New 'make completions' target

Generate shell completion files for podman and podman-remote
and for all known shells (bash, fish, zsh). Fix Readme file
in completions dir: it suggested running 'make completion',
singular; no such target existed. Since the install target
is plural, I choose to make the new target plural also.

This is intended for use in CI some day, in a check such as:

  (in contrib/cirrus/runner.sh):

    make completions
    SUGGESTION="run 'make completions' and commit all changes" ./hack/tree_status.sh

The goal would be to make sure that any new podman subcommands
or flags are accompanied by their corresponding shell helpers
on all commits.

IT IS NOT POSSIBLE TO ENFORCE THIS NOW. As I understand it,
Cobra is slow to incorporate community PRs, so the podman team
has chosen to sneak in completion files generated by an
unreleased and un-vendored version of Cobra. Running 'make
completions' right now would clobber those and result in
a diminished user experience.

I'm submitting this anyway as a stepping-stone toward that
future day when we can create such a CI hook.

[NO TESTS NEEDED]

Signed-off-by: Ed Santiago <[email protected]>

Makefile

@@ -639,6 +639,18 @@ install.libseccomp.sudo:
 	cd ../../seccomp/libseccomp && git checkout --detach $(LIBSECCOMP_COMMIT) && ./autogen.sh && ./configure --prefix=/usr && make all && make install
 
 
+.PHONY: completions
+completions: podman podman-remote
+	# key = shell, value = completion filename
+	declare -A outfiles=([bash]=%s [zsh]=_%s [fish]=%s.fish);\
+	for shell in $${!outfiles[*]}; do \
+	    for remote in "" "-remote"; do \
+	        podman="podman$$remote"; \
+	        outfile=$$(printf "completions/$$shell/$${outfiles[$$shell]}" $$podman); \
+	        ./bin/$$podman completion $$shell >| $$outfile; \
+	    done;\
+	done
+
 .PHONY: validate.completions
 validate.completions: SHELL:=/usr/bin/env bash # Set shell to bash for this target
 validate.completions:

completions/Readme.md

@@ -2,6 +2,6 @@
 
 Podman offers shell completion scripts for bash, zsh and fish. The completion scripts are available for both `podman` and `podman-remote`.
 
-The shell completion scripts are generated by `make completion`, do not edit these files directly. To install them you can run `sudo make install.completions`.
+The shell completion scripts are generated by `make completions`; do not edit these files directly. To install them you can run `sudo make install.completions`.
 
 For information about these scripts see [`man podman-completion`](../docs/source/markdown/podman-completion.1.md)