interpreter: add feature.disable_auto_if()

Add a method to downgrade an option to disabled if it is not used.
This is useful to avoid unnecessary search for dependencies;
for example

    dep = dependency('dep', required: get_option('feature').disable_auto_if(not foo))

can be used instead of the more verbose and complex

    if get_option('feature').auto() and not foo then
      dep = dependency('', required: false)
    else
      dep = dependency('dep', required: get_option('feature'))
    endif

or to avoid unnecessary dependency searches:

  dep1 = dependency('dep1', required: get_option('foo'))
  # dep2 is only used together with dep1
  dep2 = dependency('dep2', required: get_option('foo').disable_auto_if(not dep1.found()))
 ```

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/test cases/common/192 feature option/meson.build b/test cases/common/192 feature option/meson.build
index 6d26deb..b5e26fa 100644
--- a/test cases/common/192 feature option/meson.build
+++ b/test cases/common/192 feature option/meson.build
@@ -15,6 +15,8 @@ assert(not required_opt.disabled(), 'Should be enabled option')
 assert(not required_opt.auto(), 'Should be enabled option')
 assert(required_opt.allowed(), 'Should be enabled option')
 assert(required_opt.require(true, error_message: 'xyz').enabled(), 'Should be enabled option')
+assert(required_opt.disable_auto_if(true).enabled(), 'Should be enabled option')
+assert(required_opt.disable_auto_if(false).enabled(), 'Should be enabled option')
 
 assert(not optional_opt.enabled(), 'Should be auto option')
 assert(not optional_opt.disabled(), 'Should be auto option')
@@ -22,6 +24,8 @@ assert(optional_opt.auto(), 'Should be auto option')
 assert(optional_opt.allowed(), 'Should be auto option')
 assert(optional_opt.require(true).auto(), 'Should be auto option')
 assert(optional_opt.require(false, error_message: 'xyz').disabled(), 'Should be disabled auto option')
+assert(optional_opt.disable_auto_if(true).disabled(), 'Should be disabled auto option')
+assert(optional_opt.disable_auto_if(false).auto(), 'Should be auto option')
 
 assert(not disabled_opt.enabled(), 'Should be disabled option')
 assert(disabled_opt.disabled(), 'Should be disabled option')
@@ -29,6 +33,8 @@ assert(not disabled_opt.auto(), 'Should be disabled option')
 assert(not disabled_opt.allowed(), 'Should be disabled option')
 assert(disabled_opt.require(true).disabled(), 'Should be disabled option')
 assert(disabled_opt.require(false, error_message: 'xyz').disabled(), 'Should be disabled option')
+assert(disabled_opt.disable_auto_if(true).disabled(), 'Should be disabled option')
+assert(disabled_opt.disable_auto_if(false).disabled(), 'Should be disabled option')
 
 dep = dependency('threads', required : required_opt)
 assert(dep.found(), 'Should find required "threads" dep')