dependencies: defer importing a custom dependency until it is used

This lessens the amount of code imported at Meson startup by mapping
each dependency to a dictionary entry and using a programmable import to
dynamically return it.

Minus 16 files and 6399 lines of code imported at startup.

2 files changed, 4 insertions, 2 deletions

diff --git a/mesonbuild/modules/external_project.py b/mesonbuild/modules/external_project.py
index df7d8f84d..a1d851491 100644
--- a/mesonbuild/modules/external_project.py
+++ b/mesonbuild/modules/external_project.py
@@ -23,7 +23,8 @@ from . import ExtensionModule, ModuleReturnValue, NewExtensionModule, ModuleInfo
 from .. import mlog, build
 from ..compilers.compilers import CFLAGS_MAPPING
 from ..envconfig import ENV_VAR_PROG_MAP
-from ..dependencies import InternalDependency, PkgConfigDependency
+from ..dependencies import InternalDependency
+from ..dependencies.pkgconfig import PkgConfigDependency
 from ..interpreterbase import FeatureNew
 from ..interpreter.type_checking import ENV_KW, DEPENDS_KW
 from ..interpreterbase.decorators import ContainerTypeInfo, KwargInfo, typed_kwargs, typed_pos_args
diff --git a/mesonbuild/modules/gnome.py b/mesonbuild/modules/gnome.py
index 3b856227e..c538a146f 100644
--- a/mesonbuild/modules/gnome.py
+++ b/mesonbuild/modules/gnome.py
@@ -31,7 +31,8 @@ from .. import interpreter
 from .. import mesonlib
 from .. import mlog
 from ..build import CustomTarget, CustomTargetIndex, Executable, GeneratedList, InvalidArguments
-from ..dependencies import Dependency, PkgConfigDependency, InternalDependency
+from ..dependencies import Dependency, InternalDependency
+from ..dependencies.pkgconfig import PkgConfigDependency
 from ..interpreter.type_checking import DEPENDS_KW, DEPEND_FILES_KW, ENV_KW, INSTALL_DIR_KW, INSTALL_KW, NoneType, SOURCES_KW, in_set_validator
 from ..interpreterbase import noPosargs, noKwargs, FeatureNew, FeatureDeprecated
 from ..interpreterbase import typed_kwargs, KwargInfo, ContainerTypeInfo