Add API Annotations

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

1 files changed, 122 insertions, 0 deletions

diff --git a/testsuite/tests/ghc-api/annotations/parseTree.stdout b/testsuite/tests/ghc-api/annotations/parseTree.stdout
new file mode 100644
index 0000000000..b8b9aa69b7
--- /dev/null
+++ b/testsuite/tests/ghc-api/annotations/parseTree.stdout
@@ -0,0 +1,122 @@
+[(AnnotationTuple.hs:13:20, [p], (1)),
+ (AnnotationTuple.hs:13:23-29, [p], ("hello")),
+ (AnnotationTuple.hs:13:35-37, [p], (6.5)),
+ (AnnotationTuple.hs:13:38, [m], ()),
+ (AnnotationTuple.hs:13:41-52, [p], ([5, 5, 6, 7])),
+ (AnnotationTuple.hs:15:8, [p], (1)),
+ (AnnotationTuple.hs:15:11-17, [p], ("hello")),
+ (AnnotationTuple.hs:15:20-22, [p], (6.5)),
+ (AnnotationTuple.hs:15:23, [m], ()),
+ (AnnotationTuple.hs:15:24, [m], ()),
+ (AnnotationTuple.hs:15:25, [m], ()),
+ (AnnotationTuple.hs:15:26, [m], ())]
+[
+(AK AnnotationTuple.hs:1:1 AnnClose = [AnnotationTuple.hs:16:1])
+
+(AK AnnotationTuple.hs:1:1 AnnModule = [AnnotationTuple.hs:2:1-6])
+
+(AK AnnotationTuple.hs:1:1 AnnOpen = [AnnotationTuple.hs:4:1])
+
+(AK AnnotationTuple.hs:1:1 AnnSemi = [AnnotationTuple.hs:6:1])
+
+(AK AnnotationTuple.hs:1:1 AnnWhere = [AnnotationTuple.hs:2:30-34])
+
+(AK AnnotationTuple.hs:2:24-28 AnnClose = [AnnotationTuple.hs:2:28])
+
+(AK AnnotationTuple.hs:2:24-28 AnnOpen = [AnnotationTuple.hs:2:24])
+
+(AK AnnotationTuple.hs:5:1-32 AnnAs = [AnnotationTuple.hs:5:28-29])
+
+(AK AnnotationTuple.hs:5:1-32 AnnImport = [AnnotationTuple.hs:5:1-6])
+
+(AK AnnotationTuple.hs:5:1-32 AnnQualified = [AnnotationTuple.hs:5:8-16])
+
+(AK AnnotationTuple.hs:(7,1)-(10,14) AnnEqual = [AnnotationTuple.hs:7:5])
+
+(AK AnnotationTuple.hs:(7,1)-(10,14) AnnFunId = [AnnotationTuple.hs:7:1-3])
+
+(AK AnnotationTuple.hs:(7,7)-(10,14) AnnIn = [AnnotationTuple.hs:10:7-8])
+
+(AK AnnotationTuple.hs:(7,7)-(10,14) AnnLet = [AnnotationTuple.hs:7:7-9])
+
+(AK AnnotationTuple.hs:8:9-13 AnnEqual = [AnnotationTuple.hs:8:11])
+
+(AK AnnotationTuple.hs:8:9-13 AnnFunId = [AnnotationTuple.hs:8:9])
+
+(AK AnnotationTuple.hs:9:9-13 AnnEqual = [AnnotationTuple.hs:9:11])
+
+(AK AnnotationTuple.hs:9:9-13 AnnFunId = [AnnotationTuple.hs:9:9])
+
+(AK AnnotationTuple.hs:9:9-13 AnnSemi = [AnnotationTuple.hs:9:9])
+
+(AK AnnotationTuple.hs:13:1-72 AnnEqual = [AnnotationTuple.hs:13:5])
+
+(AK AnnotationTuple.hs:13:1-72 AnnFunId = [AnnotationTuple.hs:13:1-3])
