Make record selectors into ordinary functions
This biggish patch addresses Trac #2670. The main effect is to make record selectors into ordinary functions, whose unfoldings appear in interface files, in contrast to their previous existence as magic "implicit Ids". This means that the usual machinery of optimisation, analysis, and inlining applies to them, which was failing before when the selector was somewhat complicated. (Which it can be when strictness annotations, unboxing annotations, and GADTs are involved.) The change involves the following points * Changes in Var.lhs to the representation of Var. Now a LocalId can have an IdDetails as well as a GlobalId. In particular, the information that an Id is a record selector is kept in the IdDetails. While compiling the current module, the record selector *must* be a LocalId, so that it participates properly in compilation (free variables etc). This led me to change the (hidden) representation of Var, so that there is now only one constructor for Id, not two. * The IdDetails is persisted into interface files, so that an importing module can see which Ids are records selectors. * In TcTyClDecls, we generate the record-selector bindings in renamed, but not typechecked form. In this way, we can get the typechecker to add all the types and so on, which is jolly helpful especially when GADTs or type families are involved. Just like derived instance declarations. This is the big new chunk of 180 lines of code (much of which is commentary). A call to the same function, mkAuxBinds, is needed in TcInstDcls for associated types. * The typechecker therefore has to pin the correct IdDetails on to the record selector, when it typechecks it. There was a neat way to do this, by adding a new sort of signature to HsBinds.Sig, namely IdSig. This contains an Id (with the correct Name, Type, and IdDetails); the type checker uses it as the binder for the final binding. This worked out rather easily. * Record selectors are no longer "implicit ids", which entails changes to IfaceSyn.ifaceDeclSubBndrs HscTypes.implicitTyThings TidyPgm.getImplicitBinds (These three functions must agree.) * MkId.mkRecordSelectorId is deleted entirely, some 300+ lines (incl comments) of very error prone code. Happy days. * A TyCon no longer contains the list of record selectors: algTcSelIds is gone The renamer is unaffected, including the way that import and export of record selectors is handled. Other small things * IfaceSyn.ifaceDeclSubBndrs had a fragile test for whether a data constructor had a wrapper. I've replaced that with an explicit flag in the interface file. More robust I hope. * I renamed isIdVar to isId, which touched a few otherwise-unrelated files.
Showing with 803 additions and 929 deletions