99a44a0 · elk · git.iko.soy

git.iko.soy/elk

Turn incomplete pattern matches into a static error

Explain the situation with Debug.crash such that people know they do not have to do a bunch of work to show the problematic value.

commit99a44a022667e31332d73dcc2fa0fbe410136371 authorEvan Czaplicki <info@elm-lang.org> dateTue 8 Sep 2015, 21:36 (11 years ago) parent2297bbf

6 files changed+89−52

compare with master

unifiedsplit

elm-compiler.cabal+1 src/Compile.hs+2−1 src/Nitpick/PatternMatches.hs+9−9 src/Reporting/Error.hs+8 src/Reporting/Error/Pattern.hs+69 src/Reporting/Warning.hs−42

elm-compiler.cabal+1

@@ -103,6 +103,7 @@ Library

103103 Reporting.Error.Canonicalize,

104104 Reporting.Error.Docs,

105105 Reporting.Error.Helpers,

106+ Reporting.Error.Pattern,

106107 Reporting.Error.Syntax,

107108 Reporting.Error.Type,

108109 Reporting.PrettyPrint,

src/Compile.hs+2−1

@@ -45,7 +45,8 @@ compile packageName isRoot canonicalImports interfaces source =

4545 Result.mapError Error.Type $

4646 Nitpick.topLevelTypes types (Module.body validModule)

4747

48− Nitpick.patternMatches interfaces canonicalModule

48+ Result.mapError Error.Pattern $

49+ Nitpick.patternMatches interfaces canonicalModule

4950

5051 -- Add the real list of types

5152 let body = (Module.body canonicalModule) { Module.types = types }

src/Nitpick/PatternMatches.hs+9−9

@@ -17,15 +17,15 @@ import qualified AST.Variable as Var

1717import Elm.Utils ((|>))

1818import Nitpick.Pattern (Pattern(..), fromCanonicalPattern)

1919import qualified Reporting.Annotation as A

20+import qualified Reporting.Error.Pattern as Error

2021import qualified Reporting.Region as Region

2122import qualified Reporting.Result as Result

22−import qualified Reporting.Warning as Warning

2323

2424

2525patternMatches

2626 :: Module.Interfaces

2727 -> Module.CanonicalModule

28− -> Result.Result Warning.Warning e ()

28+ -> Result.Result w Error.Error ()

2929patternMatches interfaces modul =

3030 let

3131 name = Module.name modul

@@ -102,7 +102,7 @@ lookupOtherTags (Var.Canonical home name) tagDict =

102102checkExpression

103103 :: TagDict

104104 -> Canonical.Expr

105− -> Result.Result Warning.Warning e ()

105+ -> Result.Result w Error.Error ()

106106checkExpression tagDict (A.A region expression) =

107107 let

108108 go =

@@ -188,7 +188,7 @@ checkPatterns

188188 :: TagDict

189189 -> Region.Region

190190 -> [Pattern.CanonicalPattern]

191− -> Result.Result Warning.Warning e ()

191+ -> Result.Result w Error.Error ()

192192checkPatterns tagDict region patterns =

193193 checkPatternsHelp tagDict region [Anything] patterns

194194

@@ -198,14 +198,14 @@ checkPatternsHelp

198198 -> Region.Region

199199 -> [Pattern]

200200 -> [Pattern.CanonicalPattern]

201− -> Result.Result Warning.Warning e ()

201+ -> Result.Result w Error.Error ()

202202checkPatternsHelp tagDict region unhandled patterns =

203203 case (unhandled, patterns) of

204204 ([], []) ->

205205 return ()

206206

207207 (_:_, []) ->

208− Result.warn region (Warning.InexhaustivePatternMatch unhandled)

208+ Result.throw region (Error.Incomplete unhandled)

209209

210210 (_, pattern@(A.A localRegion _) : remainingPatterns) ->

211211 do newUnhandled <- filterPatterns tagDict localRegion pattern unhandled

@@ -217,7 +217,7 @@ filterPatterns

217217 -> Region.Region

218218 -> Pattern.CanonicalPattern

219219 -> [Pattern]

