[Issue 14464] New: coverage merge doesn't work

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=14464

          Issue ID: 14464
           Summary: coverage merge doesn't work
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: druntime
          Assignee: nobody at puremagic.com
          Reporter: code at dawg.eu

Using dmd_coverSetMerge(true) to combine the coverage results of multiple runs
produces garbage numbers, because the code in rt.cover that parses the existing
.lst files is broken [¹].

Enabling merge only works if .lst files already exist, otherwise coverage
generation is silently skipped.

Merging coverage reports should be the default, similar to gcov and dmd's
-prof, as overwriting existing data is rarely useful.

[¹]:
https://github.com/D-Programming-Language/druntime/blob/111892fa6ac6bb2005f4f13b4c6bad98399f65b1/src/rt/cover.d#L174

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