services: configuration: Add environment variable serializer.

This patch implements a general API to serialize configuration records
to list of pairs representing environment variables. The car of each
pair represents the variable name and the cdr the variable value.

* gnu/services/configuration/environment-variables.scm: New file.
(serialize-string-environment-variable)
(serialize-maybe-string-environment-variable)
(serialize-boolean-environment-variable)
(serialize-maybe-boolean-environment-variable)
(serialize-number-environment-variable)
(serialize-maybe-number-environment-variable): New variables.
(serialize-environment-variables): New variable.
* gnu/services/configuration/utils.scm: New file.
(uglify-snake-case): New variable.
* tests/services/configuration.scm: Add tests for environment serializer.
(wrong type for a field): Adjust error location.
* doc/guix.texi: Document it.

Change-Id: I81a166576f94d3c8f5bf78c82a02183689a3091c
Signed-off-by: Liliana Marie Prikler <liliana.prikler@gmail.com>

1 files changed, 57 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 733c86afac..198ecb3413 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -51663,6 +51663,63 @@ phone-number = 0
 is-married = true
 @end example
 
+@subsubsection Serializing to environment variables
+@cindex environment variables, serialization of configuration records
+
+There are services which expect their configuration as environment variables.
+The @code{(gnu services configuration environment-variables)} module provides
+facilities to serialize configuration records from
+@code{(gnu services configuration)} to list of pairs representing environment
+variables.
+
+For example this configuration record:
+
+@lisp
+(define-configuration/no-serialization server
+  (ssh-port
+   (number 22)
+   "The public SSH port of the server.")
+  (fqdn
+   (maybe-string)
+   "The fully qualified domain name of the server.")
+  (active?
+   (boolean #f)
+   "Whether or not the server should be activated."))
+
+(define my-server
+ (server
+  (ssh-port 20022)
+  (active? #t)))
+@end lisp
+
+with this call:
+
+@lisp
+(serialize-environment-variables my-server server-fields
+                                 #:true-value "1"
+                                 #:false-value "0")
+@end lisp
+
+would yield:
+
+@lisp
+'(("SSH_PORT" . "20022")
+  ("ACTIVE" . "1"))
+@end lisp
+
+@anchor{serialize-environment-variables-procedure}
+@deffn {Procedure} serialize-environment-variables @var{config} @var{fields} @
+         [@var{selection} #f] [@var{negate?} #f] [#:prefix #f] @
+         [#:true-value "true"] [#:false-value "false"]
+Serializes the fields whose name is included in SELECTION from CONFIG, a
+configuration from @code{(gnu services configuration)}, and FIELDS, the
+list of its field records, to a list of pairs.  When NEGATE? is #t all services
+not included in SELECTION will be serialized.  Each  pair represents an
+environment variable.  The first element of each pair is the variable name, the
+second is the value.  When PREFIX is a string it is prepended to the variable
+name.  TRUE-VALUE and FALSE-VALUE will be used as a representation for
+respectfully @code{#t} and @code{#f}.
+@end deffn
 
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