220− -> Result.Result Warning.Warning e [Pattern]

220+ -> Result.Result w Error.Error [Pattern]

221221filterPatterns tagDict region pattern unhandled =

222222 let

223223 nitPattern =

@@ -227,8 +227,8 @@ filterPatterns tagDict region pattern unhandled =

227227 intersection pat nitPattern == Nothing

228228 in

229229 if all noIntersection unhandled then

230− do Result.warn region Warning.RedundantPatternMatch

231− return unhandled

230+ Result.throw region Error.Redundant

231+

232232 else

233233 do let complementPatterns = complement tagDict nitPattern

234234 return $

src/Reporting/Error.hs+8

@@ -9,6 +9,7 @@ import Prelude hiding (print)

99import qualified Reporting.Annotation as A

1010import qualified Reporting.Error.Canonicalize as Canonicalize

1111import qualified Reporting.Error.Docs as Docs

12+import qualified Reporting.Error.Pattern as Pattern

1213import qualified Reporting.Error.Syntax as Syntax

1314import qualified Reporting.Error.Type as Type

1415import qualified Reporting.PrettyPrint as P

@@ -21,6 +22,7 @@ data Error

2122 = Syntax Syntax.Error

2223 | Canonicalize Canonicalize.Error

2324 | Type Type.Error

25+ | Pattern Pattern.Error

2426 | Docs Docs.Error

2527

2628

@@ -38,6 +40,9 @@ toReport dealiaser err =

3840 Type typeError ->

3941 Type.toReport dealiaser typeError

4042

43+ Pattern patternError ->

44+ Pattern.toReport dealiaser patternError

45+

4146 Docs docsError ->

4247 Docs.toReport docsError

4348

@@ -76,6 +81,9 @@ toJson dealiaser filePath (A.A region err) =

7681 Type typeError ->

7782 Report.toJson [] (Type.toReport dealiaser typeError)

7883

84+ Pattern patternError ->

85+ Report.toJson [] (Pattern.toReport dealiaser patternError)

86+

7987 Docs docsError ->

8088 Report.toJson [] (Docs.toReport docsError)

8189 in

src/Reporting/Error/Pattern.hsnew file+69

@@ -0,0 +1,69 @@

1+{-# OPTIONS_GHC -Wall #-}

2+module Reporting.Error.Pattern where

4+import qualified Data.Char as Char

5+import Text.PrettyPrint ((<+>))

6+import qualified Text.PrettyPrint as P

8+import qualified AST.Helpers as Help

9+import qualified AST.Type as Type

10+import qualified AST.Variable as Var

11+import qualified Nitpick.Pattern as Pattern

12+import qualified Reporting.PrettyPrint as P

13+import qualified Reporting.Region as Region

14+import qualified Reporting.Report as Report

15+

16+

17+data Error

18+ = Incomplete [Pattern.Pattern]

19+ | Redundant

20+

21+

22+-- TO REPORT

23+

24+toReport :: P.Dealiaser -> Error -> Report.Report

25+toReport dealiaser err =

26+ case err of

27+ Incomplete unhandled ->

28+ Report.simple

29+ "MISSING PATTERN"

30+ "The following `case` does not handle all possible inputs."

31+ ( "The following patterns are not being handled:\n"

32+ ++ viewPatternList unhandled

33+ ++ "\n\n"

34+ ++ "Did you add a new tag to a union type? Add how it should be handled here and"

35+ ++ "you will be all set!"

36+ ++ ""

37+ ++ "If you want to go quick and implement this later, you can end the pattern with:"

38+ ++ ""

39+ ++ " _ ->"

40+ ++ " Debug.crash \"TODO\""

41+ ++ ""

42+ ++ "When I see cases that end with this pattern, I augment the runtime error with"

43+ ++ "the module name, the relevant line numbers, and the value led down that branch."

