Try to fix cyclic import for typing.

mesonbuild/arglist.py

@@ -11,10 +11,6 @@
 import re
 import typing as T
 
-if T.TYPE_CHECKING:
-    from .linkers.linkers import StaticLinker
-    from .compilers import Compiler
-
 # execinfo is a compiler lib on BSD
 UNIXY_COMPILER_INTERNAL_LIBS = ['m', 'c', 'pthread', 'dl', 'rt', 'execinfo']
 
@@ -94,9 +90,12 @@ class CompilerArgs(T.MutableSequence[str]):
     # TODO: these should probably move too
     always_dedup_args = tuple('-l' + lib for lib in UNIXY_COMPILER_INTERNAL_LIBS)
 
-    def __init__(self, compiler: T.Union['Compiler', 'StaticLinker'],
-                 iterable: T.Optional[T.Iterable[str]] = None):
-        self.compiler = compiler
+    def __init__(self, compiler: T.Any, iterable: T.Optional[T.Iterable[str]] = None):
+        # Must be here to avoid cyclic import.
+        from .linkers.linkers import StaticLinker
+        from .compilers import Compiler
+        assert(isinstance(compiler, (StaticLinker, Compiler)))
+        self.compiler: T.Union['Compiler', 'StaticLinker'] = compiler
         self._container: T.List[str] = list(iterable) if iterable is not None else []
         self.pre: T.Deque[str] = collections.deque()
         self.post: T.Deque[str] = collections.deque()