OptionWarnings are emitted twice

[Andreas Abel]

OptionWarnings are emitted twice, e.g.:

agda/test/Succeed/LossyUnification.warn

Lines 1 to 6 in 0513851

 LossyUnification.agda:1,1-49 
 warning: -W[no]OptionRenamed 
 Option --experimental-lossy-unification is deprecated, please use --lossy-unification instead 
 LossyUnification.agda:1,1-49 
 warning: -W[no]OptionRenamed 
 Option --experimental-lossy-unification is deprecated, please use --lossy-unification instead 

Suspected reason: We are calling setOptionsFromPragma several times during processing a file.

agda/src/full/Agda/TypeChecking/Monad/Options.hs

Lines 208 to 212 in 0513851

 setOptionsFromPragma :: OptionsPragma -> TCM () 
 setOptionsFromPragma ps = setCurrentRange (pragmaRange ps) $ do 
     opts <- commandLineOptions 
     let (z, warns) = runOptM (parsePragmaOptions ps opts) 
     mapM_ (warning . OptionWarning) warns 

Found while working on:

• #7219

[Ulf Norell]

Not sure how it applies to this issue, but in #6640 I had to jump through some hoops to not get the conflicting options warning multiple times:

• Only warn when the pragma options have changed (otherwise you get the same warning for each new OPTIONS pragma in a file)

  agda/src/full/Agda/TypeChecking/Monad/Options.hs

  Lines 69 to 71 in b982f82

   check (ImpliesPragmaOption nameA valA flagA nameB valB flagB) 
     | flagA newOpts == flagA oldOpts 
     , flagB newOpts == flagB oldOpts  = pure () -- Nothing changed, don't check again. 

• Split setOptionsFromPragma into a checking and a non-checking version

  agda/src/full/Agda/TypeChecking/Monad/Options.hs

  Lines 226 to 232 in b982f82

   -- | Set pragma options without checking for consistency. 
   setOptionsFromPragma :: OptionsPragma -> TCM () 
   setOptionsFromPragma = setOptionsFromPragma' False 
    
   -- | Set pragma options and check them for consistency. 
   checkAndSetOptionsFromPragma :: OptionsPragma -> TCM () 
   checkAndSetOptionsFromPragma = setOptionsFromPragma' True 

• and propagate it to setOptionsFromSourcePragma in Interaction.Imports

  agda/src/full/Agda/Interaction/Imports.hs

  Lines 171 to 179 in b982f82

   -- | Set options from a 'Source' pragma, using the source 
   --   ranges of the pragmas for error reporting. Flag to check consistency. 
   setOptionsFromSourcePragmas :: Bool -> Source -> TCM () 
   setOptionsFromSourcePragmas checkOpts src = do 
     mapM_ setOpts (srcDefaultPragmas src) 
     mapM_ setOpts (srcFilePragmas    src) 
     where 
       setOpts | checkOpts = checkAndSetOptionsFromPragma 
               | otherwise = setOptionsFromPragma 

• and only run the check in typeCheckMain and in createInterface for non-main modules (otherwise you get the warning twice for the main module)

  agda/src/full/Agda/Interaction/Imports.hs

  Lines 420 to 425 in b982f82

   typeCheckMain mode src = do 
     -- liftIO $ putStrLn $ "This is typeCheckMain " ++ prettyShow f 
     -- liftIO . putStrLn . show =<< getVerbosity 
    
     -- For the main interface, we also remember the pragmas from the file 
     setOptionsFromSourcePragmas True src 

  agda/src/full/Agda/Interaction/Imports.hs

  Lines 1000 to 1004 in b982f82

   -- Only check consistency if not main (we check consistency for the main module in 
   -- `typeCheckMain`. 
   let checkConsistency | MainInterface{} <- isMain = False 
                        | otherwise                 = True 
   setOptionsFromSourcePragmas checkConsistency src 

[Andreas Abel]

My question here is whether we should dig out the reason why the warning is raised twice, or whether we reorganise the warning store so that duplicate warnings are just stored once.
E.g. the warning store could be a map from positions to sets of warnings. (Currently it is a plain list.)