hgweb: re-implement followlines UI selection using buttons

This changeset attempts to solve two issues with the "followlines" UI in
hgweb. First the "followlines" action is currently not easily discoverable
(one has to hover on a line for some time, wait for the invite message to
appear and then perform some action). Second, it gets in the way of natural
line selection, especially in filerevision view.

This changeset introduces an additional markup element (a <button
class="btn-followlines">) alongside each content line of the view. This button
now holds events for line selection that were previously plugged onto content
lines directly. Consequently, there's no more action on content lines, hence
restoring the "natural line selection" behavior (solving the second problem).
These buttons are hidden by default and get displayed upon hover of content
lines; then upon hover of a button itself, a text inviting followlines section
shows up. This solves the first problem (discoverability) as we now have a
clear visual element indicating that "some action could be perform" (i.e. a
button) and that is self-documented.

In followlines.js, all event listeners are now attached to these <button>
elements. The custom "floating tooltip" element is dropped as <button>
elements are now self-documented through a "title" attribute that changes
depending on preceding actions (selection started or not, in particular).

The new <button> element is inserted in followlines.js script (thus only
visible if JavaScript is activated); it contains a "+" and "-" with a
"diff-semantics" style; upon hover, it scales up.

To find the parent element under which to insert the <button> we either rely
on the "data-selectabletag" attribute (which defines the HTML tag of children
of class="sourcelines" element e.g. <span> for filerevision view and <tr> for
annotate view) or use a child of the latter elements if we find an element
with class="followlines-btn-parent" (useful for annotate view, for which we
have to find the <td> in which to insert the <button>).

On noticeable change in CSS concerns the "margin-left" of span:before
pseudo-elements in filelog view that has been increased a bit in order to
leave space for the new button to appear between line number column and
line content one.
Also note the "z-index" addition for "annotate-info" box so that the latter
appears on top of new buttons (instead of getting hidden).

In some respect, the UI similar to line commenting feature that is implemented
in popular code hosting site like GitHub, BitBucket or Kallithea.

mercurial/templates/gitweb/map

@@ -113,7 +113,7 annotateline = '
         <a href="{url|urlescape}rev/{node|short}{sessionvars%urlparameter}">changeset</a>
       </div>
     </td>
-    <td><pre><a class="linenr" href="#{lineid}">{linenumber}</a></pre></td>
+    <td class="followlines-btn-parent"><pre><a class="linenr" href="#{lineid}">{linenumber}</a></pre></td>
     <td><pre>{line|escape}</pre></td>
   </tr>'
 annotateparent = '

mercurial/templates/paper/map

@@ -94,7 +94,7 annotateline = '
         <a href="{url|urlescape}rev/{node|short}{sessionvars%urlparameter}">changeset</a>
       </div>
     </td>
-    <td class="source"><a href="#{lineid}">{linenumber}</a> {line|escape}</td>
+    <td class="source followlines-btn-parent"><a href="#{lineid}">{linenumber}</a> {line|escape}</td>
   </tr>'
 annotateparent = '
   <a href="{url|urlescape}annotate/{node|short}/{file|urlescape}{sessionvars%urlparameter}">{rev}</a>'

mercurial/templates/static/followlines.js

@@ -26,14 +26,6 document.addEventListener('DOMContentLoa
 
     var isHead = parseInt(sourcelines.dataset.ishead || "0");
 
-    // tooltip to invite on lines selection
-    var tooltip = document.createElement('div');
-    tooltip.id = 'followlines-tooltip';
-    tooltip.classList.add('hidden');
-    var initTooltipText = 'click to start following lines history from here';
-    tooltip.textContent = initTooltipText;
-    sourcelines.appendChild(tooltip);
-
     //* position "element" on top-right of cursor */
     function positionTopRight(element, event) {
         var x = (event.clientX + 10) + 'px',
@@ -42,32 +34,60 document.addEventListener('DOMContentLoa
         element.style.left = x;
     }
 
-    var tooltipTimeoutID;
-    //* move the "tooltip" with cursor (top-right) and show it after 1s */
-    function moveAndShowTooltip(e) {
-        if (typeof tooltipTimeoutID !== 'undefined') {
-            // avoid accumulation of timeout callbacks (blinking)
-            window.clearTimeout(tooltipTimeoutID);
-        }
-        tooltip.classList.add('hidden');
-        positionTopRight(tooltip, e);
-        tooltipTimeoutID = window.setTimeout(function() {
-            tooltip.classList.remove('hidden');
-        }, 1000);
-    }
-
-    // on mousemove, show tooltip close to cursor position
-    sourcelines.addEventListener('mousemove', moveAndShowTooltip);
-
     // retrieve all direct *selectable* children of class="sourcelines"
     // element
     var selectableElements = Array.prototype.filter.call(
         sourcelines.children,
         function(x) { return x.tagName === selectableTag });
 
