diff --git a/CHANGELOG.md b/CHANGELOG.md new file mode 100644 --- /dev/null +++ b/CHANGELOG.md @@ -0,0 +1,3 @@ +0.1.0 +===== +* Initial version. diff --git a/LICENSE b/LICENSE new file mode 100644 --- /dev/null +++ b/LICENSE @@ -0,0 +1,312 @@ +Mozilla Public License Version 2.0 + + 1. Definitions + +1.1. "Contributor" means each individual or legal entity that creates, contributes +to the creation of, or owns Covered Software. + +1.2. "Contributor Version" means the combination of the Contributions of others +(if any) used by a Contributor and that particular Contributor's Contribution. + + 1.3. "Contribution" means Covered Software of a particular Contributor. + +1.4. "Covered Software" means Source Code Form to which the initial Contributor +has attached the notice in Exhibit A, the Executable Form of such Source Code +Form, and Modifications of such Source Code Form, in each case including portions +thereof. + + 1.5. "Incompatible With Secondary Licenses" means + +(a) that the initial Contributor has attached the notice described in Exhibit +B to the Covered Software; or + +(b) that the Covered Software was made available under the terms of version +1.1 or earlier of the License, but not also under the terms of a Secondary +License. + +1.6. "Executable Form" means any form of the work other than Source Code Form. + +1.7. "Larger Work" means a work that combines Covered Software with other +material, in a separate file or files, that is not Covered Software. + + 1.8. "License" means this document. + +1.9. "Licensable" means having the right to grant, to the maximum extent possible, +whether at the time of the initial grant or subsequently, any and all of the +rights conveyed by this License. + + 1.10. "Modifications" means any of the following: + +(a) any file in Source Code Form that results from an addition to, deletion +from, or modification of the contents of Covered Software; or + +(b) any new file in Source Code Form that contains any Covered Software. + +1.11. "Patent Claims" of a Contributor means any patent claim(s), including +without limitation, method, process, and apparatus claims, in any patent Licensable +by such Contributor that would be infringed, but for the grant of the License, +by the making, using, selling, offering for sale, having made, import, or +transfer of either its Contributions or its Contributor Version. + +1.12. "Secondary License" means either the GNU General Public License, Version +2.0, the GNU Lesser General Public License, Version 2.1, the GNU Affero General +Public License, Version 3.0, or any later versions of those licenses. + +1.13. "Source Code Form" means the form of the work preferred for making modifications. + +1.14. "You" (or "Your") means an individual or a legal entity exercising rights +under this License. For legal entities, "You" includes any entity that controls, +is controlled by, or is under common control with You. For purposes of this +definition, "control" means (a) the power, direct or indirect, to cause the +direction or management of such entity, whether by contract or otherwise, +or (b) ownership of more than fifty percent (50%) of the outstanding shares +or beneficial ownership of such entity. + + 2. License Grants and Conditions + + 2.1. Grants + +Each Contributor hereby grants You a world-wide, royalty-free, non-exclusive +license: + +(a) under intellectual property rights (other than patent or trademark) Licensable +by such Contributor to use, reproduce, make available, modify, display, perform, +distribute, and otherwise exploit its Contributions, either on an unmodified +basis, with Modifications, or as part of a Larger Work; and + +(b) under Patent Claims of such Contributor to make, use, sell, offer for +sale, have made, import, and otherwise transfer either its Contributions or +its Contributor Version. + + 2.2. Effective Date + +The licenses granted in Section 2.1 with respect to any Contribution become +effective for each Contribution on the date the Contributor first distributes +such Contribution. + + 2.3. Limitations on Grant Scope + +The licenses granted in this Section 2 are the only rights granted under this +License. No additional rights or licenses will be implied from the distribution +or licensing of Covered Software under this License. Notwithstanding Section +2.1(b) above, no patent license is granted by a Contributor: + +(a) for any code that a Contributor has removed from