go/types, types2: implement Alias proposal (export API)

[gostls13.git] / src / go / types / check.go

// Copyright 2011 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.

// This file implements the Check function, which drives type-checking.

package types

import (
        "errors"
        "fmt"
        "go/ast"
        "go/constant"
        "go/token"
        "internal/godebug"
        "internal/goversion"
        . "internal/types/errors"
)

// nopos indicates an unknown position
var nopos token.Pos

// debugging/development support
const debug = false // leave on during development

// gotypesalias controls the use of Alias types
var gotypesalias = godebug.New("gotypesalias")

// exprInfo stores information about an untyped expression.
type exprInfo struct {
        isLhs bool // expression is lhs operand of a shift with delayed type-check
        mode  operandMode
        typ   *Basic
        val   constant.Value // constant value; or nil (if not a constant)
}

// An environment represents the environment within which an object is
// type-checked.
type environment struct {
        decl          *declInfo              // package-level declaration whose init expression/function body is checked
        scope         *Scope                 // top-most scope for lookups
        pos           token.Pos              // if valid, identifiers are looked up as if at position pos (used by Eval)
        iota          constant.Value         // value of iota in a constant declaration; nil otherwise
        errpos        positioner             // if set, identifier position of a constant with inherited initializer
        inTParamList  bool                   // set if inside a type parameter list
        sig           *Signature             // function signature if inside a function; nil otherwise
        isPanic       map[*ast.CallExpr]bool // set of panic call expressions (used for termination check)
        hasLabel      bool                   // set if a function makes use of labels (only ~1% of functions); unused outside functions
        hasCallOrRecv bool                   // set if an expression contains a function call or channel receive operation
}

// lookup looks up name in the current environment and returns the matching object, or nil.
func (env *environment) lookup(name string) Object {
        _, obj := env.scope.LookupParent(name, env.pos)
        return obj
}

// An importKey identifies an imported package by import path and source directory
// (directory containing the file containing the import). In practice, the directory
// may always be the same, or may not matter. Given an (import path, directory), an
// importer must always return the same package (but given two different import paths,
// an importer may still return the same package by mapping them to the same package
// paths).
type importKey struct {
        path, dir string
}

// A dotImportKey describes a dot-imported object in the given scope.
type dotImportKey struct {
        scope *Scope
        name  string
}

// An action describes a (delayed) action.
type action struct {
        f    func()      // action to be executed
        desc *actionDesc // action description; may be nil, requires debug to be set
}

// If debug is set, describef sets a printf-formatted description for action a.
// Otherwise, it is a no-op.
func (a *action) describef(pos positioner, format string, args ...any) {
        if debug {
                a.desc = &actionDesc{pos, format, args}
        }
}

// An actionDesc provides information on an action.
// For debugging only.
type actionDesc struct {
        pos    positioner
        format string
        args   []any
}

// A Checker maintains the state of the type checker.
// It must be created with [NewChecker].
type Checker struct {
        // package information
        // (initialized by NewChecker, valid for the life-time of checker)

        // If EnableAlias is set, alias declarations produce an Alias type.
        // Otherwise the alias information is only in the type name, which
        // points directly to the actual (aliased) type.
        enableAlias bool

        conf *Config
        ctxt *Context // context for de-duplicating instances
        fset *token.FileSet
        pkg  *Package
        *Info
        version version                // accepted language version
        posVers map[token.Pos]version  // maps file start positions to versions (may be nil)
        nextID  uint64                 // unique Id for type parameters (first valid Id is 1)
        objMap  map[Object]*declInfo   // maps package-level objects and (non-interface) methods to declaration info
        impMap  map[importKey]*Package // maps (import path, source directory) to (complete or fake) package
        valids  instanceLookup         // valid *Named (incl. instantiated) types per the validType check

        // pkgPathMap maps package names to the set of distinct import paths we've
        // seen for that name, anywhere in the import graph. It is used for
        // disambiguating package names in error messages.
        //
        // pkgPathMap is allocated lazily, so that we don't pay the price of building
        // it on the happy path. seenPkgMap tracks the packages that we've already
        // walked.
        pkgPathMap map[string]map[string]bool
        seenPkgMap map[*Package]bool

