Download page & developers guide: add a section about known problems with Cabal

doc/gf-developers.t2t

@@ -68,7 +68,7 @@ and
 To get the GF source code, you also need //Darcs//, version 2 or later.  Darcs
 is a distributed version control system, see http://darcs.net/ for
 more information. There are precompiled packages for many platforms
-available at and source code if you want to compile it yourself. Darcs
+available and source code if you want to compile it yourself. Darcs
 is also written in Haskell and so you can use GHC to compile it.
 
 
@@ -238,7 +238,7 @@ main repo, use ``darcs push``.
 For more info about what you can do with darcs, see http://darcs.net/manual/
 
 
-== Compilation from source ==
+== Compilation from source with Cabal ==
 
 The build system of GF is based on //Cabal//, which is part of the
 Haskell Platform, so no extra steps are needed to install it. In the simplest
@@ -355,6 +355,26 @@ $ cabal clean
 %
 %to prepare archive with all source codes needed to compile GF.
 
+=== Known problems with Cabal ===
+
+Some versions of Cabal (at least version 1.16) seem to have a bug that can
+cause the following error:
+
+```
+Configuring gf-3.x...
+setup: Distribution/Simple/PackageIndex.hs:124:8-13: Assertion failed
+```
+
+The exact cause of this problem is unclear, but it seems to happen
+during the configure phase if GF is already installed, so a workaround
+is to remove the existing installation with
+
+```
+ghc-pkg unregister gf
+```
+
+You can check with ``ghc-pkg list gf`` that it is gone.
+
 == Compilation with make ==
 
 If you feel more comfortable with Makefiles then there is a thin Makefile

download/index.t2t

@@ -2,6 +2,7 @@ Grammatical Framework Download and Installation
 
 
 %!style:../css/style.css
+%!postproc(html): </HEAD> <STYLE>body { color: #333; } li>code,p>code,pre { color: #730; }</STYLE></HEAD>
 %!postproc(html): <TITLE> <meta name = "viewport" content = "width = device-width"><TITLE>
 %!postproc(html): <TD><B> <TH>
 %!postproc(html): </B></TD> </TH>
@@ -19,10 +20,10 @@ What's new? See the [Release notes release-3.4.html].
 | Fedora (32-bit) | [Fedora RPMs /~hallgren/tmp/Fedora/] | ``sudo rpm -i ...``
 | Ubuntu (32-bit) | [gf_3.4-1_i386.deb gf_3.4-1_i386.deb] | ``sudo dpkg -i gf_3.4-1_i386.deb``
 | Ubuntu (64-bit) | [gf_3.4-1_amd64.deb gf_3.4-1_amd64.deb] | ``sudo dpkg -i gf_3.4-1_amd64.deb``
-| Windows | [gf-3.4-bin-windows.zip gf-3.4-bin-windows.zip] |
+| Windows | [gf-3.4-bin-windows.zip gf-3.4-bin-windows.zip] | 
-| ... | ... | ...
+%| ... | ... | ...
 
-More binary packages might be added later.
+%More binary packages might be added later.
 
 ===Notes===
 
@@ -104,6 +105,19 @@ page states that you need Xcode 3.2 or later, but in fact it appears you need
 Xcode 3.2.3 or later. If you have Xcode 3.2.2, you can get an error from the
 linker: ``ld: unknown option: -no_pie``.
 
+=== Known problems ===
+
+There seems to be a bug in some versions of Cabal that can cause
+
+```
+  Distribution/Simple/PackageIndex.hs:124:8-13: Assertion failed
+```
+
+ if GF is
+already installed. If you encounter this, you can use ``ghc-pkg unregister gf``
+to remove the installed version of GF and ``ghc-pkg list gf`` to verify that
+it is gone.
+
 ==Installing from the latest developer code==
 
 The first time: