Allow GHCi to load non-local packages by unpacking them

[mgsloan]

It'd be cool if stack ghci text unpacked text and loaded it into ghci. This is also relevant to the code recently added for also loading intermediate deps (#584) - it will need to be modified to handle the PSUpstream case.

[StevenXL]

Is this still an issue? I can run stack ghci --package text. Are we talking about something else?

[nekoniaow]

Is this still an issue? I can run stack ghci --package text. Are we talking about something else?

This seems to be about packages which are referenced from the extra-deps entry in stack.yaml.
Example:

in stack.yaml:

extra-deps:
- webdriver-w3c-0.0.3

$ stack ghci webdriver-w3c

Warning: Some targets (webdriver-w3c) are not local packages, and so cannot be directly loaded. In future versions of stack, this might be supported - see
         https://github.com/commercialhaskell/stack/issues/1441 . It can still be useful to specify these, as they will be passed to ghci via -package flags.

Note: No local targets specified, so a plain ghci will be started with no package hiding or package options.
      
      You are using snapshot: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/19/29.yaml
      
      If you want to use package hiding and options, then you can try one of the following:
      
      * If you want to start a different project configuration than <path/to/project>stack.yaml, then you can use stack init
        to create a new stack.yaml for the packages in the current directory. 
        
      * If you want to use the project configuration at <path/to/project>stack.yaml, then you can add to its 'packages' field.
      
Configuring GHCi with the following packages: 
GHCi, version 9.0.2: https://www.haskell.org/ghc/  :? for help

And with the --package option:

$ stack  ghci --package webdriver-w3c
Using main module: 1. Package `<project-package>' component <project>:exe:<project>-exe with main-is file: <path/to/project>/app/Main.hs
The following GHC options are incompatible with GHCi and have not been passed to it: -threaded
Configuring GHCi with the following packages: <project>

As you can see, the webdriver-w3c package is totally ignored.

As I understand it, that's the problem pointed by this issue.

[nekoniaow]

For those who cannot wait for this feature, a functional workaround is to use the stack unpack command:

1. comment the package entry in stack.yaml:extra-deps,
2. add the package entry in stack.yaml:packages with its version number, in my case: -webdriver-w3c-0.0.3,
3. run stack unpack webdriver-w3c to install the package sources locally

The package will then be part of the project and the regular ghci command will thus properly compile and load it:

$ stack ghci webdriver-w3c-0.0.3

In my case it wants the version number but I have not dug too much why that's needed. Maybe this is specific to this package and/or my setup?

This took me quite a few hours of browsing documentation and Stack Overflow to figure out so I hope this is helpful. ;)