• Alan Zimmerman's avatar
    Add API Annotations · 803fc5db
    Alan Zimmerman authored
    Summary:
    The final design and discussion is captured at
    https://ghc.haskell.org/trac/ghc/wiki/GhcAstAnnotations
    
    This is a proof of concept implementation of a completely
    separate annotation structure, populated in the parser,and tied to the
    AST by means of a virtual "node-key" comprising the surrounding
    SrcSpan and a value derived from the specific constructor used for the
    node.
    
    The key parts of the design are the following.
    
    == The Annotations ==
    
    In `hsSyn/ApiAnnotation.hs`
    
    ```lang=haskell
    type ApiAnns = (Map.Map ApiAnnKey SrcSpan, Map.Map SrcSpan [Located Token])
    
    type ApiAnnKey = (SrcSpan,AnnKeywordId)
    
    -- ---------------------------------------------------------------------
    
    -- | Retrieve an annotation based on the @SrcSpan@ of the annotated AST
    -- element, and the known type of the annotation.
    getAnnotation :: ApiAnns -> SrcSpan -> AnnKeywordId -> Maybe SrcSpan
    getAnnotation (anns,_) span ann = Map.lookup (span,ann) anns
    
    -- |Retrieve the comments allocated to the current @SrcSpan@
    getAnnotationComments :: ApiAnns -> SrcSpan -> [Located Token]
    getAnnotationComments (_,anns) span =
      case Map.lookup span anns of
        Just cs -> cs
        Nothing -> []
    
    -- | Note: in general the names of these are taken from the
    -- corresponding token, unless otherwise noted
    data AnnKeywordId
             = AnnAs
             | AnnBang
             | AnnClass
             | AnnClose -- ^ } or ] or ) or #) etc
             | AnnComma
             | AnnDarrow
             | AnnData
             | AnnDcolon
             ....
    ```
    
    == Capturing in the lexer/parser ==
    
    The annotations are captured in the lexer / parser by extending PState to include a field
    
    In `parser/Lexer.x`
    
    ```lang=haskell
    data PState = PState {
            ....
            annotations :: [(ApiAnnKey,SrcSpan)]
            -- Annotations giving the locations of 'noise' tokens in the
            -- source, so that users of the GHC API can do source to
            -- source conversions.
         }
    ```
    
    The lexer exposes a helper function to add an annotation
    
    ```lang=haskell
    addAnnotation :: SrcSpan -> Ann -> SrcSpan -> P ()
    addAnnotation l a v = P $ \s -> POk s {
      annotations = ((AK l a), v) : annotations s
      } ()
    
    ```
    
    The parser also has some helper functions of the form
    
    ```lang=haskell
    type MaybeAnn = Maybe (SrcSpan -> P ())
    
    gl = getLoc
    gj x = Just (gl x)
    
    ams :: Located a -> [MaybeAnn] -> P (Located a)
    ams a@(L l _) bs = (mapM_ (\a -> a l) $ catMaybes bs) >> return a
    ```
    
    This allows annotations to be captured in the parser by means of
    
    ```
    ctypedoc :: { LHsType RdrName }
            : 'forall' tv_bndrs '.' ctypedoc {% hintExplicitForall (getLoc $1) >>
                                                ams (LL $ mkExplicitHsForAllTy $2 (noLoc []) $4)
                                                    [mj AnnForall $1,mj AnnDot $3] }
            | context '=>' ctypedoc         {% ams (LL $ mkQualifiedHsForAllTy   $1 $3)
                                                   [mj AnnDarrow $2] }
            | ipvar '::' type               {% ams (LL (HsIParamTy (unLoc $1) $3))
                                                   [mj AnnDcolon $2] }
            | typedoc                       { $1 }
    ```
    
    == Parse result ==
    
    ```lang-haskell
    data HsParsedModule = HsParsedModule {
        hpm_module    :: Located (HsModule RdrName),
        hpm_src_files :: [FilePath],
           -- ^ extra source files (e.g. from #includes).  The lexer collects
           -- these from '# <file> <line>' pragmas, which the C preprocessor
           -- leaves behind.  These files and their timestamps are stored in
           -- the .hi file, so that we can force recompilation if any of
           -- them change (#3589)
        hpm_annotations :: ApiAnns
      }
    
    -- | The result of successful parsing.
    data ParsedModule =
      ParsedModule { pm_mod_summary   :: ModSummary
                   , pm_parsed_source :: ParsedSource
                   , pm_extra_src_files :: [FilePath]
                   , pm_annotations :: ApiAnns }
    ```
    
    This diff depends on D426
    
    Test Plan: sh ./validate
    
    Reviewers: austin, simonpj, Mikolaj
    
    Reviewed By: simonpj, Mikolaj
    
    Subscribers: Mikolaj, goldfire, thomie, carter
    
    Differential Revision: https://phabricator.haskell.org/D438
    
    GHC Trac Issues: #9628
    803fc5db
HscMain.hs 67.7 KB