Clojure, Programming

Leiningen doesn’t compile Protocols and Records

I don’t generally use records or protocols in my Clojure code so the fact that Clojure compiler doesn’t seem to detect changes in the function bodies of either took me by surprise recently. Googling turned up this issue for Leiningen. Reading through the issue I ended up specifying all the namespaces containing these structures in the :aot definition in the lein project.clj. This meant that the namespace was re-compiled every time but that seemed the lesser of two evils compared to the clean and build approach.

Where this issue really stung was in the method-like function specifications in the records and as usual it felt that structure and behaviour was getting muddled up again when ideally you want to keep them separate.


Hibernate temporary tables

I was surprised to discover that Hibernate makes use of temporary tables when performing deletes. The creation of the table was triggering an alert in a database monitor for an application. The monitor logged the creation of tables beginning with the prefix HT_ and a name that mirrored that of an entity tablename.

Initially I must admit that I was thrown very far off track and started looking through the schema creation scripts and codebase looking for something, even checking HT as initials against the developer names. Naturally we tried deleting the tables and soon enough they were recreated.

As with a lot of modern programming bugs the answer came through some frustrated Googling and the realisation that HT might stand for Hibernate Table. With that insight in place I was then able to find this excellent explanation of the situation and I get another self-righteous data point in my dislike of ORM.

This temporary table is required for two reasons, firstly because ORM’s do not actually do a proper mapping between the domain concepts of a relational store and objects and secondly because Hibernate wants to create a verisimilitude around the concept of a class hierarchy.

I don’t think there is a better solution than what Hibernate is offering here but I do think it is the wrong problem being solved in a clever way.


Google Chrome wants to sit at the table

I fixed a weird CSS bug last week which I think is an interesting illustration of the difficulties of implementing a standard. One of the ways that I layout our website is by using CSS Tables to provide right-sidebars and content splits. One of our components consists of an image in a left-column, content and then a button bar in a right-column.

The whole strip of content was marked as display: table-row and the columns were display: table-cell.

On Firefox this was fine and the full width of the page was used with the correct proportions for the content blocks. On Chrome however the width of the whole component was around 75% of the whole page width (with the correct proportions). After a lot of examination it appeared that Chrome genuinely felt the page was narrower at that point.

It took a few weeks to get the necessary mindshift to fix it. The problem was the interpretation of how display: table-* works when you don’t have the full hierarchy. My interpretation is that the browser fills in the implied parent elements and that worked correctly in Firefox. In Chrome however I needed to change my table-row to table for the full width of the page to be used. The implied table wasn’t the full width of the page, while the explicit one was with the implied table-row occupying the correct full width.

This worked fine on Firefox as well so the problem was solved! Always have a top-element that defines display: table.

Web Applications, Work

Using SVG in the modern website

Using SVG when you are putting together a new website is a pretty sound decision, it’s over a decade old, well-supported by browsers and the ability to scale images accurately via CSS is pretty compelling when you are rapidly trying out different layouts and proportions.

Of course until recently IE has been the bugbear but IE9 actually has pretty decent SVG support. It is now worth thinking of using SVG as the general case and IE8 as the exception which can be switched to PNG via Javascript. The first iteration of Wazoku Idea Spotlight used SVG exclusively and the second iteration will do a Modernizer based switchout for IE8 but essentially still be SVG based.

Therefore I was pretty confused when I was taking a random check at the app in IE9. Instead of displaying alt text or the images instead there was just whitespace. Quickly opening the images revealed that IE was quite happy to render them at full window size and that there was no issue with loading them.

After some confused Googling I found out that the issue was that the previous generation of SVGs were generated straight out of Adobe Illustrator where as this set are going through Inkscape where I am tweaking the colour, size and so on. Inkscape does not allow you by default to specify a property called the viewbox. Instead this is only created if you export your file as an Optimized or Plain SVG. It is an outstanding feature when you go looking through the Inkscape bug list but it is a really obscure bug (hence this blog) to track down. The reason the images were appearing as blank is that without a viewbox IE9 crops the image to the CSS dimensions rather than scaling it. Firefox and Chrome scale it as you would expect. Essentially I was seeing the top-left 32 pixels of an image that IE9 considered to be 640px square, overflow hidden.

Having found the problem I then converted a test image to Optimized SVG, who doesn’t love Optimized things after all? Well the answer to that is Chrome. Firefox (probably due to having the longest SVG heritage) did the right thing in both cases and IE9 was fine with the Optimized version. Chrome stretched the image out on the vertical and via the Developer tools it was possible to see that the Dimensions value for the image was completely incorrect with a letterbox set of dimensions rather than a square.

In the end the thing that worked everywhere was Inkscape’s Plain SVG format. Something I am fine to live with. It would be nice to be able to set a viewbox from Inkscape’s Document Properties though and I will be keeping an eye out for it on the release notes in future.

Software, Work

The Joy of Acceptance Testing: Is my bug fixed yet?

Here’s a question that should be a blast from the past: “Is my bug fixed yet?”.

I don’t know, is your acceptance test for the bug passing yet?

Acceptance tests are often sold as being the way that stakeholders know that their signed-off feature is not going to regress during iterative development. That’s true, they probably do that. What they also do though is dramatically improve communication between developers and testers. Instead of having to faf around with bug tracking, commit comment buggery and build artifact change lists you can have your test runner of choice tell you the current status of all the bugs as well as the features.

Running acceptance tests is one example where keeping the build green is not mandatory. This creates a need for a slightly more complicated build result visualisation. I like to see a simple bar split into green and red with the number of failing tests. There may be a good day or two when that bar is totally green but in general your test team should be way ahead of the developers so the red bar represents the technical deficit you are running at any given moment.

If it starts to grow you have a prompt to decide whether you need to change your priorities or developer quality bar. Asking whether a bug has been fixed or when the fix will be delivered are the wrong questions. For me the right questions are: should we fix it and how important is it?

If we are going to fix a bug we should have an acceptance test for it and its importance indicates what time frame that test should pass in.