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Simon Peyton Jones authored
This is a long-standing bug. A nested (non-top-level) binder in Core should not have an External Name, like M.x. But - Lint was not checking this invariant - The desugarer could generate programs that failed the invariant. An example is in tests/deSugar/should_compile/T13043, which had let !_ = M.scState in ... This desugared to let ds = case M.scSate of M.scState { DEFAULT -> () } in case ds of () -> ... We were wrongly re-using that scrutinee as a case binder. And Trac #13043 showed that could ultimately lead to two top-level bindings with the same closure name. Alas! - The desugarer had one other place (in DsUtils.mkCoreAppDs) that could generate bogus code This patch fixes all three bugs, and adds a regression test.
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