Make RSParsedArticle calculate a unique ID only when there’s no guid. Otherwise use the guid. Do not attempt to create a globally-unique ID — that’s out of scope for the parser and should be (and is) handled at the app’s model layer.

Frameworks/RSParser/Feeds/XML/RSAtomParser.m

@@ -195,9 +195,6 @@ static const NSInteger kLengthLength = 7;
 		[self.parser parseData:self.feedData];
 		[self.parser finishParsing];
 	}
-
-	// Optimization: make articles do calculations on this background thread.
-	[self.articles makeObjectsPerformSelector:@selector(calculateArticleID)];
 }
 
 

Frameworks/RSParser/Feeds/XML/RSParsedArticle.h

@@ -15,7 +15,7 @@
 - (nonnull instancetype)initWithFeedURL:(NSString * _Nonnull)feedURL;
 
 @property (nonatomic, readonly, nonnull) NSString *feedURL;
-@property (nonatomic, nonnull) NSString *articleID; //Calculated. Don't get until other properties have been set.
+@property (nonatomic, nonnull) NSString *articleID; //guid, if present, or calculated from other attributes. Should be unique to the feed, but not necessarily unique across different feeds. (Not suitable for a database ID.)
 
 @property (nonatomic, nullable) NSString *guid;
 @property (nonatomic, nullable) NSString *title;
@@ -30,7 +30,5 @@
 
 - (void)addEnclosure:(RSParsedEnclosure *_Nonnull)enclosure;
 
-- (void)calculateArticleID; // Optimization. Call after all properties have been set. Call on a background thread.
-
 @end
 

Frameworks/RSParser/Feeds/XML/RSParsedArticle.m

@@ -47,20 +47,26 @@
 #pragma mark - Accessors
 
 - (NSString *)articleID {
+
+	if (self.guid) {
+		return self.guid;
+	}
 	
 	if (!_articleID) {
-		_articleID = self.calculatedUniqueID;
+		_articleID = [self calculatedArticleID];
 	}
 	
 	return _articleID;
 }
 
 
-- (NSString *)calculatedUniqueID {
+- (NSString *)calculatedArticleID {
 
-	/*guid+feedID, or a combination of properties when no guid. Then hash the result.
-		In general, feeds should have guids. When they don't, re-runs are very likely,
-		because there's no other 100% reliable way to determine identity.*/
+	/*Concatenate a combination of properties when no guid. Then hash the result.
+	 In general, feeds should have guids. When they don't, re-runs are very likely,
+	 because there's no other 100% reliable way to determine identity.
+	 This is intended to create an ID unique inside a feed, but not globally unique.
+	 Not suitable for a database ID, in other words.*/
 
 	NSMutableString *s = [NSMutableString stringWithString:@""];
 	
@@ -69,11 +75,7 @@
 		datePublishedTimeStampString = [NSString stringWithFormat:@"%.0f", self.datePublished.timeIntervalSince1970];
 	}
 	
-	if (!RSParserStringIsEmpty(self.guid)) {
-		[s appendString:self.guid];
-	}
-
-	else if (!RSParserStringIsEmpty(self.link) && self.datePublished != nil) {
+	if (!RSParserStringIsEmpty(self.link) && self.datePublished != nil) {
 		[s appendString:self.link];
 		[s appendString:datePublishedTimeStampString];
 	}
@@ -99,15 +101,11 @@
 		[s appendString:self.body];
 	}
 
-	NSAssert(!RSParserStringIsEmpty(self.feedURL), nil);
-	[s appendString:self.feedURL];
-
-	return [s rsparser_md5Hash];
-}
-
-- (void)calculateArticleID {
+	else if (!RSParserStringIsEmpty(self.permalink)) {
+		[s appendString:self.permalink];
+	}
 	
-	(void)self.articleID;
+	return [s rsparser_md5Hash];
 }
 
 @end

Frameworks/RSParser/Feeds/XML/RSRSSParser.m

@@ -172,9 +172,6 @@ static const NSInteger kEnclosureLength = 10;
 		[self.parser parseData:self.feedData];
 		[self.parser finishParsing];
 	}
-	
-	// Optimization: make articles do calculations on this background thread.
-	[self.articles makeObjectsPerformSelector:@selector(calculateArticleID)];
 }
 
 

Frameworks/RSParser/RSParserTests/AtomParserTests.swift

@@ -36,4 +36,28 @@ class AtomParserTests: XCTestCase {
 
 		XCTAssertTrue(parsedFeed.homePageURL == "http://leancrew.com/all-this")
 	}
+
+	func testDaringFireball() {
+
+		let d = parserData("DaringFireball", "atom", "http://daringfireball.net/") //It’s actually an Atom feed
+		let parsedFeed = try! FeedParser.parse(d)!
+
+		for article in parsedFeed.items {
+
+			XCTAssertNotNil(article.externalURL)
+
+			if !article.title!.hasPrefix("★ ") {
+				XCTAssertNotNil(article.url)
+				XCTAssert(article.url!.hasPrefix("https://daringfireball.net/"))
+			}
+
+			XCTAssertTrue(article.uniqueID.hasPrefix("tag:daringfireball.net,2017:/"))
+
+			//			XCTAssertEqual(article.authors!.count, 1) // TODO: parse Atom authors
+
+			XCTAssertNotNil(article.datePublished)
+			XCTAssert(article.attachments == nil)
+		}
+
+	}
 }