Update on HIE Files

[Matthew Pickering]

Have you considered how this feature interacts with source plugins?

Could the generation of these files be implemented as a source plugin?
That would mean that development of the feature would not be coupled
to GHC releases.

Cheers,

Matt

On Tue, Jun 26, 2018 at 11:48 AM, Zubin Duggal <zubin.duggal at gmail.com> wrote:
> Hello all,
>
> I've been working on the HIE File
> (https://ghc.haskell.org/trac/ghc/wiki/HIEFiles) GSOC project,
>
> The design of the data structure as well as the traversal of GHCs ASTs to
> collect all the relevant info is mostly complete.
>
> We traverse the Renamed and Typechecked AST to collect the following info
> about each SrcSpan
>
> 1) Its type, if it corresponds to a binding, pattern or expression
> 2) Details about any tokens in the original source corresponding to this
> span(keywords, symbols, etc.)
> 3) The set of Constructor/Type pairs that correspond to this span in the GHC
> AST
> 4) Details about all the identifiers that occur at this SrcSpan
>
> For each occurrence of an identifier(Name or ModuleName), we store its
> type(if it has one), and classify it as one of the following based on how it
> occurs:
>
> 1) Use
> 2) Import/Export
> 3) Pattern Binding, along with the scope of the binding, and the span of the
> entire binding location(including the RHS) if it occurs as part of a top
> level declaration, do binding or let/where binding
> 4) Value Binding, along with whether it is an instance binding or not, its
> scope, and the span of its entire binding site, including the RHS
> 5) Type Declaration (class or regular) (foo :: ...)
> 6) Declaration(class, type, instance, data, type family etc.)
> 7) Type variable binding, along with its scope(which takes into account
> ScopedTypeVariables)
>
> I have updated the wiki page with more details about the Scopes associated
> with bindings:
> https://ghc.haskell.org/trac/ghc/wiki/HIEFiles#Scopeinformationaboutsymbols
>
> These annotated SrcSpans are then arranged into a interval/rose tree to aid
> lookups.
>
> We assume that no SrcSpans ever partially overlap, for any two SrcSpans that
> occur in the Renamed/Typechecked ASTs, either they are equal, disjoint, or
> strictly contained in each other. This assumption has mostly held out so far
> while testing on the entire ghc:HEAD tree, other than one case where the
> typechecker strips out parenthesis in the original source, which has been
> patched(see https://ghc.haskell.org/trac/ghc/ticket/15242).
>
> I have also written functions that lookup the binding site(including RHS)
> and scope of an identifier from the tree. Testing these functions on the
> ghc:HEAD tree, it succeeds in looking up scopes for almost all symbol
> occurrences in all source files, and I've also verified that the calculated
> scope always contains all the occurrences of the symbol. The few cases where
> this check fails is where the SrcSpans have been mangled by CPP(see
> https://ghc.haskell.org/trac/ghc/ticket/15279).
>
> The code for this currently lives here:
> https://github.com/haskell/haddock/compare/ghc-head...wz1000:hiefile-2
>
> Moving forward, the plan for the rest of the summer is
>
> 1) Move this into the GHC tree and add a flag that controls generating this
> 2) Write serializers and deserializers for this info
> 3) Teach the GHC PackageDb about .hie files
> 4) Rewrite haddocks --hyperlinked-source to use .hie files.
>
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