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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 (3 comments) (0 reactions) (0 assignees)Haskell (1,306 stars) (157 forks)batch import
good first issue

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

Tech stack
None
Domain
toolingbuild system
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.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Knowledge of HaskellFamiliarity with LiquidHaskellUnderstanding of hsc2hs preprocessing
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
35
Research direction
Investigate how LiquidHaskell processes preprocessed source files like .hsc. Look at the code in the liquidhaskell repository, particularly the modules handling GHC plugin operations and interface generation. The difference between .hsc and .hs suggests a parsing or file extension handling issue. Check if the preprocessing step affects the export of liquid type specifications. Start by examining the 'src/' directory for files that deal with source preprocessing and type export. Document findings in a comment on the issue and consider reaching out to maintainers for further guidance.