go test -coverprofile fails under Go 1.20

[prymitive]

I've upgraded go to 1.20 and suddenly I'm getting this error from testscript:

cannot merge cover profiles: cannot merge coverage profile from ...: no lines found in profile: <nil>

Seems like it might be related to coverage changes documented here: https://go.dev/testing/coverage/

Removing -coverprofile-... flag allows my tests to pass.

[mvdan]

You're absolutely right, and I've been noticing these failures with Go tip for some weeks now.

I wrote our code to collect and merge coverage profiles years ago, before upstream planned on doing the same, but properly :) So our code is not just obsolete, but also apparently broken now. I need to delete it, and check that the new go test -cover works for testscript just like our hacky stuff did.

[mvdan]

Release done: https://github.com/rogpeppe/go-internal/releases/tag/v1.10.0

[nbgraham]

I was also getting this error. Updating to latest (v1.12.0) fixed the error, but I'm not getting the total coverage.

In this walkthrough, it shows that running go test -coverprofile=cover.out
will output something like

PASS
coverage: 0.0% of statements
total coverage: 100.0% of statements

But mine shows

PASS
coverage: 100.0% of statements

with no total coverage line. The cover.out file is created, but only with coverage on main.go, not the other files in other packages that actually contain the functionality of the CLI tool.

Everything else works. I have multiple test passing and changing the expected values fails the tests as expected. It seems that everything is being run correctly.

Do I need to enable something to get the total coverage?

I'm using Go 1.21.

[nbgraham]

I found the same in the example repo
I updated to Go 1.20 and https://github.com/rogpeppe/go-internal/releases/tag/v1.10.0 and did not see the total coverage: 100.0% of statements line

I set up a test repo. I can't get deep coverage, only one package down, it seems.
https://github.com/nbgraham/go-calculator-cli

[mvdan]

Ignore the old output saying "total coverage"; the new output simply outputs that percentage directly.