allow dependency checks to bubble up feature warnings to the interpreter

It would be too difficult and probably a layering violation to give an
interpreter handle to the inner guts of every dependency. What we can do
instead is let every dependency track:

- the Feature checks it can produce,
- the version attribute for when it was implemented

while leaving the interpreter in charge of actually emitting them.

mesonbuild/dependencies/base.py

@@ -30,6 +30,7 @@ if T.TYPE_CHECKING:
     from .._typing import ImmutableListProtocol
     from ..compilers.compilers import Compiler
     from ..environment import Environment
+    from ..interpreterbase import FeatureCheckBase
     from ..build import BuildTarget, CustomTarget, IncludeDirs
     from ..mesonlib import FileOrString
 
@@ -92,6 +93,8 @@ class Dependency(HoldableObject):
         self.sources: T.List[T.Union['FileOrString', 'CustomTarget']] = []
         self.include_type = self._process_include_type_kw(kwargs)
         self.ext_deps: T.List[Dependency] = []
+        self.featurechecks: T.List['FeatureCheckBase'] = []
+        self.feature_since: T.Optional[T.Tuple[str, str]] = None
 
     def __repr__(self) -> str:
         return f'<{self.__class__.__name__} {self.name}: {self.is_found}>'

mesonbuild/interpreter/interpreter.py

@@ -1601,6 +1601,11 @@ external dependencies (including libraries) must go to "dependencies".''')
             if wanted != actual:
                 mlog.debug(f'Current include type of {args[0]} is {actual}. Converting to requested {wanted}')
                 d = d.generate_system_dependency(wanted)
+        if d.feature_since is not None:
+            version, extra_msg = d.feature_since
+            FeatureNew.single_use(f'dep {d.name!r} custom lookup', version, self.subproject, extra_msg, node)
+        for f in d.featurechecks:
+            f.use(self.subproject, node)
         return d
 
     @FeatureNew('disabler', '0.44.0')