        // information collected during type-checking of a set of package files
        // (initialized by Files, valid only for the duration of check.Files;
        // maps and lists are allocated on demand)
        files         []*ast.File               // package files
        imports       []*PkgName                // list of imported packages
        dotImportMap  map[dotImportKey]*PkgName // maps dot-imported objects to the package they were dot-imported through
        recvTParamMap map[*ast.Ident]*TypeParam // maps blank receiver type parameters to their type
        brokenAliases map[*TypeName]bool        // set of aliases with broken (not yet determined) types
        unionTypeSets map[*Union]*_TypeSet      // computed type sets for union types
        mono          monoGraph                 // graph for detecting non-monomorphizable instantiation loops

        firstErr error                 // first error encountered
        methods  map[*TypeName][]*Func // maps package scope type names to associated non-blank (non-interface) methods
        untyped  map[ast.Expr]exprInfo // map of expressions without final type
        delayed  []action              // stack of delayed action segments; segments are processed in FIFO order
        objPath  []Object              // path of object dependencies during type inference (for cycle reporting)
        cleaners []cleaner             // list of types that may need a final cleanup at the end of type-checking

        // environment within which the current object is type-checked (valid only
        // for the duration of type-checking a specific object)
        environment

        // debugging
        indent int // indentation for tracing
}

// addDeclDep adds the dependency edge (check.decl -> to) if check.decl exists
func (check *Checker) addDeclDep(to Object) {
        from := check.decl
        if from == nil {
                return // not in a package-level init expression
        }
        if _, found := check.objMap[to]; !found {
                return // to is not a package-level object
        }
        from.addDep(to)
}

// Note: The following three alias-related functions are only used
//       when Alias types are not enabled.

// brokenAlias records that alias doesn't have a determined type yet.
// It also sets alias.typ to Typ[Invalid].
// Not used if check.enableAlias is set.
func (check *Checker) brokenAlias(alias *TypeName) {
        assert(!check.enableAlias)
        if check.brokenAliases == nil {
                check.brokenAliases = make(map[*TypeName]bool)
        }
        check.brokenAliases[alias] = true
        alias.typ = Typ[Invalid]
}

// validAlias records that alias has the valid type typ (possibly Typ[Invalid]).
func (check *Checker) validAlias(alias *TypeName, typ Type) {
        assert(!check.enableAlias)
        delete(check.brokenAliases, alias)
        alias.typ = typ
}

// isBrokenAlias reports whether alias doesn't have a determined type yet.
func (check *Checker) isBrokenAlias(alias *TypeName) bool {
        assert(!check.enableAlias)
        return check.brokenAliases[alias]
}

func (check *Checker) rememberUntyped(e ast.Expr, lhs bool, mode operandMode, typ *Basic, val constant.Value) {
        m := check.untyped
        if m == nil {
                m = make(map[ast.Expr]exprInfo)
                check.untyped = m
        }
        m[e] = exprInfo{lhs, mode, typ, val}
}

// later pushes f on to the stack of actions that will be processed later;
// either at the end of the current statement, or in case of a local constant
// or variable declaration, before the constant or variable is in scope
// (so that f still sees the scope before any new declarations).
// later returns the pushed action so one can provide a description
// via action.describef for debugging, if desired.
func (check *Checker) later(f func()) *action {
        i := len(check.delayed)
        check.delayed = append(check.delayed, action{f: f})
        return &check.delayed[i]
}

// push pushes obj onto the object path and returns its index in the path.
func (check *Checker) push(obj Object) int {
        check.objPath = append(check.objPath, obj)
        return len(check.objPath) - 1
}

// pop pops and returns the topmost object from the object path.
func (check *Checker) pop() Object {
        i := len(check.objPath) - 1
        obj := check.objPath[i]
        check.objPath[i] = nil
        check.objPath = check.objPath[:i]
        return obj
}

type cleaner interface {
        cleanup()
}

// needsCleanup records objects/types that implement the cleanup method
// which will be called at the end of type-checking.
func (check *Checker) needsCleanup(c cleaner) {
        check.cleaners = append(check.cleaners, c)
}

// NewChecker returns a new [Checker] instance for a given package.
// [Package] files may be added incrementally via checker.Files.
func NewChecker(conf *Config, fset *token.FileSet, pkg *Package, info *Info) *Checker {
        // make sure we have a configuration
        if conf == nil {
                conf = new(Config)
        }

        // make sure we have an info struct
        if info == nil {
                info = new(Info)
        }

        // Note: clients may call NewChecker with the Unsafe package, which is
        // globally shared and must not be mutated. Therefore NewChecker must not
        // mutate *pkg.
        //
        // (previously, pkg.goVersion was mutated here: go.dev/issue/61212)

        return &Checker{
                enableAlias: gotypesalias.Value() == "1",
                conf:        conf,
                ctxt:        conf.Context,
                fset:        fset,
                pkg:         pkg,
                Info:        info,
                objMap:      make(map[Object]*declInfo),
                impMap:      make(map[importKey]*Package),
        }
}

// initFiles initializes the files-specific portion of checker.
// The provided files must all belong to the same package.
func (check *Checker) initFiles(files []*ast.File) {
        // start with a clean slate (check.Files may be called multiple times)
        check.files = nil
        check.imports = nil
        check.dotImportMap = nil

        check.firstErr = nil
        check.methods = nil
        check.untyped = nil
        check.delayed = nil
        check.objPath = nil
        check.cleaners = nil

        // determine package name and collect valid files
        pkg := check.pkg
        for _, file := range files {
                switch name := file.Name.Name; pkg.name {
                case "":
                        if name != "_" {
                                pkg.name = name
                        } else {
                                check.error(file.Name, BlankPkgName, "invalid package name _")
                        }
                        fallthrough

                case name:
                        check.files = append(check.files, file)

                default:
                        check.errorf(atPos(file.Package), MismatchedPkgName, "package %s; expected %s", name, pkg.name)
                        // ignore this file
                }
        }

        // collect file versions
        for _, file := range check.files {
                check.recordFileVersion(file, check.conf.GoVersion) // record package version (possibly zero version)
                if v, _ := parseGoVersion(file.GoVersion); v.major > 0 {
                        if v.equal(check.version) {
                                continue
                        }
                        // Go 1.21 introduced the feature of setting the go.mod
                        // go line to an early version of Go and allowing //go:build lines
                        // to “upgrade” the Go version in a given file.
                        // We can do that backwards compatibly.
                        // Go 1.21 also introduced the feature of allowing //go:build lines
                        // to “downgrade” the Go version in a given file.
                        // That can't be done compatibly in general, since before the
                        // build lines were ignored and code got the module's Go version.
                        // To work around this, downgrades are only allowed when the
                        // module's Go version is Go 1.21 or later.
                        // If there is no check.version, then we don't really know what Go version to apply.
                        // Legacy tools may do this, and they historically have accepted everything.
                        // Preserve that behavior by ignoring //go:build constraints entirely in that case.
                        if (v.before(check.version) && check.version.before(go1_21)) || check.version.equal(go0_0) {
                                continue
                        }
                        if check.posVers == nil {
                                check.posVers = make(map[token.Pos]version)
                        }
                        check.posVers[file.FileStart] = v
                        check.recordFileVersion(file, file.GoVersion) // overwrite package version
                }
        }
}

// A bailout panic is used for early termination.
type bailout struct{}

func (check *Checker) handleBailout(err *error) {
        switch p := recover().(type) {
        case nil, bailout:
                // normal return or early exit
                *err = check.firstErr
        default:
                // re-panic
                panic(p)
        }
}

// Files checks the provided files as part of the checker's package.
func (check *Checker) Files(files []*ast.File) error { return check.checkFiles(files) }

var errBadCgo = errors.New("cannot use FakeImportC and go115UsesCgo together")

func (check *Checker) checkFiles(files []*ast.File) (err error) {
        if check.pkg == Unsafe {
                // Defensive handling for Unsafe, which cannot be type checked, and must
                // not be mutated. See https://go.dev/issue/61212 for an example of where
                // Unsafe is passed to NewChecker.
                return nil
        }

