doc: Improve documentation of the Bash home service

* doc/guix.texi (Shells Home Services): Document ‘home-bash-extension’
  configuration record.
* gnu/home/services/shells.scm (generate-home-bash-documentation): Extract
  docstrings from ‘home-bash-extension’.
  (home-bash-configuration): Expound on docstrings.
  (home-bash-extension): Likewise.

Fixes: <https://issues.guix.gnu.org/50991>
Signed-off-by: Ludovic Courtès <ludo@gnu.org>

2 files changed, 76 insertions, 19 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 6d6dfd5177..76290d593e 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -36159,6 +36159,7 @@ Extend home-shell-profile service only if you really know what you do.
 
 @subsubheading Bash Home Service
 
+@anchor{home-bash-configuration}
 @deftp {Data Type} home-bash-configuration
 Available @code{home-bash-configuration} fields are:
 
@@ -36167,15 +36168,20 @@ Available @code{home-bash-configuration} fields are:
 The Bash package to use.
 
 @item @code{guix-defaults?} (default: @code{#t}) (type: boolean)
-Add sane defaults like reading @file{/etc/bashrc}, coloring output for
-@code{ls} provided by guix to @file{.bashrc}.
+Add sane defaults like reading @file{/etc/bashrc} and coloring the output of
+@command{ls} to the end of the @file{.bashrc} file.
 
 @item @code{environment-variables} (default: @code{()}) (type: alist)
-Association list of environment variables to set for the Bash session.
+Association list of environment variables to set for the Bash session.  The
+rules for the @code{home-environment-variables-service-type} apply
+here (@pxref{Essential Home Services}).  The contents of this field will be
+added after the contents of the @code{bash-profile} field.
 
 @item @code{aliases} (default: @code{()}) (type: alist)
-Association list of aliases to set for the Bash session.  The alias will
-automatically be quoted, so something line this:
+Association list of aliases to set for the Bash session.  The aliases
+will be defined after the contents of the @code{bashrc} field has been
+put in the @file{.bashrc} file.  The alias will automatically be quoted,
+so something line this:
 
 @lisp
 '((\"ls\" . \"ls -alF\"))
@@ -36206,7 +36212,41 @@ be read in some cases (if the shell terminates by exec'ing another
 process for example).
 
 @end table
+@end deftp
+
+You can extend the Bash service by using the @code{home-bash-extension}
+configuration record, whose fields most mirror that of
+@code{home-bash-configuration} (@pxref{home-bash-configuration}).  The
+contents of the extensions will be added to the end of the corresponding
+Bash configuration files (@pxref{Bash Startup Files,,, bash, The GNU
+Bash Reference Manual}.
+
+@deftp {Data Type} home-bash-extension
+Available @code{home-bash-extension} fields are:
+
+@table @asis
+@item @code{environment-variables} (default: @code{()}) (type: alist)
+Additional environment variables to set.  These will be combined with the
+environment variables from other extensions and the base service to form one
+coherent block of environment variables.
+
+@item @code{aliases} (default: @code{()}) (type: alist)
+Additional aliases to set.  These will be combined with the aliases from
+other extensions and the base service.
 
+@item @code{bash-profile} (default: @code{()}) (type: text-config)
+Additional text blocks to add to @file{.bash_profile}, which will be combined
+with text blocks from other extensions and the base service.
+
+@item @code{bashrc} (default: @code{()}) (type: text-config)
+Additional text blocks to add to @file{.bashrc}, which will be combined
+with text blocks from other extensions and the base service.
+
+@item @code{bash-logout} (default: @code{()}) (type: text-config)
+Additional text blocks to add to @file{.bash_logout}, which will be combined
+with text blocks from other extensions and the base service.
+
+@end table
 @end deftp
 
 @subsubheading Zsh Home Service
diff --git a/gnu/home/services/shells.scm b/gnu/home/services/shells.scm
index f24e47f762..81d07da86c 100644
--- a/gnu/home/services/shells.scm
+++ b/gnu/home/services/shells.scm
@@ -323,16 +323,21 @@ source ~/.profile
    "The Bash package to use.")
   (guix-defaults?
    (boolean #t)
-   "Add sane defaults like reading @file{/etc/bashrc}, coloring output
-for @code{ls} provided by guix to @file{.bashrc}.")
+   "Add sane defaults like reading @file{/etc/bashrc} and coloring the output of
+@command{ls} to the end of the @file{.bashrc} file.")
   (environment-variables
    (alist '())
-   "Association list of environment variables to set for the Bash session."
+   "Association list of environment variables to set for the Bash session.  The
+rules for the @code{home-environment-variables-service-type} apply
+here (@pxref{Essential Home Services}).  The contents of this field will be
+added after the contents of the @code{bash-profile} field."
    serialize-posix-env-vars)
   (aliases
    (alist '())
-   "Association list of aliases to set for the Bash session.  The alias will
-automatically be quoted, so something line this:
+   "Association list of aliases to set for the Bash session.  The aliases will be
+defined after the contents of the @code{bashrc} field has been put in the
+@file{.bashrc} file.  The alias will automatically be quoted, so something line
+this:
 
 @lisp
 '((\"ls\" . \"ls -alF\"))
@@ -450,19 +455,25 @@ if [ -f ~/.bashrc ]; then source ~/.bashrc; fi
 (define-configuration/no-serialization home-bash-extension
   (environment-variables
    (alist '())
-   "Association list of environment variables to set.")
+   "Additional environment variables to set.  These will be combined with the
+environment variables from other extensions and the base service to form one
+coherent block of environment variables.")
   (aliases
    (alist '())
-   "Association list of aliases to set.")
+   "Additional aliases to set.  These will be combined with the aliases from
+other extensions and the base service.")
   (bash-profile
    (text-config '())
-   "List of file-like objects.")
+   "Additional text blocks to add to @file{.bash_profile}, which will be combined
+with text blocks from other extensions and the base service.")
   (bashrc
    (text-config '())
-   "List of file-like objects.")
+   "Additional text blocks to add to @file{.bashrc}, which will be combined
+with text blocks from other extensions and the base service.")
   (bash-logout
    (text-config '())
-   "List of file-like objects."))
+   "Additional text blocks to add to @file{.bash_logout}, which will be combined
+with text blocks from other extensions and the base service."))
 
 (define (home-bash-extensions original-config extension-configs)
   (match original-config
@@ -646,10 +657,16 @@ Install and configure Fish, the friendly interactive shell.")))
    'home-shell-profile-configuration))
 
 (define (generate-home-bash-documentation)
-  (generate-documentation
-   `((home-bash-configuration
-      ,home-bash-configuration-fields))
-   'home-bash-configuration))
+  (string-append
+   (generate-documentation
+    `((home-bash-configuration
+       ,home-bash-configuration-fields))
+    'home-bash-configuration)
+   "\n\n"
+   (generate-documentation
+    `((home-bash-extension
+       ,home-bash-extension-fields))
+    'home-bash-extension)))
 
 (define (generate-home-zsh-documentation)
   (generate-documentation