Lexer: report indentation warnings at column 1

We use a Latin1 generated parser with Alex, but we also parses Unicode
BOM, unbreakable spaces, etc. In recent Alex, the reported column isn't
expressed in Unicode chars anymore but in bytes/ASCII chars (probably
due to
haskell/alex@ae525e3
but I haven't checked), which broke our tests (see
#8896).

To work around this we report indentation warnings at token start position,
instead of token end position (i.e. always 1). Otherwise position makes
no sense anymore for the user.

(cherry picked from commit 5f72880)

Cabal-syntax/src/Distribution/Fields/Lexer.hs

@@ -195,17 +195,17 @@ toki t pos  len  input = return $! L pos (t (B.take len input))
 tok :: Token -> Position -> Int -> ByteString -> Lex LToken
 tok  t pos _len _input = return $! L pos t
 
-checkLeadingWhitespace :: Int -> ByteString -> Lex Int
-checkLeadingWhitespace len bs
+checkLeadingWhitespace :: Position -> Int -> ByteString -> Lex Int
+checkLeadingWhitespace pos len bs
     | B.any (== 9) (B.take len bs) = do
-        addWarning LexWarningTab
-        checkWhitespace len bs
-    | otherwise = checkWhitespace len bs
+        addWarningAt pos LexWarningTab
+        checkWhitespace pos len bs
+    | otherwise = checkWhitespace pos len bs
 
-checkWhitespace :: Int -> ByteString -> Lex Int
-checkWhitespace len bs
+checkWhitespace :: Position -> Int -> ByteString -> Lex Int
+checkWhitespace pos len bs
     | B.any (== 194) (B.take len bs) = do
-        addWarning LexWarningNBSP
+        addWarningAt pos LexWarningNBSP
         return $ len - B.count 194 (B.take len bs)
     | otherwise = return len
 
@@ -313,12 +313,12 @@ bol_section = 3
 in_field_braces = 4
 in_field_layout = 5
 in_section = 6
-alex_action_0 = \_ len _ -> do
-              when (len /= 0) $ addWarning LexWarningBOM
+alex_action_0 = \pos len _ -> do
+              when (len /= 0) $ addWarningAt pos LexWarningBOM
               setStartCode bol_section
               lexToken
-alex_action_1 = \_pos len inp -> checkWhitespace len inp >> adjustPos retPos >> lexToken
-alex_action_3 = \pos len inp -> checkLeadingWhitespace len inp >>
+alex_action_1 = \pos len inp -> checkWhitespace pos len inp >> adjustPos retPos >> lexToken
+alex_action_3 = \pos len inp -> checkLeadingWhitespace pos len inp >>
                                      if B.length inp == len
                                        then return (L pos EOF)
                                        else setStartCode in_section
@@ -333,7 +333,7 @@ alex_action_12 = tok  Colon
 alex_action_13 = tok  OpenBrace
 alex_action_14 = tok  CloseBrace
 alex_action_15 = \_ _ _ -> adjustPos retPos >> setStartCode bol_section >> lexToken
-alex_action_16 = \pos len inp -> checkLeadingWhitespace len inp >>= \len' ->
+alex_action_16 = \pos len inp -> checkLeadingWhitespace pos len inp >>= \len' ->
                                   if B.length inp == len
                                     then return (L pos EOF)
                                     else setStartCode in_field_layout

Cabal-syntax/src/Distribution/Fields/LexerMonad.hs

@@ -27,6 +27,7 @@ module Distribution.Fields.LexerMonad (
     LexWarning(..),
     LexWarningType(..),
     addWarning,
+    addWarningAt,
     toPWarnings,
 
   ) where
@@ -153,3 +154,8 @@ setStartCode c = Lex $ \s -> LexResult s{ curCode = c } ()
 addWarning :: LexWarningType -> Lex ()
 addWarning wt = Lex $ \s@LexState{ curPos = pos, warnings = ws  } ->
     LexResult s{ warnings = LexWarning wt pos : ws } ()
+
+-- | Add warning at specific position
+addWarningAt :: Position -> LexWarningType -> Lex ()
+addWarningAt pos wt = Lex $ \s@LexState{ warnings = ws  } ->
+    LexResult s{ warnings = LexWarning wt pos : ws } ()

