Preserve layer and attribute descriptions across tile-join

Makefile

@@ -169,7 +169,7 @@ enumerate-test:
 	rm tests/ne_110m_admin_0_countries/out/enum.mbtiles tests/ne_110m_admin_0_countries/out/enum.check
 
 join-test: tile-join
-	./tippecanoe -f -z12 -o tests/join-population/tabblock_06001420.mbtiles tests/join-population/tabblock_06001420.json
+	./tippecanoe -f -z12 -o tests/join-population/tabblock_06001420.mbtiles -YALAND10:'Land area' -L'{"file": "tests/join-population/tabblock_06001420.json", "description": "population"}'
 	./tippecanoe -f -Z5 -z10 -o tests/join-population/macarthur.mbtiles -l macarthur tests/join-population/macarthur.json
 	./tile-join -f -Z6 -z9 -o tests/join-population/macarthur-6-9.mbtiles tests/join-population/macarthur.mbtiles
 	./tippecanoe-decode tests/join-population/macarthur-6-9.mbtiles > tests/join-population/macarthur-6-9.mbtiles.json.check
@@ -199,7 +199,7 @@ join-test: tile-join
 	cmp tests/join-population/no-macarthur.mbtiles.json.check tests/join-population/no-macarthur.mbtiles.json	
 	./tile-join --no-tile-compression -f -e tests/join-population/raw-merged-folder tests/join-population/tabblock_06001420.mbtiles tests/join-population/macarthur.mbtiles tests/join-population/macarthur2.mbtiles
 	diff -x '*.DS_Store' -rq tests/join-population/raw-merged-folder tests/join-population/raw-merged-folder-compare
-	./tippecanoe -z12 -f -e tests/join-population/tabblock_06001420-folder tests/join-population/tabblock_06001420.json
+	./tippecanoe -z12 -f -e tests/join-population/tabblock_06001420-folder -YALAND10:'Land area' -L'{"file": "tests/join-population/tabblock_06001420.json", "description": "population"}'
 	./tippecanoe -Z5 -z10 -f -e tests/join-population/macarthur-folder -l macarthur tests/join-population/macarthur.json
 	./tippecanoe -d10 -D10 -Z9 -z11 -f -e tests/join-population/macarthur2-folder -l macarthur tests/join-population/macarthur2.json
 	./tile-join -f -o tests/join-population/merged-folder.mbtiles tests/join-population/tabblock_06001420-folder tests/join-population/macarthur-folder tests/join-population/macarthur2-folder

tests/join-population/joined-no-tile-stats.mbtiles.json

@@ -3,7 +3,7 @@
 "center": "-122.299805,37.892187,12",
 "description": "tests/join-population/tabblock_06001420.mbtiles",
 "format": "pbf",
-"json": "{\"vector_layers\": [ { \"id\": \"tabblock_06001420\", \"description\": \"\", \"minzoom\": 3, \"maxzoom\": 12, \"fields\": {\"ALAND10\": \"Number\", \"AWATER10\": \"Number\", \"BLOCKCE10\": \"String\", \"COUNTYFP10\": \"String\", \"FUNCSTAT10\": \"String\", \"INTPTLAT10\": \"String\", \"INTPTLON10\": \"String\", \"MTFCC10\": \"String\", \"NAME10\": \"String\", \"STATEFP10\": \"String\", \"TRACTCE10\": \"String\", \"UACE10\": \"String\", \"UATYP10\": \"String\", \"UR10\": \"String\", \"population\": \"Mixed\"} } ]}",
+"json": "{\"vector_layers\": [ { \"id\": \"tabblock_06001420\", \"description\": \"population\", \"minzoom\": 3, \"maxzoom\": 12, \"fields\": {\"ALAND10\": \"Land area\", \"AWATER10\": \"Number\", \"BLOCKCE10\": \"String\", \"COUNTYFP10\": \"String\", \"FUNCSTAT10\": \"String\", \"INTPTLAT10\": \"String\", \"INTPTLON10\": \"String\", \"MTFCC10\": \"String\", \"NAME10\": \"String\", \"STATEFP10\": \"String\", \"TRACTCE10\": \"String\", \"UACE10\": \"String\", \"UATYP10\": \"String\", \"UR10\": \"String\", \"population\": \"Mixed\"} } ]}",
 "maxzoom": "12",
 "minzoom": "0",
 "name": "tests/join-population/tabblock_06001420.mbtiles",

tile-join.cpp

@@ -573,7 +573,46 @@ void handle_tasks(std::map<zxy, std::vector<std::string>> &tasks, std::vector<st
 	}
 }
 