44+ ++ ""

45+ ++ "That said, you almost never want this in production code. If you think there"

46+ ++ "are certain cases that are impossible in practice, consider refining how you"

47+ ++ "model the data. If it can never happen in practice, you can probably define a"

48+ ++ "union type such that the \"impossible\" cannot even be constructed in the"

49+ ++ "first place. That is how you make something \"impossible\" truly impossible."

50+ ++ ""

51+ ++ "I won't say \"I told you so\" in the runtime error, but I'll be thinking it ;)"

52+ )

53+

54+ Redundant ->

55+ Report.simple

56+ "REDUNDANT PATTERN"

57+ "The following pattern is redundant."

58+ "Any value with this shape will be handled by a previous pattern."

59+

60+

61+viewPatternList :: [Pattern.Pattern] -> String

62+viewPatternList unhandledPatterns =

63+ let

64+ (showPatterns, rest) =

65+ splitAt 4 unhandledPatterns

66+ in

67+ concatMap ((++) "\n ") $

68+ map Pattern.toString showPatterns

69+ ++ if null rest then [] else ["..."]

src/Reporting/Warning.hs−42

@@ -9,7 +9,6 @@ import Text.PrettyPrint ((<+>))

1010import qualified AST.Module.Name as ModuleName

1111import qualified AST.Type as Type

12−import qualified Nitpick.Pattern as Pattern

1312import qualified Reporting.Annotation as A

1413import qualified Reporting.PrettyPrint as P

1514import qualified Reporting.Report as Report

@@ -20,8 +19,6 @@ import qualified Reporting.Report as Report

2019data Warning

2120 = UnusedImport ModuleName.Raw

2221 | MissingTypeAnnotation String Type.Canonical

23− | InexhaustivePatternMatch [Pattern.Pattern]

24− | RedundantPatternMatch

2522

2623

2724-- TO STRING

@@ -59,32 +56,6 @@ toReport dealiaser warning =

5956 4

6057 (P.pretty dealiaser False inferredType)

6158

62− InexhaustivePatternMatch unhandled ->

63− Report.simple

64− "missing pattern"

65− "The following case expression does not handle all possible inputs."

66− ( "The following patterns are not being handled:\n"

67− ++ viewPatternList unhandled

68− ++ "\n\n"

69− ++ "If we get values like this, we have no choice but to crash! Normally this means\n"

70− ++ "you just added a new tag to a union type, but sometimes it can be because there\n"

71− ++ "is something very odd about the data you are modeling. In those rare cases, you\n"

72− ++ "probably want to either:\n"

73− ++ "\n"

74− ++ " 1. Rethink the model. Maybe some cases are \"impossible\" but it is still\n"

75− ++ " possible to construct such cases. Is there a way to model the values more\n"

76− ++ " precisely such that \"impossible\" values truly are impossible?\n"

77− ++ " 2. End the pattern match with a wildcard match that leads to an expression\n"

78− ++ " like: Debug.crash \"If you are reading this, I have made a mistake!\"\n"

79− ++ " Generally speaking, you do not want it to have to be this way."

80− )

81−

82− RedundantPatternMatch ->

83− Report.simple

84− "redundant pattern"

85− "The following pattern is redundant."

86− "Any value with this shape will be handled by a previous pattern."

87−

8859

8960-- TO JSON

9061

@@ -100,16 +71,3 @@ toJson dealiaser filePath (A.A region warning) =

10071 , "type" .= ("warning" :: String)

10172 ]

10273 ++ additionalFields

103−

104−

105−-- PATTERN WARNINGS

106−

107−viewPatternList :: [Pattern.Pattern] -> String

108−viewPatternList unhandledPatterns =

109− let

110− (showPatterns, rest) =

111− splitAt 4 unhandledPatterns

112− in

113− concatMap ((++) "\n ") $

114− map Pattern.toString showPatterns

115− ++ if null rest then [] else ["..."]