diff --git a/ChangeLog.md b/ChangeLog.md
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+# Changelog for ghc-clippy-plugin
+
+## 0.0.0.1
+
+Initial release:
+ - allows overriding warning and error messages emitted by ghc
+ - works with stack and ghcid
+ - configured using ./.clippy.dhall
diff --git a/LICENSE b/LICENSE
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+Copyright Author name here (c) 2020
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+ * Redistributions of source code must retain the above copyright
+ notice, this list of conditions and the following disclaimer.
+
+ * Redistributions in binary form must reproduce the above
+ copyright notice, this list of conditions and the following
+ disclaimer in the documentation and/or other materials provided
+ with the distribution.
+
+ * Neither the name of Author name here nor the names of other
+ contributors may be used to endorse or promote products derived
+ from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/README.md b/README.md
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+# GHC Clippy Plugin
+
+[](https://travis-ci.org/ArturGajowy/ghc-clippy-plugin)
+[](https://opensource.org/licenses/BSD-3-Clause)
+
+A helpful companion to GHC.
+
+Overrides GHC error and warning messages, to the user's liking.
+
+Configured using (how else!) regexps. Tested with stack and ghcid.
+
+## Showcase
+
+
+
+
+Left: without Clippy.
+
+Right: with Clippy, using the sample config.
+
+## But, why?
+
+For all kinds of reasons:
+ - making GHC messages more terse or more verbose
+ - adding more context for beginners
+ - stripping confusing / duplicated / rarely useful context for everyone
+ - prototyping improvements for ghc error output
+ - ever wanted GHC to speak in emoji? :smiling_imp:
+ - ... or in your mother tongue?
+ - ... or in mathematical notation?
+
+## Usage
+
+1. Add the `ghc-clippy-plugin` dependency to your project
+2. Pass `-fplugin=Clippy` in GHC options
+
+E.g. for stack:
+
+```yaml
+# file: package.yaml
+dependencies:
+ - ghc-clippy-plugin
+
+ghc-options:
+- -fplugin=Clippy
+```
+
+3. When building, you should see the following warning:
+
+```
+ghc-clippy-plugin: warning:
+ Clippy plugin couldn't start. Cause:
+ ./.clippy.dhall: openFile: does not exist (No such file or directory)
+```
+
+Make sure there was anything to compile (change a .hs file) if the warning wasn't there.
+
+Save the [sample config](/.clippy-terse.dhall) as `.clippy.dhall` in the project's root dir
+(or - more precisely - the `current directory` GHC is going to use)
+
+4. Put an error somewhere:
+
+```haskell
+oops = print mempty
+```
+
+With the sample config, this should output:
+
+```
+./app/Main.hs:19:14-19: error:
+ Type variable ‘a0’ is ambiguous in ‘mempty’.
+ Can't pick an instance for ‘(Monoid a0)’.
+ ---
+ Maybe-fix: add type annotations to disambiguate.
+ More info: compile with -fprint-potential-instances.
+ |
+19 | oops = print mempty
+ |
+```
+
+5. Enjoy the much terser output and tweak it to your heart's content! :grin:
+
+
+## Tweaking the config
+
+### Stack
+
+For `--file-watch` to pick up config changes, add in `package.yaml`:
+```yaml
+extra-source-files:
+- .clippy.dhall
+```
+
+Use `stack build --file-watch`. Make sure to have some errors handy! :)
+
+### Ghcid
+
+For ghcid to reload after config change, run it with `--reload=.clippy.dhall`.
+I tend to put the above line in `./.ghcid`.
+
+Ghcid may terminate if there are compile errors on startup.
+If that's the case, remove your errors until ghcid starts successfully :)
+
+With the above, for error messages, ghcid picks up `.clippy.dhall` changes immediately.
+
+For warnings, one needs to trigger recompilation of the file triggering them.
+One way around that is to enable `-Werror` for the period of config tweaking.
+(I put mine in `./.ghci`.)
+
+### Error message structure, section markers
+
+In GHC, each error/warning message contains 3 sections in its [ErrDoc](https://hackage.haskell.org/package/ghc-8.10.1/docs/src/ErrUtils.html#ErrDoc)
+('Important', 'Context', and 'Supplementary'). Each section contains a list of `MsgDoc`-s.
+
+Before replacing the message text, Clippy wraps each section, and each of their `MsgDoc`-s, with
+markers. This allows for more precise match targeting, including MsgDoc/section ends.
+
+To see the structure of the replaced error message, comment out the `marker removing rule` in the
+config.
+
+```dhall
+ rules =
+ [ -- rule "(>>[ICS]>)|(<[ICS]<<)|(>[ICS]>)|(<[ICS]<)" ""
+ , rule "..." "..."
+ -- ...
+ ]
+```
+
+Comment out all rules to see the structure of the original message. Sample result:
+
+```
+./app/Main.hs:27:11: error:
+ • >>I>
+ >I>
+ No instance for (Num a) arising from a use of ‘+’
+ Possible fix:
+ add (Num a) to the context of
+ the type signature for:
+ bar :: forall a. a -> a -> a
+ >C>
+ >C>
+ In the expression: a + b
+ In an equation for ‘bar’: bar a b = a + b
+ >S>
+ >C>.*?
