[PATCH 2/2] gnu: ghc: Add GHC_PACKAGE_PATH native search path.

[ericbavier]

From: Eric Bavier <address@hidden>

Benefits include: 'guix environment' more useful for ghc libraries, more
useful 'guix package --search-paths' for installed ghc libraries, cleaner
package recipes: no longer need to propagate runtime package dependencies.

* guix/build/haskell-build-system.scm (configure): Unset GHC_PACKAGE_PATH
  around cabal configure.
  (make-ghc-package-database): Use pattern directory search.
  (register): Install complete package database for the current package.
* gnu/packages/haskell.scm (ghc): Add native-search-paths field.
---
 gnu/packages/haskell.scm            |   6 +++
 guix/build/haskell-build-system.scm | 100 +++++++++++++++++++++++++++++-------
 2 files changed, 87 insertions(+), 19 deletions(-)

diff --git a/gnu/packages/haskell.scm b/gnu/packages/haskell.scm
index 34cad87..652409b 100644
--- a/gnu/packages/haskell.scm
+++ b/gnu/packages/haskell.scm
@@ -234,6 +234,12 @@
                    (string-append ghc-bootstrap-path "/" ,name "-" ,version)
                  (zero? (system* "make" "install"))))
              %standard-phases)))))))
+    (native-search-paths (list (search-path-specification
+                                (variable "GHC_PACKAGE_PATH")
+                                (files (list
+                                        (string-append "lib/ghc-" version)))
+                                (file-pattern ".*\\.conf\\.d$")
+                                (file-type 'directory))))
     (home-page "https://www.haskell.org/ghc";)
     (synopsis "The Glasgow Haskell Compiler")
     (description
diff --git a/guix/build/haskell-build-system.scm 
b/guix/build/haskell-build-system.scm
index c0cb789..59a91d5 100644
--- a/guix/build/haskell-build-system.scm
+++ b/guix/build/haskell-build-system.scm
@@ -24,6 +24,7 @@
   #:use-module (ice-9 rdelim)
   #:use-module (ice-9 regex)
   #:use-module (ice-9 match)
+  #:use-module (ice-9 vlist)
   #:export (%standard-phases
             haskell-build))
 
@@ -77,6 +78,7 @@ and parameters ~s~%"
                        (((_ . dir) ...)
                         dir)
                        (_ '())))
+         (ghc-path (getenv "GHC_PACKAGE_PATH"))
          (params (append `(,(string-append "--prefix=" out))
                          `(,(string-append "--libdir=" (or lib out) "/lib"))
                          `(,(string-append "--bindir=" (or bin out) "/bin"))
@@ -96,7 +98,11 @@ and parameters ~s~%"
                              '("--enable-tests")
                              '())
                          configure-flags)))
-    (run-setuphs "configure" params)))
+    ;; Cabal errors if GHC_PACKAGE_PATH is set during 'configure', so unset
+    ;; and restore it.
+    (unsetenv "GHC_PACKAGE_PATH")
+    (run-setuphs "configure" params)
+    (setenv "GHC_PACKAGE_PATH" ghc-path)))
 
 (define* (build #:rest empty)
   "Build a given Haskell package."
@@ -134,6 +140,12 @@ first match and return the content of the group."
       (format #t
               "Compiler ~a not supported~%" name-version)))))
 
+;;; TODO: Move this to (guix build utils)?
+(define-syntax-rule (with-null-error-port exp)
+  "Evaluate EXP with the error port pointing to the bit bucket."
+  (with-error-to-port (%make-void-port "w")
+    (lambda () exp)))
+
 (define (make-ghc-package-database system inputs outputs)
   "Generate the GHC package database."
   (let* ((haskell  (assoc-ref inputs "haskell"))
@@ -141,44 +153,94 @@ first match and return the content of the group."
                        (((_ . dir) ...)
                         dir)
                        (_ '())))
-         (conf-dirs (search-path-as-list
-                     `(,(string-append "lib/"
-                                       (package-name-version haskell)
-                                       "/package.conf.d"))
-                     input-dirs))
+         ;; Silence 'find-files' (see 'evaluate-search-paths')
+         (conf-dirs (with-null-error-port
+                     (search-path-as-list
+                      `(,(string-append "lib/" (package-name-version haskell)))
+                      input-dirs #:pattern ".*\\.conf.d$")))
          (conf-files (append-map (cut find-files <> "\\.conf$") conf-dirs)))
     (mkdir-p %tmp-db-dir)
     (for-each (lambda (file)
-                (copy-file file
-                           (string-append %tmp-db-dir "/" (basename file))))
+                (let ((dest (string-append %tmp-db-dir "/" (basename file))))
+                  (unless (file-exists? dest)
+                    (copy-file file dest))))
               conf-files)
     (zero? (system* "ghc-pkg"
                     (string-append "--package-db=" %tmp-db-dir)
                     "recache"))))
 
