivation' as deprecated.
* emacs/guix-devel.el: Add syntax for 'with-imported-modules'.
(guix-devel-keywords): Add it.
* .dir-locals.el: Likewise.

1 files changed, 42 insertions, 5 deletions

diff --git a/guix/gexp.scm b/guix/gexp.scm
index c86f4d0fd3..e9274a05f4 100644
--- a/guix/gexp.scm
+++ b/guix/gexp.scm
@@ -29,6 +29,7 @@
   #:use-module (ice-9 match)
   #:export (gexp
             gexp?
+            with-imported-modules
 
             gexp-input
             gexp-input?
@@ -98,9 +99,10 @@
 
 ;; "G expressions".
 (define-record-type <gexp>
-  (make-gexp references proc)
+  (make-gexp references modules proc)
   gexp?
   (references gexp-references)                    ;list of <gexp-input>
+  (modules    gexp-self-modules)                  ;list of module names
   (proc       gexp-proc))                         ;procedure
 
 (define (write-gexp gexp port)
@@ -384,6 +386,23 @@ whether this should be considered a \"native\" input or not."
 
 (set-record-type-printer! <gexp-output> write-gexp-output)
 
+(define (gexp-modules gexp)
+  "Return the list of Guile module names GEXP relies on."
+  (delete-duplicates
+   (append (gexp-self-modules gexp)
+           (append-map (match-lambda
+                         (($ <gexp-input> (? gexp? exp))
+                          (gexp-modules exp))
+                         (($ <gexp-input> (lst ...))
+                          (append-map (lambda (item)
+                                        (if (gexp? item)
+                                            (gexp-modules item)
+                                            '()))
+                                      lst))
+                         (_
+                          '()))
+                       (gexp-references gexp)))))
+
 (define raw-derivation
   (store-lift derivation))
 
@@ -465,7 +484,8 @@ derivation) on SYSTEM; EXP is stored in a file called SCRIPT-NAME.  When
 TARGET is true, it is used as the cross-compilation target triplet for
 packages referred to by EXP.
 
-Make MODULES available in the evaluation context of EXP; MODULES is a list of
+MODULES is deprecated in favor of 'with-imported-modules'.  Its meaning is to
+make MODULES available in the evaluation context of EXP; MODULES is a list of
 names of Guile modules searched in MODULE-PATH to be copied in the store,
 compiled, and made available in the load path during the execution of
 EXP---e.g., '((guix build utils) (guix build gnu-build-system)).
@@ -494,7 +514,9 @@ Similarly for DISALLOWED-REFERENCES, which can list items that must not be
 referenced by the outputs.
 
 The other arguments are as for 'derivation'."
-  (define %modules modules)
+  (define %modules
+    (delete-duplicates
+     (append modules (gexp-modules exp))))
   (define outputs (gexp-outputs exp))
 
   (define (graphs-file-names graphs)
@@ -724,6 +746,17 @@ and in the current monad setting (system type, etc.)"
               (simple-format #f "~a:~a" line column)))
         "<unknown location>")))
 
+(define-syntax-parameter current-imported-modules
+  ;; Current list of imported modules.
+  (identifier-syntax '()))
+
+(define-syntax-rule (with-imported-modules modules body ...)
+  "Mark the gexps defined in BODY... as requiring MODULES in their execution
+environment."
+  (syntax-parameterize ((current-imported-modules
+                         (identifier-syntax modules)))
+    body ...))
+
 (define-syntax gexp
   (lambda (s)
     (define (collect-escapes exp)
@@ -819,6 +852,7 @@ and in the current monad setting (system type, etc.)"
               (sexp    (substitute-references #'exp (zip escapes formals)))
               (refs    (map escape->ref escapes)))
          #`(make-gexp (list #,@refs)
+                      current-imported-modules
                       (lambda #,formals
                         #,sexp)))))))
 
@@ -960,8 +994,11 @@ they can refer to each other."
                        #:key (modules '()) (guile (default-guile)))
   "Return an executable script NAME that runs EXP using GUILE with MODULES in
 its search path."
-  (mlet %store-monad ((modules  (imported-modules modules))
-                      (compiled (compiled-modules modules)))
+  (define %modules
+    (append (gexp-modules exp) modules))
+
+  (mlet %store-monad ((modules  (imported-modules %modules))
+                      (compiled (compiled-modules %modules)))
     (gexp->derivation name
                       (gexp
                        (call-with-output-file (ungexp output)