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// 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.
package cache
import (
"go/ast"
"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
}
found := false
walkConstraints(f, func(c constraint.Expr) bool {
if tag, ok := c.(*constraint.TagExpr); ok {
for _, t := range standaloneTags {
if t == tag.Tag {
found = true
return false
}
}
}
return true
})
return found
}
// walkConstraints calls f for each constraint expression in the file, until
// all constraints are exhausted or f returns false.
func walkConstraints(file *ast.File, f func(constraint.Expr) bool) {
for _, cg := range file.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() > file.Name.Pos() {
continue
}
for _, comment := range cg.List {
if c, err := constraint.Parse(comment.Text); err == nil {
if !f(c) {
return
}
}
}
}
}
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