Cabal-tests/tests/ParserTests/regressions/Octree-0.5.format

@@ -1,4 +1,4 @@
-Octree-0.5.cabal:39:3: Non breaking spaces at 39:3, 41:3, 43:3
+Octree-0.5.cabal:39:1: Non breaking spaces at 39:1, 41:1, 43:1
 cabal-version: >=1.8
 name:          Octree
 version:       0.5

Cabal-tests/tests/ParserTests/regressions/monad-param.format

@@ -1,4 +1,4 @@
-monad-param.cabal:19:3: Tabs used as indentation at 19:3, 20:3
+monad-param.cabal:19:1: Tabs used as indentation at 19:1, 20:1
 name:         monad-param
 version:      0.0.1
 license:      BSD3

Cabal-tests/tests/ParserTests/regressions/th-lift-instances.format

@@ -1,4 +1,4 @@
-th-lift-instances.cabal:15:9: Tabs used as indentation at 15:9
+th-lift-instances.cabal:15:1: Tabs used as indentation at 15:1
 cabal-version:      >=1.10
 name:               th-lift-instances
 version:            0.1.4

cabal-testsuite/PackageTests/Check/PackageFiles/BOM/cabal.out

@@ -1,6 +1,6 @@
 # cabal check
 Warning: These warnings may cause trouble when distributing the package:
-Warning: pkg.cabal:1:2: Byte-order mark found at the beginning of the file
+Warning: pkg.cabal:1:1: Byte-order mark found at the beginning of the file
 Warning: The following errors will cause portability problems on other environments:
 Warning: ./pkg.cabal starts with an Unicode byte order mark (BOM). This may cause problems with older cabal versions.
 Warning: Hackage would reject this package.

templates/Lexer.x

@@ -83,22 +83,22 @@ $instresc        = $printable
 tokens :-
 
 <0> {
-  @bom?  { \_ len _ -> do
-              when (len /= 0) $ addWarning LexWarningBOM
+  @bom?  { \pos len _ -> do
+              when (len /= 0) $ addWarningAt pos LexWarningBOM
               setStartCode bol_section
               lexToken
          }
 }
 
 <bol_section, bol_field_layout, bol_field_braces> {
-  @nbspspacetab* @nl         { \_pos len inp -> checkWhitespace len inp >> adjustPos retPos >> lexToken }
+  @nbspspacetab* @nl         { \pos len inp -> checkWhitespace pos len inp >> adjustPos retPos >> lexToken }
   -- no @nl here to allow for comments on last line of the file with no trailing \n
   $spacetab* "--" $comment*  ;  -- TODO: check the lack of @nl works here
                                 -- including counting line numbers
 }
 
 <bol_section> {
-  @nbspspacetab*   { \pos len inp -> checkLeadingWhitespace len inp >>
+  @nbspspacetab*   { \pos len inp -> checkLeadingWhitespace pos len inp >>
                                      if B.length inp == len
                                        then return (L pos EOF)
                                        else setStartCode in_section
@@ -123,7 +123,7 @@ tokens :-
 }
 
 <bol_field_layout> {
-  @nbspspacetab* { \pos len inp -> checkLeadingWhitespace len inp >>= \len' ->
+  @nbspspacetab* { \pos len inp -> checkLeadingWhitespace pos len inp >>= \len' ->
                                   if B.length inp == len
                                     then return (L pos EOF)
                                     else setStartCode in_field_layout
@@ -172,17 +172,17 @@ toki t pos  len  input = return $! L pos (t (B.take len input))
 tok :: Token -> Position -> Int -> ByteString -> Lex LToken
 tok  t pos _len _input = return $! L pos t
 
-checkLeadingWhitespace :: Int -> ByteString -> Lex Int
-checkLeadingWhitespace len bs
+checkLeadingWhitespace :: Position -> Int -> ByteString -> Lex Int
+checkLeadingWhitespace pos len bs
     | B.any (== 9) (B.take len bs) = do
-        addWarning LexWarningTab
-        checkWhitespace len bs
-    | otherwise = checkWhitespace len bs
+        addWarningAt pos LexWarningTab
+        checkWhitespace pos len bs
+    | otherwise = checkWhitespace pos len bs
 
-checkWhitespace :: Int -> ByteString -> Lex Int
-checkWhitespace len bs
+checkWhitespace :: Position -> Int -> ByteString -> Lex Int
+checkWhitespace pos len bs
     | B.any (== 194) (B.take len bs) = do
-        addWarning LexWarningNBSP
+        addWarningAt pos LexWarningNBSP
         return $ len - B.count 194 (B.take len bs)
     | otherwise = return len