meson: Remove automagic dependencies

Prior to this commit there were a number of dependencies that could be
optionally found, but were not essential _and_ could not be explicitly
disabled if they were on the system.

Since meson supports the 'feature' option type (which has an 'auto'
setting), we can enable the existing logic if these options are
not set, but if explicitly enabled or disabled they will either
cause a build failure or be skipped entirely respectively.

This should make packaging more robust for distributions - there's
no way to accidentally build against a library you didn't intend
to if they're turned off!

This has required adjusting the Meson CI to not attempt to find
every feature as at least `xkbcommon` is not in the image!

.github/workflows/ccpp.yml

@@ -33,7 +33,7 @@ jobs:
       - name: set git safe directory
         run: git config --global --add safe.directory ${GITHUB_WORKSPACE}
       - name: configure meson build
-        run:  CC=clang CC_LD=lld meson setup builddir -Dhtmldoc=true -Dmandoc=true -Dauto_features=enabled
+        run:  CC=clang CC_LD=lld meson setup builddir -Dhtmldoc=true -Dmandoc=true
       - name: run build
         run: ninja -C builddir
 

meson.build

@@ -210,9 +210,27 @@ endif
 sed = find_program('sed', required: true)
 
 # Optional dependencies
-# First we check for things specified by the user (i.e. no automagic)
-# Then we check for automagic dependencies.
-# Tip: 'Feature' types will always report 'not found' if disabled
+# Tip: 'Feature' types always report 'not found' if disabled
+
+freetype = dependency('freetype2', required: get_option('freetype'))
+if freetype.found()
+    all_found_deps += freetype
+    summary_depvals += {'freetype': freetype}
+    conf.set10('HAVE_XFT', true)
+    freetype_dep_opts = ['xft', 'fontconfig']
+    freetype_deps = []
+    foreach d : freetype_dep_opts
+        freetype_dep = dependency(d, required: true)
+        if freetype_dep.found()
+            freetype_deps += freetype_dep
+            summary_depvals += {d: freetype_dep}
+            conf.set10('HAVE_' + d.to_upper().underscorify(), true)
+        endif
+    endforeach
+    if freetype_deps.length() > 0
+        all_found_deps += freetype_deps
+    endif
+endif
 
 fribidi = dependency(
     'fribidi',
@@ -266,16 +284,18 @@ endif
 librsvg = dependency(
     'librsvg-2.0',
     version: '>=2.13.92',
-    required: get_option('rsvg'),
+    required: get_option('svg'),
 )
 if librsvg.found()
     all_found_deps += librsvg
     conf.set10('HAVE_RSVG', true)
     # We need at least one of these dependencies
-    svg_opt_deps = ['cairo', 'cairo-svg', 'libsvg-cairo']
+    svg_backends = ['cairo', 'cairo-svg', 'libsvg-cairo']
     svg_deps = []
-    foreach d : svg_opt_deps
-        svg_dep = dependency(d, required: false)
+    foreach d : svg_backends
+        # By treating these as features we can let automagic find one or more backends
+        # or we can explicitly set one or more backends as required, or disable ones we don't want to use.
+        svg_dep = dependency(d, required: get_option(d))
         if svg_dep.found()
             svg_deps += svg_dep
             summary_depvals += {d: svg_dep}
@@ -284,6 +304,7 @@ if librsvg.found()
         endif
     endforeach
     if svg_deps.length() == 0
+        # If everything is set to auto we need to explicitly fail here.
         error(
             'librsvg found but also require one of: ' + svg_opt_deps.join(' '),
         )
@@ -298,63 +319,35 @@ if sm.found()
     conf.set10('SESSION', true)
 endif
 
+xcursor = dependency('xcursor', required: get_option('xcursor'))
+if xcursor.found()
+    all_found_deps += xcursor
+    conf.set10('HAVE_XCURSOR', true)
+endif
+
 xext = dependency('xext', required: get_option('xext'))
 if xext.found()
     all_found_deps += xext
     conf.set10('HAVE_SHAPE', true)
 endif
 
