Re: [GHC] #12137: Warning about “INLINE binder is (non-rule) loop breaker” with `-dcore-lint`

[GHC]

#12137: Warning about “INLINE binder is (non-rule) loop breaker” with `-dcore-lint`
-------------------------------------+-------------------------------------
        Reporter:  Iceland_jack      |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Description changed by Iceland_jack:

@@ -1,1 +1,1 @@
- With this code using `lens`
+ Using `lens`
@@ -74,1 +74,1 @@
- which works perfectly fine without `-dcore-lint` but fails with
+ which works perfectly fine without `-dcore-lint` but gives a warning with

New description:

 Using `lens`

 {{{#!hs
 {-# Language TemplateHaskell #-}

 import Control.Lens

 data Config   = Config   { _companyName :: String }
 data AppState = AppState { _asConfig    :: Config }

 makeClassy ''Config

 instance HasConfig AppState where
   config = undefined
 }}}

 gives

 {{{
 $ ghci -ignore-dot-ghci -dcore-lint /tmp/tvQq.hs
 GHCi, version 8.0.1: http://www.haskell.org/ghc/  :? for help
 [1 of 1] Compiling Main             ( /tmp/tvQq.hs, interpreted )
 *** Core Lint warnings : in result of Simplifier ***
 /tmp/tvQq.hs:10:10: warning:
     [RHS of $ccompanyName_a7EP :: Lens' AppState String]
     INLINE binder is (non-rule) loop breaker: $ccompanyName_a7EP

 *** Core Lint warnings : in result of Simplifier ***
 /tmp/tvQq.hs:10:10: warning:
     [RHS of $ccompanyName_a7EP :: Lens' AppState String]
     INLINE binder is (non-rule) loop breaker: $ccompanyName_a7EP

 Ok, modules loaded: Main.
 *Main>
 }}}

 ----

 `makeClass` actually dumps

 {{{
 <interactive>:64:54-72: Splicing declarations
     makeClassy ''Config
   ======>
     class HasConfig c_axo7 where
       config :: Lens' c_axo7 Config
       companyName :: Lens' c_axo7 String
       {-# INLINE companyName #-}
       companyName = (.) config companyName
     instance HasConfig Config where
       {-# INLINE companyName #-}
       config = id
       companyName = iso (\ (Config x_axo8) -> x_axo8) Config
 }}}

 Using that to create a small example

 ----

 {{{#!hs
 data Config = Config { name :: String }
 class HasConfig a where
   config :: a -> Config
   companyName :: a -> String
   {-# INLINE companyName #-}
   companyName a = name (config a)

 instance HasConfig Config where
   {-# INLINE companyName #-}
   config = id
   companyName = name . config
 }}}

 which works perfectly fine without `-dcore-lint` but gives a warning with

 {{{
 $ ghci -ignore-dot-ghci  -dcore-lint /tmp/tvQq.hs
 GHCi, version 8.0.1: http://www.haskell.org/ghc/  :? for help
 [1 of 1] Compiling Main             ( /tmp/tvQq.hs, interpreted )
 *** Core Lint warnings : in result of Simplifier ***
 /tmp/tvQq.hs:11:3: warning:
     [RHS of $ccompanyName_a18Q :: Config -> String]
     INLINE binder is (non-rule) loop breaker: $ccompanyName_a18Q

 *** Core Lint warnings : in result of Simplifier ***
 /tmp/tvQq.hs:11:3: warning:
     [RHS of $ccompanyName_a18Q :: Config -> String]
     INLINE binder is (non-rule) loop breaker: $ccompanyName_a18Q

 Ok, modules loaded: Main.
 }}}

--

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12137#comment:1>
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