Excessive polymorhism hurts v2-repl in Cabal

[blackgnezdo]

Describe the bug

Loading Cabal library into repl is harder than it could be.

To Reproduce
Steps to reproduce the behavior:

% git log -n1 | cat
commit 50d59cfc82fad32f2c708339a083b48a1c36dc30
Merge: 120e5394a bf66f07dc
Author: Oleg Grenrus <oleg.grenrus@iki.fi>
Date:   Fri May 22 20:50:55 2020 +0300

    Merge pull request #6831 from phadej/fix-windows-gh-actions
    
    Fix Windows GitHub Action
% cabal --version
cabal-install version 3.3.0.0
compiled using version 3.3.0.0 of the Cabal library 
% pwd
/home/greg/s/cabal/Cabal
% cabal v2-repl
Build profile: -w ghc-8.10.1 -O1
In order, the following will be built (use -v for more details):
 - Cabal-3.3.0.0 (lib) (first run)
Preprocessing library for Cabal-3.3.0.0..
GHCi, version 8.10.1: https://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/greg/.ghci
[  1 of 245] Compiling Distribution.Compat.Async ( Distribution/Compat/Async.hs, interpreted )
...
[ 80 of 245] Compiling Distribution.Types.ComponentId ( Distribution/Types/ComponentId.hs, interpreted )

Distribution/Types/ComponentId.hs:66:39: error:
    • Could not deduce (Foldable t0) arising from a use of ‘elem’
      from the context: CabalParsing m
        bound by the type signature for:
                   parsec :: forall (m :: * -> *). CabalParsing m => m ComponentId
        at Distribution/Types/ComponentId.hs:65:3-8
      The type variable ‘t0’ is ambiguous
      These potential instances exist:
        instance Foldable NonEmptySet
          -- Defined at Distribution/Compat/NonEmptySet.hs:71:10
        instance Foldable (Either a) -- Defined in ‘Data.Foldable’
        instance Foldable Identity -- Defined in ‘Data.Functor.Identity’
        ...plus six others
        ...plus 53 instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the second argument of ‘(||)’, namely ‘c `elem` "-_."’
      In the expression: isAlphaNum c || c `elem` "-_."
      In an equation for ‘abi_char’:
          abi_char c = isAlphaNum c || c `elem` "-_."
   |
66 |    where abi_char c = isAlphaNum c || c `elem` "-_."
   |                                       ^^^^^^^^^^^^^^

Distribution/Types/ComponentId.hs:66:48: error:
    • Could not deduce (IsString (t0 Char))
        arising from the literal ‘"-_."’
      from the context: CabalParsing m
        bound by the type signature for:
                   parsec :: forall (m :: * -> *). CabalParsing m => m ComponentId
        at Distribution/Types/ComponentId.hs:65:3-8
      The type variable ‘t0’ is ambiguous
      These potential instances exist:
        instance IsString a => IsString (Identity a)
          -- Defined in ‘Data.String’
        instance (a ~ Char) => IsString [a] -- Defined in ‘Data.String’
        ...plus three instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the second argument of ‘elem’, namely ‘"-_."’
      In the second argument of ‘(||)’, namely ‘c `elem` "-_."’
      In the expression: isAlphaNum c || c `elem` "-_."
   |
66 |    where abi_char c = isAlphaNum c || c `elem` "-_."
   |                                                ^^^^^

Expected behavior

Code loads without errors.

System information

• OpenBSD 6.7
• cabal 3.3.0.0, ghc-8.10.1

Additional context

This can be resolved by explicit type annotations, but it's probably not the best way to deal with the errors:

diff --git a/Cabal/Distribution/Simple/GHC/EnvironmentParser.hs b/Cabal/Distribution/Simple/GHC/EnvironmentParser.hs
index f0ff8bc9c..27713132c 100644
--- a/Cabal/Distribution/Simple/GHC/EnvironmentParser.hs
+++ b/Cabal/Distribution/Simple/GHC/EnvironmentParser.hs
@@ -29,7 +29,7 @@ parseEnvironmentFileLine =      GhcEnvFileComment             <$> comment
     where
         comment = P.string "--" *> P.many (P.noneOf "\r\n")
         unitId = P.try $ P.string "package-id" *> P.spaces *>
-            (mkUnitId <$> P.many1 (P.satisfy $ \c -> isAlphaNum c || c `elem` "-_.+"))
+            (mkUnitId <$> P.many1 (P.satisfy $ \c -> isAlphaNum c || c `elem` ("-_.+" :: String)))
         packageDb = (P.string "global-package-db"      *> pure GlobalPackageDB)
                 <|> (P.string "user-package-db"        *> pure UserPackageDB)
                 <|> (P.string "package-db" *> P.spaces *> (SpecificPackageDB <$> P.many1 (P.noneOf "\r\n") <* P.lookAhead P.endOfLine))
diff --git a/Cabal/Distribution/Simple/PreProcess.hs b/Cabal/Distribution/Simple/PreProcess.hs
index a34e38baa..aede8934a 100644
--- a/Cabal/Distribution/Simple/PreProcess.hs
+++ b/Cabal/Distribution/Simple/PreProcess.hs
@@ -542,7 +542,7 @@ ppC2hs bi lbi clbi =
                                                  --
                                                  --
                                                  -- DO NOT add Installed.cxxOptions unless this changes!
-                                 , c `elem` "DIU" ] ]
+                                 , c `elem` ("DIU" :: String) ] ]
           --TODO: install .chi files for packages, so we can --include
           -- those dirs here, for the dependencies
 