-    // add a "followlines-select" class to change cursor type in CSS
+    var btnTitleStart = 'start following lines history from here';
+    var btnTitleEnd = 'terminate line block selection here';
+
+    //** return a <button> element with +/- spans */
+    function createButton() {
+        var btn = document.createElement('button');
+        btn.title = btnTitleStart;
+        btn.classList.add('btn-followlines');
+        var plusSpan = document.createElement('span');
+        plusSpan.classList.add('followlines-plus');
+        plusSpan.textContent = '+';
+        btn.appendChild(plusSpan);
+        var br = document.createElement('br');
+        btn.appendChild(br);
+        var minusSpan = document.createElement('span');
+        minusSpan.classList.add('followlines-minus');
+        minusSpan.textContent = '−';
+        btn.appendChild(minusSpan);
+        return btn;
+    }
+
+    // extend DOM with CSS class for selection highlight and action buttons
+    var followlinesButtons = []
     for (var i = 0; i < selectableElements.length; i++) {
         selectableElements[i].classList.add('followlines-select');
+        var btn = createButton();
+        followlinesButtons.push(btn);
+        // insert the <button> as child of `selectableElements[i]` unless the
+        // latter has itself a child  with a "followlines-btn-parent" class
+        // (annotate view)
+        var btnSupportElm = selectableElements[i];
+        var childSupportElms = btnSupportElm.getElementsByClassName(
+            'followlines-btn-parent');
+        if ( childSupportElms.length > 0 ) {
+            btnSupportElm = childSupportElms[0];
+        }
+        var refNode = btnSupportElm.children[0]; // node to insert <button> before
+        btnSupportElm.insertBefore(btn, refNode);
+    }
+
+    // ** re-initialize followlines buttons */
+    function resetButtons() {
+        for (var i = 0; i < followlinesButtons.length; i++) {
+            var btn = followlinesButtons[i];
+            btn.title = btnTitleStart;
+            btn.classList.remove('btn-followlines-end');
+            btn.classList.remove('btn-followlines-hidden');
+        }
     }
 
     var lineSelectedCSSClass = 'followlines-selected';
@@ -100,27 +120,54 document.addEventListener('DOMContentLoa
         return selectableParent(parent);
     }
 
+    // ** update buttons title and style upon first click */
+    function updateButtons(selectable) {
+        for (var i = 0; i < followlinesButtons.length; i++) {
+            var btn = followlinesButtons[i];
+            btn.title = btnTitleEnd;
+            btn.classList.add('btn-followlines-end');
+        }
+        // on clicked button, change title to "cancel"
+        var clicked = selectable.getElementsByClassName('btn-followlines')[0];
+        clicked.title = 'cancel';
+        clicked.classList.remove('btn-followlines-end');
+    }
+
+    //** add `listener` on "click" event for all `followlinesButtons` */
+    function buttonsAddEventListener(listener) {
+        for (var i = 0; i < followlinesButtons.length; i++) {
+            followlinesButtons[i].addEventListener('click', listener);
+        }
+    }
+
+    //** remove `listener` on "click" event for all `followlinesButtons` */
+    function buttonsRemoveEventListener(listener) {
+        for (var i = 0; i < followlinesButtons.length; i++) {
+            followlinesButtons[i].removeEventListener('click', listener);
+        }
+    }
+
     //** event handler for "click" on the first line of a block */
     function lineSelectStart(e) {
-        var startElement = selectableParent(e.target);
+        var startElement = selectableParent(e.target.parentElement);
         if (startElement === null) {
             // not a "selectable" element (maybe <a>): abort, keeping event
             // listener registered for other click with a "selectable" target
             return;
         }
 
-        // update tooltip text
-        tooltip.textContent = 'click again to terminate line block selection here';
+        // update button tooltip text and CSS
+        updateButtons(startElement);
 
         var startId = parseInt(startElement.id.slice(1));
         startElement.classList.add(lineSelectedCSSClass); // CSS
 
         // remove this event listener
-        sourcelines.removeEventListener('click', lineSelectStart);
+        buttonsRemoveEventListener(lineSelectStart);
 
