internal/coverage/decodemeta: mishandled function literal flag in covdata read

[thanm]

What version of Go are you using (go version)?

$ go version
go version devel go1.21-46d19b3ac9 Thu Jan 19 10:19:48 2023 -0500 linux/amd64

Does this issue reproduce with the latest release?

Only on tip / go 1.20

What operating system and processor architecture are you using (go env)?

linux/amd64

What did you do?

Build this program with "-cover" and run to collect coverage profile.

https://go.dev/play/p/Gs7UJrWz86r?v=gotip

E.g.

$ go build -o prog.exe -cover prog.go
$ mkdir /tmp/covdata
$ GOCOVERDIR=/tmp/covdata ./prog.exe
$ go tool covdata func -i=tmp/covdata
...

What did you expect to see?

Coverage profile includes "main".

What did you see instead?

Coverage profile is missing "main":

$ go tool covdata func -i=/tmp/covdata
/tmp/prog.go:5:	*Atyp.Set	100.0%
/tmp/prog.go:9:	Atyp.Get	100.0%
total                        (statements)	100.0%
$

What's happening here is that there is a coding error in the handling of the function literal flag in the meta-data decoder., this code here:

	lit := d.r.ReadULEB128()
	if lit != 0 {
		f.Lit = true
	}

is written incorrectly. The update to f.Lit should be unconditional (since we can't make any assumptions about the state of the FuncDesc passed in). If clients always pass in a zero FuncDesc everything will appear to work ok, but if not, the state of the "Lit" field will be whatever it was set to on the last go around.

[gopherbot]

Change https://go.dev/cl/462955 mentions this issue: internal/coverage/decodemeta: fix coding error in func literal handling

[cherrymui]

Do you plan to get this in to Go 1.20? If so, you may want to comment on #57854. Thanks.

[thanm]

Thanks Cherry. Yes, I personally think this change is appropriate for 1.20. I'll add a note.

[gopherbot]

Change https://go.dev/cl/463418 mentions this issue: [release-branch.go1.20] internal/coverage/decodemeta: fix coding error in func literal handling