build: Remove the install_completions option

The bash-completion and fish dependencies are already optional, and
there's no dependency required for Z shell.  The shell completions for
Bash and fish won't be generated and installed if they are absent.  So
the build option isn't reducing the dependency burden.

The build option is a way to disable the generation and installation of
the shell completions, regardless of whether the necessary dependencies
are present or not.  The only use-case for this is when installing to a
non-system-wide prefix while hacking on Toolbox as a non-root user,
because the locations for the completions in the shells' APIs might not
be accessible.  Being able to disable the completions prevents the
installation from failing.

Fallout from bafbbe8

containers#1123
containers#840

build: Add options to override the locations for the shell completions

This is particularly relevant for Z shell, because, unlike Bash's
bash-completion.pc and fish's fish.pc, it doesn't have an API to detect
the location for the shell completions and Debian and Fedora use
different locations [1, 2].  Namely, /usr/share/zsh/vendor-completions
and /usr/share/zsh/site-functions.

An option to specify the locations for the shell completions can
optimize the build if there's an alternate API for the location that
doesn't involve using bash-completion.pc and fish.pc as build
dependencies.  eg., Fedora provides the _tmpfilesdir RPM macro to
specify the location for vendor-supplied tmpfiles.d(5) files, which
makes it possible to avoid having systemd as a build dependency [3].

Finally, when installing to a non-system-wide prefix while hacking on
Toolbox as a non-root user, the locations for the completions in the
shells' APIs might not be accessible.  Being able to override the
locations prevents the installation from failing.

[1] Debian zsh commit bf0a44a8744469b5
    https://salsa.debian.org/debian/zsh/-/commit/bf0a44a8744469b5
    https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=620452

[2] https://src.fedoraproject.org/rpms/zsh/blob/f37/f/zsh.spec

[3] Fedora toolbox commit 9bebde5bb60f36e3
    https://src.fedoraproject.org/rpms/toolbox/c/9bebde5bb60f36e3

containers#1123
containers#840

completion/meson.build

@@ -1,45 +1,35 @@
 generate_completions_program = find_program('generate_completions.py')
 
-if bash_completion_dep.found()
-  bashcompletionsdir = bash_completion_dep.get_variable(pkgconfig: 'completionsdir')
-else
-  bashcompletionsdir = get_option('datadir') / 'bash-completion' / 'completions'
-  message('bash-completion not found: using', get_option('prefix') / bashcompletionsdir, 'as a falback install directory')
-endif
-
-if fish_dep.found()
-  fishcompletionsdir = fish_dep.get_variable(pkgconfig: 'completionsdir')
-else
-  fishcompletionsdir = get_option('datadir') / 'fish' / 'completions'
-  message('fish not found: using', get_option('prefix') / fishcompletionsdir, 'as a fallback install directory')
+if bashcompletionsdir != ''
+  custom_target(
+    'bash-completion',
+    capture: true,
+    command: [generate_completions_program, meson.global_source_root() / 'src', 'bash'],
+    depends: [toolbox_go],
+    install: true,
+    install_dir: bashcompletionsdir,
+    output: 'toolbox'
+)
 endif
 
-custom_target(
-  'bash-completion',
-  capture: true,
-  command: [generate_completions_program, meson.global_source_root() / 'src', 'bash'],
-  depends: [toolbox_go],
-  install: true,
-  install_dir: bashcompletionsdir,
-  output: 'toolbox'
+if fishcompletionsdir != ''
+  custom_target(
+    'fish-completion',
+    capture: true,
+    command: [generate_completions_program, meson.global_source_root() / 'src', 'fish'],
+    depends: [toolbox_go],
+    install: true,
+    install_dir: fishcompletionsdir,
+    output: 'toolbox.fish'
 )
+endif
 
 custom_target(
   'zsh-completion',
   capture: true,
   command: [generate_completions_program, meson.global_source_root() / 'src', 'zsh'],
   depends: [toolbox_go],
   install: true,
-  install_dir: get_option('datadir') / 'zsh' / 'site-functions',
+  install_dir: zshcompletionsdir,
   output: '_toolbox'
 )
-
-custom_target(
-  'fish-completion',
-  capture: true,
-  command: [generate_completions_program, meson.global_source_root() / 'src', 'fish'],
-  depends: [toolbox_go],
-  install: true,
-  install_dir: fishcompletionsdir,
-  output: 'toolbox.fish'
-)

meson.build

@@ -18,8 +18,21 @@ go_md2man = find_program('go-md2man')
 shellcheck = find_program('shellcheck', required: false)
 skopeo = find_program('skopeo', required: false)
 
-bash_completion_dep = dependency('bash-completion', required: false)
-fish_dep = dependency('fish', required: false)
+bashcompletionsdir = get_option('bash_completions_dir')
+if bashcompletionsdir == ''
+  bash_completion_dep = dependency('bash-completion', required: false)
+  if bash_completion_dep.found()
+    bashcompletionsdir = bash_completion_dep.get_variable(pkgconfig: 'completionsdir')
+  endif
+endif
+
+fishcompletionsdir = get_option('fish_completions_dir')
+if fishcompletionsdir == ''
+  fish_completion_dep = dependency('fish', required: false)
+  if fish_completion_dep.found()
+    fishcompletionsdir = fish_completion_dep.get_variable(pkgconfig: 'completionsdir')
+  endif
+endif
 
 migration_path_for_coreos_toolbox = get_option('migration_path_for_coreos_toolbox')
 profiledir = get_option('profile_dir')
@@ -33,6 +46,11 @@ if tmpfilesdir == '' or not fs.exists('/run/.containerenv')
   endif
 endif
 
+zshcompletionsdir = get_option('zsh_completions_dir')
+if zshcompletionsdir == ''
+  zshcompletionsdir = join_paths(get_option('datadir'), 'zsh', 'site-functions')
+endif
+
 toolbox_sh = files('toolbox')
 
 if shellcheck.found()
@@ -70,8 +88,6 @@ subdir('data')
 subdir('doc')
 subdir('profile.d')
 subdir('src')
-if get_option('install_completions')
-  subdir('completion')
-endif
+subdir('completion')
 
 meson.add_install_script('meson_post_install.py')

meson_options.txt

@@ -1,3 +1,15 @@
+option(
+  'bash_completions_dir',
+  description: 'Directory for Bash completion scripts',
+  type: 'string',
+)
+
+option(
+  'fish_completions_dir',
+  description: 'Directory for fish completion scripts',
+  type: 'string',
+)
+
 option(
   'migration_path_for_coreos_toolbox',
   description: 'Offer a migration path to users of github.com/coreos/toolbox',
@@ -19,8 +31,7 @@ option(
 )
 
 option(
-  'install_completions',
-  description: 'Install bash, zsh and fish command completions',
-  type: 'boolean',
-  value: true,
+  'zsh_completions_dir',
+  description: 'Directory for Z shell completion scripts (default=$datadir/zsh/site-functions)',
+  type: 'string',
 )