         //** event handler for "click" on the last line of the block */
         function lineSelectEnd(e) {
-            var endElement = selectableParent(e.target);
+            var endElement = selectableParent(e.target.parentElement);
             if (endElement === null) {
                 // not a <span> (maybe <a>): abort, keeping event listener
                 // registered for other click with <span> target
@@ -128,27 +175,18 document.addEventListener('DOMContentLoa
             }
 
             // remove this event listener
-            sourcelines.removeEventListener('click', lineSelectEnd);
+            buttonsRemoveEventListener(lineSelectEnd);
 
-            // hide tooltip and disable motion tracking
-            tooltip.classList.add('hidden');
-            sourcelines.removeEventListener('mousemove', moveAndShowTooltip);
-            window.clearTimeout(tooltipTimeoutID);
-
-            //* restore initial "tooltip" state */
-            function restoreTooltip() {
-                tooltip.textContent = initTooltipText;
-                sourcelines.addEventListener('mousemove', moveAndShowTooltip);
-            }
+            // reset button tooltip text
+            resetButtons();
 
             // compute line range (startId, endId)
             var endId = parseInt(endElement.id.slice(1));
             if (endId == startId) {
                 // clicked twice the same line, cancel and reset initial state
-                // (CSS, event listener for selection start, tooltip)
+                // (CSS, event listener for selection start)
                 removeSelectedCSSClass();
-                sourcelines.addEventListener('click', lineSelectStart);
-                restoreTooltip();
+                buttonsAddEventListener(lineSelectStart);
                 return;
             }
             var inviteElement = endElement;
@@ -169,31 +207,37 document.addEventListener('DOMContentLoa
             inviteElement.appendChild(div);
             // set position close to cursor (top-right)
             positionTopRight(div, e);
+            // hide all buttons
+            for (var i = 0; i < followlinesButtons.length; i++) {
+                followlinesButtons[i].classList.add('btn-followlines-hidden');
+            }
 
             //** event handler for cancelling selection */
             function cancel() {
                 // remove invite box
                 div.parentNode.removeChild(div);
                 // restore initial event listeners
-                sourcelines.addEventListener('click', lineSelectStart);
-                sourcelines.removeEventListener('click', cancel);
+                buttonsAddEventListener(lineSelectStart);
+                buttonsRemoveEventListener(cancel);
+                for (var i = 0; i < followlinesButtons.length; i++) {
+                    followlinesButtons[i].classList.remove('btn-followlines-hidden');
+                }
                 // remove styles on selected lines
                 removeSelectedCSSClass();
-                // restore tooltip element
-                restoreTooltip();
+                resetButtons();
             }
 
             // bind cancel event to click on <button>
             button.addEventListener('click', cancel);
             // as well as on an click on any source line
-            sourcelines.addEventListener('click', cancel);
+            buttonsAddEventListener(cancel);
         }
 
-        sourcelines.addEventListener('click', lineSelectEnd);
+        buttonsAddEventListener(lineSelectEnd);
 
     }
 
-    sourcelines.addEventListener('click', lineSelectStart);
+    buttonsAddEventListener(lineSelectStart);
 
     //** return a <div id="followlines"> and inner cancel <button> elements */
     function followlinesBox(targetUri, fromline, toline, isHead) {

mercurial/templates/static/style-gitweb.css

@@ -86,6 +86,7 td.annotate {
   white-space: nowrap;
 }
 div.annotate-info {
+  z-index: 5;
   display: none;
   position: absolute;
   background-color: #FFFFFF;
@@ -152,7 +153,7 pre.sourcelines > span:before {
 	-ms-user-select: none;
 	user-select: none;
 	display: inline-block;
-	margin-left: -5em;
+	margin-left: -6em;
 	width: 4em;
 	color: #999;
 	text-align: right;
@@ -177,11 +178,6 pre.sourcelines.stripes > span:target {
 }
 
 /* Followlines */
-div.page_body table tbody.sourcelines > tr.followlines-select:hover,
-div.page_body pre.sourcelines > span.followlines-select:hover {
-  cursor: cell;
-}
-
 tbody.sourcelines > tr.followlines-selected,
 pre.sourcelines > span.followlines-selected {
   background-color: #99C7E9 !important;
@@ -219,21 +215,62 div.followlines-link {
   font-family: sans-serif;
 }
 
