app-shells/bash: uncouple 10-gentoo-color.bash; warn of bad .bashrc

Some users choose to manage /etc/bash/bashrc directly and disregard any
of its updates outright. Additionally, some users have ~/.bashrc as a
copy of ${FILESDIR}/bashrc which is either exact or which contains only
trivial modifications, meaning that the bashrc.d drop-ins end up being
sourced twice. For both of these scenarios, users will presently
encounter a diagnostic message indicating that the genfun_has_readline
function does not exist. In turn, that is because the function is
declared by /etc/bash/bashrc, while also being used by
/etc/bash/bashrc.d/10-gentoo-color.bash.

Since there is no particular need for 10-gentoo-color.bash to be coupled
in this manner, jettison the function. Instead, have bashrc consider the
exit status of the "shopt -s no_empty_cmd_completion" command and have
10-gentoo-color.bash perform its own test.

Additionally, implement a new bashrc.d drop-in named
"15-gentoo-bashrc-check.bash". Its purpose is to check whether ~/.bashrc
exists as a copy of ${FILESDIR}/bashrc and instruct the user as to how
to remedy the situation. After performing the check, it touches a file
under ${TMPDIR} so that it can subsequently avoid driving the user mad.
I recommend that this drop-in be removed one year hence. I disliked
having to do this but consider it to be in the public interest.

Signed-off-by: Kerin Millar <kfm@plushkava.net>
Bug: https://bugs.gentoo.org/934523
Signed-off-by: Sam James <sam@gentoo.org>

3 files changed, 33 insertions, 11 deletions

diff --git a/app-shells/bash/files/bashrc-r1 b/app-shells/bash/files/bashrc-r1
index 6f4631568119..deb0ce97d4a7 100644
--- a/app-shells/bash/files/bashrc-r1
+++ b/app-shells/bash/files/bashrc-r1
@@ -5,16 +5,15 @@ if [[ $- != *i* ]]; then
 	return
 fi
 
-# A convenient function to determine whether bash has readline support.
-genfun_has_readline() [[ $(shopt -p direxpand 2>/dev/null) ]]
+# Disable errexit in case the user enabled it then chose to re-source this file.
+shopt -u -o errexit
 
-# The following two shell options require for bash to have readline support.
-genfun_has_readline &&
+# Disable completion when the input buffer is empty. Mute STDERR because this
+# option is only present in the case that bash was built with readline support.
+shopt -s no_empty_cmd_completion 2>/dev/null &&
 
-# Disable completion when the input buffer is empty.
-shopt -s no_empty_cmd_completion &&
-
-# Append to HISTFILE rather than overwrite upon exiting, per bug #139609.
+# Append to HISTFILE rather than overwrite upon exiting, per bug #139609. This
+# option also requires for bash to have been built with readline support.
 shopt -s histappend
 
 # Initialise PROMPT_COMMAND as an array, which is permitted as of bash 5.1.
@@ -28,5 +27,3 @@ for _ in /etc/bash/bashrc.d/*; do
 		source "$_"
 	fi
 done
-
-unset -f genfun_has_readline
diff --git a/app-shells/bash/files/bashrc.d/10-gentoo-color.bash b/app-shells/bash/files/bashrc.d/10-gentoo-color.bash
index 6192bfaf4394..f0c5983b66e1 100644
--- a/app-shells/bash/files/bashrc.d/10-gentoo-color.bash
+++ b/app-shells/bash/files/bashrc.d/10-gentoo-color.bash
@@ -34,7 +34,8 @@ elif (( gentoo_color == 16777216 )); then
 	export COLORTERM=truecolor
 fi
 
-if (( gentoo_color <= 0 )) || ! genfun_has_readline; then
+# For direxpand to be missing indicates that bash is lacking readline support.
+if (( gentoo_color <= 0 )) || [[ ! $(shopt -p direxpand 2>/dev/null) ]]; then
 	# Define a prompt without color.
 	PS1='\u@\h \w \$ '
 elif (( EUID == 0 )); then
diff --git a/app-shells/bash/files/bashrc.d/15-gentoo-bashrc-check.bash b/app-shells/bash/files/bashrc.d/15-gentoo-bashrc-check.bash
new file mode 100644
index 000000000000..8f2b0405c6b9
--- /dev/null
+++ b/app-shells/bash/files/bashrc.d/15-gentoo-bashrc-check.bash
@@ -0,0 +1,24 @@
+# /etc/bash/bashrc.d/15-gentoo-bashrc-check.bash
+
+# Some users have ~/.bashrc as a copy of ${FILESDIR}/bashrc which either matches
+# exactly or is only trivially modified. Such is an improper state of affairs
+# and results in the bashrc.d drop-ins being sourced twice. Warn them that they
+# should use the skeleton file instead. This drop-in should be removed no sooner
+# than one year from the date of its introduction.
+
+if [[ -e ${TMPDIR:-/tmp}/.gentoo-bashrc-check-${EUID} || ! -f ~/.bashrc ]]; then
+	return
+fi
+
+{
+	if grep -qxF 'for sh in /etc/bash/bashrc.d/* ; do' -- ~/.bashrc; then
+		cat >&3 <<'EOF'
+WARNING! Your ~/.bashrc file is based on an old copy of /etc/bash/bashrc, which
+is not intended for use within a home directory. Please either delete ~/.bashrc
+or replace it with a copy of /etc/skel/.bashrc before optionally customizing it
+further. Neglecting to do so may result in bash behaving unexpectedly.
+
+EOF
+	fi
+	touch -- "${TMPDIR:-/tmp}/.gentoo-bashrc-check-${EUID}"
+} 3>&2 2>/dev/null