cython: wire up support for emitting and using depfiles

This solves rebuild issues when e.g. importing a .pxd header from a .pyx
file, just like C/C++ source headers. The transpiler needs to run again
in this case.

This functionality is present in the 3.0.0 alphas of cython, and is also
available in an unreleased maintenance branch of 0.29 -- see
cython/cython#5158

mesonbuild/backend/ninjabackend.py

@@ -2216,10 +2216,17 @@ def generate_cython_compile_rules(self, compiler: 'Compiler') -> None:
         description = 'Compiling Cython source $in'
         command = compiler.get_exelist()
 
-        args = ['$ARGS', '$in']
+        depargs = compiler.get_dependency_gen_args('$out', '$DEPFILE')
+        if depargs:
+            depfile = '$out.dep'
+        else:
+            depfile = None
+
+        args = depargs + ['$ARGS', '$in']
         args += NinjaCommandArg.list(compiler.get_output_args('$out'), Quoting.none)
         self.add_rule(NinjaRule(rule, command + args, [],
                                 description,
+                                depfile=depfile,
                                 extra='restat = 1'))
 
     def generate_rust_compile_rules(self, compiler):

mesonbuild/compilers/cython.py

@@ -6,7 +6,7 @@
 import typing as T
 
 from .. import coredata
-from ..mesonlib import EnvironmentException, OptionKey
+from ..mesonlib import EnvironmentException, OptionKey, version_compare
 from .compilers import Compiler
 
 if T.TYPE_CHECKING:
@@ -39,6 +39,14 @@ def get_optimization_args(self, optimization_level: str) -> T.List[str]:
         # compiler might though
         return []
 
+    def get_dependency_gen_args(self, outtarget: str, outfile: str) -> T.List[str]:
+        if version_compare(self.version, '>=3.0.0'):
+            return ['-M']
+        return []
+
+    def get_depfile_suffix(self) -> str:
+        return 'dep'
+
     def sanity_check(self, work_dir: str, environment: 'Environment') -> None:
         code = 'print("hello world")'
         with self.cached_compile(code, environment.coredata) as p: