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Refactored the error handling (#474)
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* Refactored the error handling

This commit reimplements the error handling of encorec. Before, an error
carried the message that should be displayed, meaning that the more
detailed a message you wanted, the more bloated the error handling code
got. The new model introduces a datatype `Error` which has one
constructor for each kind of error, and showing this value prints the
error message. For example, if there is a type mismatch error, instead
of writing
```
tcError $ "Expected type '" ++ show ty1 ++ "' but found '" ++ show ty2 ++ "'"
```
you now write
```
tcError $ TypeMismatchError ty1 ty2
```

The hope is that this will encourage writing better error messages, and
also that it will reduce code duplication when the same kind of error
message needs to be thrown by two different places in the code. As an
added bonus, we can now catch specific errors:
```
matchTypes (getResultType expected) (getResultType ty)
  `catchError` (\case
                 TCError (TypeMismatchError _ _) _ ->
                     tcError $ TypeMismatchError ty expected
                 TCError err _ -> tcError err
               )
```

If the first line above throws a `TypeMismatchError`, we will catch it
and throw a new error. If it's another error we will pass this error
along.

* Reacting to Kiko's comments

This commit can be squashed after review!
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@EliasC
EliasC authored and Kiko committed Jun 16, 2016
1 parent f7c54c4 commit fb3c1aa
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Showing 7 changed files with 442 additions and 291 deletions.
4 changes: 2 additions & 2 deletions src/ir/AST/PrettyPrinter.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -49,7 +49,7 @@ ppProgram Program{bundle, etl, imports, typedefs, functions, classes} =
vcat (map ppClassDecl classes) $+$
"" -- new line at end of file

ppEmbedded EmbedTL{etlheader=header, etlbody=code} =
ppEmbedded EmbedTL{etlheader=header, etlbody=code} =
ppHeader header code

ppHeader header code =
Expand Down Expand Up @@ -198,7 +198,7 @@ ppExpr FutureChain {future, chain} =
ppExpr future <+> "~~>" <+> ppExpr chain
ppExpr Get {val} = "get" <+> ppExpr val
ppExpr Yield {val} = "yield" <+> ppExpr val
ppExpr Eos {} = "eos" <> parens empty
ppExpr Eos {} = "eos"
ppExpr Await {val} = "await" <+> ppExpr val
ppExpr IsEos {target} = ppExpr target <> "." <> "eos" <> parens empty
ppExpr StreamNext {target} = ppExpr target <> "." <> "next" <> parens empty
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4 changes: 2 additions & 2 deletions src/types/Typechecker/Environment.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -112,7 +112,7 @@ mergeEnvs Env{classTable = classTable,
bt = bt'} =
Env{classTable = Map.union classTable classTable',
traitTable = Map.union traitTable traitTable',
typeSynonymTable = Map.union typeSynonymTable typeSynonymTable',
typeSynonymTable = Map.union typeSynonymTable typeSynonymTable',
globals = globs ++ globs',
locals = locals ++ locals',
bindings = binds ++ binds',
Expand Down Expand Up @@ -199,7 +199,7 @@ methodLookup ty m env
ms = map (\t -> traitMethodLookup t m env) traits
ret <- find isJust ms
return $ fromJust ret
| otherwise = error "methodLookup in non-ref type"
| otherwise = Nothing

capabilityLookup :: Type -> Environment -> Maybe Type
capabilityLookup ty env
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6 changes: 3 additions & 3 deletions src/types/Typechecker/Prechecker.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -153,13 +153,13 @@ instance Precheckable MethodDecl where
(checkMainParams $ hparams mheader')
when (isStreamMethod m) $ do
unless (isActiveClassType thisType) $
tcError "Cannot have streaming methods in a passive class"
tcError PassiveStreamingMethodError
when (isConstructor m) $
tcError "Constructor cannot be streaming"
tcError StreamingConstructorError
let mtype = htype mheader'
return $ setType mtype m{mheader = mheader'}
where
checkMainParams params =
unless (map ptype params `elem` allowedMainArguments) $
tcError "Main method must have argument type () or ([String])"
tcError MainMethodArgumentsError
allowedMainArguments = [[], [arrayType stringObjectType]]
265 changes: 258 additions & 7 deletions src/types/Typechecker/TypeError.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@ module Typechecker.TypeError (Backtrace
,emptyBT
,Pushable(push)
,TCError(TCError)
,Error(..)
,TCWarning(TCWarning)
,Warning(..)
,currentMethodFromBacktrace) where
Expand All @@ -17,6 +18,7 @@ import Text.PrettyPrint
import Text.Parsec(SourcePos)
import Data.Maybe
import Data.List
import Text.Printf (printf)

import Identifiers
import Types
Expand Down Expand Up @@ -60,7 +62,7 @@ instance Show BacktraceNode where
| otherwise =
let str = show $ nest 2 $ ppSugared expr
in "In expression: \n" ++ str
show (BTTypedef tl) =
show (BTTypedef tl) =
concat ["In typedef '", show tl, "'"]

type Backtrace = [(SourcePos, BacktraceNode)]
Expand Down Expand Up @@ -110,24 +112,273 @@ instance Pushable Expr where
instance Pushable Typedef where
push t@(Typedef {typedefdef}) = pushMeta t (BTTypedef typedefdef)

refTypeName :: Type -> String
refTypeName ty
| isClassType ty = "class '" ++ getId ty ++ "'"
| isTraitType ty = "trait '" ++ getId ty ++ "'"
| isCapabilityType ty = "capability '" ++ show ty ++ "'"
| otherwise = error $ "Util.hs: No refTypeName for " ++
Types.showWithKind ty

-- | The data type for a type checking error. Showing it will
-- produce an error message and print the backtrace.
newtype TCError = TCError (String, Backtrace)
data TCError = TCError Error Backtrace
instance Show TCError where
show (TCError (msg, [])) =
show (TCError err []) =
" *** Error during typechecking *** \n" ++
msg ++ "\n"
show (TCError (msg, bt@((pos, _):_))) =
show err ++ "\n"
show (TCError err bt@((pos, _):_)) =
" *** Error during typechecking *** \n" ++
show pos ++ "\n" ++
msg ++ "\n" ++
show err ++ "\n" ++
concatMap showBT bt
where
showBT (pos, node) =
showBT (_, node) =
case show node of
"" -> ""
s -> s ++ "\n"

data Error =
DistinctTypeParametersError Type
| WrongNumberOfMethodArgumentsError Name Type Int Int
| WrongNumberOfFunctionArgumentsError Name Int Int
| WrongNumberOfTypeParametersError Type Int Type Int
| MissingFieldRequirementError FieldDecl Type
| CovarianceViolationError FieldDecl Type Type
| RequiredFieldMismatchError FieldDecl Type Type Bool
| NonDisjointConjunctionError Type Type FieldDecl
| OverriddenMethodError Name Type
| IncludedMethodConflictError Name Type Type
| MissingMethodRequirementError FunctionHeader Type
| UnknownTraitError Type
| UnknownRefTypeError Type
| MalformedCapabilityError Type
| RecursiveTypesynonymError Type
| DuplicateThingError String String
| PassiveStreamingMethodError
| StreamingConstructorError
| MainMethodArgumentsError
| FieldNotFoundError Name Type
| MethodNotFoundError Name Type
| TraitsInActiveClassError
| NonCallableTargetError Type
| NonSendableTargetError Type
| MainMethodCallError
| ConstructorCallError
| ExpectingOtherTypeError String Type
| NonStreamingContextError Expr
| UnboundFunctionError Name
| NonFunctionTypeError Type
| BottomTypeInferenceError
| IfInferenceError
| IfBranchMismatchError Type Type
| EmptyMatchClauseError
| ActiveMatchError
| MatchInferenceError
| ThisReassignmentError
| PatternTypeMismatchError Expr Type
| NonMaybeExtractorPatternError Expr
| InvalidPatternError Expr
| CannotReadFieldError Expr
| NonAssignableLHSError
| ValFieldAssignmentError Name Type
| UnboundVariableError Name
| ObjectCreationError Type
| NonIterableError Type
| EmptyArrayLiteralError
| NonIndexableError Type
| NonSizeableError Type
| FormatStringLiteralError
| UnprintableExpressionError Type
| WrongNumberOfPrintArgumentsError Int Int
| UnaryOperandMismatchError UnaryOp Type
| BinaryOperandMismatchError BinaryOp String Type Type
| UndefinedBinaryOperatorError BinaryOp
| NullTypeInferenceError
| CannotBeNullError Type
| TypeMismatchError Type Type
| TypeWithCapabilityMismatchError Type Type Type
| TypeVariableAmbiguityError Type Type Type
| FreeTypeVariableError Type
| SimpleError String

arguments 1 = "argument"
arguments _ = "arguments"

instance Show Error where
show (DistinctTypeParametersError ty) =
printf "Type parameters of '%s' must be distinct" (show ty)
show (WrongNumberOfMethodArgumentsError name targetType expected actual) =
let nameWithKind =
(if name == Name "_init"
then "Constructor"
else "Method '" ++ show name ++ "'") ++
" in " ++ refTypeName targetType
in printf "%s expects %d %s. Got %d"
nameWithKind expected (arguments expected) actual
show (WrongNumberOfFunctionArgumentsError name expected actual) =
printf "Function %s expects %d %s. Got %d"
(show name) expected (arguments expected) actual
show (WrongNumberOfTypeParametersError ty1 n1 ty2 n2) =
printf "'%s' expects %d type %s, but '%s' has %d"
(show ty1) n1 (arguments n1) (show ty2) n2
show (MissingFieldRequirementError field trait) =
printf "Cannot find field '%s' required by included %s"
(show field) (refTypeName trait)
show (CovarianceViolationError field expected trait) =
printf ("Field '%s' must have a subtype of '%s' to meet " ++
"the requirements of included %s")
(show field) (show expected) (refTypeName trait)
show (RequiredFieldMismatchError field expected trait isSub) =
printf ("Field '%s' must exactly match type '%s' " ++
"to meet the requirements of included %s%s")
(show field) (show expected) (refTypeName trait)
(if isSub
then ". Consider turning '" ++ show (fname field) ++
"' into a val-field in " ++ refTypeName trait
else "")
show (NonDisjointConjunctionError left right field) =
printf
"Conjunctive traits '%s' and '%s' cannot share mutable field '%s'"
(show left) (show right) (show field)
show (OverriddenMethodError name trait) =
printf "Method '%s' is defined both in current class and %s"
(show name) (refTypeName trait)
show (IncludedMethodConflictError name left right) =
printf "Conflicting inclusion of method '%s' from %s and %s"
(show name) (refTypeName left) (refTypeName right)
show (MissingMethodRequirementError header trait) =
printf "Cannot find method '%s' required by included %s"
(show $ ppFunctionHeader header) (refTypeName trait)
show (UnknownTraitError ty) =
printf "Couldn't find trait '%s'" (getId ty)
show (UnknownRefTypeError ty) =
printf "Couldn't find class, trait or typedef '%s'" (show ty)
show (MalformedCapabilityError ty) =
printf "Cannot form capability with %s" (Types.showWithKind ty)
show (RecursiveTypesynonymError ty) =
printf "Type synonyms cannot be recursive. One of the culprits is %s"
(getId ty)
show (DuplicateThingError kind thing) =
printf "Duplicate %s of %s" kind thing
show PassiveStreamingMethodError =
"Cannot have streaming methods in a passive class"
show StreamingConstructorError =
"Constructor cannot be streaming"
show MainMethodArgumentsError =
"Main method must have argument type () or ([String])"
show (FieldNotFoundError name ty) =
printf "No field '%s' in %s"
(show name) (refTypeName ty)
show (MethodNotFoundError name ty) =
let nameWithKind = if name == Name "_init"
then "constructor"
else "method '" ++ show name ++ "'"
targetType = if isRefType ty
then refTypeName ty
else Types.showWithKind ty
in printf "No %s in %s"
nameWithKind targetType
show (TraitsInActiveClassError) =
"Traits can only be used for passive classes"
show (NonCallableTargetError targetType) =
printf "Cannot call method on expression of type '%s'"
(show targetType)
show (NonSendableTargetError targetType) =
printf "Cannot send message to expression of type '%s'"
(show targetType)
show MainMethodCallError = "Cannot call the main method"
show ConstructorCallError =
"Constructor method 'init' can only be called during object creation"
show (ExpectingOtherTypeError something ty) =
printf "Expected %s but found expression of type '%s'"
something (show ty)
show (NonStreamingContextError e) =
printf "Cannot have '%s' outside of a streaming method"
(show $ ppSugared e)
show (UnboundFunctionError name) =
