cmd/go: re-enable build JSON from go test -json, now with GODEBUG

This re-enables the behavior of CL 536399 (by effectively reverting CL
628955), so now go test -json again includes build output and failures
as JSON rather than text.

However, since this behavior is clearly enough to trip up some build
systems, this CL includes a GODEBUG=gotestjsonbuildtext that can be
set to 1 to revert to the old behavior.

Fixes #70402.
Updates #62067.

Cq-Include-Trybots: luci.golang.try:gotip-darwin-arm64_13,gotip-linux-amd64-longtest,gotip-windows-amd64-longtest
Change-Id: I84e778cd844783dacfc83433e391b5ccb5925127
Reviewed-on: https://go-review.googlesource.com/c/go/+/629335
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Austin Clements <austin@google.com>

Author: aclements

doc/godebug.md

@@ -168,6 +168,14 @@ For Go 1.24, it now defaults to multipathtcp="2", thus
 enabled by default on listerners. Using multipathtcp="0" reverts to the
 pre-Go 1.24 behavior.
 
+Go 1.24 changed the behavior of `go test -json` to emit build errors as JSON
+instead of text.
+These new JSON events are distinguished by new `Action` values,
+but can still cause problems with CI systems that aren't robust to these events.
+This behavior can be controlled with the `gotestjsonbuildtext` setting.
+Using `gotestjsonbuildtext=1` restores the 1.23 behavior.
+This setting will be removed in a future release, Go 1.28 at the earliest.
+
 ### Go 1.23
 
 Go 1.23 changed the channels created by package time to be unbuffered

doc/next/3-tools.md

@@ -4,9 +4,13 @@
 
 The `go build` and `go install` commands now accept a `-json` flag that reports
 build output and failures as structured JSON output on standard output.
-Furthermore, passing `-json` to `go test` now reports build output and failures
-in addition to test results in JSON. For details of the reporting format, see
-`go help buildjson`.
+For details of the reporting format, see `go help buildjson`.
+
+Furthermore, `go test -json` now reports build output and failures in JSON,
+interleaved with test result JSON.
+These are distinguished by new `Action` types, but if they cause problems in
+a test integration system, you can revert to the text build output by setting
+`GODEBUG=gotestjsonbuildtext=1`.
 
 ### Cgo {#cgo}
 

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

@@ -6,11 +6,13 @@ package test
 
 import (
 	"cmd/go/internal/base"
+	"cmd/go/internal/cfg"
 	"cmd/go/internal/cmdflag"
 	"cmd/go/internal/work"
 	"errors"
 	"flag"
 	"fmt"
+	"internal/godebug"
 	"os"
 	"path/filepath"
 	"strconv"
@@ -25,6 +27,8 @@ import (
 // our command line are for us, and some are for the test binary, and
 // some are for both.
 
+var gotestjsonbuildtext = godebug.New("gotestjsonbuildtext")
+
 func init() {
 	work.AddBuildFlags(CmdTest, work.OmitVFlag|work.OmitJSONFlag)
 
@@ -33,7 +37,6 @@ func init() {
 	cf.StringVar(&testO, "o", "", "")
 	work.AddCoverFlags(CmdTest, &testCoverProfile)
 	cf.Var((*base.StringsFlag)(&work.ExecCmd), "exec", "")
-	// TODO(austin): Make test -json imply build -json.
 	cf.BoolVar(&testJSON, "json", false, "")
 	cf.Var(&testVet, "vet", "")
 
@@ -354,8 +357,11 @@ func testFlags(args []string) (packageNames, passToTest []string) {
 		delete(addFromGOFLAGS, "v")
 		delete(addFromGOFLAGS, "test.v")
 
-		// TODO(austin,#70402): Re-enable this once LUCI can handle build JSON in the test stream.
-		//cfg.BuildJSON = true
+		if gotestjsonbuildtext.Value() == "1" {
+			gotestjsonbuildtext.IncNonDefault()
+		} else {
+			cfg.BuildJSON = true
+		}
 	}
 
 	// Inject flags from GOFLAGS before the explicit command-line arguments.

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

@@ -1,8 +1,7 @@
-# TODO(austin,#70402)
-skip
-
 [short] skip
 
+env GODEBUG=gotestjsonbuildtext=0
+
 # There are several places where paths appear in JSON in regexps here.
 # For the path separator we use (/|\\\\).
 # Unfortunately, we can't just use ${/} because, while script test automatically
@@ -52,6 +51,16 @@ stdout '"Action":"output","Package":"m/veterror","Output":"FAIL\\tm/veterror \[b
 stdout '"Action":"fail","Package":"m/veterror","Elapsed":.*,"FailedBuild":"m/veterror \[m/veterror.test\]"'
 ! stderr '.'
 
+# Test that the GODEBUG fallback works.
+env GODEBUG=gotestjsonbuildtext=1
+! go test -json -o=$devnull ./builderror
+stderr '# m/builderror \[m/builderror.test\]\n'
+stderr 'builderror'${/}'main_test.go:3:11: undefined: y\n'
+stdout '"Action":"start","Package":"m/builderror"'
+stdout '"Action":"output","Package":"m/builderror","Output":"FAIL\\tm/builderror \[build failed\]\\n"'
+stdout '"Action":"fail","Package":"m/builderror","Elapsed":.*,"FailedBuild":"m/builderror \[m/builderror\.test\]"'
+
+
 -- go.mod --
 module m
 go 1.21

src/internal/godebugs/table.go

@@ -30,6 +30,7 @@ var All = []Info{
 	{Name: "gocachehash", Package: "cmd/go"},
 	{Name: "gocachetest", Package: "cmd/go"},
 	{Name: "gocacheverify", Package: "cmd/go"},
+	{Name: "gotestjsonbuildtext", Package: "cmd/go", Changed: 24, Old: "1"},
 	{Name: "gotypesalias", Package: "go/types", Changed: 23, Old: "0"},
 	{Name: "http2client", Package: "net/http"},
 	{Name: "http2debug", Package: "net/http", Opaque: true},

src/runtime/metrics/doc.go

@@ -250,6 +250,11 @@ Below is the full list of supported metrics, ordered lexicographically.
 		The number of non-default behaviors executed by the cmd/go
 		package due to a non-default GODEBUG=gocacheverify=... setting.
 
+	/godebug/non-default-behavior/gotestjsonbuildtext:events
+		The number of non-default behaviors executed by the cmd/go
+		package due to a non-default GODEBUG=gotestjsonbuildtext=...
+		setting.
+
 	/godebug/non-default-behavior/gotypesalias:events
 		The number of non-default behaviors executed by the go/types
 		package due to a non-default GODEBUG=gotypesalias=... setting.