-div#followlines-tooltip {
+.btn-followlines {
   display: none;
-  position: fixed;
-  background-color: #ffc;
-  border: 1px solid #999;
-  padding: 2px;
+  cursor: pointer;
+  box-sizing: content-box;
+  font-size: 11px;
+  width: 13px;
+  height: 13px;
+  border-radius: 3px;
+  margin: 0px;
+  margin-top: -2px;
+  padding: 0px;
+  background-color: #E5FDE5;
+  border: 1px solid #9BC19B;
+  font-family: monospace;
+  text-align: center;
+  line-height: 5px;
+}
+
+tr .btn-followlines {
+  position: absolute;
 }
 
-.sourcelines:hover > div#followlines-tooltip {
+span .btn-followlines {
+  float: left;
+}
+
+span.followlines-select .btn-followlines {
+  margin-left: -1.6em;
+}
+
+.btn-followlines:hover {
+  transform: scale(1.1, 1.1);
+}
+
+.btn-followlines .followlines-plus {
+  color: green;
+}
+
+.btn-followlines .followlines-minus {
+  color: red;
+}
+
+.btn-followlines-end {
+  background-color: #ffdcdc;
+}
+
+.sourcelines tr:hover .btn-followlines,
+.sourcelines span.followlines-select:hover > .btn-followlines {
   display: inline;
 }
 
-.sourcelines:hover > div#followlines-tooltip.hidden {
+.btn-followlines-hidden,
+.sourcelines tr:hover .btn-followlines-hidden {
   display: none;
 }
+
 /* Graph */
 div#wrapper {
 	position: relative;

mercurial/templates/static/style-paper.css

@@ -214,6 +214,7 td.annotate {
   white-space: nowrap;
 }
 div.annotate-info {
+  z-index: 5;
   display: none;
   position: absolute;
   background-color: #FFFFFF;
@@ -267,7 +268,7 td.annotate:hover div.annotate-info { di
   -ms-user-select: none;
   user-select: none;
   display: inline-block;
-  margin-left: -5em;
+  margin-left: -6em;
   width: 4em;
   font-size: smaller;
   color: #999;
@@ -280,11 +281,7 td.annotate:hover div.annotate-info { di
   background-color: #bfdfff;
 }
 
-div.overflow table tbody.sourcelines > tr.followlines-select:hover,
-div.overflow pre.sourcelines > span.followlines-select:hover {
-  cursor: cell;
-}
-
+/* Followlines */
 tbody.sourcelines > tr.followlines-selected,
 pre.sourcelines > span.followlines-selected {
   background-color: #99C7E9;
@@ -322,19 +319,59 div.followlines-link {
   font-family: sans-serif;
 }
 
-div#followlines-tooltip {
+.btn-followlines {
   display: none;
-  position: fixed;
-  background-color: #ffc;
-  border: 1px solid #999;
-  padding: 2px;
+  cursor: pointer;
+  box-sizing: content-box;
+  font-size: 12px;
+  width: 13px;
+  height: 13px;
+  border-radius: 3px;
+  margin: 0px;
+  margin-top: -2px;
+  padding: 0px;
+  background-color: #E5FDE5;
+  border: 1px solid #9BC19B;
+  font-family: monospace;
+  text-align: center;
+  line-height: 5px;
+}
+
+tr .btn-followlines {
+  position: absolute;
 }
 
-.sourcelines:hover > div#followlines-tooltip {
+span .btn-followlines {
+  float: left;
+}
+
+span.followlines-select .btn-followlines {
+  margin-left: -1.5em;
+}
+
+.btn-followlines:hover {
+  transform: scale(1.2, 1.2);
+}
+
+.btn-followlines .followlines-plus {
+  color: green;
+}
+
+.btn-followlines .followlines-minus {
+  color: red;
+}
+
+.btn-followlines-end {
+  background-color: #ffdcdc;
+}
+
+.sourcelines tr:hover .btn-followlines,
+.sourcelines span.followlines-select:hover > .btn-followlines {
   display: inline;
 }
 
-.sourcelines:hover > div#followlines-tooltip.hidden {
+.btn-followlines-hidden,
+.sourcelines tr:hover .btn-followlines-hidden {
   display: none;
 }
 

tests/test-hgweb.t

@@ -340,7 +340,7 static file
 
   $ get-with-headers.py --twice localhost:$HGPORT 'static/style-gitweb.css' - date etag server
   200 Script output follows
-  content-length: 8463
+  content-length: 8985
   content-type: text/css
   
   body { font-family: sans-serif; font-size: 12px; border:solid #d9d8d1; border-width:1px; margin:10px; background: white; color: black; }
@@ -431,6 +431,7 static file
     white-space: nowrap;
   }
   div.annotate-info {
+    z-index: 5;
     display: none;
     position: absolute;
     background-color: #FFFFFF;
@@ -497,7 +498,7 static file
   	-ms-user-select: none;
   	user-select: none;
   	display: inline-block;
-  	margin-left: -5em;
+  	margin-left: -6em;
   	width: 4em;
   	color: #999;
   	text-align: right;
@@ -522,11 +523,6 static file
   }
   
