ucsd-progsys/liquidhaskell

Specs not exported from preprocessed source code

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#2,132 opened on Jan 1, 2023

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good first issue

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Description

Consider the following example, where the source for the A module is preprocessed with hsc2hs:

# A.hsc
module A where

{-@ type Foo = { v : Int | v = 5 } @-}

# B.hs
module B where

import A

{-@ foo :: Foo @-}
foo = 5

LH fails with the following error:

[1 of 2] Compiling A

**** LIQUID: SAFE (0 constraints checked) **************************************
[2 of 2] Compiling B
ghc: panic! (the 'impossible' happened)
  (GHC version 8.10.7:
	[src/B.hs:5:12-14 Unknown type constructor `Foo`
                     matchTyCon: Foo]

If A.hsc is renamed to A.hs instead, then everything works fine. This problem might be hsc2hs-specific, but I suspect it's a more general problem with preprocessed source code.

Version of LH used: 0.8.10.7 (latest release on Hackage at time of writing)

Contributor guide

Research direction
Investigate how Liquid Haskell processes preprocessed source files (e.g., .hsc). The issue suggests that spec exports from such files are lost. Look into the handling of imports and symbol resolution in the LH codebase, particularly where it interacts with GHC's module system. Check if there is a filter or condition that skips preprocessed files when collecting exported specs.
Tech stack
None
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
HaskellLiquid Haskell
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40