Monotonic locations (#17632)

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, 3 insertions, 3 deletions

diff --git a/compiler/GHC.hs b/compiler/GHC.hs
index f973507dee..af0fb5885a 100644
--- a/compiler/GHC.hs
+++ b/compiler/GHC.hs
@@ -1397,7 +1397,7 @@ addSourceToTokens _ _ [] = []
 addSourceToTokens loc buf (t@(L span _) : ts)
     = case span of
       UnhelpfulSpan _ -> (t,"") : addSourceToTokens loc buf ts
-      RealSrcSpan s   -> (t,str) : addSourceToTokens newLoc newBuf ts
+      RealSrcSpan s _ -> (t,str) : addSourceToTokens newLoc newBuf ts
         where
           (newLoc, newBuf, str) = go "" loc buf
           start = realSrcSpanStart s
@@ -1417,13 +1417,13 @@ showRichTokenStream ts = go startLoc ts ""
     where sourceFile = getFile $ map (getLoc . fst) ts
           getFile [] = panic "showRichTokenStream: No source file found"
           getFile (UnhelpfulSpan _ : xs) = getFile xs
-          getFile (RealSrcSpan s : _) = srcSpanFile s
+          getFile (RealSrcSpan s _ : _) = srcSpanFile s
           startLoc = mkRealSrcLoc sourceFile 1 1
           go _ [] = id
           go loc ((L span _, str):ts)
               = case span of
                 UnhelpfulSpan _ -> go loc ts
-                RealSrcSpan s
+                RealSrcSpan s _
                  | locLine == tokLine -> ((replicate (tokCol - locCol) ' ') ++)
                                        . (str ++)
                                        . go tokEnd ts