[GHC] #14381: Consider making ghc-pkg fill in abi-depends based on depends

[GHC]

#14381: Consider making ghc-pkg fill in abi-depends based on depends
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        Reporter:  ezyang            |                Owner:  tdammers
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.4.2
       Component:  ghc-pkg           |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4159
       Wiki Page:                    |
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Comment (by tdammers):

 OK, I have a patch incoming that should do the trick.

 One issue though is that there is a theoretical possibility of the same
 package database being mentioned multiple times; this would sabotage the
 "get packages below the current one in the stack" logic, because right
 now, two package databases are considered "the same" iff their locations
 are equal, and the "get packages below this one in the stack" logic
 consists of popping all package db's off the stack that are not the same
 as the "current" one. So if we have a stack like this one:

 {{{#!hs
 [ "foo/bar"
 , "baz/quux"
 , "foo/bar"
 , "pizza/olives"
 ]
 }}}

 ...and we're trying to get all the package databases below the second
 occurrence of "foo/bar", we would want to get just {{{ ["foo/bar",
 "pizza/olives"]}}}, but we will in fact get the entire stack.

 Question is whether this is ever going to be a problem in practice - I
 would assume that having the same package database in the stack more than
 once would pose all sorts of problems anyway.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14381#comment:10>
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