// Copyright 2009 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 types

import (
	"fmt"
	"internal/goversion"
	"internal/lazyregexp"
	"log"
	"strconv"

	"cmd/compile/internal/base"
)

// A lang is a language version broken into major and minor numbers.
type lang struct {
	major, minor int
}

// Copyright 2019 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 goversion

// Version is the Go 1.x version which is currently
// in development and will eventually get released.
//
// It should be updated at the start of each development cycle to be
// the version of the next Go 1.x release. See golang.org/issue/40705.

package types

import (
	"fmt"
	"go/ast"
	"go/token"
	"go/version"
	"internal/goversion"
)

// A goVersion is a Go language version string of the form "go1.%d"
// where d is the minor version number. goVersion strings don't
// contain release numbers ("go1.20.1" is not a valid goVersion).
type goVersion string

// asGoVersion returns v as a goVersion (e.g., "go1.20.1" becomes "go1.20").

func (pkg *Package) SetName(name string) { pkg.name = name }

// GoVersion returns the minimum Go version required by this package.
// If the minimum version is unknown, GoVersion returns the empty string.
// Individual source files may specify a different minimum Go version,
// as reported in the [go/ast.File.GoVersion] field.
func (pkg *Package) GoVersion() string { return pkg.goVersion }

// Scope returns the (complete or incomplete) package scope

package versions

import (
	"go/types"
)

// GoVersion returns the Go version of the type package.
// It returns zero if no version can be determined.
func GoVersion(pkg *types.Package) string {
	// TODO(taking): x/tools can call GoVersion() [from 1.21] after 1.25.
	if pkg, ok := any(pkg).(interface{ GoVersion() string }); ok {
		return pkg.GoVersion()
	}
	return ""

cp go.mod.21 go.mod
go list -f '{{.Module.GoVersion}} {{.DefaultGODEBUG}}'
! stdout panicnil
stdout randautoseed=0

# Go 1.21 work module should NOT set panicnil=1 in Go 1.20 dependency.
cp go.mod.21 go.mod
go list -f '{{.Module.GoVersion}} {{.DefaultGODEBUG}}' q
! stdout panicnil=1
! stdout randautoseed

go mod download rsc.io/panicnil # for go.sum
go list -f '{{.Module.GoVersion}} {{.DefaultGODEBUG}}' rsc.io/panicnil

		{Sym{goVersion: ver118, Name: "type..eq.[9]debug/elf.intName"}, ""},
		{Sym{goVersion: ver118, Name: "type..hash.debug/elf.ProgHeader"}, ""},
		{Sym{goVersion: ver118, Name: "type..eq.runtime._panic"}, ""},
		{Sym{goVersion: ver118, Name: "type..hash.struct { runtime.gList; runtime.n int32 }"}, ""},

	if p.Name != "main" {
		return ""
	}
	goVersion := modload.MainModules.GoVersion()
	if modload.RootMode == modload.NoRoot && p.Module != nil {
		// This is go install pkg@version or go run pkg@version.
		// Use the Go version from the package.
		// If there isn't one, then assume Go 1.20,
		// the last version before GODEBUGs were introduced.
		goVersion = p.Module.GoVersion
		if goVersion == "" {
			goVersion = "1.20"
		}
	}

	// 1) types.Info.FileVersion, which follows the cascade:
	//   1.a) file version (ast.File.GoVersion),
	//   1.b) the package version (types.Config.GoVersion), or
	// 2) is some unknown Future version.
	//
	// File versions require a valid package version to be provided to types
	// in Config.GoVersion. Config.GoVersion is either from the package's module
	// or the toolchain (go run). This value should be provided by go/packages

	}
	modload.ForceUseModules = true
	modload.RootMode = modload.NeedRoot

	goVersion := graphGo.String()
	if goVersion != "" && gover.Compare(gover.Local(), goVersion) < 0 {
		toolchain.SwitchOrFatal(ctx, &gover.TooNewError{
			What:      "-go flag",
			GoVersion: goVersion,
		})
	}

	mg, err := modload.LoadModGraph(ctx, goVersion)
	if err != nil {
		base.Fatal(err)
	}

	w := bufio.NewWriter(os.Stdout)