 (define* (register #:key name system inputs outputs #:allow-other-keys)
-  "Generate the compiler registration file for a given Haskell package.  Don't
-generate the cache as it would clash in user profiles."
+  "Generate the compiler registration and binary package database files for a
+given Haskell package."
+
+  (define (line-items str)
+    ;; Return a list of the whitespace-delimited "words" in a string
+    (remove string-null?
+            (map string-trim-both (string-split str char-set:whitespace))))
+
+  (define (conf-depends conf-file)
+    ;; Return a list of pkg-ids from the "depends" field in CONF-FILE
+    (let ((port (open-input-file conf-file))
+          (field-rx (make-regexp "^(.*):")))
+      (let loop ((collecting #f)
+                 (deps '()))
+        (let* ((line (read-line port))
+               (field (and=> (regexp-exec field-rx line)
+                             (cut match:substring <> 1))))
+          (cond
+           ((and=> field (cut string=? <> "depends"))
+            ;; The first dependency is listed on the same line as "depends:",
+            ;; so drop those characters.  A line may list more than one .conf.
+            (let ((d (line-items (string-drop line 8))))
+              (loop #t (append d deps))))
+           ((and collecting field)
+            (begin
+              (close-port port)
+              (reverse! deps)))
+           (collecting
+            (loop #t (append (line-items line) deps)))
+           (else (loop #f deps)))))))
+
+  (define (install-transitive-deps conf-file src dest)
+    ;; Copy .conf files from SRC to DEST for dependencies in CONF-FILE, and
+    ;; their dependencies, etc.
+    (let loop ((seen vlist-null)
+               (lst (conf-depends conf-file)))
+      (match lst
+        (() #t)                         ;done
+        ((id . tail)
+         (if (not (vhash-assoc id seen))
+             (let ((dep-conf  (string-append src  "/" id ".conf"))
+                   (dep-conf* (string-append dest "/" id ".conf")))
+               (copy-file (pk 'from dep-conf) (pk 'to dep-conf*))
+               (loop (vhash-cons id #t seen)
+                     (append lst (conf-depends dep-conf))))
+             (loop seen tail))))))
+
   (let* ((out (assoc-ref outputs "out"))
          (haskell  (assoc-ref inputs "haskell"))
          (lib (string-append out "/lib"))
          (config-dir (string-append lib "/"
                                     (package-name-version haskell)
-                                    "/package.conf.d"))
+                                    "/" name ".conf.d"))
          (id-rx (make-regexp "^id: *(.*)$"))
          (config-file (string-append out "/" name ".conf"))
          (params
           (list (string-append "--gen-pkg-config=" config-file))))
     (run-setuphs "register" params)
     ;; The conf file is created only when there is a library to register.
-    (when (file-exists? config-file)
-      (mkdir-p config-dir)
-      (let ((config-file-name+id
-             (call-with-ascii-input-file config-file (cut grep id-rx <>))))
-        (rename-file config-file
-                     (string-append config-dir "/" config-file-name+id
-                                    ".conf"))))
-    #t))
+    (or (not (file-exists? config-file))
+        (begin
+          (mkdir-p config-dir)
+          (let* ((config-file-name+id
+                  (call-with-ascii-input-file config-file (cut grep id-rx 
<>))))
+            (install-transitive-deps config-file %tmp-db-dir config-dir)
+            (rename-file config-file
+                         (string-append config-dir "/"
+                                        config-file-name+id ".conf"))
+            (zero? (system* "ghc-pkg"
+                            (string-append "--package-db=" config-dir)
+                            "recache")))))))
 
 (define* (check #:key tests? test-target #:allow-other-keys)
   "Run the test suite of a given Haskell package."
-- 
2.4.3