        // Note: parseGoVersion and the subsequent checks should happen once,
        //       when we create a new Checker, not for each batch of files.
        //       We can't change it at this point because NewChecker doesn't
        //       return an error.
        check.version, err = parseGoVersion(check.conf.GoVersion)
        if err != nil {
                return err
        }
        if check.version.after(version{1, goversion.Version}) {
                return fmt.Errorf("package requires newer Go version %v", check.version)
        }
        if check.conf.FakeImportC && check.conf.go115UsesCgo {
                return errBadCgo
        }

        defer check.handleBailout(&err)

        print := func(msg string) {
                if check.conf._Trace {
                        fmt.Println()
                        fmt.Println(msg)
                }
        }

        print("== initFiles ==")
        check.initFiles(files)

        print("== collectObjects ==")
        check.collectObjects()

        print("== packageObjects ==")
        check.packageObjects()

        print("== processDelayed ==")
        check.processDelayed(0) // incl. all functions

        print("== cleanup ==")
        check.cleanup()

        print("== initOrder ==")
        check.initOrder()

        if !check.conf.DisableUnusedImportCheck {
                print("== unusedImports ==")
                check.unusedImports()
        }

        print("== recordUntyped ==")
        check.recordUntyped()

        if check.firstErr == nil {
                // TODO(mdempsky): Ensure monomorph is safe when errors exist.
                check.monomorph()
        }

        check.pkg.goVersion = check.conf.GoVersion
        check.pkg.complete = true

        // no longer needed - release memory
        check.imports = nil
        check.dotImportMap = nil
        check.pkgPathMap = nil
        check.seenPkgMap = nil
        check.recvTParamMap = nil
        check.brokenAliases = nil
        check.unionTypeSets = nil
        check.ctxt = nil

        // TODO(rFindley) There's more memory we should release at this point.

        return
}

// processDelayed processes all delayed actions pushed after top.
func (check *Checker) processDelayed(top int) {
        // If each delayed action pushes a new action, the
        // stack will continue to grow during this loop.
        // However, it is only processing functions (which
        // are processed in a delayed fashion) that may
        // add more actions (such as nested functions), so
        // this is a sufficiently bounded process.
        for i := top; i < len(check.delayed); i++ {
                a := &check.delayed[i]
                if check.conf._Trace {
                        if a.desc != nil {
                                check.trace(a.desc.pos.Pos(), "-- "+a.desc.format, a.desc.args...)
                        } else {
                                check.trace(nopos, "-- delayed %p", a.f)
                        }
                }
                a.f() // may append to check.delayed
                if check.conf._Trace {
                        fmt.Println()
                }
        }
        assert(top <= len(check.delayed)) // stack must not have shrunk
        check.delayed = check.delayed[:top]
}

// cleanup runs cleanup for all collected cleaners.
func (check *Checker) cleanup() {
        // Don't use a range clause since Named.cleanup may add more cleaners.
        for i := 0; i < len(check.cleaners); i++ {
                check.cleaners[i].cleanup()
        }
        check.cleaners = nil
}

func (check *Checker) record(x *operand) {
        // convert x into a user-friendly set of values
        // TODO(gri) this code can be simplified
        var typ Type
        var val constant.Value
        switch x.mode {
        case invalid:
                typ = Typ[Invalid]
        case novalue:
                typ = (*Tuple)(nil)
        case constant_:
                typ = x.typ
                val = x.val
        default:
                typ = x.typ
        }
        assert(x.expr != nil && typ != nil)

        if isUntyped(typ) {
                // delay type and value recording until we know the type
                // or until the end of type checking
                check.rememberUntyped(x.expr, false, x.mode, typ.(*Basic), val)
        } else {
                check.recordTypeAndValue(x.expr, x.mode, typ, val)
        }
}

func (check *Checker) recordUntyped() {
        if !debug && check.Types == nil {
                return // nothing to do
        }

        for x, info := range check.untyped {
                if debug && isTyped(info.typ) {
                        check.dump("%v: %s (type %s) is typed", x.Pos(), x, info.typ)
                        unreachable()
                }
                check.recordTypeAndValue(x, info.mode, info.typ, info.val)
        }
}

func (check *Checker) recordTypeAndValue(x ast.Expr, mode operandMode, typ Type, val constant.Value) {
        assert(x != nil)
        assert(typ != nil)
        if mode == invalid {
                return // omit
        }
        if mode == constant_ {
                assert(val != nil)
                // We check allBasic(typ, IsConstType) here as constant expressions may be
                // recorded as type parameters.
                assert(!isValid(typ) || allBasic(typ, IsConstType))
        }
        if m := check.Types; m != nil {
                m[x] = TypeAndValue{mode, typ, val}
        }
}

