This programme is intended to be used by any GHC developers working on GHC.Parser
or GHC.Parser.PostProcess, and who want to check that their changes do not break the API
Annotations.

It does a basic test that all annotations do make it to the final AST, and dumps
a list of the annotations generated for a given file, so that they can be
checked against the source being parsed for sanity.

This utility is also intended to be used in tests, so that when new features are
added the expected annotations are also captured.

Usage

In a test Makefile

  $(CHECK_API_ANNOTATIONS) "`'$(TEST_HC)' $(TEST_HC_OPTS) --print-libdir | tr -d '\r'`" FileToParse.hs

See examples in (REPO_HOME)/testsuite/tests/ghc-api/annotations/Makefile


Description of operation
------------------------

The programme is called with the name of a haskell source file.

It uses the GHC API to load and parse this, and extracts the API annotations.

These are of the form

    Map.Map ApiAnnKey [SrcSpan]

where

    type ApiAnnKey = (SrcSpan,AnnKeywordId)

So an annotation is a key comprising the parent SrcSpan in the ParsedSource
together with an AnnKeywordId, and this maps to a list of locations where the
specific keyword item occurs in the original source.

The utility extracts all SrcSpans in the ParsedSource, and makes sure that for
every ApiAnnKey the SrcSpan is actually present in the final ParsedSource. This
is to ensure that when a given parser production is postprocessed anywhere along
the line the relevant SrcSpan is not discarded, thus detaching the annotation
from the final output.

It also provides a list of each ApiAnnKey and the corresponding source
locations, so these can be checked against the original source for correctness.

Example
-------

Test10255.hs in the ghc-api/annotations tests has the following source

------------------------------
1:{-# LANGUAGE ScopedTypeVariables #-}
2:module Test10255 where
3:
4:import Data.Maybe
5:
6:fob (f :: (Maybe t -> Int)) =
7:  undefined
------------------------------

The output of this utility is

------------------------------------------------------------------------
---Problems (should be empty list)---
[]
---Annotations-----------------------
-- SrcSpan the annotation is attached to, AnnKeywordId,
--    list of locations the keyword item appears in
[
((Test10255.hs:1:1,AnnModule), [Test10255.hs:2:1-6]),
((Test10255.hs:1:1,AnnWhere), [Test10255.hs:2:18-22]),
((Test10255.hs:4:1-17,AnnImport), [Test10255.hs:4:1-6]),
((Test10255.hs:4:1-17,AnnSemi), [Test10255.hs:6:1]),
((Test10255.hs:(6,1)-(7,11),AnnEqual), [Test10255.hs:6:29]),
((Test10255.hs:(6,1)-(7,11),AnnFunId), [Test10255.hs:6:1-3]),
((Test10255.hs:(6,1)-(7,11),AnnSemi), [Test10255.hs:8:1]),
((Test10255.hs:6:5-27,AnnCloseP), [Test10255.hs:6:27]),
((Test10255.hs:6:5-27,AnnOpenP), [Test10255.hs:6:5]),
((Test10255.hs:6:6-26,AnnDcolon), [Test10255.hs:6:8-9]),
((Test10255.hs:6:11-26,AnnCloseP), [Test10255.hs:6:26]),
((Test10255.hs:6:11-26,AnnOpenP), [Test10255.hs:6:11]),
((Test10255.hs:6:12-18,AnnRarrow), [Test10255.hs:6:20-21]),
((Test10255.hs:6:12-25,AnnRarrow), [Test10255.hs:6:20-21]),
((<no location info>,AnnEofPos), [Test10255.hs:8:1])
]
------------------------------------------------------------------------

To interpret this, firstly the problems list is empty, so there are not
annotations that do not appear in the final AST.

Secondly, the list of annotations and locations can be checked against the test
source code to ensure that every AnnKeywordId does in fact appear.

It will return a zero exit code if the list of problems is empty, non-zero
otherwise.

Note: In some cases, such as T10269 in the ghc-api/annotations tests the list is
non-empty, due to postprocessing of the parsed result. In general this should
only happen for an `AnnVal` and if it does the actual annotations provided need
to be inspected to check that an equivalent annotation is provided.
