Fix WTS regression in iswiki when link prefix and link trail overlap.

See example regression in the comments of
I5ae8435322c78dd1df170d7a3543fff3642759b1.

Change-Id: I30d98cd35a8260c0b2b8d18beb10d7a286c624a5

lib/wts.ConstrainedText.js

@@ -43,6 +43,7 @@ var escapeLine = function(line, cb) {
 		line: line,
 		pos: 0,
 	};
+	var safeLeft = '';
 	for (state.pos = 0; state.pos < line.length; state.pos++) {
 		var chunk = line[state.pos];
 		// Process the escapes for this chunk, given escaped previous chunk
@@ -54,9 +55,16 @@ var escapeLine = function(line, cb) {
 		if (cb) {
 			cb(state.leftContext.slice(origPos), chunk.node);
 		}
+		if (thisEscape.greedy) {
+			// protect the left context: this will be matched greedily
+			// by this chunk, so there's no chance that a subsequent
+			// token will include this in its prefix.
+			safeLeft += state.leftContext;
+			state.leftContext = '';
+		}
 	}
 	// right context should be empty here.
-	return state.leftContext;
+	return safeLeft + state.leftContext;
 };
 
 /**
@@ -255,8 +263,22 @@ var WikiLinkText = function WikiLinkText(text, node, wikiConfig, type) {
 		badPrefix: noTrails ? undefined : wikiConfig.linkPrefixRegex,
 		badSuffix: noTrails ? undefined : wikiConfig.linkTrailRegex,
 	});
+	// We match link trails greedily when they exist.
+	if (!(noTrails || /\]$/.test(text))) {
+		this.greedy = true;
+	}
 };
 inherits(WikiLinkText, RegExpConstrainedText);
+WikiLinkText.prototype.escape = function(state) {
+	var r = WikiLinkText.super_.prototype.escape.call(this, state);
+	// If previous token was also a WikiLink, its linktrail will
+	// eat up any possible linkprefix characters, so we don't need
+	// a <nowiki> in this case.  (Eg: [[a]]-[[b]] in iswiki; the -
+	// character is both a link prefix and a link trail, but it gets
+	// preferentially associated with the [[a]] as a link trail.)
+	r.greedy = this.greedy;
+	return r;
+};
 WikiLinkText._fromSelSer = function(text, node, dataParsoid, env) {
 	// interwiki links have type == 'mw:ExtLink', but they are written
 	// with [[ ]] and get link trails -- so as far as we're concerned

tests/parserTests.txt

@@ -21173,6 +21173,18 @@ parsoid=html2wt
 this is not a link: <nowiki>http://example.com</nowiki>
 !! end
 
+!! test
+Links 15. Link trails can't become link prefixes.
+!! options
+language=is
+!! wikitext
+[[Söfnuður]]-[[00]]
+!! html/php
+<p><a href="/wiki/S%C3%B6fnu%C3%B0ur" title="Söfnuður">Söfnuður-</a><a href="/wiki/00" title="00">00</a>
+</p>
+!! html/parsoid
+<p><a rel="mw:WikiLink" href="Söfnuður" title="Söfnuður" data-parsoid='{"stx":"simple","tail":"-"}'>Söfnuður-</a><a rel="mw:WikiLink" href="00" title="00">00</a></p>
+!! end
 
 #### --------------- Quotes ---------------
 #### 1. Quotes inside <b> and <i>