// Copyright 2021 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 noder

import (
	"fmt"
	"regexp"
	"sort"

	"cmd/compile/internal/base"
	"cmd/compile/internal/syntax"
	"cmd/compile/internal/types2"
	"cmd/internal/src"
)

var versionErrorRx = regexp.MustCompile(`requires go[0-9]+\.[0-9]+ or later`)

// checkFiles configures and runs the types2 checker on the given
// parsed source files and then returns the result.
func checkFiles(noders []*noder) (posMap, *types2.Package, *types2.Info) {
	if base.SyntaxErrors() != 0 {
		base.ErrorExit()
	}

	// setup and syntax error reporting
	var m posMap
	files := make([]*syntax.File, len(noders))
	for i, p := range noders {
		m.join(&p.posMap)
		files[i] = p.file
	}

	// typechecking
	ctxt := types2.NewContext()
	importer := gcimports{
		ctxt:     ctxt,
		packages: make(map[string]*types2.Package),
	}
	conf := types2.Config{
		Context:            ctxt,
		GoVersion:          base.Flag.Lang,
		IgnoreBranchErrors: true, // parser already checked via syntax.CheckBranches mode
		Error: func(err error) {
			terr := err.(types2.Error)
			msg := terr.Msg
			// if we have a version error, hint at the -lang setting
			if versionErrorRx.MatchString(msg) {
				msg = fmt.Sprintf("%s (-lang was set to %s; check go.mod)", msg, base.Flag.Lang)
			}
			base.ErrorfAt(m.makeXPos(terr.Pos), "%s", msg)
		},
		Importer: &importer,
		Sizes:    &gcSizes{},
	}
	info := &types2.Info{
		StoreTypesInSyntax: true,
		Defs:               make(map[*syntax.Name]types2.Object),
		Uses:               make(map[*syntax.Name]types2.Object),
		Selections:         make(map[*syntax.SelectorExpr]*types2.Selection),
		Implicits:          make(map[syntax.Node]types2.Object),
		Scopes:             make(map[syntax.Node]*types2.Scope),
		Instances:          make(map[*syntax.Name]types2.Instance),
		// expand as needed
	}

	pkg, err := conf.Check(base.Ctxt.Pkgpath, files, info)

	// Check for anonymous interface cycles (#56103).
	if base.Debug.InterfaceCycles == 0 {
		var f cycleFinder
		for _, file := range files {
			syntax.Inspect(file, func(n syntax.Node) bool {
				if n, ok := n.(*syntax.InterfaceType); ok {
					if f.hasCycle(n.GetTypeInfo().Type.(*types2.Interface)) {
						base.ErrorfAt(m.makeXPos(n.Pos()), "invalid recursive type: anonymous interface refers to itself (see https://go.dev/issue/56103)")

						for typ := range f.cyclic {
							f.cyclic[typ] = false // suppress duplicate errors
						}
					}
					return false
				}
				return true
			})
		}
	}

	// Implementation restriction: we don't allow not-in-heap types to
	// be used as type arguments (#54765).
	{
		type nihTarg struct {
			pos src.XPos
			typ types2.Type
		}
		var nihTargs []nihTarg

		for name, inst := range info.Instances {
			for i := 0; i < inst.TypeArgs.Len(); i++ {
				if targ := inst.TypeArgs.At(i); isNotInHeap(targ) {
					nihTargs = append(nihTargs, nihTarg{m.makeXPos(name.Pos()), targ})
				}
			}
		}
		sort.Slice(nihTargs, func(i, j int) bool {
			ti, tj := nihTargs[i], nihTargs[j]
			return ti.pos.Before(tj.pos)
		})
		for _, targ := range nihTargs {
			base.ErrorfAt(targ.pos, "cannot use incomplete (or unallocatable) type as a type argument: %v", targ.typ)
		}
	}

	base.ExitIfErrors()
	if err != nil {
		base.FatalfAt(src.NoXPos, "conf.Check error: %v", err)
	}

	return m, pkg, info
}

// A cycleFinder detects anonymous interface cycles (go.dev/issue/56103).
type cycleFinder struct {
	cyclic map[*types2.Interface]bool
}

// hasCycle reports whether typ is part of an anonymous interface cycle.
func (f *cycleFinder) hasCycle(typ *types2.Interface) bool {
	// We use Method instead of ExplicitMethod to implicitly expand any
	// embedded interfaces. Then we just need to walk any anonymous
	// types, keeping track of *types2.Interface types we visit along
	// the way.
	for i := 0; i < typ.NumMethods(); i++ {
		if f.visit(typ.Method(i).Type()) {
			return true
		}
	}
	return false
}

// visit recursively walks typ0 to check any referenced interface types.
func (f *cycleFinder) visit(typ0 types2.Type) bool {
	for { // loop for tail recursion
		switch typ := typ0.(type) {
		default:
			base.Fatalf("unexpected type: %T", typ)

		case *types2.Basic, *types2.Named, *types2.TypeParam:
			return false // named types cannot be part of an anonymous cycle
		case *types2.Pointer:
			typ0 = typ.Elem()
		case *types2.Array:
			typ0 = typ.Elem()
		case *types2.Chan:
			typ0 = typ.Elem()
		case *types2.Map:
			if f.visit(typ.Key()) {
				return true
			}
			typ0 = typ.Elem()
		case *types2.Slice:
			typ0 = typ.Elem()

		case *types2.Struct:
			for i := 0; i < typ.NumFields(); i++ {
				if f.visit(typ.Field(i).Type()) {
					return true
				}
			}
			return false

		case *types2.Interface:
			// The empty interface (e.g., "any") cannot be part of a cycle.
			if typ.NumExplicitMethods() == 0 && typ.NumEmbeddeds() == 0 {
				return false
			}

			// As an optimization, we wait to allocate cyclic here, after
			// we've found at least one other (non-empty) anonymous
			// interface. This means when a cycle is present, we need to
			// make an extra recursive call to actually detect it. But for
			// most packages, it allows skipping the map allocation
			// entirely.
			if x, ok := f.cyclic[typ]; ok {
				return x
			}
			if f.cyclic == nil {
				f.cyclic = make(map[*types2.Interface]bool)
			}
			f.cyclic[typ] = true
			if f.hasCycle(typ) {
				return true
			}
			f.cyclic[typ] = false
			return false

		case *types2.Signature:
			return f.visit(typ.Params()) || f.visit(typ.Results())
		case *types2.Tuple:
			for i := 0; i < typ.Len(); i++ {
				if f.visit(typ.At(i).Type()) {
					return true
				}
			}
			return false
		}
	}
}