-void decode(struct reader *readers, std::map<std::string, layermap_entry> &layermap, sqlite3 *outdb, const char *outdir, struct stats *st, std::vector<std::string> &header, std::map<std::string, std::vector<std::string>> &mapping, std::set<std::string> &exclude, int ifmatched, std::string &attribution, std::string &description, std::set<std::string> &keep_layers, std::set<std::string> &remove_layers, std::string &name, json_object *filter) {
+void handle_vector_layers(json_object *vector_layers, std::map<std::string, layermap_entry> &layermap, std::map<std::string, std::string> &attribute_descriptions) {
+	if (vector_layers != NULL && vector_layers->type == JSON_ARRAY) {
+		for (size_t i = 0; i < vector_layers->length; i++) {
+			if (vector_layers->array[i]->type == JSON_HASH) {
+				json_object *id = json_hash_get(vector_layers->array[i], "id");
+				json_object *desc = json_hash_get(vector_layers->array[i], "description");
+
+				if (id != NULL && desc != NULL && id->type == JSON_STRING && desc->type == JSON_STRING) {
+					std::string sid = id->string;
+					std::string sdesc = desc->string;
+
+					if (sdesc.size() != 0) {
+						auto f = layermap.find(sid);
+						if (f != layermap.end()) {
+							f->second.description = sdesc;
+						}
+					}
+				}
+
+				json_object *fields = json_hash_get(vector_layers->array[i], "fields");
+				if (fields != NULL && fields->type == JSON_HASH) {
+					for (size_t j = 0; j < fields->length; j++) {
+						if (fields->keys[j]->type == JSON_STRING && fields->values[j]->type) {
+							const char *desc2 = fields->values[j]->string;
+
+							if (strcmp(desc2, "Number") != 0 &&
+							    strcmp(desc2, "String") != 0 &&
+							    strcmp(desc2, "Boolean") != 0 &&
+							    strcmp(desc2, "Mixed") != 0) {
+								attribute_descriptions.insert(std::pair<std::string, std::string>(fields->keys[j]->string, desc2));
+							}
+						}
+					}
+				}
+			}
+		}
+	}
+}
+
+void decode(struct reader *readers, std::map<std::string, layermap_entry> &layermap, sqlite3 *outdb, const char *outdir, struct stats *st, std::vector<std::string> &header, std::map<std::string, std::vector<std::string>> &mapping, std::set<std::string> &exclude, int ifmatched, std::string &attribution, std::string &description, std::set<std::string> &keep_layers, std::set<std::string> &remove_layers, std::string &name, json_object *filter, std::map<std::string, std::string> &attribute_descriptions) {
 	std::vector<std::map<std::string, layermap_entry>> layermaps;
 	for (size_t i = 0; i < CPUS; i++) {
 		layermaps.push_back(std::map<std::string, layermap_entry>());
@@ -749,6 +788,27 @@ void decode(struct reader *readers, std::map<std::string, layermap_entry> &layer
 			}
 			sqlite3_finalize(r->stmt);
 		}
+		if (sqlite3_prepare_v2(db, "SELECT value from metadata where name = 'json'", -1, &r->stmt, NULL) == SQLITE_OK) {
+			if (sqlite3_step(r->stmt) == SQLITE_ROW) {
+				const unsigned char *s = sqlite3_column_text(r->stmt, 0);
+
+				if (s != NULL) {
+					json_pull *jp = json_begin_string((const char *) s);
+					json_object *o = json_read_tree(jp);
+
+					if (o != NULL && o->type == JSON_HASH) {
+						json_object *vector_layers = json_hash_get(o, "vector_layers");
+
+						handle_vector_layers(vector_layers, layermap, attribute_descriptions);
+						json_free(o);
+					}
+
+					json_end(jp);
+				}
+			}
+
+			sqlite3_finalize(r->stmt);
+		}
 
 		// Closes either real db or temp mirror of metadata.json
 		if (sqlite3_close(db) != SQLITE_OK) {
@@ -990,7 +1050,9 @@ int main(int argc, char **argv) {
 		*rr = r;
 	}
 
-	decode(readers, layermap, outdb, out_dir, &st, header, mapping, exclude, ifmatched, attribution, description, keep_layers, remove_layers, name, filter);
+	std::map<std::string, std::string> attribute_descriptions;
+
+	decode(readers, layermap, outdb, out_dir, &st, header, mapping, exclude, ifmatched, attribution, description, keep_layers, remove_layers, name, filter, attribute_descriptions);
 
 	if (set_attribution.size() != 0) {
 		attribution = set_attribution;
@@ -1002,7 +1064,7 @@ int main(int argc, char **argv) {
 		name = set_name;
 	}
 
-	mbtiles_write_metadata(outdb, out_dir, name.c_str(), st.minzoom, st.maxzoom, st.minlat, st.minlon, st.maxlat, st.maxlon, st.midlat, st.midlon, 0, attribution.size() != 0 ? attribution.c_str() : NULL, layermap, true, description.c_str(), !pg, std::map<std::string, std::string>());
+	mbtiles_write_metadata(outdb, out_dir, name.c_str(), st.minzoom, st.maxzoom, st.minlat, st.minlon, st.maxlat, st.maxlon, st.midlat, st.midlon, 0, attribution.size() != 0 ? attribution.c_str() : NULL, layermap, true, description.c_str(), !pg, attribute_descriptions);
 
 	if (outdb != NULL) {
 		mbtiles_close(outdb, argv[0]);