   /* Followlines */
-  div.page_body table tbody.sourcelines > tr.followlines-select:hover,
-  div.page_body pre.sourcelines > span.followlines-select:hover {
-    cursor: cell;
-  }
-  
   tbody.sourcelines > tr.followlines-selected,
   pre.sourcelines > span.followlines-selected {
     background-color: #99C7E9 !important;
@@ -564,21 +560,62 static file
     font-family: sans-serif;
   }
   
-  div#followlines-tooltip {
+  .btn-followlines {
     display: none;
-    position: fixed;
-    background-color: #ffc;
-    border: 1px solid #999;
-    padding: 2px;
+    cursor: pointer;
+    box-sizing: content-box;
+    font-size: 11px;
+    width: 13px;
+    height: 13px;
+    border-radius: 3px;
+    margin: 0px;
+    margin-top: -2px;
+    padding: 0px;
+    background-color: #E5FDE5;
+    border: 1px solid #9BC19B;
+    font-family: monospace;
+    text-align: center;
+    line-height: 5px;
+  }
+  
+  tr .btn-followlines {
+    position: absolute;
   }
   
-  .sourcelines:hover > div#followlines-tooltip {
+  span .btn-followlines {
+    float: left;
+  }
+  
+  span.followlines-select .btn-followlines {
+    margin-left: -1.6em;
+  }
+  
+  .btn-followlines:hover {
+    transform: scale(1.1, 1.1);
+  }
+  
+  .btn-followlines .followlines-plus {
+    color: green;
+  }
+  
+  .btn-followlines .followlines-minus {
+    color: red;
+  }
+  
+  .btn-followlines-end {
+    background-color: #ffdcdc;
+  }
+  
+  .sourcelines tr:hover .btn-followlines,
+  .sourcelines span.followlines-select:hover > .btn-followlines {
     display: inline;
   }
   
-  .sourcelines:hover > div#followlines-tooltip.hidden {
+  .btn-followlines-hidden,
+  .sourcelines tr:hover .btn-followlines-hidden {
     display: none;
   }
+  
   /* Graph */
   div#wrapper {
   	position: relative;