printf "Unbound function variable '%s'" (show name)
show (NonFunctionTypeError ty) =
printf "Cannot use value of type '%s' as a function" (show ty)
show BottomTypeInferenceError = "Cannot infer type of 'Nothing'"
show IfInferenceError = "Cannot infer result type of if-statement"
show (IfBranchMismatchError ty1 ty2) =
"Type mismatch in different branches of if-statement:\n" ++
" then: " ++ show ty1 ++ "\n" ++
" else: " ++ show ty2
show EmptyMatchClauseError = "Match statement must have at least one clause"
show ActiveMatchError = "Cannot match on an active object"
show MatchInferenceError = "Cannot infer result type of match expression"
show ThisReassignmentError = "Cannot rebind variable 'this'"
show (PatternTypeMismatchError pattern ty) =
printf "Pattern '%s' does not match expected type '%s'"
(show $ ppSugared pattern) (show ty)
show (NonMaybeExtractorPatternError pattern) =
printf "Extractor '%s' must return a Maybe type to be used as a pattern"
(show $ ppSugared pattern)
show (InvalidPatternError pattern) =
printf "'%s' is not a valid pattern"
(show $ ppSugared pattern)
show (CannotReadFieldError target) =
printf "Cannot read field of expression '%s' of %s"
(show $ ppSugared target) (Types.showWithKind $ getType target)
show NonAssignableLHSError =
"Left-hand side cannot be assigned to"
show (ValFieldAssignmentError name targetType) =
printf "Cannot assign to val-field '%s' in %s"
(show name) (refTypeName targetType)
show (UnboundVariableError name) =
printf "Unbound variable '%s'" (show name)
show (ObjectCreationError ty)
| isMainType ty = "Cannot create additional Main objects"
| isCapabilityType ty =
printf "Cannot create instance of %s (type must be a class)"
(refTypeName ty)
| otherwise = printf "Cannot create object of type '%s'" (show ty)
show (NonIterableError ty) =
printf "Type '%s' is not iterable" (show ty)
show EmptyArrayLiteralError = "Array literal must have at least one element"
show (NonIndexableError ty) =
printf "Type '%s' is not indexable" (show ty)
show (NonSizeableError ty) =
printf "Type '%s' has no size" (show ty)
show FormatStringLiteralError =
"Formatted printing expects first argument to be a string literal"
show (UnprintableExpressionError ty) =
printf "Expression of type '%s' is not printable" (show ty)
show (WrongNumberOfPrintArgumentsError expected actual) =
printf ("Wrong number of arguments to print. Format string " ++
"expects %d %s. Found %d") expected (arguments expected) actual
show (UnaryOperandMismatchError op ty) =
printf "Operator '%s' is not defined for values of type '%s'"
(show op) (show ty)
show (BinaryOperandMismatchError op kind lType rType) =
printf ("Operator '%s' is only defined for %s types\n" ++
" Left type: %s\n" ++
" Right type: %s")
(show op) kind (show lType) (show rType)
show (UndefinedBinaryOperatorError op) =
printf "Undefined binary operator '%s'" (show op)
show NullTypeInferenceError =
"Cannot infer type of null valued expression. " ++
"Try adding type annotations"
show (CannotBeNullError ty) =
printf ("Null valued expression cannot have type '%s' " ++
"(must have reference type)") (show ty)
show (TypeMismatchError actual expected) =
printf "Type '%s' does not match expected type '%s'"
(show actual) (show expected)
show (TypeWithCapabilityMismatchError actual cap expected) =
printf "Type '%s' with capability '%s' does not match expected type '%s'"
(show actual) (show cap) (show expected)
show (TypeVariableAmbiguityError expected ty1 ty2) =
printf "Type variable '%s' cannot be bound to both '%s' and '%s'"
(show expected) (show ty1) (show ty2)
show (FreeTypeVariableError ty) =
printf "Type variable '%s' is unbound" (show ty)
show (SimpleError msg) = msg


data TCWarning = TCWarning Backtrace Warning
instance Show TCWarning where
show (TCWarning [] w) =
Expand Down
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