Covered Software; or + +(b) for infringements caused by: (i) Your and any other third party's modifications +of Covered Software, or (ii) the combination of its Contributions with other +software (except as part of its Contributor Version); or + +(c) under Patent Claims infringed by Covered Software in the absence of its +Contributions. + +This License does not grant any rights in the trademarks, service marks, or +logos of any Contributor (except as may be necessary to comply with the notice +requirements in Section 3.4). + + 2.4. Subsequent Licenses + +No Contributor makes additional grants as a result of Your choice to distribute +the Covered Software under a subsequent version of this License (see Section +10.2) or under the terms of a Secondary License (if permitted under the terms +of Section 3.3). + + 2.5. Representation + +Each Contributor represents that the Contributor believes its Contributions +are its original creation(s) or it has sufficient rights to grant the rights +to its Contributions conveyed by this License. + + 2.6. Fair Use + +This License is not intended to limit any rights You have under applicable +copyright doctrines of fair use, fair dealing, or other equivalents. + + 2.7. Conditions + +Sections 3.1, 3.2, 3.3, and 3.4 are conditions of the licenses granted in +Section 2.1. + + 3. Responsibilities + + 3.1. Distribution of Source Form + +All distribution of Covered Software in Source Code Form, including any Modifications +that You create or to which You contribute, must be under the terms of this +License. You must inform recipients that the Source Code Form of the Covered +Software is governed by the terms of this License, and how they can obtain +a copy of this License. You may not attempt to alter or restrict the recipients' +rights in the Source Code Form. + + 3.2. Distribution of Executable Form + + If You distribute Covered Software in Executable Form then: + +(a) such Covered Software must also be made available in Source Code Form, +as described in Section 3.1, and You must inform recipients of the Executable +Form how they can obtain a copy of such Source Code Form by reasonable means +in a timely manner, at a charge no more than the cost of distribution to the +recipient; and + +(b) You may distribute such Executable Form under the terms of this License, +or sublicense it under different terms, provided that the license for the +Executable Form does not attempt to limit or alter the recipients' rights +in the Source Code Form under this License. + + 3.3. Distribution of a Larger Work + +You may create and distribute a Larger Work under terms of Your choice, provided +that You also comply with the requirements of this License for the Covered +Software. If the Larger Work is a combination of Covered Software with a work +governed by one or more Secondary Licenses, and the Covered Software is not +Incompatible With Secondary Licenses, this License permits You to additionally +distribute such Covered Software under the terms of such Secondary License(s), +so that the recipient of the Larger Work may, at their option, further distribute +the Covered Software under the terms of either this License or such Secondary +License(s). + + 3.4. Notices + +You may not remove or alter the substance of any license notices (including +copyright notices, patent notices, disclaimers of warranty, or limitations +of liability) contained within the Source Code Form of the Covered Software, +except that You may alter any license notices to the extent required to remedy +known factual inaccuracies. + + 3.5. Application of Additional Terms + +You may choose to offer, and to charge a fee for, warranty, support, indemnity +or liability obligations to one or more recipients of Covered Software. However, +You may do so only on Your own behalf, and not on behalf of any Contributor. +You must make it absolutely clear that any such warranty, support, indemnity, +or liability obligation is offered by You alone, and You hereby agree to indemnify +every Contributor for any liability incurred by such Contributor as a result +of warranty, support, indemnity or liability terms You offer. You may include +additional disclaimers of warranty and limitations of liability specific to +any jurisdiction. + + 4. Inability to Comply Due to Statute or Regulation + +If it is impossible for You to comply with any of the terms of this License +with respect to some or all of