[PATCH v4 3/3] mmc-utils: Add bash completion

[Torstein Eide <torsteine+linux@gmail.com>]

Add a bash completion script in completion/mmc that completes subcommands
and /dev/mmcblkN device paths for all mmc commands.

Subcommand completion is driven by parsing 'mmc help' output rather than
maintaining a parallel hardcoded verb list, so it stays in sync as
commands are added or removed.

The completion directory is named 'completion/' rather than
'bash-completion/' so shell-specific scripts for other shells (zsh,
fish, etc.) can be placed alongside it without renaming.

Add bashcompletiondir variable to the Makefile (defaulting to the
standard /usr/share/bash-completion/completions) and install the
script as part of 'make install'. The install path can be overridden
at build time with make bashcompletiondir=<path>.

Signed-off-by: Torstein Eide <torsteine+linux@gmail.com>
---
 Makefile       |  5 ++++-
 completion/mmc | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++
 docs/HOWTO.rst |  6 ++++++
 3 files changed, 62 insertions(+), 1 deletion(-)
 create mode 100644 completion/mmc

diff --git a/Makefile b/Makefile
index bf8c006..607d372 100644
--- a/Makefile
+++ b/Makefile
@@ -7,6 +7,8 @@ AM_CFLAGS = -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2 \
 	    -DSD_IDS_PATH=\"$(idsdir)/sdcard.ids\" \
 	    -DMMC_IDS_PATH=\"$(idsdir)/multimediacard.ids\"
 CFLAGS ?= -g -O2
+idsdir = /usr/share/misc
+bashcompletiondir = /usr/share/bash-completion/completions
 objects = \
 	mmc.o \
 	mmc_cmds.o \
@@ -23,7 +25,6 @@ override CFLAGS := $(CHECKFLAGS) $(AM_CFLAGS) $(CFLAGS)
 INSTALL = install
 prefix ?= /usr/local
 bindir = $(prefix)/bin
-idsdir ?= /usr/share/misc
 LIBS=
 RESTORE_LIBS=
 mandir = /usr/share/man
@@ -63,6 +64,8 @@ install: $(progs)
 	$(INSTALL) -m755 -d $(DESTDIR)$(idsdir)
 	$(INSTALL) -m 644 sdcard.ids $(DESTDIR)$(idsdir)
 	$(INSTALL) -m 644 multimediacard.ids $(DESTDIR)$(idsdir)
+	$(INSTALL) -m755 -d $(DESTDIR)$(bashcompletiondir)
+	$(INSTALL) -m 644 completion/mmc $(DESTDIR)$(bashcompletiondir)/mmc
 
 -include $(foreach obj,$(objects), $(dir $(obj))/.$(notdir $(obj)).d)
 
diff --git a/completion/mmc b/completion/mmc
new file mode 100644
index 0000000..1924c15
--- /dev/null
+++ b/completion/mmc
@@ -0,0 +1,52 @@
+_mmc_complete() {
+	local cur prev words cword
+	_init_completion || return
+
+	local devices
+	devices=$(compgen -G "/dev/mmcblk*" 2>/dev/null | grep -E '^/dev/mmcblk[0-9]+$')
+
+	local mmcbin
+	mmcbin=$(type -P "${words[0]}") || return
+
+	# "mmc help" prints one "Usage for command\t<verb words...> <args...>"
+	# line per command. Argument placeholders always start with '<', so
+	# stripping from the first '<' onward leaves just the verb words.
+	local verbs
+	verbs=$("$mmcbin" help 2>/dev/null | sed -n 's/^Usage for command[[:space:]]*//p' | sed 's/<.*//')
+	[[ -z $verbs ]] && return
+
+	local -a typed=("${words[@]:1:cword-1}")
+	local -A next_words=()
+	local have_leaf=
+
+	local line i match
+	while IFS= read -r line; do
+		[[ -z $line ]] && continue
+		local -a w
+		read -ra w <<<"$line"
+		[[ ${#w[@]} -lt ${#typed[@]} ]] && continue
+
+		match=1
+		for ((i = 0; i < ${#typed[@]}; i++)); do
+			if [[ ${w[i]} != "${typed[i]}" ]]; then
+				match=0
+				break
+			fi
+		done
+		[[ $match -eq 0 ]] && continue
+
+		if [[ ${#w[@]} -gt ${#typed[@]} ]]; then
+			next_words[${w[${#typed[@]}]}]=1
+		else
+			have_leaf=1
+		fi
+	done <<<"$verbs"
+
+	if [[ ${#next_words[@]} -gt 0 ]]; then
+		COMPREPLY=($(compgen -W "${!next_words[*]}" -- "$cur"))
+	elif [[ -n $have_leaf ]]; then
+		COMPREPLY=($(compgen -W "$devices" -- "$cur"))
+	fi
+}
+
+complete -F _mmc_complete mmc
diff --git a/docs/HOWTO.rst b/docs/HOWTO.rst
index 0b486e4..3aba86f 100644
--- a/docs/HOWTO.rst
+++ b/docs/HOWTO.rst
@@ -2,6 +2,12 @@
 
 Running mmc-utils
 -----------------
+**Bash completion**
+    Source ``completion/mmc`` to enable tab-completion for all subcommands and
+    device paths. When installed via ``make install``, the file is placed in
+    ``$(bashcompletiondir)`` (default: ``/usr/share/bash-completion/completions/mmc``)
+    and loaded automatically by bash-completion.
+
 **Name**
     mmc - a tool for configuring MMC storage devices
 **Synopsis**
-- 
2.53.0