#3398: Unicode output in GHC
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Reporter: simonmar | Owner:
Type: bug | Status: new
Priority: high | Milestone: 6.12.1
Component: Compiler | Version: 6.11
Severity: normal | Keywords:
Difficulty: Unknown | Testcase: 2816
Os: Unknown/Multiple | Architecture: Unknown/Multiple
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Unicode output is somewhat broken in GHC as a whole. We should fix it
properly.
Most output is generated by the Pretty module. Pretty has two ways to
output:
* `printLeftRender`, which is used when the rendering mode is `LeftMode`.
This method uses the `BufWrite` module to speed up output. For
`FastStrings`,
the output will be in UTF-8, for strings and other characters the
output
takes the low 8 bits of each character.
* `printDoc`, when used in modes other than `LeftMode` (e.g. for things
like
error messages and `-ddump`), calls `hPutStr` for strings which uses
the
prevailing encoding on stdout. However, it calls `hPutFS` for
`FastStrings`,
which always emits UTF-8.
* In GHCi, there is an additional layer due to Haskeline, which pipes all
the
output through its own decoder (or tries to, I think there are cases
not
covered).
This is all a bit of a mess.
We should be using the Unicode layer in the IO library for all
encoding/decoding now. I suggest that:
* we leave `printLeftRender` alone. It is used for printing things like
the
`.s` file, and never outputs any Unicode characters because everything
is
Z-encoded.
* `printDoc`, instead of `hPutFS`, should use `hPutStr . decodeFS`
* We get rid of the Haskeline decoding layer.
However, this will introduce a regression on Windows, because the
Haskeline encoding layer currently does code-page encoding. Judah has
mentioned looking at doing code-page encoding in the GHC IO library, so
let's see what happens there.
Once this is done, we can do #2507 (quotation characters in error
messages).
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3398>
GHC <http://www.haskell.org/ghc/>
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