tests/test-highlight.t

@@ -314,7 +314,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l1">     1</a> <span class="sd">&quot;&quot;&quot;Fun with generators. Corresponding Haskell implementation:</span></td>
+  <td class="source followlines-btn-parent"><a href="#l1">     1</a> <span class="sd">&quot;&quot;&quot;Fun with generators. Corresponding Haskell implementation:</span></td>
   </tr>
   <tr id="l2" class="thisrev">
   <td class="annotate parity0">
@@ -331,7 +331,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l2">     2</a> </td>
+  <td class="source followlines-btn-parent"><a href="#l2">     2</a> </td>
   </tr>
   <tr id="l3" class="thisrev">
   <td class="annotate parity0">
@@ -348,7 +348,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l3">     3</a> <span class="sd">primes = 2 : sieve [3, 5..]</span></td>
+  <td class="source followlines-btn-parent"><a href="#l3">     3</a> <span class="sd">primes = 2 : sieve [3, 5..]</span></td>
   </tr>
   <tr id="l4" class="thisrev">
   <td class="annotate parity0">
@@ -365,7 +365,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l4">     4</a> <span class="sd">    where sieve (p:ns) = p : sieve [n | n &lt;- ns, mod n p /= 0]</span></td>
+  <td class="source followlines-btn-parent"><a href="#l4">     4</a> <span class="sd">    where sieve (p:ns) = p : sieve [n | n &lt;- ns, mod n p /= 0]</span></td>
   </tr>
   <tr id="l5" class="thisrev">
   <td class="annotate parity0">
@@ -382,7 +382,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l5">     5</a> <span class="sd">&quot;&quot;&quot;</span></td>
+  <td class="source followlines-btn-parent"><a href="#l5">     5</a> <span class="sd">&quot;&quot;&quot;</span></td>
   </tr>
   <tr id="l6" class="thisrev">
   <td class="annotate parity0">
@@ -399,7 +399,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l6">     6</a> </td>
+  <td class="source followlines-btn-parent"><a href="#l6">     6</a> </td>
   </tr>
   <tr id="l7" class="thisrev">
   <td class="annotate parity0">
@@ -416,7 +416,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l7">     7</a> <span class="kn">from</span> <span class="nn">itertools</span> <span class="kn">import</span> <span class="n">dropwhile</span><span class="p">,</span> <span class="n">ifilter</span><span class="p">,</span> <span class="n">islice</span><span class="p">,</span> <span class="n">count</span><span class="p">,</span> <span class="n">chain</span></td>
+  <td class="source followlines-btn-parent"><a href="#l7">     7</a> <span class="kn">from</span> <span class="nn">itertools</span> <span class="kn">import</span> <span class="n">dropwhile</span><span class="p">,</span> <span class="n">ifilter</span><span class="p">,</span> <span class="n">islice</span><span class="p">,</span> <span class="n">count</span><span class="p">,</span> <span class="n">chain</span></td>
   </tr>
   <tr id="l8" class="thisrev">
   <td class="annotate parity0">
@@ -433,7 +433,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l8">     8</a> </td>
+  <td class="source followlines-btn-parent"><a href="#l8">     8</a> </td>
   </tr>
   <tr id="l9" class="thisrev">
   <td class="annotate parity0">
@@ -450,7 +450,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l9">     9</a> <span class="kn">def</span> <span class="nf">primes</span><span class="p">():</span></td>
+  <td class="source followlines-btn-parent"><a href="#l9">     9</a> <span class="kn">def</span> <span class="nf">primes</span><span class="p">():</span></td>
   </tr>
   <tr id="l10" class="thisrev">
   <td class="annotate parity0">
@@ -467,7 +467,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l10">    10</a>     <span class="sd">&quot;&quot;&quot;Generate all primes.&quot;&quot;&quot;</span></td>
+  <td class="source followlines-btn-parent"><a href="#l10">    10</a>     <span class="sd">&quot;&quot;&quot;Generate all primes.&quot;&quot;&quot;</span></td>
   </tr>
   <tr id="l11" class="thisrev">
   <td class="annotate parity0">
@@ -484,7 +484,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l11">    11</a>     <span class="kn">def</span> <span class="nf">sieve</span><span class="p">(</span><span class="n">ns</span><span class="p">):</span></td>
+  <td class="source followlines-btn-parent"><a href="#l11">    11</a>     <span class="kn">def</span> <span class="nf">sieve</span><span class="p">(</span><span class="n">ns</span><span class="p">):</span></td>
   </tr>
   <tr id="l12" class="thisrev">
   <td class="annotate parity0">
@@ -501,7 +501,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l12">    12</a>         <span class="n">p</span> <span class="o">=</span> <span class="n">ns</span><span class="o">.</span><span class="n">next</span><span class="p">()</span></td>
+  <td class="source followlines-btn-parent"><a href="#l12">    12</a>         <span class="n">p</span> <span class="o">=</span> <span class="n">ns</span><span class="o">.</span><span class="n">next</span><span class="p">()</span></td>
   </tr>
   <tr id="l13" class="thisrev">
   <td class="annotate parity0">
@@ -518,7 +518,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l13">    13</a>         <span class="c"># It is important to yield *here* in order to stop the</span></td>
