hotdoc module: add dedicated depends kwarg, deprecate file deps in dependencies

We consistently use the "dependencies" kwarg to refer to C-like
CFLAGS/LDFLAGS interfaces. And for hotdoc, we actually accept libraries
for this as well, as we may want to document their (generated?) sources,
so we want their CFLAGS too.

But we also accepted custom targets and just added a build order
dependency on these, which was odd and typically we call that "depends".
Let's deprecate this in favor of the depends kwarg.

mesonbuild/modules/hotdoc.py

@@ -23,7 +23,10 @@ from mesonbuild.coredata import MesonException
 from . import ModuleReturnValue, ModuleInfo
 from . import ExtensionModule
 from ..dependencies import Dependency, InternalDependency
-from ..interpreterbase import InvalidArguments, noPosargs, noKwargs, typed_kwargs, ContainerTypeInfo, KwargInfo, typed_pos_args
+from ..interpreterbase import (
+    InvalidArguments, noPosargs, noKwargs, typed_kwargs, FeatureDeprecated,
+    ContainerTypeInfo, KwargInfo, typed_pos_args
+)
 from ..interpreter import CustomTargetHolder
 from ..interpreter.type_checking import NoneType
 from ..programs import ExternalProgram
@@ -290,6 +293,7 @@ class HotdocTargetBuilder:
         self.process_extra_assets()
         self.add_extension_paths(self.kwargs.pop('extra_extension_paths'))
         self.process_subprojects()
+        self.extra_depends.extend(self.kwargs.pop('depends'))
 
         install = self.kwargs.pop('install')
         self.process_extra_args()
@@ -415,9 +419,17 @@ class HotDocModule(ExtensionModule):
         # --c-include-directories
         KwargInfo(
             'dependencies',
-            ContainerTypeInfo(list, (Dependency, build.StaticLibrary, build.SharedLibrary)),
+            ContainerTypeInfo(list, (Dependency, build.StaticLibrary, build.SharedLibrary,
+                                     build.CustomTarget, build.CustomTargetIndex)),
+            listify=True,
+            default=[],
+        ),
+        KwargInfo(
+            'depends',
+            ContainerTypeInfo(list, (build.CustomTarget, build.CustomTargetIndex)),
             listify=True,
             default=[],
+            since='0.64.1',
         ),
         KwargInfo('gi_c_source_roots', ContainerTypeInfo(list, str), listify=True, default=[]),
         KwargInfo('extra_assets', ContainerTypeInfo(list, str), listify=True, default=[]),
@@ -428,6 +440,9 @@ class HotDocModule(ExtensionModule):
     )
     def generate_doc(self, state, args, kwargs):
         project_name = args[0]
+        if any(isinstance(x, (build.CustomTarget, build.CustomTargetIndex)) for x in kwargs['dependencies']):
+            FeatureDeprecated.single_use('hotdoc.generate_doc dependencies argument with custom_target',
+                                         '0.64.1', state.subproject, 'use `depends`', state.current_node)
         builder = HotdocTargetBuilder(project_name, state, self.hotdoc, self.interpreter, kwargs)
         target, install_script = builder.make_targets()
         targets = [target]