[Issue 16994] New: Apparently faulty symbol resolution in some cases

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=16994

          Issue ID: 16994
           Summary: Apparently faulty symbol resolution in some cases
           Product: D
           Version: D2
          Hardware: x86
                OS: Mac OS X
            Status: NEW
          Severity: major
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: meapineapple at gmail.com

This error is occurring in a large project I'm working on as of this commit:
https://github.com/pineapplemachine/mach.d/commit/e1f7f91db0293ef24a974398fb598bbba3e9f336

These tests can be reproduced by running the following command:
rdmd -I"path/to/cloned/repo/mach.d" -debug -g -unittest --main
"path/to/module.d"

When this module is compiled using rdmd, dmd v2.072.0 on OSX Mavericks, unit
tests pass:
https://github.com/pineapplemachine/mach.d/blob/e1f7f91db0293ef24a974398fb598bbba3e9f336/mach/range/map/plural.d

When this module, which imports the above plural.d, is compiled by the same
means, the unit tests for that module, mach/range/map/plural.d, fail:
https://github.com/pineapplemachine/mach.d/blob/e1f7f91db0293ef24a974398fb598bbba3e9f336/mach/range/readme.d

When this module, which imports the above mach/range/readme.d, is compiled by
the same means, the unit tests for all modules - including
mach/range/map/plural.d - pass. Same goes for every other module that I have
tried compiling and running tests for, which also import the above modules:
https://github.com/pineapplemachine/mach.d/blob/e1f7f91db0293ef24a974398fb598bbba3e9f336/mach/range/package.d

I have verified that in all the above cases, the unit tests are indeed being
evaluated; the apparent success of the tests cannot be due to the tests simply
being skipped.

One of the dependencies of mach/range/map/plural.d is mach/meta/varreduce.d as
seen here:
https://github.com/pineapplemachine/mach.d/blob/e1f7f91db0293ef24a974398fb598bbba3e9f336/mach/meta/varreduce.d

varreduce.d defines `varreduce`, which performs a reduce HOF upon a sequence of
variadic arguments. It also defines a number of functions abstracting and
calling `varreduce`, including `varmin`, which finds the minimum, and `varsum`,
which calculates the sum. For example, `varmin(4, 2, 5) == 2` and `varsum(4, 2,
5) == 11`.

The `length` property of `MapPluralRange` defined in plural.d uses `varmin` to
calculate the minimum length of several constituent ranges. (It may help to
think of this range as a sort of `zip`, where the length of the resulting range
is equivalent to the length of its shortest input.) Except for when these tests
are performed as a result of compiling the aforementioned readme.d, this
property behaves as expected and does in fact return the shortest length.

When tests are performed as a result of compiling readme.d, the shortest length
is returned when there are two or fewer member ranges. (i.e. `varmin` receives
two or fewer arguments.) When there are three or more member ranges, the
`length` property returns the sum of the lengths instead of the minimum, as
though symbol lookup were causing the implementation of `varsum` to be
evaluated instead of `varmin`. This behavior has remained consistent across a
number of different test cases. I have been unable to reproduce it in any case
except for the compilation and testing of mach/range/readme.d.

All of the dependencies of that `length` property, including `varmin`, are
thoroughly unit tested and the level of verification makes it very unlikely
that this issue could result from an incorrect implementation of any of those
dependencies.

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