gopls/internal/cache: fail loudly on command-line-arguments modules

We could do more, but this is a minimal change addressing
golang/go#61543.

Fixes golang/go#61543

Change-Id: I1535ffcf9246d2d8abad384cab4a29c24696a220
Reviewed-on: https://go-review.googlesource.com/c/tools/+/578455
Auto-Submit: Robert Findley <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Alan Donovan <[email protected]>

Author: findleyr

gopls/internal/cache/load.go

@@ -202,6 +202,14 @@ func (s *Snapshot) load(ctx context.Context, allowNetwork bool, scopes ...loadSc
 	filterFunc := s.view.filterFunc()
 	newMetadata := make(map[PackageID]*metadata.Package)
 	for _, pkg := range pkgs {
+		if pkg.Module != nil && strings.Contains(pkg.Module.Path, "command-line-arguments") {
+			// golang/go#61543: modules containing "command-line-arguments" cause
+			// gopls to get all sorts of confused, because anything containing the
+			// string "command-line-arguments" is treated as a script. And yes, this
+			// happened in practice! (https://xkcd.com/327). Rather than try to work
+			// around this very rare edge case, just fail loudly.
+			return fmt.Errorf(`load failed: module name in %s contains "command-line-arguments", which is disallowed`, pkg.Module.GoMod)
+		}
 		// The Go command returns synthetic list results for module queries that
 		// encountered module errors.
 		//

gopls/internal/test/marker/testdata/fixedbugs/issue61543.txt

@@ -0,0 +1,13 @@
+This test verifies that we fail loudly if a module name contains
+command-line-arguments.
+
+-- flags --
+-errors_ok
+
+-- go.mod --
+module command-line-arguments //@diag("module", re`command-line-arguments.*disallowed`)
+
+go 1.12
+
+-- x/x.go --
+package x //@diag("x", re`command-line-arguments.*disallowed`)