tool/gocross: don't absorb --tags flags passed to subcommand

Fixes tailscale/corp#15117

Signed-off-by: David Anderson <danderson@tailscale.com>

tool/gocross/autoflags.go

@@ -166,7 +166,7 @@ func autoflagsForTest(argv []string, env *Environment, goroot, nativeGOOS, nativ
 	// commandline and environment modifications.
 	newArgv = append(newArgv, argv[:2]...) // Program name and `go` tool subcommand
 
-	filteredArgvPostSubcmd, originalTags := extractTags(argv[2:])
+	filteredArgvPostSubcmd, originalTags := extractTags(argv[1], argv[2:])
 
 	newArgv = append(newArgv, buildFlags...)
 	tags = append(tags, originalTags...)
@@ -201,7 +201,7 @@ func autoflagsForTest(argv []string, env *Environment, goroot, nativeGOOS, nativ
 // extractTags parses out "-tags=foo,bar" (or double hyphen or "-tags",
 // "foo,bar") in its various forms and returns v filtered to remove the 0, 1 or
 // 2 build tag elements, then the tags parsed, split on commas ("foo", "bar").
-func extractTags(v []string) (filtered, tags []string) {
+func extractTags(gocmd string, v []string) (filtered, tags []string) {
 	for len(v) > 0 {
 		e := v[0]
 		if strings.HasPrefix(e, "--tags=") {
@@ -225,6 +225,15 @@ func extractTags(v []string) (filtered, tags []string) {
 			}
 			continue
 		}
+		if gocmd == "run" && !strings.HasPrefix(e, "-") {
+			// go run can include arguments to pass to the program
+			// being run. They all appear after the name of the
+			// package or Go file to run, so when we hit the first
+			// non-flag positional argument, stop extracting tags and
+			// wrap up.
+			filtered = append(filtered, v...)
+			break
+		}
 		filtered = append(filtered, e)
 		v = v[1:]
 	}

tool/gocross/autoflags_test.go

@@ -416,6 +416,33 @@ TS_LINK_FAIL_REFLECT=0 (was <nil>)`,
 				"./cmd/tailcontrol",
 			},
 		},
+		{
+			name: "linux_amd64_to_linux_amd64_go_run_tags",
+
+			argv:         []string{"go", "run", "./cmd/mkctr", "--tags=foo"},
+			goroot:       "/goroot",
+			nativeGOOS:   "linux",
+			nativeGOARCH: "amd64",
+
+			envDiff: `CC=cc (was <nil>)
+CGO_CFLAGS=-O3 -std=gnu11 (was <nil>)
+CGO_ENABLED=1 (was <nil>)
+CGO_LDFLAGS= (was <nil>)
+GOARCH=amd64 (was <nil>)
+GOARM=5 (was <nil>)
+GOMIPS=softfloat (was <nil>)
+GOOS=linux (was <nil>)
+GOROOT=/goroot (was <nil>)
+TS_LINK_FAIL_REFLECT=0 (was <nil>)`,
+			wantArgv: []string{
+				"go", "run",
+				"-trimpath",
+				"-tags=tailscale_go,osusergo,netgo",
+				"-ldflags", "-X tailscale.com/version.longStamp=1.2.3-long -X tailscale.com/version.shortStamp=1.2.3 -X tailscale.com/version.gitCommitStamp=abcd -X tailscale.com/version.extraGitCommitStamp=defg '-extldflags=-static'",
+				"./cmd/mkctr",
+				"--tags=foo",
+			},
+		},
 	}
 
 	for _, test := range tests {
@@ -442,61 +469,76 @@ func TestExtractTags(t *testing.T) {
 	s := func(ss ...string) []string { return ss }
 	tests := []struct {
 		name string
+		cmd  string
 		in   []string
 		filt []string // want filtered
 		tags []string // want tags
 	}{
 		{
 			name: "one_hyphen_tags",
+			cmd:  "build",
 			in:   s("foo", "-tags=a,b", "bar"),
 			filt: s("foo", "bar"),
 			tags: s("a", "b"),
 		},
 		{
 			name: "two_hyphen_tags",
+			cmd:  "build",
 			in:   s("foo", "--tags=a,b", "bar"),
 			filt: s("foo", "bar"),
 			tags: s("a", "b"),
 		},
 		{
 			name: "one_hypen_separate_arg",
+			cmd:  "build",
 			in:   s("foo", "-tags", "a,b", "bar"),
 			filt: s("foo", "bar"),
 			tags: s("a", "b"),
 		},
 		{
 			name: "two_hypen_separate_arg",
+			cmd:  "build",
 			in:   s("foo", "--tags", "a,b", "bar"),
 			filt: s("foo", "bar"),
 			tags: s("a", "b"),
 		},
 		{
 			name: "equal_empty",
+			cmd:  "build",
 			in:   s("foo", "--tags=", "bar"),
 			filt: s("foo", "bar"),
 			tags: s(),
 		},
 		{
 			name: "arg_empty",
+			cmd:  "build",
 			in:   s("foo", "--tags", "", "bar"),
 			filt: s("foo", "bar"),
 			tags: s(),
 		},
 		{
 			name: "arg_empty_truncated",
+			cmd:  "build",
 			in:   s("foo", "--tags"),
 			filt: s("foo"),
 			tags: s(),
 		},
+		{
+			name: "go_run_with_program_tags",
+			cmd:  "run",
+			in:   s("--foo", "--tags", "bar", "my/package/name", "--tags", "qux"),
+			filt: s("--foo", "my/package/name", "--tags", "qux"),
+			tags: s("bar"),
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			filt, tags := extractTags(tt.in)
+			filt, tags := extractTags(tt.cmd, tt.in)
 			if !reflect.DeepEqual(filt, tt.filt) {
-				t.Errorf("extractTags(%q) filtered = %q; want %q", tt.in, filt, tt.filt)
+				t.Errorf("extractTags(%q, %q) filtered = %q; want %q", tt.cmd, tt.in, filt, tt.filt)
 			}
 			if !reflect.DeepEqual(tags, tt.tags) {
-				t.Errorf("extractTags(%q) tags = %q; want %q", tt.in, tags, tt.tags)
+				t.Errorf("extractTags(%q, %q) tags = %q; want %q", tt.cmd, tt.in, tags, tt.tags)
 			}
 		})
 	}