Unconditional invalidation of macro class (without companion object) in batch mode

[jackkoenig]

Summary

From batch mode, SBT incremental compilation unconditionally invalidates a macro class if the class doesn't have a companion object.
Note that this behavior does not occur in interactive mode.

Steps

git clone git@github.com:jackkoenig/sbt-macro-dependency.git
cd sbt-macro-dependency
sbt compile
sbt compile

Problem

On the second sbt compile, the following debug message will be printed:

Invalidating /scratch/koenig/sbt-macro-dependency/macros/target/scala-2.12/classes/mymacros/MyMacro.class: could not find class mymacros.MyMacro$ on the classpath.

And then the "main" project is recompiled because it depends on MyMacro.class

Expectation

Since nothing has changed, nothing should recompile.

Notes

If you run in interactive mode and comile twice, it doesn't recompile anything (as expected).
If you add a companion object for MyMacro, it doesn't recompile anything (as expected), even in batch mode as in the issue above.

Versions

SBT Version: 1.1.1
Scala Version: 2.12.4 (also 2.11.12)

[eed3si9n]

Thanks for the report and repro project.