From 6ed6c110c874a746b002aca148192c3cbc819d7f Mon Sep 17 00:00:00 2001 From: Alec Theriault Date: Fri, 5 Jan 2018 09:59:59 -0800 Subject: Fix infinite loop when specializing instance heads (#723) * Fix infinite loop when specializing instance heads The bug can only be triggered from TH, hence why it went un-noticed for so long. * Add test for #679 and #710 --- html-test/ref/Bug679.html | 196 ++++++++++++++++++++++++++++++++++++++++++++++ html-test/src/Bug679.hs | 24 ++++++ 2 files changed, 220 insertions(+) create mode 100644 html-test/ref/Bug679.html create mode 100644 html-test/src/Bug679.hs (limited to 'html-test') diff --git a/html-test/ref/Bug679.html b/html-test/ref/Bug679.html new file mode 100644 index 00000000..ddec7a12 --- /dev/null +++ b/html-test/ref/Bug679.html @@ -0,0 +1,196 @@ +Bug679

Safe Haskell	None

Bug679

Documentation

data Bar a #

Constructors

Bar

Instances

Foo (Bar a) #
Instance details Methods foo :: Bar a -> Bar a #

class Foo a where #

Minimal complete definition

foo

Methods

foo :: a -> a #

Instances

Foo (Bar a) #
Instance details Methods foo :: Bar a -> Bar a #

\ No newline at end of file diff --git a/html-test/src/Bug679.hs b/html-test/src/Bug679.hs new file mode 100644 index 00000000..dba194c4 --- /dev/null +++ b/html-test/src/Bug679.hs @@ -0,0 +1,24 @@ +{-# LANGUAGE TemplateHaskell #-} + +module Bug679 where + +import Language.Haskell.TH + +data Bar a = Bar + +$(do + a <- newName "a" + + let classN = mkName "Foo" + let methodN = mkName "foo" + + methodTy <- [t| $(varT a) -> $(varT a) |] + let cla = ClassD [] classN [PlainTV a] [] [SigD methodN methodTy] + + -- Note that we are /reusing/ the same type variable 'a' as in the class + instanceHead <- [t| $(conT classN) (Bar $(varT a)) |] + idCall <- [e| id |] + let ins = InstanceD Nothing [] instanceHead [FunD methodN [Clause [] (NormalB idCall) []]] + + pure [cla,ins]) + -- cgit v1.2.3