Bug 17300 – Enable setting code coverage options on the command line

The core.runtime functions dmd_coverSetMerge, dmd_coverSourcePath, and dmd_coverDestPath are quite use when generating code coverage reports. This is especially true when generating reports involving multiple runs, multiple executable sharing code, etc. The main downside is that they are only available from the source code being compiled. It would be much more flexible to have a run-time configurable setting. One use case is with unit tests run directly as result of a compiler build line. Another is building an executable with code coverage turned on, then running the executable multiple times for tests. One solution might be to use "--DRT-<option>" command line arguments, similar to those used to set GC options on the command line. (See https://dlang.org/spec/garbage.html#gc_config). These are nice because they are processed and removed prior to any other command line argument processing.

Commit pushed to master at https://github.com/dlang/druntime https://github.com/dlang/druntime/commit/269d720186185c51df3560b066bee4cbe9fbeb7e Fix issue 17300 - Make coverage reports configurable via --DRT-covopt The coverage module has a couple of options that can be set through some weirdly looking dmd_coverSetMerge(), dmd_coverSourcePath() and dmd_coverDestPath() functions (I guess the dmd prefix comes from pre-druntime times). These options don't only use non standard names, they also don't use the standard --DRT-xxx / DRT_XXX runtime options passing mechanism, and they can only be overridden in code. This commit plugs the runtime options mechanism and adds support to set these options via --DRT-covopt (and matching environment variables), providing the sub-options merge, dstpath and srcpath. The old functions are kept for backwards compatibility (they are used by DMD itself for example), but should probably be removed in some distant future.

Commit pushed to stable at https://github.com/dlang/druntime https://github.com/dlang/druntime/commit/269d720186185c51df3560b066bee4cbe9fbeb7e Fix issue 17300 - Make coverage reports configurable via --DRT-covopt