internal/coverage: fix bug in text-format coverage output with multiple packages

In ProcessCoverTestDir pass the selected set of packages to
EmitTextual in addition to EmitPercent, so that when we have runs with
multiple packages selected but without -coverpkg, text format output
for package P was incorrectly including output for P's covered
dependencies. This is in effect an extension of the fix for issue
65570.

Includes a cmd/go script test to verify correct behavior; ideally it
would be nice to locate this test in .../internal/coverage somewhere
but at the moment script tests are only supported for
cmd/{go,compile,link}.

Updates #65570.
Fixes #70244.

Change-Id: Ia0bb10155353aa0f2ead46e81a2aaa71bde4ef82
Reviewed-on: https://go-review.googlesource.com/c/go/+/627316
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Than McIntosh <thanm@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/go/testdata/script/cover_coverprofile_nocoverpkg.txt

@@ -0,0 +1,50 @@
+# Testcase for #70244. In this bug we're doing a "go test -coverprofile"
+# run for a pair of packages, the first one without tests and the second
+# one with tests. When writing the profile for the second test, profile
+# data from the first package was leaking into the output (we should
+# only see lines in the output profile for the package whose test is
+# being run).
+
+[short] skip
+
+# Kick off test.
+go test -vet=off -count=1 -coverprofile=cov.p ./...
+
+# Generate a function profile.
+go tool cover -func=cov.p
+
+# Prior to GOEXPERIMENT=coverageredesign we should see no output at all for
+# pkg1 (since it has no tests).
+[!GOEXPERIMENT:coverageredesign] ! stdout 'pkg1'
+
+# With GOEXPERIMENT=coverageredesign enabled we should see zero percent
+# coverage for pkg1's DoSomething, not 100% (as in the bug).
+[GOEXPERIMENT:coverageredesign] stdout 'cov/pkg1/file.go:3:\s+DoSomething\s+0.0%'
+
+-- go.mod --
+module cov
+
+-- pkg1/file.go --
+package pkg1
+
+func DoSomething() bool {
+	return true
+}
+-- pkg2/file.go --
+package pkg2
+
+func DoSomething() bool {
+	return true
+}
+-- pkg2/file_test.go --
+package pkg2
+
+import (
+	"cov/pkg1"
+	"testing"
+)
+
+func TestSmth(t *testing.T) {
+	pkg1.DoSomething()
+	DoSomething()
+}

src/internal/coverage/cfile/testsupport.go

@@ -109,7 +109,7 @@ func ProcessCoverTestDir(dir string, cfile string, cm string, cpkg string, w io.
 
 	// Emit text output.
 	if tf != nil {
-		if err := ts.cf.EmitTextual(nil, tf); err != nil {
+		if err := ts.cf.EmitTextual(selpkgs, tf); err != nil {
 			return err
 		}
 		tfClosed = true