channels: Always provide a <channel-metadata> record.

This simplifies the code since one no longer needs to think about
whether '.guix-channel' was present.

* guix/channels.scm (read-channel-metadata): Always pass a string as the
first argument to 'channel-metadata'.
(read-channel-metadata-from-source): Always return a <channel-metadata>
record.
(channel-instance-dependencies): Remove now unneeded 'match'.
(standard-module-derivation): Assume DIRECTORY is never #f and contains
a leading slash.
* tests/channels.scm (channel-metadata-directory)
(channel-metadata-dependencies): New procedures.
("channel-instance-metadata returns #f if .guix-channel does not
exist"): Remove.
("channel-instance-metadata returns default if .guix-channel does not
exist"): New test.
(make-instance): Use 'write' instead of 'display' when creating
'.guix-channel'.
(instance--no-deps): Remove dependencies.
(instance--sub-directory): New variable.
("channel-instance-metadata and default dependencies")
("channel-instance-metadata and directory"): New tests.
("latest-channel-instances excludes duplicate channel dependencies"):
Expect 'channel-commit' to return a string and adjust accordingly.

1 files changed, 12 insertions, 15 deletions

diff --git a/guix/channels.scm b/guix/channels.scm
index 87ad729a70..415246cbd1 100644
--- a/guix/channels.scm
+++ b/guix/channels.scm
@@ -110,8 +110,8 @@
 (define-record-type <channel-metadata>
   (channel-metadata directory dependencies)
   channel-metadata?
-  (directory     channel-metadata-directory)
-  (dependencies  channel-metadata-dependencies))
+  (directory     channel-metadata-directory)      ;string with leading slash
+  (dependencies  channel-metadata-dependencies))  ;list of <channel>
 
 (define (channel-reference channel)
   "Return the \"reference\" for CHANNEL, an sexp suitable for
@@ -129,7 +129,9 @@ if valid metadata could not be read from PORT."
      (let ((directory    (and=> (assoc-ref properties 'directory) first))
            (dependencies (or (assoc-ref properties 'dependencies) '())))
        (channel-metadata
-        directory
+        (cond ((not directory) "/")
+              ((string-prefix? "/" directory) directory)
+              (else (string-append "/" directory)))
         (map (lambda (item)
                (let ((get (lambda* (key #:optional default)
                             (or (and=> (assoc-ref item key) first) default))))
@@ -157,29 +159,26 @@ if valid metadata could not be read from PORT."
 
 (define (read-channel-metadata-from-source source)
   "Return a channel-metadata record read from channel's SOURCE/.guix-channel
-description file, or return #F if SOURCE/.guix-channel does not exist."
+description file, or return the default channel-metadata record if that file
+doesn't exist."
   (catch 'system-error
     (lambda ()
       (call-with-input-file (string-append source "/.guix-channel")
         read-channel-metadata))
     (lambda args
       (if (= ENOENT (system-error-errno args))
-          #f
+          (channel-metadata "/" '())
           (apply throw args)))))
 
 (define (channel-instance-metadata instance)
   "Return a channel-metadata record read from the channel INSTANCE's
-description file, or return #F if the channel instance does not include the
-file."
+description file or its default value."
   (read-channel-metadata-from-source (channel-instance-checkout instance)))
 
 (define (channel-instance-dependencies instance)
   "Return the list of channels that are declared as dependencies for the given
 channel INSTANCE."
-  (match (channel-instance-metadata instance)
-    (#f '())
-    (($ <channel-metadata> directory dependencies)
-     dependencies)))
+  (channel-metadata-dependencies (channel-instance-metadata instance)))
 
 (define* (latest-channel-instances store channels #:optional (previous-channels '()))
   "Return a list of channel instances corresponding to the latest checkouts of
@@ -261,7 +260,7 @@ objects.  The assumption is that SOURCE contains package modules to be added
 to '%package-module-path'."
 
   (let* ((metadata (read-channel-metadata-from-source source))
-         (directory (and=> metadata channel-metadata-directory)))
+         (directory (channel-metadata-directory metadata)))
 
     (define build
       ;; This is code that we'll run in CORE, a Guix instance, with its own
@@ -281,9 +280,7 @@ to '%package-module-path'."
               (string-append #$output "/share/guile/site/"
                              (effective-version)))
 
-            (let* ((subdir (if #$directory
-                               (string-append "/" #$directory)
-                               ""))
+            (let* ((subdir #$directory)
                    (source (string-append #$source subdir)))
               (compile-files source go (find-files source "\\.scm$"))
               (mkdir-p (dirname scm))