the Covered Software due to statute, judicial +order, or regulation then You must: (a) comply with the terms of this License +to the maximum extent possible; and (b) describe the limitations and the code +they affect. Such description must be placed in a text file included with +all distributions of the Covered Software under this License. Except to the +extent prohibited by statute or regulation, such description must be sufficiently +detailed for a recipient of ordinary skill to be able to understand it. + + 5. Termination + +5.1. The rights granted under this License will terminate automatically if +You fail to comply with any of its terms. However, if You become compliant, +then the rights granted under this License from a particular Contributor are +reinstated (a) provisionally, unless and until such Contributor explicitly +and finally terminates Your grants, and (b) on an ongoing basis, if such Contributor +fails to notify You of the non-compliance by some reasonable means prior to +60 days after You have come back into compliance. Moreover, Your grants from +a particular Contributor are reinstated on an ongoing basis if such Contributor +notifies You of the non-compliance by some reasonable means, this is the first +time You have received notice of non-compliance with this License from such +Contributor, and You become compliant prior to 30 days after Your receipt +of the notice. + +5.2. If You initiate litigation against any entity by asserting a patent infringement +claim (excluding declaratory judgment actions, counter-claims, and cross-claims) +alleging that a Contributor Version directly or indirectly infringes any patent, +then the rights granted to You by any and all Contributors for the Covered +Software under Section 2.1 of this License shall terminate. + +5.3. In the event of termination under Sections 5.1 or 5.2 above, all end +user license agreements (excluding distributors and resellers) which have +been validly granted by You or Your distributors under this License prior +to termination shall survive termination. + + 6. Disclaimer of Warranty + +Covered Software is provided under this License on an "as is" basis, without +warranty of any kind, either expressed, implied, or statutory, including, +without limitation, warranties that the Covered Software is free of defects, +merchantable, fit for a particular purpose or non-infringing. The entire risk +as to the quality and performance of the Covered Software is with You. Should +any Covered Software prove defective in any respect, You (not any Contributor) +assume the cost of any necessary servicing, repair, or correction. This disclaimer +of warranty constitutes an essential part of this License. No use of any Covered +Software is authorized under this License except under this disclaimer. + + 7. Limitation of Liability + +Under no circumstances and under no legal theory, whether tort (including +negligence), contract, or otherwise, shall any Contributor, or anyone who +distributes Covered Software as permitted above, be liable to You for any +direct, indirect, special, incidental, or consequential damages of any character +including, without limitation, damages for lost profits, loss of goodwill, +work stoppage, computer failure or malfunction, or any and all other commercial +damages or losses, even if such party shall have been informed of the possibility +of such damages. This limitation of liability shall not apply to liability +for death or personal injury resulting from such party's negligence to the +extent applicable law prohibits such limitation. Some jurisdictions do not +allow the exclusion or limitation of incidental or consequential damages, +so this exclusion and limitation may not apply to You. + + 8. Litigation + +Any litigation relating to this License may be brought only in the courts +of a jurisdiction where the defendant maintains its principal place of business +and such litigation shall be governed by laws of that jurisdiction, without +reference to its conflict-of-law provisions. Nothing in this Section shall +prevent a party's ability to bring cross-claims or counter-claims. + + 9. Miscellaneous + +This License represents the complete agreement concerning the subject matter +hereof. If any provision of this License is held to be unenforceable, such +provision shall be reformed only to the extent necessary to make it enforceable. +Any law or regulation which provides