cmd/go: enable -x in go mod graph

Updates #35849

Change-Id: Ifa18e448c0d436c18d7204ac755cd36bc28cd612
Reviewed-on: https://go-review.googlesource.com/c/go/+/448935
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/go/alldocs.go

@@ -1248,7 +1248,7 @@
 //
 // Usage:
 //
-//	go mod graph [-go=version]
+//	go mod graph [-go=version] [-x]
 //
 // Graph prints the module requirement graph (with replacements applied)
 // in text form. Each line in the output has two space-separated fields: a module
@@ -1259,6 +1259,8 @@
 // given Go version, instead of the version indicated by the 'go' directive
 // in the go.mod file.
 //
+// The -x flag causes graph to print the commands graph executes.
+//
 // See https://golang.org/ref/mod#go-mod-graph for more about 'go mod graph'.
 //
 // # Initialize new module in current directory

src/cmd/go/internal/modcmd/graph.go

@@ -12,13 +12,14 @@ import (
 	"os"
 
 	"cmd/go/internal/base"
+	"cmd/go/internal/cfg"
 	"cmd/go/internal/modload"
 
 	"golang.org/x/mod/module"
 )
 
 var cmdGraph = &base.Command{
-	UsageLine: "go mod graph [-go=version]",
+	UsageLine: "go mod graph [-go=version] [-x]",
 	Short:     "print module requirement graph",
 	Long: `
 Graph prints the module requirement graph (with replacements applied)
@@ -30,6 +31,8 @@ The -go flag causes graph to report the module graph as loaded by the
 given Go version, instead of the version indicated by the 'go' directive
 in the go.mod file.
 
+The -x flag causes graph to print the commands graph executes.
+
 See https://golang.org/ref/mod#go-mod-graph for more about 'go mod graph'.
 	`,
 	Run: runGraph,
@@ -41,6 +44,7 @@ var (
 
 func init() {
 	cmdGraph.Flag.Var(&graphGo, "go", "")
+	cmdGraph.Flag.BoolVar(&cfg.BuildX, "x", false, "")
 	base.AddChdirFlag(&cmdGraph.Flag)
 	base.AddModCommonFlags(&cmdGraph.Flag)
 }

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

@@ -4,6 +4,11 @@ go mod graph
 stdout '^m rsc.io/quote@v1.5.2$'
 stdout '^rsc.io/quote@v1.5.2 rsc.io/sampler@v1.3.0$'
 ! stdout '^m rsc.io/sampler@v1.3.0$'
+! stderr 'get '$GOPROXY
+
+rm $GOPATH/pkg/mod/cache/download/rsc.io/quote
+go mod graph -x
+stderr 'get '$GOPROXY
 
 -- go.mod --
 module m

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

@@ -57,7 +57,7 @@ stdout '^example.net/requireincompatible@v0.1.0 example.com/retract/incompatible
 # Unsupported go versions should be rejected, since we don't know
 # what versions they would report.
 ! go mod graph -go=1.99999999999
-stderr '^invalid value "1\.99999999999" for flag -go: maximum supported Go version is '$goversion'\nusage: go mod graph \[-go=version\]\nRun ''go help mod graph'' for details.$'
+stderr '^invalid value "1\.99999999999" for flag -go: maximum supported Go version is '$goversion'\nusage: go mod graph \[-go=version\] \[-x\]\nRun ''go help mod graph'' for details.$'
 
 
 -- go.mod --