FakeVim: Fix infinite loop when replacing empty text

Change-Id: Ie4ba6420889b0a6a5712b43a11f8366aa9a30edc
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Reviewed-by: hjk <hjk121@nokiamail.com>

src/plugins/fakevim/fakevim_test.cpp

@@ -2206,6 +2206,17 @@ void FakeVimPlugin::test_vim_substitute()
     COMMAND("'<,'>s/^/*", "abc" N "**def" N X "**ghi" N "jkl");
     KEYS("u", "abc" N X "*def" N "*ghi" N "jkl");
     KEYS("gv:s/^/+<CR>", "abc" N "+*def" N X "+*ghi" N "jkl");
+
+    // replace empty string
+    data.setText("abc");
+    COMMAND("s//--/g", "--a--b--c");
+
+    // remove characters
+    data.setText("abc def");
+    COMMAND("s/[abde]//g", "c f");
+    COMMAND("undo | s/[bcef]//g", "a d");
+    COMMAND("undo | s/\\w//g", " ");
+    COMMAND("undo | s/f\\|$/-/g", "abc de-");
 }
 
 void FakeVimPlugin::test_vim_ex_yank()

src/plugins/fakevim/fakevimhandler.cpp

@@ -623,10 +623,22 @@ static bool substituteText(QString *text, QRegExp &pattern, const QString &repla
 {
     bool substituted = false;
     int pos = 0;
+    int right = -1;
     while (true) {
         pos = pattern.indexIn(*text, pos, QRegExp::CaretAtZero);
         if (pos == -1)
             break;
+
+        // ensure that substitution is advancing towards end of line
+        if (right == text->size() - pos) {
+            ++pos;
+            if (pos == text->size())
+                break;
+            continue;
+        }
+
+        right = text->size() - pos;
+
         substituted = true;
         QString matched = text->mid(pos, pattern.cap(0).size());
         QString repl;
@@ -652,7 +664,7 @@ static bool substituteText(QString *text, QRegExp &pattern, const QString &repla
             }
         }
         text->replace(pos, matched.size(), repl);
-        pos += qMax(1, repl.size());
+        pos += (repl.isEmpty() && matched.isEmpty()) ? 1 : repl.size();
 
         if (pos >= text->size() || !global)
             break;