that the language of a contract shall +be construed against the drafter shall not be used to construe this License +against a Contributor. + + 10. Versions of the License + + 10.1. New Versions + +Mozilla Foundation is the license steward. Except as provided in Section 10.3, +no one other than the license steward has the right to modify or publish new +versions of this License. Each version will be given a distinguishing version +number. + + 10.2. Effect of New Versions + +You may distribute the Covered Software under the terms of the version of +the License under which You originally received the Covered Software, or under +the terms of any subsequent version published by the license steward. + + 10.3. Modified Versions + +If you create software not governed by this License, and you want to create +a new license for such software, you may create and use a modified version +of this License if you rename the license and remove any references to the +name of the license steward (except to note that such modified license differs +from this License). + +10.4. Distributing Source Code Form that is Incompatible With Secondary Licenses + +If You choose to distribute Source Code Form that is Incompatible With Secondary +Licenses under the terms of this version of the License, the notice described +in Exhibit B of this License must be attached. Exhibit A - Source Code Form +License Notice + +This Source Code Form is subject to the terms of the Mozilla Public License, +v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain +one at http://mozilla.org/MPL/2.0/. + +If it is not possible or desirable to put the notice in a particular file, +then You may include the notice in a location (such as a LICENSE file in a +relevant directory) where a recipient would be likely to look for such a notice. + +You may add additional accurate notices of copyright ownership. + +Exhibit B - "Incompatible With Secondary Licenses" Notice + +This Source Code Form is "Incompatible With Secondary Licenses", as defined +by the Mozilla Public License, v. 2.0. diff --git a/README.md b/README.md new file mode 100644 --- /dev/null +++ b/README.md @@ -0,0 +1,23 @@ +# uncaught-exception + +[![GitHub CI](https://github.com/serokell/uncaught-exception/workflows/CI/badge.svg)](https://github.com/serokell/uncaught-exception/actions) +[![Hackage](https://img.shields.io/hackage/v/uncaught-exception.svg)](https://hackage.haskell.org/package/uncaught-exception) +[![Stackage LTS](http://stackage.org/package/uncaught-exception/badge/lts)](http://stackage.org/lts/package/uncaught-exception) +[![Stackage Nightly](http://stackage.org/package/uncaught-exception/badge/nightly)](http://stackage.org/nightly/package/uncaught-exception) +[![License: MPL 2.0](https://img.shields.io/badge/License-MPL%202.0-brightgreen.svg)](https://github.com/serokell/o-clock/blob/master/LICENSE) + +The goal of this small library is to make it easy to customize handling of uncaught exceptions in Haskell applications. +The default handler of uncaught exceptions uses the `Show` type class to print the exception. +However, in some cases you may want to use `displayException` which renders the exception value in a human-friendly manner. +You can find more details about motivation and implementation of this library in its Haddock documentation and [this blog post](https://serokell.io/blog/uncaught-exception-handling). + +## For Contributors + +Please see [CONTRIBUTING.md](.github/CONTRIBUTING.md) for more information. + +## About Serokell + +`uncaught-exception` is maintained and funded with ❤️ by [Serokell](https://serokell.io/). +The names and logo for Serokell are trademark of Serokell OÜ. + +We love open source software! See [our other projects](https://serokell.io/community?utm_source=github) or [hire us](https://serokell.io/hire-us?utm_source=github) to design, develop and grow your idea! diff --git a/demo/Main.hs b/demo/Main.hs new file mode 100644 --- /dev/null +++ b/demo/Main.hs @@ -0,0 +1,35 @@ +-- SPDX-FileCopyrightText: 2020 Serokell +-- +-- SPDX-License-Identifier: MPL-2.0 + +{-# LANGUAGE DerivingStrategies #-} +{-# LANGUAGE LambdaCase #-} + +module Main + ( main + ) where + +import Control.Exception (Exception(..), throwIO) +import System.Environment (getArgs) + +import Control.Exception.Uncaught + +data MyException = MyException + deriving stock Show + +instance Exception MyException where + displayException MyException = "displayException" + +main :: IO () +main = do + method <- getArgs >>= \case + [m] -> pure m + _ -> fail "Pass only one argument" + f method $ throwIO MyException + where + f :: String -> IO a -> IO a + f "id" = id + f "displayUncaughtException" = displayUncaughtException + f "withDisplayExceptionHandler" = withDisplayExceptionHandler + f "setDisplayExceptionHandler" = (setDisplayExceptionHandler >>) + f method = const $ fail $ "Unknown method: " <> method diff --git a/src/Control/Exception/Uncaught.hs b/src/Control/Exception/Uncaught.hs new file mode 100644 --- /dev/null +++ b/src/Control/Exception/Uncaught.hs @@ -0,0 +1,140 @@ +-- SPDX-FileCopyrightText: 2020 Serokell +-- +-- SPDX-License-Identifier: MPL-2.0 + +-- | Customize uncaught exception handler. +-- +-- When any thread of your Haskell application throws an exception +-- that does not get caught explicitly, the Haskell runtime system will +-- handle it and print based on the 'Show' instance (by default). This +-- behavior can be customized using the 'setUncaughtExceptionHandler' +-- function. However, implementing your own uncaught exception handler +-- sounds like a tricky task because you should keep a bunch of things +-- in mind: +-- +-- 1. You should flush stdout. +-- 2. You should print output to stderr rather than stdout. +-- 3. You should take care of the exit code of your application and the +-- 'ExitCode' data type. +-- +-- The aim of this module is to handle all these concerns and provide +-- easy-to-use functions that capture common cases when you want to +-- modify behavior of the default uncaught exception handler. +-- Currently we consider only one case: using 'displayException' instead +-- of the 'Show' methods. It's debatable whether 'displayException' is +-- more appropriate to print uncaught exceptions. Even though +-- 'displayException' is not used by default, we believe there are cases +-- when it makes sense to use it for printing. +-- +-- We intentionally provide more than one implementation with similar types +-- and semantics. We expect that over time these functions +-- will be better tested and some feedback will be gathered that +-- will let us figure out which approach is better. + +module Control.Exception.Uncaught + ( displayUncaughtException + , withDisplayExceptionHandler + , setDisplayExceptionHandler + + -- * Exported just in case you want to do something special + , DisplayExceptionInShow (..) + , wrapException + ) where + +import Control.Exception + (Deadlock, Exception(..), SomeAsyncException, SomeException, handle, throwIO) +import Data.Maybe (isNothing) +import GHC.Conc.Sync (getUncaughtExceptionHandler, setUncaughtExceptionHandler) +import System.Exit (ExitCode) + +-- | Customise default uncaught exception handling to use +-- 'displayException' instead of 'show'. This function is supposed to +-- be applied to the body of @main@. Note that it only affects exceptions +-- in the current thread, other threads are not affected. +-- It is adviced to use the @async@ package that propagates exceptions +-- from the child thread to the parent thread. +-- +-- It works by catching all exceptions and wrapping them into +-- a wrapper data type whose 'show' method uses 'displayException'. +-- The wrapped exception is re-thrown and the default exception +-- handler will handle it. 'displayException' will be used for printing +-- because that's how 'show' of the wrapper data type is implemented. +-- Some exceptions are not wrapped: +-- +-- 1. 'ExitCode' exception because it's treated specially and affects +-- exit code of the application. If we catch 'ExitSuccess', wrap it into +-- another data type and re-throw, the program will end with non-zero code +-- which is not desirable. +-- 2. Asynchronous exceptions. There are not many of them and applying +-- 'displayException' to them usually does not give big benefit. +-- However, some of them may be handled somewhat specially by the runtime +-- system and we don't want to mess up with that. +-- We recognize asynchronous exceptions by casting to 'SomeAsyncException' +-- the same way as the @safe-exceptions@ library. +displayUncaughtException :: IO a -> IO a +displayUncaughtException = handle (throwIO . wrapException) + +-- | Customise default uncaught exception handling to use +-- 'displayException' instead of 'show'. This function is supposed to +-- be applied to the body of @main@. +-- +-- It works similarly to 'displayUncaughtException', but