Preprocessor line control suppressed by comments

Using the preprocessor and "purely functional" parser from the GHC API, SrcSpan annotations in the AST turned out wrong. I have created a minimal example to reproduce. It comprises three files, PPBugDemo.hs, ppbug.hs and ppbug.h. PPBugDemo is the program calling the GHC API. It prints the contents of ppbug.hs and ppbug.h, to show clearly what goes wrong.

Here is PPBugDemo:

module PPBugDemo where

import GHC
import GHC.Paths
import DriverPipeline
import DriverPhases
import HscMain
import DynFlags
import ErrUtils
import Outputable
import System.Directory

main :: IO ()
main = do
	{- Initialising Ghc and getting dynflags + environment -}
	(df,env) <- defaultErrorHandler defaultLogAction $ runGhc (Just libdir) $ do
		fs' <- getSessionDynFlags
		let fs = fs' { includePaths = includePaths fs' ++ ["."] }
		setSessionDynFlags fs
		s <- getSession
		return (fs,s)

	{- Running the preprocessor and cleaning up after it;
	 - it *must* (don't know why) go via a temp-file -}
	(df,fn') <- preprocess env ("ppbug.hs", Just $ Cpp HsSrcFile)
	cnt <- readFile fn'
	removeFile fn'

	{- Warnings aren't relevant to this example, so ignore them -}
	let res = either (printBagOfErrors df >> fail "FAILED") snd (parser cnt df "ppbug.hs")

	{- Reporting results -}
	let showCnt = unlines . zipWith (\n l -> show n ++ '\t':l) [1..] . lines
	org <- readFile "ppbug.hs"
	hdr <- readFile "ppbug.h"
	putStrLn $ "Original file:\n"     ++ showCnt org
	putStrLn $ "Header file:\n"       ++ showCnt hdr
	putStrLn $ "Preprocessed file:\n" ++ showCnt cnt
	putStrLn . showSDocDebug . ppr $ res

and here is the resulting output:

Original file:
1	{-# LANGUAGE CPP #-}
2	{-
3	#include "ppbug.h"
4	-}
5	type Foo = Int
6	

Header file:
1	bar [] = []
2	bar (x:xs) = bar xs

Preprocessed file:
1	# 1 "ppbug.hs"
2	# 1 "<built-in>"
3	# 1 "<command-line>"
4	# 1 "ppbug.hs"
5	{-# LANGUAGE CPP #-}
6	{-
7	
8	# 1 "ppbug.h" 1
9	bar [] = []
10	bar (x:xs) = bar xs
11	# 4 "ppbug.hs" 2
12	-}
13	type Foo = Int
14	

{ppbug.hs:1:1}
{ppbug.hs:9:1-14}
type {ppbug.hs:9:6-8}
     Foo{tc} =
    {ppbug.hs:9:12-14}
    Int{tc}

The parser has annotated the AST with location information for Foo. It says it's on line 9 of ppbug.hs, whilst it actually came from line 5. Line 11 from the output of the preprocessor sets the line number back to 4 (starting from line 12), but it seems this line control is ignored for residing in comments.

Trac metadata

Trac field	Value
Version	7.4.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Parser)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture