cmd/go: re-enable 'go list -m' with -mod=vendor for limited patterns

I had prohibited 'go list -m' with -mod=vendor because the module
graph is incomplete, but I've realized that many queries do not
actually require the full graph — and may, in fact, be driven using
modules previously reported by 'go list' for specific, vendored
packages. Queries for those modules should succeed.

Updates #33848

Change-Id: I1000b4cf586a830bb78faf620ebf62d73a3cb300
Reviewed-on: https://go-review.googlesource.com/c/go/+/203138
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

1 files changed, 10 insertions, 5 deletions

diff --git a/src/cmd/go/internal/list/list.go b/src/cmd/go/internal/list/list.go
index 7965a84f99..b393c67ddb 100644
--- a/src/cmd/go/internal/list/list.go
+++ b/src/cmd/go/internal/list/list.go
@@ -381,17 +381,22 @@ func runList(cmd *base.Command, args []string) {
 			base.Fatalf("go list -test cannot be used with -m")
 		}
 
-		buildModIsDefault := (cfg.BuildMod == "")
 		if modload.Init(); !modload.Enabled() {
 			base.Fatalf("go list -m: not using modules")
 		}
 
 		modload.InitMod() // Parses go.mod and sets cfg.BuildMod.
 		if cfg.BuildMod == "vendor" {
-			if buildModIsDefault {
-				base.Fatalf("go list -m: can't list modules using the vendor directory\n\tUse -mod=mod or -mod=readonly to ignore it.")
-			} else {
-				base.Fatalf("go list -m: can't list modules with -mod=vendor\n\tUse -mod=mod or -mod=readonly to ignore the vendor directory.")
+			for _, arg := range args {
+				// In vendor mode, the module graph is incomplete: it contains only the
+				// explicit module dependencies and the modules that supply packages in
+				// the import graph. Reject queries that imply more information than that.
+				if arg == "all" {
+					base.Fatalf("go list -m: can't compute 'all' using the vendor directory\n\t(Use -mod=mod or -mod=readonly to bypass.)")
+				}
+				if strings.Contains(arg, "...") {
+					base.Fatalf("go list -m: can't match module patterns using the vendor directory\n\t(Use -mod=mod or -mod=readonly to bypass.)")
+				}
 			}
 		}