implement GNUish VPATH

1 files changed, 20 insertions, 7 deletions

diff --git a/yapymake/makefile/__init__.py b/yapymake/makefile/__init__.py
index ee1cb74..a3e65d7 100644
--- a/yapymake/makefile/__init__.py
+++ b/yapymake/makefile/__init__.py
@@ -310,7 +310,12 @@ class Makefile:
     def target(self, name: str) -> 'Target':
         # TODO implement .DEFAULT
         # it's not POSIXful, but GNU make will use inference rules for defined targets with no commands,
+        # and also VPATH is a thing that exists!
         follow_gnu = True # TODO implement .POSIX and scope it properly
+        if follow_gnu and 'VPATH' in self._macros:
+            vpath_options = self.expand_macros(tokenize('$(VPATH)')).split(os.pathsep)
+        else:
+            vpath_options = []
         if name not in self._targets or (follow_gnu and len(self._targets[name].commands) == 0):
             # > When no target rule is found to update a target, the inference rules shall be checked. The suffix of
             # > the target (.s1) to be built...
@@ -325,13 +330,21 @@ class Makefile:
                     if rule.s1 == suffix:
                         # > whose prerequisite file ($*.s2) exists.
                         prerequisite_path = PurePath(name).with_suffix(rule.s2)
-                        if ImpurePath(prerequisite_path).exists():
-                            if name in self._targets:
-                                # we got here by following GNU
-                                self._warn(f'warning: non-POSIX use of inference rule {rule.s1}{rule.s2} on explicit '
-                                           f'target {name}')
-                            self._targets[name] = Target(name, [str(prerequisite_path)], rule.commands)
-                            break
+                        if prerequisite_path.is_absolute():
+                            prerequisite_path_options = [prerequisite_path]
+                        else:
+                            prerequisite_path_options = [prerequisite_path] + \
+                                                        [PurePath(vpath, prerequisite_path) for vpath in vpath_options]
+                        for i, prerequisite in enumerate(prerequisite_path_options):
+                            if ImpurePath(prerequisite).exists():
+                                if name in self._targets:
+                                    # we got here by following GNU
+                                    self._warn(f'warning: non-POSIX use of inference rule {rule.s1}{rule.s2} on '
+                                               f'explicit target {name}')
+                                if i > 0:
+                                    self._warn('warning: non-POSIX use of VPATH fallback')
+                                self._targets[name] = Target(name, [str(prerequisite)], rule.commands)
+                                break
         if name not in self._targets:
             # we tried inference, it didn't work
             # is there a default?