ci: Disable Haddock on Docgent and Haskell-backend branches.

.travis.yml

@@ -79,12 +79,16 @@ before_install:
     [ -z ${WITH_BUILTIN_ARRAYS} ] ||
     STACK_FLAGS="${STACK_FLAGS} --flag cogent:builtin-arrays"
 
-  # Pandoc causes Haddock to choke; so, with Docgent enabled, no fish.
+  # Pandoc causes Stack to choke; so, with Docgent enabled, no fish.
   # - <https://github.com/commercialhaskell/stack/issues/3989>
   # - <https://github.com/commercialhaskell/stack/issues/4428>
+  #
+  # `haskell-src-exts' causes Haddock to choke (by segfaulting?!)
+  # - <https://travis-ci.org/NICTA/cogent/jobs/656011492>
   - >-
-    [ -z ${WITH_DOCGENT} ] &&
-    STACK_FLAGS="${STACK_FLAGS} --haddock --haddock-deps"
+    [ -z ${WITH_DOCGENT} ] || [ -z ${WITH_HASKELL_BACKEND} ] &&
+    STACK_FLAGS="${STACK_FLAGS} --haddock --haddock-deps";
+    true
 
   - >-
     export STACK_FLAGS;