instead of +-- catching and throwing exceptions it modifies the uncaught exception +-- handler to wrap the exception before processing it. +-- As a consequence, it affects __all__ threads. +-- When the action finishes, the uncaught exception handler +-- is restored (normally it should not matter because the function is +-- supposed to be applied to the whole @main@). +-- +-- Note that it may cause race condition if the passed action spawns another +-- thread that throws an uncaught exception when the passed action stops. +-- There is a global variable that stores the uncaught exception handler. +-- Hence it's recommended to use functions from the @async@ package to spawn +-- threads, so that they are stopped before their parent. +-- +-- The handler won't be restored in case of exception thrown by the passed action +-- because otherwise it wouldn't work. +-- Specifically, if we restored the handler in case of +-- exception (e. g. using @bracket@), it would be restored before the +-- uncaught exception handler would be called (because the uncaught +-- exception handler is called after everything). +withDisplayExceptionHandler :: IO a -> IO a +withDisplayExceptionHandler action = do + handler <- getUncaughtExceptionHandler + setUncaughtExceptionHandler (handler . wrapException) + action <* setUncaughtExceptionHandler handler + +-- | A version of 'withDisplayExceptionHandler' that updates the handler forever. +-- The only difference is that it doesn't restore the default handler. +-- This function should give more predictable behavior in case there are +-- multiple threads. +setDisplayExceptionHandler :: IO () +setDisplayExceptionHandler = do + handler <- getUncaughtExceptionHandler + setUncaughtExceptionHandler (handler . wrapException) + +---------------------------------------------------------------------------- +-- Helpers +---------------------------------------------------------------------------- + +-- | Helper data type used by 'displayUncaughtException'. +-- It causes @show@ to call @displayException@. +-- When an exception of this type is caught, it will be @show@n and +-- that will call @displayException@ of the wrapped exception. +newtype DisplayExceptionInShow = DisplayExceptionInShow SomeException + +instance Show DisplayExceptionInShow where + show (DisplayExceptionInShow se) = displayException se + +instance Exception DisplayExceptionInShow + +wrapException :: SomeException -> SomeException +wrapException e + | isSyncException e + , Nothing <- fromException @Deadlock e + , Nothing <- fromException @ExitCode e = + toException $ DisplayExceptionInShow e + | otherwise = e + where + isSyncException :: SomeException -> Bool + isSyncException = isNothing . fromException @SomeAsyncException diff --git a/uncaught-exception.cabal b/uncaught-exception.cabal new file mode 100644 --- /dev/null +++ b/uncaught-exception.cabal @@ -0,0 +1,60 @@ +cabal-version: 2.2 + +-- SPDX-FileCopyrightText: 2020 Serokell +-- +-- SPDX-License-Identifier: MPL-2.0 + +name: uncaught-exception +version: 0.1.0 +synopsis: Customize uncaught exception handling. +description: See README.md for details. +homepage: https://github.com/serokell/uncaught-exception +bug-reports: https://github.com/serokell/uncaught-exception/issues +license: MPL-2.0 +license-file: LICENSE +author: Serokell +maintainer: Serokell +copyright: 2020 Serokell +build-type: Simple +extra-doc-files: CHANGELOG.md + , README.md +tested-with: GHC == 8.6.5 + , GHC == 8.8.3 + , GHC == 8.10.1 + +source-repository head + type: git + location: git@github.com:serokell/uncaught-exception.git + +common common-options + build-depends: base >= 4.9 && < 5 + ghc-options: + -- Source: https://medium.com/mercury-bank/enable-all-the-warnings-a0517bc081c3 + -Weverything + -Wno-missing-exported-signatures + -Wno-missing-import-lists + -Wno-missed-specialisations + -Wno-all-missed-specialisations + -Wno-unsafe + -Wno-safe + -Wno-missing-local-signatures + -Wno-monomorphism-restriction + -Wno-implicit-prelude + if impl(ghc >= 8.10.1) + ghc-options: -Wno-prepositive-qualified-module + -Wno-missing-safe-haskell-mode + + default-language: Haskell2010 + + +library + import: common-options + hs-source-dirs: src + exposed-modules: Control.Exception.Uncaught + default-extensions: TypeApplications + +executable uncaught-exception-demo + import: common-options + main-is: Main.hs + hs-source-dirs: demo + build-depends: uncaught-exception