cmd/go: add go list -deps

This gives an easy way to query properties of all the deps
of a set of packages, in a single go list invocation.
Go list has already done the hard work of loading these
packages, so exposing them is more efficient than
requiring a second invocation.

This will be helpful for tools asking cmd/go about build
information.

Change-Id: I90798e386246b24aad92dd13cb9e3788c7d30e91
Reviewed-on: https://go-review.googlesource.com/107776
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/cmd/go/alldocs.go

@@ -579,7 +579,7 @@
 //
 // Usage:
 //
-// 	go list [-e] [-f format] [-json] [build flags] [packages]
+// 	go list [-deps] [-e] [-f format] [-json] [build flags] [packages]
 //
 // List lists the packages named by the import paths, one per line.
 //
@@ -683,6 +683,10 @@
 // The -json flag causes the package data to be printed in JSON format
 // instead of using the template format.
 //
+// The -deps flag causes list to iterate over not just the named packages
+// but also all their dependencies. It visits them in a depth-first post-order
+// traversal, so that a package is listed only after all its dependencies.
+//
 // The -e flag changes the handling of erroneous packages, those that
 // cannot be found or are malformed. By default, the list command
 // prints an error to standard error for each erroneous package and
@@ -1688,14 +1692,13 @@
 // 	    Writes test binary as -c would.
 //
 // 	-memprofile mem.out
-// 	    Write a memory profile to the file after all tests have passed.
+// 	    Write an allocation profile to the file after all tests have passed.
 // 	    Writes test binary as -c would.
 //
 // 	-memprofilerate n
-// 	    Enable more precise (and expensive) memory profiles by setting
-// 	    runtime.MemProfileRate. See 'go doc runtime.MemProfileRate'.
-// 	    To profile all memory allocations, use -test.memprofilerate=1
-// 	    and pass --alloc_space flag to the pprof tool.
+// 	    Enable more precise (and expensive) memory allocation profiles by
+// 	    setting runtime.MemProfileRate. See 'go doc runtime.MemProfileRate'.
+// 	    To profile all memory allocations, use -test.memprofilerate=1.
 //
 // 	-mutexprofile mutex.out
 // 	    Write a mutex contention profile to the specified file

src/cmd/go/go_test.go

@@ -1902,6 +1902,21 @@ func TestGoListDeps(t *testing.T) {
 	tg.tempFile("src/p1/p2/p3/p4/p.go", "package p4\n")
 	tg.run("list", "-f", "{{.Deps}}", "p1")
 	tg.grepStdout("p1/p2/p3/p4", "Deps(p1) does not mention p4")
+
+	tg.run("list", "-deps", "p1")
+	tg.grepStdout("p1/p2/p3/p4", "-deps p1 does not mention p4")
+
+	// Check the list is in dependency order.
+	tg.run("list", "-deps", "math")
+	want := "internal/cpu\nunsafe\nmath\n"
+	out := tg.stdout.String()
+	if !strings.Contains(out, "internal/cpu") {
+		// Some systems don't use internal/cpu.
+		want = "unsafe\nmath\n"
+	}
+	if tg.stdout.String() != want {
+		t.Fatalf("list -deps math: wrong order\nhave %q\nwant %q", tg.stdout.String(), want)
+	}
 }
 
 // Issue 4096. Validate the output of unsuccessful go install foo/quxx.

src/cmd/go/internal/list/list.go

@@ -20,7 +20,7 @@ import (
 )
 
 var CmdList = &base.Command{
-	UsageLine: "list [-e] [-f format] [-json] [build flags] [packages]",
+	UsageLine: "list [-deps] [-e] [-f format] [-json] [build flags] [packages]",
 	Short:     "list packages",
 	Long: `
 List lists the packages named by the import paths, one per line.
@@ -125,6 +125,10 @@ for the go/build package's Context type.
 The -json flag causes the package data to be printed in JSON format
 instead of using the template format.
 
+The -deps flag causes list to iterate over not just the named packages
+but also all their dependencies. It visits them in a depth-first post-order
+traversal, so that a package is listed only after all its dependencies.
+
 The -e flag changes the handling of erroneous packages, those that
 cannot be found or are malformed. By default, the list command
 prints an error to standard error for each erroneous package and
@@ -146,6 +150,7 @@ func init() {
 	work.AddBuildFlags(CmdList)
 }
 
+var listDeps = CmdList.Flag.Bool("deps", false, "")
 var listE = CmdList.Flag.Bool("e", false, "")
 var listFmt = CmdList.Flag.String("f", "{{.ImportPath}}", "")
 var listJson = CmdList.Flag.Bool("json", false, "")
@@ -201,6 +206,15 @@ func runList(cmd *base.Command, args []string) {
 		pkgs = load.Packages(args)
 	}
 
+	if *listDeps {
+		// Note: This changes the order of the listed packages
+		// from "as written on the command line" to
+		// "a depth-first post-order traversal".
+		// (The dependency exploration order for a given node
+		// is alphabetical, same as listed in .Deps.)
+		pkgs = load.PackageList(pkgs)
+	}
+
 	// Estimate whether staleness information is needed,
 	// since it's a little bit of work to compute.
 	needStale := *listJson || strings.Contains(*listFmt, ".Stale")