+  <td class="source followlines-btn-parent"><a href="#l13">    13</a>         <span class="c"># It is important to yield *here* in order to stop the</span></td>
   </tr>
   <tr id="l14" class="thisrev">
   <td class="annotate parity0">
@@ -535,7 +535,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l14">    14</a>         <span class="c"># infinite recursion.</span></td>
+  <td class="source followlines-btn-parent"><a href="#l14">    14</a>         <span class="c"># infinite recursion.</span></td>
   </tr>
   <tr id="l15" class="thisrev">
   <td class="annotate parity0">
@@ -552,7 +552,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l15">    15</a>         <span class="kn">yield</span> <span class="n">p</span></td>
+  <td class="source followlines-btn-parent"><a href="#l15">    15</a>         <span class="kn">yield</span> <span class="n">p</span></td>
   </tr>
   <tr id="l16" class="thisrev">
   <td class="annotate parity0">
@@ -569,7 +569,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l16">    16</a>         <span class="n">ns</span> <span class="o">=</span> <span class="n">ifilter</span><span class="p">(</span><span class="kn">lambda</span> <span class="n">n</span><span class="p">:</span> <span class="n">n</span> <span class="o">%</span> <span class="n">p</span> <span class="o">!=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">ns</span><span class="p">)</span></td>
+  <td class="source followlines-btn-parent"><a href="#l16">    16</a>         <span class="n">ns</span> <span class="o">=</span> <span class="n">ifilter</span><span class="p">(</span><span class="kn">lambda</span> <span class="n">n</span><span class="p">:</span> <span class="n">n</span> <span class="o">%</span> <span class="n">p</span> <span class="o">!=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">ns</span><span class="p">)</span></td>
   </tr>
   <tr id="l17" class="thisrev">
   <td class="annotate parity0">
@@ -586,7 +586,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l17">    17</a>         <span class="kn">for</span> <span class="n">n</span> <span class="ow">in</span> <span class="n">sieve</span><span class="p">(</span><span class="n">ns</span><span class="p">):</span></td>
+  <td class="source followlines-btn-parent"><a href="#l17">    17</a>         <span class="kn">for</span> <span class="n">n</span> <span class="ow">in</span> <span class="n">sieve</span><span class="p">(</span><span class="n">ns</span><span class="p">):</span></td>
   </tr>
   <tr id="l18" class="thisrev">
   <td class="annotate parity0">
@@ -603,7 +603,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l18">    18</a>             <span class="kn">yield</span> <span class="n">n</span></td>
+  <td class="source followlines-btn-parent"><a href="#l18">    18</a>             <span class="kn">yield</span> <span class="n">n</span></td>
   </tr>
   <tr id="l19" class="thisrev">
   <td class="annotate parity0">
@@ -620,7 +620,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l19">    19</a> </td>
+  <td class="source followlines-btn-parent"><a href="#l19">    19</a> </td>
   </tr>
   <tr id="l20" class="thisrev">
   <td class="annotate parity0">
@@ -637,7 +637,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l20">    20</a>     <span class="n">odds</span> <span class="o">=</span> <span class="n">ifilter</span><span class="p">(</span><span class="kn">lambda</span> <span class="n">i</span><span class="p">:</span> <span class="n">i</span> <span class="o">%</span> <span class="mi">2</span> <span class="o">==</span> <span class="mi">1</span><span class="p">,</span> <span class="n">count</span><span class="p">())</span></td>
+  <td class="source followlines-btn-parent"><a href="#l20">    20</a>     <span class="n">odds</span> <span class="o">=</span> <span class="n">ifilter</span><span class="p">(</span><span class="kn">lambda</span> <span class="n">i</span><span class="p">:</span> <span class="n">i</span> <span class="o">%</span> <span class="mi">2</span> <span class="o">==</span> <span class="mi">1</span><span class="p">,</span> <span class="n">count</span><span class="p">())</span></td>
   </tr>
   <tr id="l21" class="thisrev">
   <td class="annotate parity0">
@@ -654,7 +654,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l21">    21</a>     <span class="kn">return</span> <span class="n">chain</span><span class="p">([</span><span class="mi">2</span><span class="p">],</span> <span class="n">sieve</span><span class="p">(</span><span class="n">dropwhile</span><span class="p">(</span><span class="kn">lambda</span> <span class="n">n</span><span class="p">:</span> <span class="n">n</span> <span class="o">&lt;</span> <span class="mi">3</span><span class="p">,</span> <span class="n">odds</span><span class="p">)))</span></td>
+  <td class="source followlines-btn-parent"><a href="#l21">    21</a>     <span class="kn">return</span> <span class="n">chain</span><span class="p">([</span><span class="mi">2</span><span class="p">],</span> <span class="n">sieve</span><span class="p">(</span><span class="n">dropwhile</span><span class="p">(</span><span class="kn">lambda</span> <span class="n">n</span><span class="p">:</span> <span class="n">n</span> <span class="o">&lt;</span> <span class="mi">3</span><span class="p">,</span> <span class="n">odds</span><span class="p">)))</span></td>
