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// Copyright (c) Tailscale Inc & contributors
// SPDX-License-Identifier: BSD-3-Clause
package main
import (
"bytes"
"go/ast"
"go/format"
"go/parser"
"go/token"
"go/types"
"path"
"slices"
"strconv"
"strings"
"tailscale.com/util/must"
)
// mustFormatFile formats a Go source file and adjust "json" imports.
// It panics if there are any parsing errors.
//
// - "encoding/json" is imported under the name "jsonv1" or "jsonv1std"
// - "encoding/json/v2" is rewritten to import "github.com/go-json-experiment/json" instead
// - "encoding/json/jsontext" is rewritten to import "github.com/go-json-experiment/json/jsontext" instead
// - "github.com/go-json-experiment/json" is imported under the name "jsonv2"
// - "github.com/go-json-experiment/json/v1" is imported under the name "jsonv1"
//
// If no changes to the file is made, it returns input.
func mustFormatFile(in []byte) (out []byte) {
fset := token.NewFileSet()
f := must.Get(parser.ParseFile(fset, "", in, parser.ParseComments))
// Check for the existence of "json" imports.
jsonImports := make(map[string][]*ast.ImportSpec)
for _, imp := range f.Imports {
switch pkgPath := must.Get(strconv.Unquote(imp.Path.Value)); pkgPath {
case
"encoding/json",
"encoding/json/v2",
"encoding/json/jsontext",
"github.com/go-json-experiment/json",
"github.com/go-json-experiment/json/v1",
"github.com/go-json-experiment/json/jsontext":
jsonImports[pkgPath] = append(jsonImports[pkgPath], imp)
}
}
if len(jsonImports) == 0 {
return in
}
// Best-effort local type-check of the file
// to resolve local declarations to detect shadowed variables.
typeInfo := &types.Info{Uses: make(map[*ast.Ident]types.Object)}
(&types.Config{
Error: func(err error) {},
}).Check("", fset, []*ast.File{f}, typeInfo)
// Rewrite imports to instead use "github.com/go-json-experiment/json".
// This ensures that code continues to build even if
// goexperiment.jsonv2 is *not* specified.
// As of https://github.com/go-json-experiment/json/pull/186,
// imports to "github.com/go-json-experiment/json" are identical
// to the standard library if built with goexperiment.jsonv2.
for fromPath, toPath := range map[string]string{
"encoding/json/v2": "github.com/go-json-experiment/json",
"encoding/json/jsontext": "github.com/go-json-experiment/json/jsontext",
} {
for _, imp := range jsonImports[fromPath] {
imp.Path.Value = strconv.Quote(toPath)
jsonImports[toPath] = append(jsonImports[toPath], imp)
}
delete(jsonImports, fromPath)
}
// While in a transitory state, where both v1 and v2 json imports
// may exist in our codebase, always explicitly import with
// either jsonv1 or jsonv2 in the package name to avoid ambiguities
// when looking at a particular Marshal or Unmarshal call site.
renames := make(map[string]string) // mapping of old names to new names
deletes := make(map[*ast.ImportSpec]bool) // set of imports to delete
for pkgPath, imps := range jsonImports {
var newName string
switch pkgPath {
case "encoding/json":
newName = "jsonv1"
// If "github.com/go-json-experiment/json/v1" is also imported,
// then use jsonv1std for "encoding/json" to avoid a conflict.
if len(jsonImports["github.com/go-json-experiment/json/v1"]) > 0 {
newName += "std"
}
case "github.com/go-json-experiment/json":
newName = "jsonv2"
case "github.com/go-json-experiment/json/v1":
newName = "jsonv1"
}
// Rename the import if different than expected.
if oldName := importName(imps[0]); oldName != newName && newName != "" {
renames[oldName] = newName
pos := imps[0].Pos() // preserve original positioning
imps[0].Name = ast.NewIdent(newName)
imps[0].Name.NamePos = pos
}
// For all redundant imports, use the first imported name.
for _, imp := range imps[1:] {
renames[importName(imp)] = importName(imps[0])
deletes[imp] = true
}
}
if len(deletes) > 0 {
f.Imports = slices.DeleteFunc(f.Imports, func(imp *ast.ImportSpec) bool {
return deletes[imp]
})
for _, decl := range f.Decls {
if genDecl, ok := decl.(*ast.GenDecl); ok && genDecl.Tok == token.IMPORT {
genDecl.Specs = slices.DeleteFunc(genDecl.Specs, func(spec ast.Spec) bool {
return deletes[spec.(*ast.ImportSpec)]
})
}
}
}
if len(renames) > 0 {
ast.Walk(astVisitor(func(n ast.Node) bool {
if sel, ok := n.(*ast.SelectorExpr); ok {
if id, ok := sel.X.(*ast.Ident); ok {
// Just because the selector looks like "json.Marshal"
// does not mean that it is referencing the "json" package.
// There could be a local "json" declaration that shadows
// the package import. Check partial type information
// to see if there was a local declaration.
if obj, ok := typeInfo.Uses[id]; ok {
if _, ok := obj.(*types.PkgName); !ok {
return true
}
}
if newName, ok := renames[id.String()]; ok {
id.Name = newName
}
}
}
return true
}), f)
}
bb := new(bytes.Buffer)
must.Do(format.Node(bb, fset, f))
return must.Get(format.Source(bb.Bytes()))
}
// importName is the local package name used for an import.
// If no explicit local name is used, then it uses string parsing
// to derive the package name from the path, relying on the convention
// that the package name is the base name of the package path.
func importName(imp *ast.ImportSpec) string {
if imp.Name != nil {
return imp.Name.String()
}
pkgPath, _ := strconv.Unquote(imp.Path.Value)
pkgPath = strings.TrimRight(pkgPath, "/v0123456789") // exclude version directories
return path.Base(pkgPath)
}
// astVisitor is a function that implements [ast.Visitor].
type astVisitor func(ast.Node) bool
func (f astVisitor) Visit(node ast.Node) ast.Visitor {
if !f(node) {
return nil
}
return f
}
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