@@ -568,7 +568,7 @@ getCppOptions bi lbi
     = platformDefines lbi
    ++ cppOptions bi
    ++ ["-I" ++ dir | dir <- PD.includeDirs bi]
-   ++ [opt | opt@('-':c:_) <- PD.ccOptions bi ++ PD.cxxOptions bi, c `elem` "DIU"]
+   ++ [opt | opt@('-':c:_) <- PD.ccOptions bi ++ PD.cxxOptions bi, c `elem` ("DIU"::String)]
 
 platformDefines :: LocalBuildInfo -> [String]
 platformDefines lbi =
diff --git a/Cabal/Distribution/Types/ComponentId.hs b/Cabal/Distribution/Types/ComponentId.hs
index e275ab6e5..c8be73912 100644
--- a/Cabal/Distribution/Types/ComponentId.hs
+++ b/Cabal/Distribution/Types/ComponentId.hs
@@ -63,7 +63,7 @@ instance Pretty ComponentId where
 
 instance Parsec ComponentId where
   parsec = mkComponentId `fmap` P.munch1 abi_char
-   where abi_char c = isAlphaNum c || c `elem` "-_."
+   where abi_char c = isAlphaNum c || c `elem` ("-_." :: String)
 
 instance NFData ComponentId where
     rnf = rnf . unComponentId

[phadej]

Do you have `:set -XOverloadesStrings` in your global `.ghci`. Could you change it to `:seti`, so it would only applied to code you enter in the repl, not all the code interpreted by GHCi?

