1 files changed, 50 insertions, 0 deletions
diff --git a/gopls/internal/lsp/cache/standalone_go116.go b/gopls/internal/lsp/cache/standalone_go116.go
new file mode 100644
index 000000000..2f72d5f54
--- /dev/null
+++ b/gopls/internal/lsp/cache/standalone_go116.go
@@ -0,0 +1,50 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build go1.16
+// +build go1.16
+
+package cache
+
+import (
+	"go/build/constraint"
+	"go/parser"
+	"go/token"
+)
+
+// isStandaloneFile reports whether a file with the given contents should be
+// considered a 'standalone main file', meaning a package that consists of only
+// a single file.
+func isStandaloneFile(src []byte, standaloneTags []string) bool {
+	f, err := parser.ParseFile(token.NewFileSet(), "", src, parser.PackageClauseOnly|parser.ParseComments)
+	if err != nil {
+		return false
+	}
+
+	if f.Name == nil || f.Name.Name != "main" {
+		return false
+	}
+
+	for _, cg := range f.Comments {
+		// Even with PackageClauseOnly the parser consumes the semicolon following
+		// the package clause, so we must guard against comments that come after
+		// the package name.
+		if cg.Pos() > f.Name.Pos() {
+			continue
+		}
+		for _, comment := range cg.List {
+			if c, err := constraint.Parse(comment.Text); err == nil {
+				if tag, ok := c.(*constraint.TagExpr); ok {
+					for _, t := range standaloneTags {
+						if t == tag.Tag {
+							return true
+						}
+					}
+				}
+			}
+		}
+	}
+
+	return false
+}