runtime/coverage: out-of-bounds panic in `VisitFuncs` via `processCoverTestDir`

[gopherbot]

#!watchflakes
post <- log ~ `panic: runtime error: slice bounds out of range` && log ~ `^\s*runtime/coverage\.\(\*emitState\)\.VisitFuncs`

Issue created automatically to collect these failures.

Example (log):

vcs-test.golang.org rerouted to http://127.0.0.1:43053
https://vcs-test.golang.org rerouted to https://127.0.0.1:44521
go test proxy running at GOPROXY=http://127.0.0.1:40533/mod
2023/11/14 16:00:23 http: TLS handshake error from 127.0.0.1:50386: read tcp 127.0.0.1:44521->127.0.0.1:50386: read: connection reset by peer
2023/11/14 16:00:39 http: TLS handshake error from 127.0.0.1:50772: read tcp 127.0.0.1:44521->127.0.0.1:50772: read: connection reset by peer
2023/11/14 16:00:39 http: TLS handshake error from 127.0.0.1:50792: read tcp 127.0.0.1:44521->127.0.0.1:50792: read: connection reset by peer
2023/11/14 16:00:39 http: TLS handshake error from 127.0.0.1:50780: EOF
2023/11/14 16:00:44 http: TLS handshake error from 127.0.0.1:50906: EOF
2023/11/14 16:00:44 http: TLS handshake error from 127.0.0.1:50916: EOF
2023/11/14 16:00:44 http: TLS handshake error from 127.0.0.1:50922: EOF
...
--- FAIL: TestScript (0.06s)
    --- FAIL: TestScript/cover_pkgall_runtime (6.05s)
        script_test.go:132: 2023-11-14T16:01:03Z
        script_test.go:134: $WORK=/workdir/tmp/cmd-go-test-1942127129/tmpdir4285299461/cover_pkgall_runtime1388929147
        script_test.go:156: 
            > env GO111MODULE=off
            # Issue 23882 (6.045s)
            > [short] skip
            [condition not met]
            > go test -coverpkg=all x
...
            testing.(*M).Run.deferwrap1()
            	/workdir/go/src/testing/testing.go:2004 +0x27 fp=0xa104df8 sp=0xa104df0 pc=0x820cd67
            testing.(*M).Run(0xa05e0a0)
            	/workdir/go/src/testing/testing.go:2055 +0x12fb fp=0xa104f68 sp=0xa104df8 pc=0x820c99b
            main.main()
            	_testmain.go:81 +0x195 fp=0xa104fac sp=0xa104f68 pc=0x822e025
            runtime.main()
            	/workdir/go/src/runtime/proc.go:271 +0x4e7 fp=0xa104ff0 sp=0xa104fac pc=0x80b9c07
            runtime.goexit({})
            	/workdir/go/src/runtime/asm_386.s:1363 +0x1 fp=0xa104ff4 sp=0xa104ff0 pc=0x81141d1

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "cmd/go" && test == "TestScript"

2023-11-14 15:24 linux-386-longtest go@31f0af1e cmd/go.TestScript (log)

vcs-test.golang.org rerouted to http://127.0.0.1:43053
https://vcs-test.golang.org rerouted to https://127.0.0.1:44521
go test proxy running at GOPROXY=http://127.0.0.1:40533/mod
2023/11/14 16:00:23 http: TLS handshake error from 127.0.0.1:50386: read tcp 127.0.0.1:44521->127.0.0.1:50386: read: connection reset by peer
2023/11/14 16:00:39 http: TLS handshake error from 127.0.0.1:50772: read tcp 127.0.0.1:44521->127.0.0.1:50772: read: connection reset by peer
2023/11/14 16:00:39 http: TLS handshake error from 127.0.0.1:50792: read tcp 127.0.0.1:44521->127.0.0.1:50792: read: connection reset by peer
2023/11/14 16:00:39 http: TLS handshake error from 127.0.0.1:50780: EOF
2023/11/14 16:00:44 http: TLS handshake error from 127.0.0.1:50906: EOF
2023/11/14 16:00:44 http: TLS handshake error from 127.0.0.1:50916: EOF
2023/11/14 16:00:44 http: TLS handshake error from 127.0.0.1:50922: EOF
...
--- FAIL: TestScript (0.06s)
    --- FAIL: TestScript/cover_pkgall_runtime (6.05s)
        script_test.go:132: 2023-11-14T16:01:03Z
        script_test.go:134: $WORK=/workdir/tmp/cmd-go-test-1942127129/tmpdir4285299461/cover_pkgall_runtime1388929147
        script_test.go:156: 
            > env GO111MODULE=off
            # Issue 23882 (6.045s)
            > [short] skip
            [condition not met]
            > go test -coverpkg=all x
...
            testing.(*M).Run.deferwrap1()
            	/workdir/go/src/testing/testing.go:2004 +0x27 fp=0xa104df8 sp=0xa104df0 pc=0x820cd67
            testing.(*M).Run(0xa05e0a0)
            	/workdir/go/src/testing/testing.go:2055 +0x12fb fp=0xa104f68 sp=0xa104df8 pc=0x820c99b
            main.main()
            	_testmain.go:81 +0x195 fp=0xa104fac sp=0xa104f68 pc=0x822e025
            runtime.main()
            	/workdir/go/src/runtime/proc.go:271 +0x4e7 fp=0xa104ff0 sp=0xa104fac pc=0x80b9c07
            runtime.goexit({})
            	/workdir/go/src/runtime/asm_386.s:1363 +0x1 fp=0xa104ff4 sp=0xa104ff0 pc=0x81141d1

— watchflakes

[bcmills]

(attn @thanm)

[gopherbot]

Sorry, but there were parse errors in the watch flakes script.
The script I found was:

#!watchflakes
post <- log ~ `panic: runtime error: slice bounds out of range` && log ~ `^\s*runtime/coverage\.\(\*emitState\)\.VisitFuncs

And the problems were:

script:2.74: newline in backquoted regexp

See https://go.dev/wiki/Watchflakes for details.

— watchflakes