-# Automagic optional dependencies
-# TODO: Automagic dependencies are a nightmare for
-# downstream packagers who need to know what is
-# and is not enabled for a package at build-time
-# not what was randomly also found on their system.
-
-# We should either make these required or hide them behind
-# a feature flag.
-
-freetype = dependency('freetype2', required: false)
-if freetype.found()
-    all_found_deps += freetype
-    summary_depvals += {'freetype': freetype}
-    conf.set10('HAVE_XFT', true)
-    freetype_opt_deps = ['xft', 'fontconfig']
-    freetype_deps = []
-    foreach d : freetype_opt_deps
-        # These deps were previously listed as 'optional', but with 'required: true'
-        freetype_dep = dependency(d, required: false)
-        if freetype_dep.found()
-            freetype_deps += freetype_dep
-            summary_depvals += {d: freetype_dep}
-            conf.set10('HAVE_' + d.to_upper().underscorify(), true)
-        endif
-    endforeach
-    if freetype_deps.length() > 0
-        all_found_deps += freetype_deps
-    endif
-endif
-
-xkbcommon = dependency('xkbcommon', required: false)
+xkbcommon = dependency('xkbcommon', required: get_option('xkbcommon'))
 if xkbcommon.found()
     all_found_deps += xkbcommon
     conf.set10('HAVE_X11_XKBLIB_H', true)
-    summary_depvals += {'xkbcommon': xkbcommon}
 endif
 
-xpm = dependency('xpm', required: false)
+xpm = dependency('xpm', required: get_option('xpm'))
 if xpm.found()
     all_found_deps += xpm
     conf.set10('HAVE_XPM', true)
-    summary_depvals += {'xpm': xpm}
 endif
 
-automagic_opt_deps = ['xcursor', 'xrender']
-foreach ad : automagic_opt_deps
-    this_dep = dependency(ad, required: true)
-    summary_depvals += {ad: this_dep}
-    conf.set10('HAVE_' + ad.to_upper().underscorify(), true)
-    all_found_deps += this_dep
-endforeach
+xrender = dependency('xrender', required: get_option('xrender'))
+if xrender.found()
+    all_found_deps += xrender
+    conf.set10('HAVE_XRENDER', true)
+endif
 
 # Hard-coded
 non_configurable_ops = [
@@ -534,11 +527,16 @@ summary(
 
 featurevals = {
     'bidi': fribidi.found() ? fribidi : false,
+    'freetype': freetype.found() ? freetype : false,
     'Go Modules': golang.found(),
     'iconv': iconv.found(),
     'NLS': libintl.found(),
     'Session Management': sm.found() ? sm : false,
     'Shaped Windows': xext.found() ? xext : false,
+    'Xcursor': xcursor.found() ? xcursor : false,
+    'xkbcommon': xkbcommon.found() ? xkbcommon : false,
+    'XRender': xrender.found() ? xrender : false,
+    'XPM support': xpm.found() ? xpm : false,
     'PNG support': libpng.found() ? libpng : false,
     'SVG support': librsvg.found() ? librsvg : false,
 }

meson.options

@@ -4,6 +4,24 @@ option(
     value: 'auto',
     description: 'Enable fribidi support',
 )
+option(
+    'cairo',
+    type: 'feature',
+    value: 'auto',
+    description: 'Use Cairo as a librsvg backend',
+)
+option(
+    'cairo-svg',
+    type: 'feature',
+    value: 'auto',
+    description: 'Use CairoSVG as a librsvg backend',
+)
+option(
+    'freetype',
+    type: 'feature',
+    value: 'auto',
+    description: 'Enable freetype support',
+)
 option(
     'golang',
     type: 'feature',
@@ -22,6 +40,12 @@ option(
     value: 'auto',
     description: 'Enable iconv support',
 )
+option(
+    'libsvg-cairo',
+    type: 'feature',
+    value: 'auto',
+    description: 'Use librsvg as a librsvg backend',
+)
 option(
     'mandoc',
     type: 'boolean',
@@ -42,20 +66,44 @@ option(
     description: 'Enable readline support for FvwmConsole (disabled if using Go)',
 )
 option(
-    'rsvg',
+    'sm',
+    type: 'feature',
+    value: 'auto',
+    description: 'Enable session management support',
+)
+option(
+    'svg',
     type: 'feature',
     value: 'auto',
     description: 'Enable svg support',
 )
 option(
-    'sm',
+    'xcursor',
     type: 'feature',
     value: 'auto',
-    description: 'Enable session management support',
+    description: 'Enable Xcursor support',
 )
 option(
     'xext',
     type: 'feature',
     value: 'auto',
-    description: 'Enable shaped window support',
+    description: 'Enable shaped window support via Xext',
+)
+option(
+    'xkbcommon',
+    type: 'feature',
+    value: 'auto',
+    description: 'Enable xkbcommon support',
+)
+option(
+    'xrender',
+    type: 'feature',
+    value: 'auto',
+    description: 'Enable XRender support',
+)
+option(
+    'xpm',
+    type: 'feature',
+    value: 'auto',
+    description: 'Enable X PixMap (xpm) support',
 )