+
+(AK AnnotationTuple.hs:13:1-72 AnnSemi = [AnnotationTuple.hs:12:1])
+
+(AK AnnotationTuple.hs:13:19-53 AnnClose = [AnnotationTuple.hs:13:53])
+
+(AK AnnotationTuple.hs:13:19-53 AnnOpen = [AnnotationTuple.hs:13:19])
+
+(AK AnnotationTuple.hs:13:20 AnnComma = [AnnotationTuple.hs:13:21])
+
+(AK AnnotationTuple.hs:13:23-29 AnnComma = [AnnotationTuple.hs:13:33])
+
+(AK AnnotationTuple.hs:13:35-37 AnnComma = [AnnotationTuple.hs:13:38])
+
+(AK AnnotationTuple.hs:13:39 AnnComma = [AnnotationTuple.hs:13:39])
+
+(AK AnnotationTuple.hs:13:41-52 AnnClose = [AnnotationTuple.hs:13:52])
+
+(AK AnnotationTuple.hs:13:41-52 AnnOpen = [AnnotationTuple.hs:13:41])
+
+(AK AnnotationTuple.hs:13:42 AnnComma = [AnnotationTuple.hs:13:43])
+
+(AK AnnotationTuple.hs:13:45 AnnComma = [AnnotationTuple.hs:13:46])
+
+(AK AnnotationTuple.hs:13:48 AnnComma = [AnnotationTuple.hs:13:49])
+
+(AK AnnotationTuple.hs:13:55-72 AnnClose = [AnnotationTuple.hs:13:72])
+
+(AK AnnotationTuple.hs:13:55-72 AnnOpen = [AnnotationTuple.hs:13:55])
+
+(AK AnnotationTuple.hs:13:56-62 AnnComma = [AnnotationTuple.hs:13:63])
+
+(AK AnnotationTuple.hs:13:61-62 AnnClose = [AnnotationTuple.hs:13:62])
+
+(AK AnnotationTuple.hs:13:61-62 AnnOpen = [AnnotationTuple.hs:13:61])
+
+(AK AnnotationTuple.hs:15:1-41 AnnEqual = [AnnotationTuple.hs:15:5])
+
+(AK AnnotationTuple.hs:15:1-41 AnnFunId = [AnnotationTuple.hs:15:1-3])
+
+(AK AnnotationTuple.hs:15:1-41 AnnSemi = [AnnotationTuple.hs:14:1])
+
+(AK AnnotationTuple.hs:15:7-27 AnnClose = [AnnotationTuple.hs:15:27])
+
+(AK AnnotationTuple.hs:15:7-27 AnnOpen = [AnnotationTuple.hs:15:7])
+
+(AK AnnotationTuple.hs:15:8 AnnComma = [AnnotationTuple.hs:15:9])
+
+(AK AnnotationTuple.hs:15:11-17 AnnComma = [AnnotationTuple.hs:15:18])
+
+(AK AnnotationTuple.hs:15:20-22 AnnComma = [AnnotationTuple.hs:15:23])
+
+(AK AnnotationTuple.hs:15:24 AnnComma = [AnnotationTuple.hs:15:24])
+
+(AK AnnotationTuple.hs:15:25 AnnComma = [AnnotationTuple.hs:15:25])
+
+(AK AnnotationTuple.hs:15:26 AnnComma = [AnnotationTuple.hs:15:26])
+
+(AK AnnotationTuple.hs:15:33-41 AnnClose = [AnnotationTuple.hs:15:41])
+
+(AK AnnotationTuple.hs:15:33-41 AnnOpen = [AnnotationTuple.hs:15:33])
+
+(AK AnnotationTuple.hs:15:39-40 AnnClose = [AnnotationTuple.hs:15:40])
+
+(AK AnnotationTuple.hs:15:39-40 AnnOpen = [AnnotationTuple.hs:15:39])
+
+(AK <no location info> AnnEofPos = [AnnotationTuple.hs:21:1])
+]
+