cmd/go: support the -overlay flag for go mod commands

Move the declaration of the -overlay flag to base.AddModCommonFlags,
where other flags that are needed for go mod commands and for builds
are declared. The flag's already initialized in modload.Init so
there's no additional work needed to be done to support it in the go
mod commands.

For #39958

Change-Id: I70725d620cc69cb820f6ed923d626f4fe041b1c5
Reviewed-on: https://go-review.googlesource.com/c/go/+/272126
Trust: Michael Matloob <matloob@golang.org>
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Jay Conrod <jayconrod@google.com>

src/cmd/go/internal/base/flag.go

@@ -8,6 +8,7 @@ import (
 	"flag"
 
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/fsys"
 	"cmd/go/internal/str"
 )
 
@@ -66,4 +67,5 @@ func AddModFlag(flags *flag.FlagSet) {
 func AddModCommonFlags(flags *flag.FlagSet) {
 	flags.BoolVar(&cfg.ModCacheRW, "modcacherw", false, "")
 	flags.StringVar(&cfg.ModFile, "modfile", "", "")
+	flags.StringVar(&fsys.OverlayFile, "overlay", "", "")
 }

src/cmd/go/internal/work/build.go

@@ -267,6 +267,11 @@ func AddBuildFlags(cmd *base.Command, mask BuildFlagMask) {
 	}
 	if mask&OmitModCommonFlags == 0 {
 		base.AddModCommonFlags(&cmd.Flag)
+	} else {
+		// Add the overlay flag even when we don't add the rest of the mod common flags.
+		// This only affects 'go get' in GOPATH mode, but add the flag anyway for
+		// consistency.
+		cmd.Flag.StringVar(&fsys.OverlayFile, "overlay", "", "")
 	}
 	cmd.Flag.StringVar(&cfg.BuildContext.InstallSuffix, "installsuffix", "", "")
 	cmd.Flag.Var(&load.BuildLdflags, "ldflags", "")
@@ -279,8 +284,6 @@ func AddBuildFlags(cmd *base.Command, mask BuildFlagMask) {
 	cmd.Flag.BoolVar(&cfg.BuildTrimpath, "trimpath", false, "")
 	cmd.Flag.BoolVar(&cfg.BuildWork, "work", false, "")
 
-	cmd.Flag.StringVar(&fsys.OverlayFile, "overlay", "", "")
-
 	// Undocumented, unstable debugging flags.
 	cmd.Flag.StringVar(&cfg.DebugActiongraph, "debug-actiongraph", "", "")
 	cmd.Flag.StringVar(&cfg.DebugTrace, "debug-trace", "", "")

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

@@ -32,14 +32,20 @@ cmp $WORK/overlay/get_doesnt_add_dep_go_mod $WORK/want_go_mod
 cd $WORK/gopath/src/overlay-sum-used
 ! go get -d .
 stderr 'SECURITY ERROR'
+! go mod verify
+stderr 'SECURITY ERROR'
 go get -d -overlay overlay.json .
+go mod verify -overlay overlay.json
 # Overlaid go.sum is not rewritten.
 # Copy an incomplete file to the overlay file, and expect an error
 # attempting to update the file
 cp incomplete-sum-file $WORK/overlay/overlay-sum-used-correct-sums
 ! go get -d -overlay overlay.json .
 stderr 'overlaid files can''t be opened for write'
 cmp incomplete-sum-file $WORK/overlay/overlay-sum-used-correct-sums
+! go mod tidy -overlay overlay.json
+stderr 'overlaid files can''t be opened for write'
+cmp incomplete-sum-file $WORK/overlay/overlay-sum-used-correct-sums
 
 # -overlay works with -modfile.
 # There's an empty go.mod file in the directory, and the file alternate.mod is