derivations: Raise an error when a module file is not found.

Suggested by Jookia.

* guix/derivations.scm (&file-search-error): New error condition.
(search-path*): Raise it when 'search-path' returns #f.
* guix/gexp.scm (search-path*): Remove.
* guix/ui.scm (call-with-error-handling): Add case for
'file-search-error?'.
* tests/derivations.scm ("build-expression->derivation and invalid
module name"): New test.

guix/derivations.scm

@@ -90,7 +90,11 @@ (define-module (guix derivations)
             build-derivations
             built-derivations
 
+            file-search-error?
+            file-search-error-file-name
+            file-search-error-search-path
 
+            search-path*
             module->source-file-name
             build-expression->derivation)
 
@@ -1036,10 +1040,22 @@ (define* (imported-files store files              ;deprecated
                                   #:guile-for-build guile
                                   #:local-build? #t)))
 
+;; The "file not found" error condition.
+(define-condition-type &file-search-error &error
+  file-search-error?
+  (file     file-search-error-file-name)
+  (path     file-search-error-search-path))
+
 (define search-path*
   ;; A memoizing version of 'search-path' so 'imported-modules' does not end
   ;; up looking for the same files over and over again.
-  (memoize search-path))
+  (memoize (lambda (path file)
+             "Search for FILE in PATH and memoize the result.  Raise a
+'&file-search-error' condition if it could not be found."
+             (or (search-path path file)
+                 (raise (condition
+                         (&file-search-error (file file)
+                                             (path path))))))))
 
 (define (module->source-file-name module)
   "Return the file name corresponding to MODULE, a Guile module name (a list

guix/gexp.scm

@@ -902,11 +902,6 @@ (define build
                       #:guile-for-build guile
                       #:local-build? #t)))
 
-(define search-path*
-  ;; A memoizing version of 'search-path' so 'imported-modules' does not end
-  ;; up looking for the same files over and over again.
-  (memoize search-path))
-
 (define* (imported-modules modules
                            #:key (name "module-import")
                            (system (%current-system))

guix/ui.scm

@@ -461,6 +461,11 @@ (define (port-filename* port)
              (leave (_ "reference to invalid output '~a' of derivation '~a'~%")
                     (derivation-missing-output c)
                     (derivation-file-name (derivation-error-derivation c))))
+            ((file-search-error? c)
+             (leave (_ "file '~a' could not be found in these \
+directories:~{ ~a~}~%")
+                    (file-search-error-file-name c)
+                    (file-search-error-search-path c)))
             ((message-condition? c)
              ;; Normally '&message' error conditions have an i18n'd message.
              (leave (_ "~a~%")

tests/derivations.scm

@@ -570,6 +570,15 @@ (define %coreutils
 
 (test-skip (if (%guile-for-build) 0 8))
 
+(test-equal "build-expression->derivation and invalid module name"
+  '(file-search-error "guix/module/that/does/not/exist.scm")
+  (guard (c ((file-search-error? c)
+             (list 'file-search-error
+                   (file-search-error-file-name c))))
+    (build-expression->derivation %store "foo" #t
+                                  #:modules '((guix module that
+                                                    does not exist)))))
+
 (test-assert "build-expression->derivation and derivation-prerequisites"
   (let ((drv (build-expression->derivation %store "fail" #f)))
     (any (match-lambda