coredata: Ignore directories when searching for machine files

Otherwise having an output directory matching the name of the cross file
in the current working directory will cause an error. This patch instead
collects any invalid names and prints them along with the error message
when no valid file can be found.

Fixes #5640

mesonbuild/coredata.py

@@ -389,14 +389,17 @@ class CoreData:
         if not filenames:
             return []
 
-        real = []
+        found_invalid = []  # type: typing.List[str]
+        missing = []        # type: typing.List[str]
+        real = []           # type: typing.List[str]
         for i, f in enumerate(filenames):
             f = os.path.expanduser(os.path.expandvars(f))
             if os.path.exists(f):
                 if os.path.isfile(f):
                     real.append(os.path.abspath(f))
+                    continue
                 elif os.path.isdir(f):
-                    raise MesonException('Cross and native files must not be directories')
+                    found_invalid.append(os.path.abspath(f))
                 else:
                     # in this case we've been passed some kind of pipe, copy
                     # the contents of that file into the meson private (scratch)
@@ -410,8 +413,8 @@ class CoreData:
                     # Also replace the command line argument, as the pipe
                     # probably wont exist on reconfigure
                     filenames[i] = copy
-                continue
-            elif sys.platform != 'win32':
+                    continue
+            if sys.platform != 'win32':
                 paths = [
                     os.environ.get('XDG_DATA_HOME', os.path.expanduser('~/.local/share')),
                 ] + os.environ.get('XDG_DATA_DIRS', '/usr/local/share:/usr/share').split(':')
@@ -421,9 +424,14 @@ class CoreData:
                         real.append(path_to_try)
                         break
                 else:
-                    raise MesonException('Cannot find specified {} file: {}'.format(ftype, f))
-                continue
+                    missing.append(f)
+            else:
+                missing.append(f)
 
+        if missing:
+            if found_invalid:
+                mlog.log('Found invalid candidates for', ftype, 'file:', *found_invalid)
+            mlog.log('Could not find any valid candidate for', ftype, 'files:', *missing)
             raise MesonException('Cannot find specified {} file: {}'.format(ftype, f))
         return real