Add a cheap OrderedSet implementation

This just makes an OrderedDict look more like a set class. This results
in neater code than if we use OrderedDict to hold sets directly.

There is a "real" OrderedSet implementation available here, but it lacks
a clear license: https://code.activestate.com/recipes/576694/

1 files changed, 16 insertions, 0 deletions

diff --git a/mesonbuild/mesonlib.py b/mesonbuild/mesonlib.py
index c7368d5..f0bf9ee 100644
--- a/mesonbuild/mesonlib.py
+++ b/mesonbuild/mesonlib.py
@@ -16,6 +16,7 @@
 
 import stat
 import platform, subprocess, operator, os, shutil, re
+import collections
 
 from glob import glob
 
@@ -672,3 +673,18 @@ def get_filenames_templates_dict(inputs, outputs):
         if values['@OUTDIR@'] == '':
             values['@OUTDIR@'] = '.'
     return values
+
+class OrderedSet(collections.OrderedDict):
+    '''
+    A 'set' equivalent that preserves the order in which items are added.
+
+    This is a hack implementation that wraps OrderedDict. It may not be the
+    most efficient solution and might need fixing to override more methods.
+    '''
+    def __init__(self, iterable=None):
+        if iterable:
+            self.update(iterable)
+
+    def update(self, iterable):
+        for item in iterable:
+            self[item] = True