add zsh and bash completion scripts

Closes: resurrecting-open-source-projects#314

README.md

@@ -99,6 +99,9 @@ Debian users can install scrot from their package manager:
 $ sudo apt install scrot
 ```
 
+Bash and Zsh completion scripts are available in [etc/](./etc).
+Distro packagers are encouraged to install them to the appropriate directory.
+
 ## Author ##
 
 scrot was originally developed by Tom Gilbert.

TODO.md

@@ -11,6 +11,15 @@ Look for any bugs reported downstream or in our github issues and fix them:
 - <https://bugzilla.redhat.com/buglist.cgi?bug_status=NEW&bug_status=ASSIGNED&bug_status=REOPENED&component=scrot&product=Fedora>
 - <https://bugs.gentoo.org/buglist.cgi?quicksearch=scrot>
 
+## Shell completion improvements
+
+- Improve the bash completion script. Currently it's quite rudimentary.
+- Filter out mutually exclusive options in zsh completion. E.g if `-b` is
+  already provided then `--border` should no longer be considered a potential
+  match.
+- Add some way to explicitly install zsh/bash completion scripts. E.g via the
+  configure script `./configure --with-zsh-completion-path=...`.
+
 ## Switch to newer Imlib2 interfaces
 
 These will require a minimum version bump on imlib2 and so has to be done with

etc/bash-completion/scrot

@@ -0,0 +1,29 @@
+#!/bin/bash
+#
+# Copyright 2024 NRK <nrk@disroot.org>
+#
+# This is free and unencumbered software released into the public domain.
+# For more information, please refer to <https://unlicense.org/>
+
+_scrot_autocomp() {
+	local -a _scrot_opt_list
+	IFS=$'\n' _scrot_opt_list=( $(scrot --list-options=tsv) ) 2>/dev/null
+	local _scrot_opts=""
+	for ln in "${_scrot_opt_list[@]}"; do
+		local -a tokens
+		IFS=$'\t' tokens=( ${ln} )
+
+		local sopt="${tokens[0]}"
+		local lopt="${tokens[1]}"
+		# TODO: better support for flags that accept argument
+		# local argtype=${tokens[2]%%:*}
+		# local argdesc=${tokens[2]#*:}
+		# local desc="[${tokens[3]}]"
+		_scrot_opts+="--${lopt} "
+		if [[ "$sopt" = [[:alnum:]]* ]]; then
+			_scrot_opts+="-${sopt} "
+		fi
+	done
+	printf "%s" "${_scrot_opts% }"
+}
+complete -W "$(_scrot_autocomp)" scrot

etc/zsh-completion/_scrot

@@ -0,0 +1,30 @@
+#compdef scrot
+#
+# Copyright 2024 NRK <nrk@disroot.org>
+#
+# This is free and unencumbered software released into the public domain.
+# For more information, please refer to <https://unlicense.org/>
+
+local -a args
+local list=$($~words[1] --list-options=tsv) 2>/dev/null
+for ln in ${(f)list}; do
+    IFS=$'\t' local tokens=( ${=ln} )
+
+    local sopt="${tokens[1]}"
+    local lopt="${tokens[2]}"
+    local argtype=${tokens[3]%%:*}
+    local argdesc=${tokens[3]#*:}
+    local desc="[${tokens[4]}]"
+
+    case "$argtype" in
+        R) desc+=":$argdesc" ;; # Required
+        O) sopt+="+"; lopt+="=" ;; # Optional
+        N) ;; # None
+    esac
+
+    if [[ "${sopt}" = [[:alnum:]]* ]]; then
+        args+=( "-${sopt}${desc}" )
+    fi
+    args+=( "--${lopt}${desc}" )
+done
+_arguments "${args[@]}"