Fix compilation with template-haskell-2.15 (GHC-8.8) about safecopy

[RyanGlScott]

I've submitted #77 for the third bullet point.

[marco-comini]

Hi, I don't know what is going on with my system, but I have the strong impression that is not my fault but something wrong with the metadata...

I am using ghc 8.8.1

If I try to install safecopy (without version numbers) it installs safecopy-0.3 (an incredibly old version!)

cabal install --dry-run safecopy
In order, the following would be built (use -v for more details):

• safecopy-0.3 (lib:safecopy) (requires build)

while when I try explicitly the latest version

cabal install --dry-run safecopy-0.10.1
Resolving dependencies...
cabal: Could not resolve dependencies:
[__0] trying: ghc-8.8.1/installed-8.8... (user goal)
[__1] next goal: safecopy (user goal)
[__1] rejecting: safecopy-0.10.1 (conflict: ghc =>
template-haskell==2.15.0.0/installed-2.1..., safecopy =>
template-haskell<2.15)
[__1] rejecting: safecopy-0.10.0, safecopy-0.9.4.3, safecopy-0.9.4.2,
safecopy-0.9.4.1, safecopy-0.9.4, safecopy-0.9.3.3, safecopy-0.9.3.2,
safecopy-0.9.3.1, safecopy-0.9.3, safecopy-0.9.2, safecopy-0.9.1,
safecopy-0.9.0.1, safecopy-0.9.0, safecopy-0.8.6, safecopy-0.8.5,
safecopy-0.8.4, safecopy-0.8.3, safecopy-0.8.2, safecopy-0.8.1,
safecopy-0.8.0, safecopy-0.7.2, safecopy-0.7.1, safecopy-0.7.0,
safecopy-0.6.3, safecopy-0.6.2, safecopy-0.6.1, safecopy-0.6.0,
safecopy-0.5.1, safecopy-0.5, safecopy-0.4.3, safecopy-0.4.2, safecopy-0.4.1,
safecopy-0.4, safecopy-0.3, safecopy-0.2, safecopy-0.1 (constraint from user
target requires ==0.10.1)
[__1] fail (backjumping, conflict set: ghc, safecopy)
After searching the rest of the dependency tree exhaustively, these were the
goals I've had most trouble fulfilling: safecopy, ghc

[ddssff]

The current version of safecopy does indeed specify template-haskell < 2.15. There is a pull request that adds support but it hasn't been merged yet. Am I mistaken to think that template-haskell-2.15 has never worked with any version of safecopy? (Edit: I added template-haskell < 2.15 to the metadata on hackage.haskell.org recently, but I'm wondering if without that metadata the compile always failed.)

[RyanGlScott]

Am I mistaken to think that template-haskell-2.15 has never worked with any version of safecopy?

As far as I can tell, no released version of safecopy builds with template-haskell-2.15.

There is a pull request that adds support but it hasn't been merged yet.

Speaking of which, is there any reason not to merge #77 at this point?