tsc --build mode: "<package> is out of date", when it is up-to-date

[yortus]

TypeScript Version: 3.0.0-dev.20180630

Search Terms:
build mode, out of date, incremental

Steps to Reproduce

Set up @RyanCavanaugh's learn-a sample repo as per his instructions. Run tsc -b packages --verbose to see everything gets built the first time. Now add an empty declaration file at pkg1/src/bar.d.ts. Run tsc -b packages --verbose several more times in succession.

Expected behavior:

Build for pkg1 should be skipped since its output is up-to-date. pkg1/src/bar.d.ts is never going to generate any output.

Actual behavior:

On every build, tsc reports Project 'packages/pkg1/tsconfig.json' is out of date because output file 'packages/pkg1/lib/bar.js' does not exist, and re-builds pkg1.

Related Issues:

#3469