func (check *Checker) recordBuiltinType(f ast.Expr, sig *Signature) {
        // f must be a (possibly parenthesized, possibly qualified)
        // identifier denoting a built-in (including unsafe's non-constant
        // functions Add and Slice): record the signature for f and possible
        // children.
        for {
                check.recordTypeAndValue(f, builtin, sig, nil)
                switch p := f.(type) {
                case *ast.Ident, *ast.SelectorExpr:
                        return // we're done
                case *ast.ParenExpr:
                        f = p.X
                default:
                        unreachable()
                }
        }
}

// recordCommaOkTypes updates recorded types to reflect that x is used in a commaOk context
// (and therefore has tuple type).
func (check *Checker) recordCommaOkTypes(x ast.Expr, a []*operand) {
        assert(x != nil)
        assert(len(a) == 2)
        if a[0].mode == invalid {
                return
        }
        t0, t1 := a[0].typ, a[1].typ
        assert(isTyped(t0) && isTyped(t1) && (isBoolean(t1) || t1 == universeError))
        if m := check.Types; m != nil {
                for {
                        tv := m[x]
                        assert(tv.Type != nil) // should have been recorded already
                        pos := x.Pos()
                        tv.Type = NewTuple(
                                NewVar(pos, check.pkg, "", t0),
                                NewVar(pos, check.pkg, "", t1),
                        )
                        m[x] = tv
                        // if x is a parenthesized expression (p.X), update p.X
                        p, _ := x.(*ast.ParenExpr)
                        if p == nil {
                                break
                        }
                        x = p.X
                }
        }
}

// recordInstance records instantiation information into check.Info, if the
// Instances map is non-nil. The given expr must be an ident, selector, or
// index (list) expr with ident or selector operand.
//
// TODO(rfindley): the expr parameter is fragile. See if we can access the
// instantiated identifier in some other way.
func (check *Checker) recordInstance(expr ast.Expr, targs []Type, typ Type) {
        ident := instantiatedIdent(expr)
        assert(ident != nil)
        assert(typ != nil)
        if m := check.Instances; m != nil {
                m[ident] = Instance{newTypeList(targs), typ}
        }
}

func instantiatedIdent(expr ast.Expr) *ast.Ident {
        var selOrIdent ast.Expr
        switch e := expr.(type) {
        case *ast.IndexExpr:
                selOrIdent = e.X
        case *ast.IndexListExpr:
                selOrIdent = e.X
        case *ast.SelectorExpr, *ast.Ident:
                selOrIdent = e
        }
        switch x := selOrIdent.(type) {
        case *ast.Ident:
                return x
        case *ast.SelectorExpr:
                return x.Sel
        }
        panic("instantiated ident not found")
}

func (check *Checker) recordDef(id *ast.Ident, obj Object) {
        assert(id != nil)
        if m := check.Defs; m != nil {
                m[id] = obj
        }
}

func (check *Checker) recordUse(id *ast.Ident, obj Object) {
        assert(id != nil)
        assert(obj != nil)
        if m := check.Uses; m != nil {
                m[id] = obj
        }
}

func (check *Checker) recordImplicit(node ast.Node, obj Object) {
        assert(node != nil)
        assert(obj != nil)
        if m := check.Implicits; m != nil {
                m[node] = obj
        }
}

func (check *Checker) recordSelection(x *ast.SelectorExpr, kind SelectionKind, recv Type, obj Object, index []int, indirect bool) {
        assert(obj != nil && (recv == nil || len(index) > 0))
        check.recordUse(x.Sel, obj)
        if m := check.Selections; m != nil {
                m[x] = &Selection{kind, recv, obj, index, indirect}
        }
}

func (check *Checker) recordScope(node ast.Node, scope *Scope) {
        assert(node != nil)
        assert(scope != nil)
        if m := check.Scopes; m != nil {
                m[node] = scope
        }
}

func (check *Checker) recordFileVersion(file *ast.File, version string) {
        if m := check.FileVersions; m != nil {
                m[file] = version
        }
}