make -coverprofile include toolexec processes (#216)

testscript already included magic to also account for commands in the
total code coverage. That does not happen with plain tests, since those
only include coverage from the main test process.

The main problem was that, before, indirectly executed commands did not
properly save their coverage profile anywhere for testscript to collect
it at the end. In other words, we only collected coverage from direct
garble executions like "garble -help", but not indirect ones like "go
build -toolexec=garble".

	$ go test -coverprofile=cover.out
	PASS
	coverage: 3.6% of statements
	total coverage: 16.6% of statements
	ok  	mvdan.cc/garble	6.453s

After the delicate changes to testscript, any direct or indirect
executions of commands all go through $PATH and properly count towards
the total coverage:

	$ go test -coverprofile=cover.out
	PASS
	coverage: 3.6% of statements
	total coverage: 90.5% of statements
	ok  	mvdan.cc/garble	33.258s

Note that we can also get rid of our code to set up $PATH, since
testscript now does it for us.

goversion.txt needed minor tweaks, since we no longer set up $WORK/.bin.

Finally, note that we disable the reuse of $GOCACHE when collecting
coverage information. This is to do "full builds", as otherwise the
cached package builds would result in lower coverage.

Fixes #35.

go.mod

@@ -5,7 +5,7 @@ go 1.15
 require (
 	github.com/Binject/debug v0.0.0-20210101210738-1b03ff50b8a5
 	github.com/google/go-cmp v0.5.4
-	github.com/rogpeppe/go-internal v1.6.3-0.20201011174404-9f985d550aa7
+	github.com/rogpeppe/go-internal v1.7.1-0.20210131190821-dc4b49510d96
 	golang.org/x/mod v0.4.1
 	golang.org/x/tools v0.0.0-20210115202250-e0d201561e39
 )

go.sum

@@ -7,8 +7,8 @@ github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORN
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
 github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
-github.com/rogpeppe/go-internal v1.6.3-0.20201011174404-9f985d550aa7 h1:gsBBcK+87059lM2pDrOQWXGoVx9qYgoBasBMJ74eCYI=
-github.com/rogpeppe/go-internal v1.6.3-0.20201011174404-9f985d550aa7/go.mod h1:xXDCJY+GAPziupqXw64V24skbSoqbTEfhy4qGm1nDQc=
+github.com/rogpeppe/go-internal v1.7.1-0.20210131190821-dc4b49510d96 h1:E/aJC0lqUPDEdRwu6g+J/Egnf7hPxvgcaAffAvw2qkA=
+github.com/rogpeppe/go-internal v1.7.1-0.20210131190821-dc4b49510d96/go.mod h1:xXDCJY+GAPziupqXw64V24skbSoqbTEfhy4qGm1nDQc=
 github.com/yuin/goldmark v1.2.1/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=

main_test.go

@@ -10,7 +10,6 @@ import (
 	"go/ast"
 	"go/printer"
 	"go/token"
-	"io"
 	"math"
 	mathrand "math/rand"
 	"os"
@@ -67,21 +66,13 @@ func TestScripts(t *testing.T) {
 				"GOFLAGS=-mod=readonly", // TODO(mvdan): remove once we switch to Go 1.16
 				"gofullversion="+runtime.Version(),
 			)
-			bindir := filepath.Join(env.WorkDir, ".bin")
-			if err := os.Mkdir(bindir, 0o777); err != nil {
-				return err
-			}
-			binfile := filepath.Join(bindir, "garble")
-			if runtime.GOOS == "windows" {
-				binfile += ".exe"
-			}
-			if err := os.Symlink(os.Args[0], binfile); err != nil {
-				if err := copyFile(os.Args[0], binfile); err != nil { // Fallback to copy if symlink failed. Useful for Windows not elevated processes
-					return err
-				}
+
+			if os.Getenv("TESTSCRIPT_COVER_DIR") != "" {
+				// Don't reuse the build cache if we want to collect
+				// code coverage. Otherwise, many toolexec calls would
+				// be avoided and the coverage would be incomplete.
+				env.Vars = append(env.Vars, "GOCACHE="+filepath.Join(env.WorkDir, "go-cache-tmp"))
 			}
-			env.Vars = append(env.Vars, fmt.Sprintf("PATH=%s%c%s", bindir, filepath.ListSeparator, os.Getenv("PATH")))
-			env.Vars = append(env.Vars, "TESTSCRIPT_COMMAND=garble")
 			return nil
 		},
 		Cmds: map[string]func(ts *testscript.TestScript, neg bool, args []string){
@@ -99,23 +90,6 @@ func TestScripts(t *testing.T) {
 	testscript.Run(t, p)
 }
 
-func copyFile(from, to string) error {
-	writer, err := os.Create(to)
-	if err != nil {
-		return err
-	}
-	defer writer.Close()
-
-	reader, err := os.Open(from)
-	if err != nil {
-		return err
-	}
-	defer reader.Close()
-
-	_, err = io.Copy(writer, reader)
-	return err
-}
-
 type binaryCache struct {
 	name    string
 	modtime time.Time

testdata/scripts/basic.txt

@@ -27,7 +27,7 @@ stdout 'unknown'
 
 [short] stop # checking that the build is reproducible is slow
 
-# Check that we fail if the user used "go build -toolexec garble" instead of "garble build" 
+# Check that we fail if the user used "go build -toolexec garble" instead of "garble build"
 ! exec go build -a -toolexec=garble main.go
 stderr 'not running "garble \[command\]"'
 

testdata/scripts/goversion.txt

@@ -1,7 +1,9 @@
 # TODO: Place file direct to .bin directory
+mkdir .bin
 cp go.sh .bin/go
 cp go.bat .bin/go.bat
 chmod 777 .bin/go
+env PATH=.bin${:}${PATH}
 
 # Check incorrect go install
 env GO_VERSION=''