Origin preservation

[Virtlink]

Origin tracking allows to see the original (source) terms a transformed term belongs to. This is used, for example, to put error messages in the source code. Origin tracking/preservation in Stratego and Spoofax is currently broken: origins are only preserved for the all, some, and one built-in Stratego strategies.

This issue tracks work on fixing origin preservation.

• Implement performance benchmarks for Stratego
• Measure current Stratego performance
• Implement origin tracking in main ITermFactory implementation Add buildX methods to ITermFactory that preserve the origin of the replaced term #20
• Write tests for origin tracking in main ITermFactory implementation
• Change Stratego compiler to generate code to call the new ITermFactory origin preserving methods
• Measure new Stratego performance
• Fix any performance regressions

@Apanatshka outlines the background and ideas here. In its essence, it boils down to implementing origin preservation (that is, copy the origin of a source term instead of taking the source term as the origin, as in origin tracking) by taking the origin of the input term when building a new term (!C()). In many situations, such as congruences, rules, and where-clauses, the Stratego code is desugared down to basic Stratego match and build strategies. Origin tracking on terms build is expected to solve 90% of origin preservation problems, but might have some implications on performance and effects on compiler optimizations.