   </tr>
   <tr id="l22" class="thisrev">
   <td class="annotate parity0">
@@ -671,7 +671,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l22">    22</a> </td>
+  <td class="source followlines-btn-parent"><a href="#l22">    22</a> </td>
   </tr>
   <tr id="l23" class="thisrev">
   <td class="annotate parity0">
@@ -688,7 +688,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l23">    23</a> <span class="kn">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">&quot;__main__&quot;</span><span class="p">:</span></td>
+  <td class="source followlines-btn-parent"><a href="#l23">    23</a> <span class="kn">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">&quot;__main__&quot;</span><span class="p">:</span></td>
   </tr>
   <tr id="l24" class="thisrev">
   <td class="annotate parity0">
@@ -705,7 +705,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l24">    24</a>     <span class="kn">import</span> <span class="nn">sys</span></td>
+  <td class="source followlines-btn-parent"><a href="#l24">    24</a>     <span class="kn">import</span> <span class="nn">sys</span></td>
   </tr>
   <tr id="l25" class="thisrev">
   <td class="annotate parity0">
@@ -722,7 +722,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l25">    25</a>     <span class="kn">try</span><span class="p">:</span></td>
+  <td class="source followlines-btn-parent"><a href="#l25">    25</a>     <span class="kn">try</span><span class="p">:</span></td>
   </tr>
   <tr id="l26" class="thisrev">
   <td class="annotate parity0">
@@ -739,7 +739,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l26">    26</a>         <span class="n">n</span> <span class="o">=</span> <span class="nb">int</span><span class="p">(</span><span class="n">sys</span><span class="o">.</span><span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">])</span></td>
+  <td class="source followlines-btn-parent"><a href="#l26">    26</a>         <span class="n">n</span> <span class="o">=</span> <span class="nb">int</span><span class="p">(</span><span class="n">sys</span><span class="o">.</span><span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">])</span></td>
   </tr>
   <tr id="l27" class="thisrev">
   <td class="annotate parity0">
@@ -756,7 +756,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l27">    27</a>     <span class="kn">except</span> <span class="p">(</span><span class="ne">ValueError</span><span class="p">,</span> <span class="ne">IndexError</span><span class="p">):</span></td>
+  <td class="source followlines-btn-parent"><a href="#l27">    27</a>     <span class="kn">except</span> <span class="p">(</span><span class="ne">ValueError</span><span class="p">,</span> <span class="ne">IndexError</span><span class="p">):</span></td>
   </tr>
   <tr id="l28" class="thisrev">
   <td class="annotate parity0">
@@ -773,7 +773,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l28">    28</a>         <span class="n">n</span> <span class="o">=</span> <span class="mi">10</span></td>
+  <td class="source followlines-btn-parent"><a href="#l28">    28</a>         <span class="n">n</span> <span class="o">=</span> <span class="mi">10</span></td>
   </tr>
   <tr id="l29" class="thisrev">
   <td class="annotate parity0">
@@ -790,7 +790,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l29">    29</a>     <span class="n">p</span> <span class="o">=</span> <span class="n">primes</span><span class="p">()</span></td>
+  <td class="source followlines-btn-parent"><a href="#l29">    29</a>     <span class="n">p</span> <span class="o">=</span> <span class="n">primes</span><span class="p">()</span></td>
   </tr>
   <tr id="l30" class="thisrev">
   <td class="annotate parity0">
@@ -807,7 +807,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l30">    30</a>     <span class="kn">print</span> <span class="s">&quot;The first </span><span class="si">%d</span><span class="s"> primes: </span><span class="si">%s</span><span class="s">&quot;</span> <span class="o">%</span> <span class="p">(</span><span class="n">n</span><span class="p">,</span> <span class="nb">list</span><span class="p">(</span><span class="n">islice</span><span class="p">(</span><span class="n">p</span><span class="p">,</span> <span class="n">n</span><span class="p">)))</span></td>
+  <td class="source followlines-btn-parent"><a href="#l30">    30</a>     <span class="kn">print</span> <span class="s">&quot;The first </span><span class="si">%d</span><span class="s"> primes: </span><span class="si">%s</span><span class="s">&quot;</span> <span class="o">%</span> <span class="p">(</span><span class="n">n</span><span class="p">,</span> <span class="nb">list</span><span class="p">(</span><span class="n">islice</span><span class="p">(</span><span class="n">p</span><span class="p">,</span> <span class="n">n</span><span class="p">)))</span></td>
   </tr>
   <tr id="l31" class="thisrev">
   <td class="annotate parity0">
@@ -824,7 +824,7 hgweb fileannotate, html
   <a href="/rev/1af356141006">changeset</a>
   </div>
   </td>
-  <td class="source"><a href="#l31">    31</a> </td>
+  <td class="source followlines-btn-parent"><a href="#l31">    31</a> </td>
   </tr>
   </tbody>
   </table>