Adding bold to Haddock (part 2)

Posted on August 15, 2013 by Fūzetsu

A while ago, I wrote about adding support for bold to Haddock. Last time, I added tests and made the initial implementation. Now I’m going to briefly go over which files one needs to change for the back-ends.

There are three back-ends: LaTeX, Hoogle and XHtml. XHtml is the one people see the most, I imagine. There are no tests for either Hoogle nor LaTeX and I suspect they might have seen a fair amount of breakage already. I haven’t heard direct complaints though so I’ll look into verifying these later.

First in Utils.hs we add a new default field called markupBold to the idMarkup identity record and immediately after we add a new pattern covering DocBold to the markup function. This is used throughout the back-ends as a uniform interface. We also need to add a pattern for DocBold in the renameDoc function Rename.hs. From what I gather from the very scarce comments, this module renames things such as identifiers into a more human-friendly form: there’s no need to render something as Foo.Bar.Baz if we’re in Foo.Bar. Unfortunately, it’s 500 LOC of juggling of GHC’s types so I can’t be certain. Also add the new pattern to the rename function in LexParseRn.hs which runs the actual look-up.

Updating the interfaces is quite simple in this case. In each of

 src/Haddock/Backends/Hoogle.hs
 src/Haddock/Backends/LaTeX.hs
 src/Haddock/Backends/Xhtml/DocMarkup.hs

find the function where other markup is translated and add your change. For example for LateX, it was a 3 line change:

   markupEmphasis             = \p v -> emph (p v),
+  markupBold                 = \p v -> bold (p v),
   markupMonospaced           = \p _ -> tt (p Mono),

-- snip…

+bold :: LaTeX -> LaTeX
+bold ltx = text "\\textbf" <> braces ltx

It’s easy to look around and see how things are done and mimic the behaviour. Last but not least, there’s a InterfaceFile.hs which unsurprisingly deals with Haddock’s interface file. This file can be used later by Haddock to link against packages it has already generated documentation for. Look at the Binary instance for Doc id and change it accordingly. If you change the instance, make sure to bump the binaryInterfaceVersion. Also update the binaryInterfaceVersionCompatibility. This will ensure that we get a nice error message if we try to link between incompatible versions rather than weird behaviour. This file is only relevant if you add/remove markup or structurally change existing one. Simple parser changes to existing markup do not affect this file.

I am not bumping this until everything is finalised and ready for release but I have to be careful to not let any test docs I generate with it get out of the sandbox.

We’re done, both test-suites pass. Here’s a list of changes I had to make all together. The majority is just the tests, with very few actual code changes (and some of it is just clobbering whitespace &c).

12 files changed, 170 insertions(+), 12 deletions(-)
 html-test/ref/Bold.html                 | 102
 html-test/src/Bold.hs                   |   9
 src/Haddock/Backends/Hoogle.hs          |   7
 src/Haddock/Backends/LaTeX.hs           |   3
 src/Haddock/Backends/Xhtml/DocMarkup.hs |   1
 src/Haddock/Interface/LexParseRn.hs     |   1
 src/Haddock/Interface/Rename.hs         |   7
 src/Haddock/InterfaceFile.hs            |   6
 src/Haddock/Parser.hs                   |  13
 src/Haddock/Types.hs                    |   3
 src/Haddock/Utils.hs                    |  11
 test/Haddock/ParseSpec.hs               |  19

It’s time for some images. What use is all this if it doesn’t look pretty in the end? Here’s the result of the efforts. Generating docs for the following code

-- | Module : File
module File where

-- | /SomeType/
data SomeType

-- | __Othertype__
data OtherType

-- | Here's some __bold__
foo :: SomeType -> SomeType
foo = undefined

-- | __Multi-word bold__
bar :: OtherType -> OtherType
bar = undefined

-- | __No multi-line
-- bold, no sir__
baz :: [a] -> [a]
baz = undefined

-- | __Can't escape \\__ the underscores__
qux :: SomeType -> OtherType
qux = undefined

-- | __Can't even have a single unescaped _ in the string__
quux :: t
quux = undefined

-- | __No other /markup/ inside either__
corge :: OtherType -> SomeType
corge = undefined

yields us

naive bold implementation

naive bold implementation

Something that I wanted to do for a while and that was further motivated by a recent Trac ticket was to allow markup inside of emphasis (and now bold). There’s also a much less recent ticket about multi-line emphasis (and now bold). Here’s an exclusive preview of both of these features. In fact, even I’m actually rendering the documentation for the first time to inspect with my eyes as I rely on tests otherwise:

markup inside markup

markup inside markup

Also, something I’m less enthusiastic about, multi-line markup:

multi-line bold

multi-line bold

See the first ticket I linked to for reasoning. I’m writing a tool on a side to help to determine the effects of various changes on existing documentation but it is not usable it. It’s difficult to reliably extract Haddock comments from thousands of files without actually building the projects. I’m thinking of using haskell-src-exts to help and make this task easier but there’s a problem with this approach as well. Currently I compensate for the lack of such tool with tests.

I might write a post in the future on the progress of this and if and how the problems were solved (or weren’t solved!). A warning system enabled with a flag might be nice in Haddock itself but this is not currently planned.

As a side note, I had problem with my e-mail address from 4th to 14th of August, so if you tried to contact me and didn’t get a reply, please try again.