Convert dtrace from bool to feature option type

Now dtrace can be enabled by default in distros that use
-Dauto_features=enabled or for developers who already have dtrace
installed, while it's still disabled for developers who do not have
dtrace installed. See #3354

.gitlab-ci.yml

@@ -186,7 +186,7 @@ fedora-x86_64:
             --localstatedir=/var
             --libdir=lib
             -Dsystemtap=true
-            -Ddtrace=true
+            -Ddtrace=enabled
             -Dinstalled_tests=true
             -Ddocumentation=true
             -Dintrospection=enabled
@@ -241,7 +241,7 @@ debian-stable-x86_64:
             --localstatedir=/var
             --libdir=lib
             -Dsystemtap=true
-            -Ddtrace=true
+            -Ddtrace=enabled
             _build
     - meson compile -C _build
     - .gitlab-ci/run-tests.sh
@@ -343,7 +343,7 @@ installed-tests:
             --prefix=/usr --libdir=/usr/lib64
             -Dinstalled_tests=true
             -Ddefault_library=both
-            -Ddtrace=false
+            -Ddtrace=disabled
             _build
     - meson compile -C _build
     - sudo meson install -C _build
@@ -384,7 +384,7 @@ G_DISABLE_ASSERT:
     - meson setup ${MESON_COMMON_OPTIONS}
             --werror
             -Dsystemtap=true
-            -Ddtrace=true
+            -Ddtrace=enabled
             -Dinstalled_tests=true
             -Dglib_assert=false
             -Dintrospection=enabled
@@ -422,7 +422,7 @@ valgrind:
     - meson setup ${MESON_COMMON_OPTIONS}
             --werror
             -Dsystemtap=true
-            -Ddtrace=true
+            -Ddtrace=enabled
             -Dinstalled_tests=true
             -Dintrospection=enabled
             _build
@@ -767,7 +767,7 @@ scan-build:
             --libdir=lib
             -Dglib_debug=enabled
             -Dsystemtap=true
-            -Ddtrace=true
+            -Ddtrace=enabled
             -Dinstalled_tests=true
             -Dintrospection=enabled
             _scan_build
@@ -797,7 +797,7 @@ scan-build:
             --localstatedir=/var
             --libdir=lib
             -Dsystemtap=true
-            -Ddtrace=true
+            -Ddtrace=enabled
             -Dinstalled_tests=true
             -Dintrospection=enabled
             _coverity_build

meson.build

@@ -2519,19 +2519,35 @@ elif host_system == 'cygwin'
 endif
 
 # Tracing: dtrace
-want_dtrace = get_option('dtrace')
-enable_dtrace = false
+dtrace_option = get_option('dtrace')
+enable_dtrace = dtrace_option.allowed()
 
-# Since dtrace support is opt-in we just error out if it was requested but
-# is not available. We don't bother with autodetection yet.
-if want_dtrace
-  if glib_have_carbon
+if glib_have_carbon
+  if dtrace_option.enabled()
     error('GLib dtrace support not yet compatible with macOS dtrace')
+  else
+    enable_dtrace = false
   endif
-  dtrace = find_program('dtrace', required : true) # error out if not found
+endif
+
+if enable_dtrace
+  dtrace = find_program('dtrace', required : dtrace_option)
+  if not dtrace.found()
+    enable_dtrace = false
+  endif
+endif
+
+if enable_dtrace
   if not cc.has_header('sys/sdt.h')
-    error('dtrace support needs sys/sdt.h header')
+    if dtrace_option.enabled()
+      error('dtrace support needs sys/sdt.h header')
+    else
+      enable_dtrace = false
+    endif
   endif
+endif
+
+if enable_dtrace
   # FIXME: autotools build also passes -fPIC -DPIC but is it needed in this case?
   dtrace_obj_gen = generator(dtrace,
     output : '@BASENAME@.o',
@@ -2552,7 +2568,6 @@ with open(output, "w") as f:
   f.write(contents)
 ''', dtrace.full_path(), '-h', '-s', '@INPUT@', '-o', '@OUTPUT@'])
   glib_conf.set('HAVE_DTRACE', 1)
-  enable_dtrace = true
 endif
 
 if cc.has_header_symbol('sys/ptrace.h', 'PTRACE_O_EXITKILL')
@@ -2696,7 +2711,7 @@ endif
 summary({
   'xattr' : xattr_dep.length() > 0,
   'man-pages' : get_option('man-pages'),
-  'dtrace' : get_option('dtrace'),
+  'dtrace' : enable_dtrace,
   'systemtap' : enable_systemtap,
   'sysprof' : libsysprof_capture_dep.found(),
   'documentation' : get_option('documentation'),

meson_options.txt

@@ -50,8 +50,9 @@ option('man-pages',
        deprecated : { 'true': 'enabled', 'false': 'disabled' })
 
 option('dtrace',
-       type : 'boolean',
-       value : false,
+       type : 'feature',
+       value : 'auto',
+       deprecated : { 'true': 'enabled', 'false': 'disabled' },
        description : 'include tracing support for dtrace')
 
 option('systemtap',