From 4b04d703ab12747bf44dc923cccabb1098c4298c Mon Sep 17 00:00:00 2001
From: Shane Carr <shane@unicode.org>
Date: Fri, 3 May 2019 19:09:43 -0700
Subject: [PATCH] ICU-20593 Buildtool: Implementing new "additive" mode.

---
 icu4c/source/data/buildtool/__main__.py       |  5 ++++
 icu4c/source/data/buildtool/filtration.py     | 30 ++++++++++++-------
 .../data/buildtool/filtration_schema.json     | 14 ++++++++-
 3 files changed, 38 insertions(+), 11 deletions(-)

diff --git a/icu4c/source/data/buildtool/__main__.py b/icu4c/source/data/buildtool/__main__.py
index 75993a82c6a..36d99207e55 100644
--- a/icu4c/source/data/buildtool/__main__.py
+++ b/icu4c/source/data/buildtool/__main__.py
@@ -156,6 +156,11 @@ class Config(object):
         if "collationUCAData" in self.filters_json_data:
             self.coll_han_type = self.filters_json_data["collationUCAData"]
 
+        # Either "additive" or "subtractive"
+        self.strategy = "subtractive"
+        if "strategy" in self.filters_json_data:
+            self.strategy = self.filters_json_data["strategy"]
+
     def _parse_filter_file(self, f):
         # Use the Hjson parser if it is available; otherwise, use vanilla JSON.
         try:
diff --git a/icu4c/source/data/buildtool/filtration.py b/icu4c/source/data/buildtool/filtration.py
index 48d78e3c4f3..a74a7a743c6 100644
--- a/icu4c/source/data/buildtool/filtration.py
+++ b/icu4c/source/data/buildtool/filtration.py
@@ -247,15 +247,21 @@ def _preprocess_file_filters(requests, config):
     all_categories = list(sorted(all_categories))
     json_data = config.filters_json_data
     filters = {}
+    default_filter_json = "exclude" if config.strategy == "additive" else "include"
     for category in all_categories:
+        filter_json = default_filter_json
+        # Figure out the correct filter to create
         if "featureFilters" in json_data and category in json_data["featureFilters"]:
-            filters[category] = Filter.create_from_json(
-                json_data["featureFilters"][category]
-            )
-        elif "localeFilter" in json_data and category[-5:] == "_tree":
-            filters[category] = Filter.create_from_json(
-                json_data["localeFilter"]
-            )
+            filter_json = json_data["featureFilters"][category]
+        if filter_json == "include" and "localeFilter" in json_data and category.endswith("_tree"):
+            filter_json = json_data["localeFilter"]
+        # Resolve the filter JSON into a filter object
+        if filter_json == "exclude":
+            filters[category] = ExclusionFilter()
+        elif filter_json == "include":
+            pass  # no-op
+        else:
+            filters[category] = Filter.create_from_json(filter_json)
     if "featureFilters" in json_data:
         for category in json_data["featureFilters"]:
             if category not in all_categories:
@@ -264,8 +270,9 @@ def _preprocess_file_filters(requests, config):
 
 
 class ResourceFilterInfo(object):
-    def __init__(self, category):
+    def __init__(self, category, strategy):
         self.category = category
+        self.strategy = strategy
         self.filter_tmp_dir = "filters/%s" % category
         self.input_files = None
         self.filter_files = None
@@ -311,7 +318,10 @@ class ResourceFilterInfo(object):
                 for file in files
             )
         ]
-        self.rules_by_file = [[] for _ in range(len(files))]
+        if self.strategy == "additive":
+            self.rules_by_file = [["-/*"] for _ in range(len(files))]
+        else:
+            self.rules_by_file = [["+/*"] for _ in range(len(files))]
 
     def add_rules(self, file_filter, rules):
         for file, rule_list in zip(self.input_files, self.rules_by_file):
@@ -369,7 +379,7 @@ def _apply_resource_filters(all_requests, config):
         for category in entry["categories"]:
             # not defaultdict because we need to pass arguments to the constructor
             if category not in collected:
-                filter_info = ResourceFilterInfo(category)
+                filter_info = ResourceFilterInfo(category, config.strategy)
                 filter_info.apply_to_requests(all_requests)
                 collected[category] = filter_info
             else:
diff --git a/icu4c/source/data/buildtool/filtration_schema.json b/icu4c/source/data/buildtool/filtration_schema.json
index 479c65affe6..929cdb5ed66 100644
--- a/icu4c/source/data/buildtool/filtration_schema.json
+++ b/icu4c/source/data/buildtool/filtration_schema.json
@@ -7,10 +7,22 @@
     "description": "JSON Schema for an ICU data filter file",
     "type": "object",
     "properties": {
+        "strategy": {
+            "type": "string",
+            "enum": ["additive", "subtractive"]
+        },
         "localeFilter": { "$ref": "#/definitions/filter" },
         "featureFilters": {
             "type": "object",
-            "additionalProperties": { "$ref": "#/definitions/filter" }
+            "additionalProperties": {
+                "oneOf": [
+                    { "$ref": "#/definitions/filter" },
+                    {
+                        "type": "string",
+                        "enum": ["include", "exclude"]
+                    }
+                ]
+            }
         },
         "resourceFilters": {
             "type": "array",