+category: Development, Compiler Plugin
+homepage: https://github.com/ArturGajowy/ghc-clippy-plugin#readme
+bug-reports: https://github.com/ArturGajowy/ghc-clippy-plugin/issues
+author: Artur Gajowy
+maintainer: artur.gajowy@gmail.com
+copyright: 2020 Artur Gajowy
+license: BSD3
+license-file: LICENSE
+build-type: Simple
+extra-source-files:
+ README.md
+ ChangeLog.md
+
+source-repository head
+ type: git
+ location: https://github.com/ArturGajowy/ghc-clippy-plugin
+
+library
+ exposed-modules:
+ Clippy
+ other-modules:
+ Paths_ghc_clippy_plugin
+ hs-source-dirs:
+ src
+ ghc-options: -fobject-code -Wall
+ build-depends:
+ base >=4.7 && <5
+ , dhall >=1.30.0 && <1.33
+ , ghc >=8.8.2 && <8.11
+ , text >=1.2.3.2 && <1.3
+ , text-icu >=0.7.0 && <0.8
+ , text-regex-replace >=0.1.1 && <0.2
+ default-language: Haskell2010
diff --git a/src/Clippy.hs b/src/Clippy.hs
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+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE TypeApplications #-}
+
+module Clippy
+ ( plugin
+ )
+where
+
+import Bag
+import Control.Exception (SomeException, tryJust)
+import Data.Bifunctor
+import Data.Function
+import Data.IORef
+import Data.String (fromString)
+import qualified Data.Text as T
+import Data.Text.ICU (regex)
+import Data.Text.ICU.Replace (replaceAll)
+import Dhall
+import ErrUtils
+import GhcPlugins hiding (Rule, (<>))
+import Prelude hiding (print)
+import TcPluginM
+import TcRnTypes
+
+plugin :: Plugin
+plugin =
+ defaultPlugin
+ { tcPlugin = const $ Just $
+ TcPlugin
+ { tcPluginInit = pure ()
+ , tcPluginSolve = \_ _ _ _ -> pure $ TcPluginOk [] []
+ , tcPluginStop = const $ loadConfig >>= either cantInitializeWarning replaceMessages
+ }
+ , pluginRecompile = purePlugin
+ }
+
+newtype Config = Config { rules :: [Rule] } deriving Generic
+instance FromDhall Config
+
+data Rule = Rule
+ { match :: Text
+ , print :: Text
+ }
+ deriving Generic
+instance FromDhall Rule
+
+data PEnv = PEnv
+ { showMsgDoc :: MsgDoc -> Text
+ , config :: Config
+ }
+
+loadConfig :: TcPluginM (Either String Config)
+loadConfig = tcPluginIO
+ . tryJust (Just . show @SomeException)
+ $ inputFile auto "./.clippy.dhall"
+
+cantInitializeWarning :: String -> TcPluginM ()
+cantInitializeWarning cause = do
+ dynFlags <- hsc_dflags <$> getTopEnv
+ let warning = mkPlainWarnMsg dynFlags _span msgDoc
+ _span = mkGeneralSrcSpan $ mkFastString "ghc-clippy-plugin"
+ msgDoc = text "Clippy plugin couldn't start. Cause:" $$ text cause
+ tcPluginIO $ printOrThrowWarnings dynFlags $ unitBag warning
+
+replaceMessages :: Config -> TcPluginM ()
+replaceMessages conf = do
+ errsRef <- tcl_errs . snd <$> getEnvs
+ dynFlags <- hsc_dflags <$> getTopEnv
+ let _showMsgDoc = T.pack . showSDoc dynFlags
+ replaceErrMsgs = fmap $ replaceErrMsgDoc $ PEnv _showMsgDoc conf
+ tcPluginIO $ modifyIORef errsRef (bimap replaceErrMsgs replaceErrMsgs)
+
+replaceErrMsgDoc :: PEnv -> ErrMsg -> ErrMsg
+replaceErrMsgDoc env e = e { errMsgDoc = replaceMsgDocs env (errMsgDoc e) }
+
+replaceMsgDocs :: PEnv -> ErrDoc -> ErrDoc
+replaceMsgDocs env e = e
+ { errDocImportant = replaceMsgDocsGroup env "I" (errDocImportant e)
+ , errDocContext = replaceMsgDocsGroup env "C" (errDocContext e)
+ , errDocSupplementary = replaceMsgDocsGroup env "S" (errDocSupplementary e)
+ }
+
+replaceMsgDocsGroup :: PEnv -> Text -> [MsgDoc] -> [MsgDoc]
+replaceMsgDocsGroup env label msgDocs = text . T.unpack <$> filtered
+ where
+ filtered = filter (not . T.null . T.strip) (T.lines replaced)
+ replaced = replaceText env wrapped
+ wrapped = (env & showMsgDoc) . vcat $ wrapGroup label msgDocs
+
+replaceText :: PEnv -> Text -> Text
+replaceText env t = foldr replaceRule t (rules . config $ env)
+
+replaceRule :: Rule -> Text -> Text
+replaceRule rule = replaceAll (regex [] $ rule & match) (fromString . T.unpack $ rule & print)
+
+wrapGroup :: Text -> [MsgDoc] -> [MsgDoc]
+wrapGroup label group =
+ [open $ ">" <> label] ++ (wrapDoc label <$> group) ++ [close $ label <> "<"]
+
+wrapDoc :: Text -> MsgDoc -> MsgDoc
+wrapDoc label doc = vcat [open label, doc, close label]
+
+open :: Text -> MsgDoc
+open label = text . T.unpack $ ">" <> label <> ">"
+
+close :: Text -> MsgDoc
+close label = text . T.unpack $ "<" <> label <> "<"