testing: add -fullpath to go test

When -test.fullpath flag is provided to go test,
go test displays the full file names in error messages.

Fixes #37708

Change-Id: I6096e75ed816fd42205810f20624e495047a73a2
Reviewed-on: https://go-review.googlesource.com/c/go/+/463837
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>

src/cmd/go/alldocs.go

@@ -2987,6 +2987,9 @@
 //	-failfast
 //	    Do not start new tests after the first test failure.
 //
+//	-fullpath
+//	    Show full file names in the error messages.
+//
 //	-fuzz regexp
 //	    Run the fuzz test matching the regular expression. When specified,
 //	    the command line argument must match exactly one package within the

src/cmd/go/internal/test/flagdefs.go

@@ -19,6 +19,7 @@ var passFlagToTest = map[string]bool{
 	"cpu":                  true,
 	"cpuprofile":           true,
 	"failfast":             true,
+	"fullpath":             true,
 	"fuzz":                 true,
 	"fuzzminimizetime":     true,
 	"fuzztime":             true,

src/cmd/go/internal/test/test.go

@@ -240,6 +240,9 @@ control the execution of any test:
 	-failfast
 	    Do not start new tests after the first test failure.
 
+	-fullpath
+	    Show full file names in the error messages.
+
 	-fuzz regexp
 	    Run the fuzz test matching the regular expression. When specified,
 	    the command line argument must match exactly one package within the

src/cmd/go/internal/test/testflag.go

@@ -50,6 +50,7 @@ func init() {
 	cf.StringVar(&testCPUProfile, "cpuprofile", "", "")
 	cf.Bool("failfast", false, "")
 	cf.StringVar(&testFuzz, "fuzz", "", "")
+	cf.Bool("fullpath", false, "")
 	cf.StringVar(&testList, "list", "", "")
 	cf.StringVar(&testMemProfile, "memprofile", "", "")
 	cf.String("memprofilerate", "", "")

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

@@ -0,0 +1,21 @@
+[short] skip
+
+# test with -fullpath
+! go test ./x/... -fullpath
+stdout '^ +.+/gopath/src/x/fullpath/fullpath_test.go:8: test failed'
+# test without -fullpath
+! go test ./x/...
+stdout '^ +fullpath_test.go:8: test failed'
+
+-- go.mod --
+module example
+-- x/fullpath/fullpath_test.go --
+package fullpath_test
+
+import (
+	"testing"
+)
+
+func TestFullPath(t *testing.T) {
+	t.Error("test failed")
+}

src/testing/testing.go

@@ -441,6 +441,7 @@ func Init() {
 	parallel = flag.Int("test.parallel", runtime.GOMAXPROCS(0), "run at most `n` tests in parallel")
 	testlog = flag.String("test.testlogfile", "", "write test action log to `file` (for use only by cmd/go)")
 	shuffle = flag.String("test.shuffle", "off", "randomize the execution order of tests and benchmarks")
+	fullPath = flag.Bool("test.fullpath", false, "show full file names in error messages")
 
 	initBenchmarkFlags()
 	initFuzzFlags()
@@ -472,6 +473,7 @@ var (
 	parallel             *int
 	shuffle              *string
 	testlog              *string
+	fullPath             *bool
 
 	haveExamples bool // are there examples?
 
@@ -751,8 +753,9 @@ func (c *common) decorate(s string, skip int) string {
 	file := frame.File
 	line := frame.Line
 	if file != "" {
-		// Truncate file name at last file name separator.
+		if *fullPath {
-		if index := strings.LastIndex(file, "/"); index >= 0 {
+			// If relative path, truncate file name at last file name separator.
+		} else if index := strings.LastIndex(file, "/"); index >= 0 {
 			file = file[index+1:]
 		} else if index = strings.LastIndex(file, "\\"); index >= 0 {
 			file = file[index+1:]