Different approach to ensuring marker.clear works well with undo

The previous approach was quite misguided.

lib/codemirror.js

@@ -1508,22 +1508,17 @@ window.CodeMirror = (function() {
 
     function TextMarker(type, style) { this.lines = []; this.type = type; if (style) this.style = style; }
     TextMarker.prototype.clear = operation(function() {
-      var min, max, seen = {};
+      var min, max;
       for (var i = 0; i < this.lines.length; ++i) {
-        var line = this.lines[i], lineN = lineNo(line);
-        seen[lineN] = newHL(line.text, line.markedSpans);
+        var line = this.lines[i];
         var span = getMarkedSpanFor(line.markedSpans, this);
-        if (span.from != null) min = lineN;
-        if (span.to != null) max = lineN;
+        if (span.from != null) min = lineNo(line);
+        if (span.to != null) max = lineNo(line);
         line.markedSpans = removeMarkedSpan(line.markedSpans, span);
       }
-      if (min != null) {
-        changes.push({from: min, to: max + 1});
-        var old = [];
-        for (var i = min; i <= max; ++i) old.push(seen[i]);
-        history.addChange(min, old.length, old, true);
-      }
+      if (min != null) changes.push({from: min, to: max + 1});
       this.lines.length = 0;
+      this.explicitlyCleared = true;
     });
     TextMarker.prototype.find = function() {
       var from, to;
@@ -1545,18 +1540,16 @@ window.CodeMirror = (function() {
       var marker = new TextMarker("range", className);
       if (options) for (var opt in options) if (options.hasOwnProperty(opt))
         marker[opt] = options[opt];
-      var curLine = from.line, old = [];
+      var curLine = from.line;
       doc.iter(curLine, to.line + 1, function(line) {
         var span = {from: curLine == from.line ? from.ch : null,
                     to: curLine == to.line ? to.ch : null,
                     marker: marker};
-        old.push(newHL(line.text, line.markedSpans));
         line.markedSpans = (line.markedSpans || []).concat([span]);
         marker.lines.push(line);
         ++curLine;
       });
       changes.push({from: from.line, to: to.line + 1});
-      history.addChange(from.line, old.length, old, true);
       return marker;
     }
 
@@ -2463,7 +2456,15 @@ window.CodeMirror = (function() {
   // hl stands for history-line, a data structure that can be either a
   // string (line without markers) or a {text, markedSpans} object.
   function hlText(val) { return typeof val == "string" ? val : val.text; }
-  function hlSpans(val) { return typeof val == "string" ? null : val.markedSpans; }
+  function hlSpans(val) {
+    if (typeof val == "string") return null;
+    var spans = val.markedSpans, out = null;
+    for (var i = 0; i < spans.length; ++i) {
+      if (spans[i].marker.explicitlyCleared) { if (!out) out = spans.slice(0, i); }
+      else if (out) out.push(spans[i]);
+    }
+    return !out ? spans : out.length ? out : null;
+  }
   function newHL(text, spans) { return spans ? {text: text, markedSpans: spans} : text; }
 
   function detachMarkedSpans(line) {
@@ -2888,12 +2889,12 @@ window.CodeMirror = (function() {
     this.closed = false;
   }
   History.prototype = {
-    addChange: function(start, added, old, minor) {
+    addChange: function(start, added, old) {
       this.undone.length = 0;
       var time = +new Date, cur = lst(this.done), last = cur && lst(cur);
       var dtime = time - this.time;
 
-      if (cur && !this.closed && (this.compound || minor)) {
+      if (cur && !this.closed && this.compound) {
         cur.push({start: start, added: added, old: old});
       } else if (dtime > 400 || !last || this.closed ||
                  last.start > start + old.length || last.start + last.added < start) {