Monotonic locations (#17632)wip/monotonic-loc

When GHC is parsing a file generated by a tool, e.g. by the C preprocessor, the
tool may insert #line pragmas to adjust the locations reported to the user.

As the result, the locations recorded in RealSrcLoc are not monotonic. Elements
that appear later in the StringBuffer are not guaranteed to have a higher
line/column number.

In fact, there are no guarantees whatsoever, as #line pragmas can arbitrarily
modify locations. This lack of guarantees makes ideas such as #17544
infeasible.

This patch adds an additional bit of information to every SrcLoc:

	newtype BufPos = BufPos { bufPos :: Int }

A BufPos represents the location in the StringBuffer, unaffected by any
pragmas.

Updates haddock submodule.

Metric Increase:
    haddock.Cabal
    haddock.base
    haddock.compiler
    MultiLayerModules
    Naperian
    parsing001
    T12150

1 files changed, 2 insertions, 2 deletions

diff --git a/compiler/main/HeaderInfo.hs b/compiler/main/HeaderInfo.hs
index f7b2cd7fc5..8d88f7b097 100644
--- a/compiler/main/HeaderInfo.hs
+++ b/compiler/main/HeaderInfo.hs
@@ -192,7 +192,7 @@ lazyGetToks dflags filename handle = do
                   _other -> do rest <- lazyLexBuf handle state' eof size
                                return (t : rest)
       _ | not eof   -> getMore handle state size
-        | otherwise -> return [L (RealSrcSpan (last_loc state)) ITeof]
+        | otherwise -> return [L (mkSrcSpanPs (last_loc state)) ITeof]
                          -- parser assumes an ITeof sentinel at the end
 
   getMore :: Handle -> PState -> Int -> IO [Located Token]
@@ -216,7 +216,7 @@ getToks dflags filename buf = lexAll (pragState dflags buf loc)
   lexAll state = case unP (lexer False return) state of
                    POk _      t@(L _ ITeof) -> [t]
                    POk state' t -> t : lexAll state'
-                   _ -> [L (RealSrcSpan (last_loc state)) ITeof]
+                   _ -> [L (mkSrcSpanPs (last_loc state)) ITeof]
 
 
 -- | Parse OPTIONS and LANGUAGE pragmas of the source file.