#7092: Spurious shadowing warnings for names generated with newName
-----------------------------------------------+----------------------------
Reporter: a.ulrich | Owner:
Type: bug | Status: new
Priority: normal | Component: Template
Haskell
Version: 7.4.2 | Keywords:
Os: Linux | Architecture: x86
Failure: Incorrect warning at compile-time | Testcase:
Blockedby: | Blocking:
Related: |
-----------------------------------------------+----------------------------
When multiple names are generated with newName in the same scope and with
the same prefix argument for newName, ghc -Wall generates shadowing
warnings although the names should be unique and no shadowing actually
happens.
{{{
{-# LANGUAGE TemplateHaskell #-}
module A where
import Language.Haskell.TH
code :: Q Exp
code = do
n1 <- newName "foo"
n2 <- newName "foo"
letE [valD (varP n1) (normalB [| (1 :: Int) |]) []]
$ letE [valD (varP n2) (normalB [| (2 :: Int) |]) []]
$ appE (appE [| ((+) :: Int -> Int -> Int)|] (varE n1)) (varE n2)
}}}
When loaded in ghci (7.4.2), warnings are generated:
{{{
[au@lift Trash]$ ghci -XTemplateHaskell -Wall -ddump-splices
GHCi, version 7.4.2: http://www.haskell.org/ghc/ :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Prelude> :l a
[1 of 1] Compiling A ( a.hs, interpreted )
Ok, modules loaded: A.
*A> $(code)
Loading package pretty-1.1.1.0 ... linking ... done.
Loading package array-0.4.0.0 ... linking ... done.
Loading package deepseq-1.3.0.0 ... linking ... done.
Loading package containers-0.4.2.1 ... linking ... done.
Loading package template-haskell ... linking ... done.
<interactive>:3:3-6: Splicing expression
code
======>
let foo_aYh = 1 :: Int in
let foo_aYi = 2 :: Int in (+) :: Int -> Int -> Int foo_aYh foo_aYi
<interactive>:3:3-6: Splicing expression
code
======>
let foo_aYp = 1 :: Int in
let foo_aYq = 2 :: Int in (+) :: Int -> Int -> Int foo_aYp foo_aYq
<interactive>:3:3-6: Splicing expression
code
======>
let foo_aYx = 1 :: Int in
let foo_aYy = 2 :: Int in (+) :: Int -> Int -> Int foo_aYx foo_aYy
<interactive>:3:3-6: Splicing expression
code
======>
let foo_aYJ = 1 :: Int in
let foo_aYK = 2 :: Int in (+) :: Int -> Int -> Int foo_aYJ foo_aYK
<interactive>:3:3:
Warning: This binding for `foo' shadows the existing binding
bound at <interactive>:3:3
<interactive>:3:3:
Warning: This binding for `foo' shadows the existing binding
bound at <interactive>:3:3
3
*A>
}}}
The spliced code looks like what I would expect: n1 and n2 are unique-
looking names. The result is 3, so n1 does not actually seem to be
shadowed by n2. Interestingly, the warnings only refer to the prefix "foo"
and do not include the suffix appended by newName.
{{{
[au@lift Repositories]$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.7/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian
4.7.1-5' --with-bugurl=file:///usr/share/doc/gcc-4.7/README.Bugs
--enable-languages=c,c++,go,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.7 --enable-shared --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.7
--libdir=/usr/lib --enable-nls --with-sysroot=/
--enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-gnu-unique-object
--enable-plugin --enable-objc-gc --with-arch-32=i586
--with-tune=generic --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 4.7.1 (Debian 4.7.1-5)
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7092>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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