…

Sent from my iPhone

On 23. May 2020, at 0.27, Greg Steuck ***@***.***> wrote:  Describe the bug Loading Cabal library into repl is harder than it could be. To Reproduce Steps to reproduce the behavior: % git log -n1 | cat git log -n1 | cat commit 50d59cf Merge: 120e539 bf66f07 Author: Oleg Grenrus ***@***.***> Date: Fri May 22 20:50:55 2020 +0300 Merge pull request #6831 from phadej/fix-windows-gh-actions Fix Windows GitHub Action % cabal --version cabal --version cabal-install version 3.3.0.0 compiled using version 3.3.0.0 of the Cabal library % pwd pwd /home/greg/s/cabal/Cabal % cabal v2-repl cabal v2-repl Build profile: -w ghc-8.10.1 -O1 In order, the following will be built (use -v for more details): - Cabal-3.3.0.0 (lib) (first run) Preprocessing library for Cabal-3.3.0.0.. GHCi, version 8.10.1: https://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/greg/.ghci [ 1 of 245] Compiling Distribution.Compat.Async ( Distribution/Compat/Async.hs, interpreted ) ... [ 80 of 245] Compiling Distribution.Types.ComponentId ( Distribution/Types/ComponentId.hs, interpreted ) Distribution/Types/ComponentId.hs:66:39: error: • Could not deduce (Foldable t0) arising from a use of ‘elem’ from the context: CabalParsing m bound by the type signature for: parsec :: forall (m :: * -> *). CabalParsing m => m ComponentId at Distribution/Types/ComponentId.hs:65:3-8 The type variable ‘t0’ is ambiguous These potential instances exist: instance Foldable NonEmptySet -- Defined at Distribution/Compat/NonEmptySet.hs:71:10 instance Foldable (Either a) -- Defined in ‘Data.Foldable’ instance Foldable Identity -- Defined in ‘Data.Functor.Identity’ ...plus six others ...plus 53 instances involving out-of-scope types (use -fprint-potential-instances to see them all) • In the second argument of ‘(||)’, namely ‘c `elem` "-_."’ In the expression: isAlphaNum c || c `elem` "-_." In an equation for ‘abi_char’: abi_char c = isAlphaNum c || c `elem` "-_." | 66 | where abi_char c = isAlphaNum c || c `elem` "-_." | ^^^^^^^^^^^^^^ Distribution/Types/ComponentId.hs:66:48: error: • Could not deduce (IsString (t0 Char)) arising from the literal ‘"-_."’ from the context: CabalParsing m bound by the type signature for: parsec :: forall (m :: * -> *). CabalParsing m => m ComponentId at Distribution/Types/ComponentId.hs:65:3-8 The type variable ‘t0’ is ambiguous These potential instances exist: instance IsString a => IsString (Identity a) -- Defined in ‘Data.String’ instance (a ~ Char) => IsString [a] -- Defined in ‘Data.String’ ...plus three instances involving out-of-scope types (use -fprint-potential-instances to see them all) • In the second argument of ‘elem’, namely ‘"-_."’ In the second argument of ‘(||)’, namely ‘c `elem` "-_."’ In the expression: isAlphaNum c || c `elem` "-_." | 66 | where abi_char c = isAlphaNum c || c `elem` "-_." | ^^^^^ Expected behavior Code loads without errors. System information OpenBSD 6.7 cabal 3.3.0.0, ghc-8.10.1 Additional context This can be resolved by explicit type annotations, but it's probably not the best way to deal with the errors: diff --git a/Cabal/Distribution/Simple/GHC/EnvironmentParser.hs b/Cabal/Distribution/Simple/GHC/EnvironmentParser.hs index f0ff8bc9c..27713132c 100644 --- a/Cabal/Distribution/Simple/GHC/EnvironmentParser.hs +++ b/Cabal/Distribution/Simple/GHC/EnvironmentParser.hs @@ -29,7 +29,7 @@ parseEnvironmentFileLine = GhcEnvFileComment <$> comment where comment = P.string "--" *> P.many (P.noneOf "\r\n") unitId = P.try $ P.string "package-id" *> P.spaces *> - (mkUnitId <$> P.many1 (P.satisfy $ \c -> isAlphaNum c || c `elem` "-_.+")) + (mkUnitId <$> P.many1 (P.satisfy $ \c -> isAlphaNum c || c `elem` ("-_.+" :: String))) packageDb = (P.string "global-package-db" *> pure GlobalPackageDB) <|> (P.string "user-package-db" *> pure UserPackageDB) <|> (P.string "package-db" *> P.spaces *> (SpecificPackageDB <$> P.many1 (P.noneOf "\r\n") <* P.lookAhead P.endOfLine)) diff --git a/Cabal/Distribution/Simple/PreProcess.hs b/Cabal/Distribution/Simple/PreProcess.hs index a34e38baa..aede8934a 100644 --- a/Cabal/Distribution/Simple/PreProcess.hs +++ b/Cabal/Distribution/Simple/PreProcess.hs @@ -542,7 +542,7 @@ ppC2hs bi lbi clbi = -- -- -- DO NOT add Installed.cxxOptions unless this changes! - , c `elem` "DIU" ] ] + , c `elem` ("DIU" :: String) ] ] --TODO: install .chi files for packages, so we can --include -- those dirs here, for the dependencies @@ -568,7 +568,7 @@ getCppOptions bi lbi = platformDefines lbi ++ cppOptions bi ++ ["-I" ++ dir | dir <- PD.includeDirs bi] - ++ [opt | opt@('-':c:_) <- PD.ccOptions bi ++ PD.cxxOptions bi, c `elem` "DIU"] + ++ [opt | opt@('-':c:_) <- PD.ccOptions bi ++ PD.cxxOptions bi, c `elem` ("DIU"::String)] platformDefines :: LocalBuildInfo -> [String] platformDefines lbi = diff --git a/Cabal/Distribution/Types/ComponentId.hs b/Cabal/Distribution/Types/ComponentId.hs index e275ab6e5..c8be73912 100644 --- a/Cabal/Distribution/Types/ComponentId.hs +++ b/Cabal/Distribution/Types/ComponentId.hs @@ -63,7 +63,7 @@ instance Pretty ComponentId where instance Parsec ComponentId where parsec = mkComponentId `fmap` P.munch1 abi_char - where abi_char c = isAlphaNum c || c `elem` "-_." + where abi_char c = isAlphaNum c || c `elem` ("-_." :: String) instance NFData ComponentId where rnf = rnf . unComponentId — You are receiving this because you are subscribed to this thread. 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[blackgnezdo]

Yup, I did :) Thanks for the prompt diagnosis.