How to build a program depending on a Yesod application

Question

I created a Yesod application using stack new project yesod-postgres. Beside the web application, I want to create another program which uses the same database model and database connection.

I added a second executable section (a copy of the first) in the cabal file with a different name and main-is: myprogram.hs. I can now run stack build && stack exec myprogram successfully.

The problem is that the build always takes more than 1 minute:

$ stack build
project-0.0.0: unregistering
yesod-persistent-1.4.0.6: configure
yesod-persistent-1.4.0.6: build
yesod-persistent-1.4.0.6: copy/register
yesod-form-1.4.9: configure
yesod-form-1.4.9: build
yesod-form-1.4.9: copy/register
yesod-auth-1.4.15: configure
yesod-auth-1.4.15: build
yesod-auth-1.4.15: copy/register
yesod-1.4.3.1: configure
yesod-1.4.3.1: build
yesod-1.4.3.1: copy/register
classy-prelude-yesod-0.12.8: configure
classy-prelude-yesod-0.12.8: build
classy-prelude-yesod-0.12.8: copy/register
project-0.0.0: build
Preprocessing library project-0.0.0...
In-place registering project-0.0.0...
Preprocessing executable 'myprogram' for project-0.0.0...
Linking .stack-work/dist/x86_64-linux/Cabal-1.22.5.0/build/myprogram/myprogram ...
Preprocessing executable 'project' for project-0.0.0...
Linking .stack-work/dist/x86_64-linux/Cabal-1.22.5.0/build/project/project ...
project-0.0.0: copy/register
Installing library in
/home/jakob/projects/project/project/.stack-work/install/x86_64-linux/lts-6.27/7.10.3/lib/x86_6
4-linux-ghc-7.10.3/project-0.0.0-1qruVQVcU0k2yXxF1Z1w7r
Installing executable(s) in
/home/jakob/projects/project/project/.stack-work/install/x86_64-linux/lts-6.27/7.10.3/bin
Registering project-0.0.0...
Completed 6 action(s).

How can I speed up the build process? How can I prevent stack from rebuilding the yesod dependencies every time?

Answer 1

This isn't specific to adding a second executable; it happens even with a fresh yesod-postgres project with a single executable.

Instead it appears to be a bug in Stack's lts-6.27 package set (and possibly others?). Here's a workaround. In your stack.yaml, add the following extra-dep:

extra-deps:
- yesod-persistent-1.4.0.6

and run stack build. Then, a second stack build should run without rebuilding anything.