3 files changed, 25 insertions, 6 deletions
diff --git a/scripts/lib/fontbuild/features.py b/scripts/lib/fontbuild/features.py
index 3b52f76..2de484d 100755
--- a/scripts/lib/fontbuild/features.py
+++ b/scripts/lib/fontbuild/features.py
@@ -150,6 +150,23 @@ class FilterFeatureWriter(FDKSyntaxFeatureWriter):
             super(FilterFeatureWriter, self).languageSystem(langTag, scriptTag)
 
 
+def compileFeatureRE(name):
+    """Compiles a feature-matching regex using feaTool's template."""
+    featureRE = list(parser.featureContentRE)
+    featureRE.insert(2, name)
+    featureRE.insert(6, name)
+    return re.compile("".join(featureRE))
+
+
+def updateFeature(font, name, value):
+    """Add a feature definition, or replace existing one."""
+    featureRE = compileFeatureRE(name)
+    if featureRE.search(font.features.text):
+        font.features.text = featureRE.sub(value, font.features.text)
+    else:
+        font.features.text += "\n" + value
+
+
 def readFeatureFile(font, text):
     """Incorporate valid definitions from feature text into font."""
     writer = FilterFeatureWriter(set(font.keys()))
diff --git a/scripts/lib/fontbuild/markFeature.py b/scripts/lib/fontbuild/markFeature.py
index c966085..e2e36c1 100755
--- a/scripts/lib/fontbuild/markFeature.py
+++ b/scripts/lib/fontbuild/markFeature.py
@@ -1,3 +1,6 @@
+from fontbuild.features import updateFeature
+
+
 aliases = [["uni0430", "a"], ["uni0435", "e"], ["uni0440", "p"], ["uni0441", "c"], ["uni0445", "x"], ["uni0455", "s"], ["uni0456", "i"], ["uni0471", "psi"]]
 
 def GetAliaseName(gname):
@@ -79,6 +82,4 @@ def GenerateFeature_mark(font):
 
   text += "} mark;\n"
 
-  if "mark" not in font.features.tags:
-    font.features.tags.append("mark")
-  font.features.values["mark"] = text
+  updateFeature(font, "mark", text)
diff --git a/scripts/lib/fontbuild/mkmkFeature.py b/scripts/lib/fontbuild/mkmkFeature.py
index e2195f5..a839dae 100755
--- a/scripts/lib/fontbuild/mkmkFeature.py
+++ b/scripts/lib/fontbuild/mkmkFeature.py
@@ -1,3 +1,6 @@
+from fontbuild.features import updateFeature
+
+
 def CreateAccNameList(font, acc_anchor_name):
 	lst = []
 	for g in font:
@@ -56,6 +59,4 @@ def GenerateFeature_mkmk(font):
 
   text += "} mkmk;\n"
 
-  if "mkmk" not in font.features.tags:
-    font.features.tags.append("mkmk")
-  font.features.values["mkmk"] = text
+  updateFeature(font, "mkmk", text)