* tree-ssa-reassoc.c (reassociate_bb): Clarify code slighly.

[official-gcc.git] / libgo / go / go / types / decl.go

// Copyright 2014 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 (
        "go/ast"
        "go/constant"
        "go/token"
)

func (check *Checker) reportAltDecl(obj Object) {
        if pos := obj.Pos(); pos.IsValid() {
                // We use "other" rather than "previous" here because
                // the first declaration seen may not be textually
                // earlier in the source.
                check.errorf(pos, "\tother declaration of %s", obj.Name()) // secondary error, \t indented
        }
}

func (check *Checker) declare(scope *Scope, id *ast.Ident, obj Object, pos token.Pos) {
        // spec: "The blank identifier, represented by the underscore
        // character _, may be used in a declaration like any other
        // identifier but the declaration does not introduce a new
        // binding."
        if obj.Name() != "_" {
                if alt := scope.Insert(obj); alt != nil {
                        check.errorf(obj.Pos(), "%s redeclared in this block", obj.Name())
                        check.reportAltDecl(alt)
                        return
                }
                obj.setScopePos(pos)
        }
        if id != nil {
                check.recordDef(id, obj)
        }
}

// objDecl type-checks the declaration of obj in its respective (file) context.
// See check.typ for the details on def and path.
func (check *Checker) objDecl(obj Object, def *Named, path []*TypeName) {
        if obj.Type() != nil {
                return // already checked - nothing to do
        }

        if trace {
                check.trace(obj.Pos(), "-- declaring %s", obj.Name())
                check.indent++
                defer func() {
                        check.indent--
                        check.trace(obj.Pos(), "=> %s", obj)
                }()
        }

        d := check.objMap[obj]
        if d == nil {
                check.dump("%s: %s should have been declared", obj.Pos(), obj.Name())
                unreachable()
        }

        // save/restore current context and setup object context
        defer func(ctxt context) {
                check.context = ctxt
        }(check.context)
        check.context = context{
                scope: d.file,
        }

        // Const and var declarations must not have initialization
        // cycles. We track them by remembering the current declaration
        // in check.decl. Initialization expressions depending on other
        // consts, vars, or functions, add dependencies to the current
        // check.decl.
        switch obj := obj.(type) {
        case *Const:
                check.decl = d // new package-level const decl
                check.constDecl(obj, d.typ, d.init)
        case *Var:
                check.decl = d // new package-level var decl
                check.varDecl(obj, d.lhs, d.typ, d.init)
        case *TypeName:
                // invalid recursive types are detected via path
                check.typeDecl(obj, d.typ, def, path, d.alias)
        case *Func:
                // functions may be recursive - no need to track dependencies
                check.funcDecl(obj, d)
        default:
                unreachable()
        }
}

func (check *Checker) constDecl(obj *Const, typ, init ast.Expr) {
        assert(obj.typ == nil)

        if obj.visited {
                obj.typ = Typ[Invalid]
                return
        }
        obj.visited = true

        // use the correct value of iota
        assert(check.iota == nil)
        check.iota = obj.val
        defer func() { check.iota = nil }()

        // provide valid constant value under all circumstances
        obj.val = constant.MakeUnknown()

        // determine type, if any
        if typ != nil {
                t := check.typ(typ)
                if !isConstType(t) {
                        check.errorf(typ.Pos(), "invalid constant type %s", t)
                        obj.typ = Typ[Invalid]
                        return
                }
                obj.typ = t
        }

        // check initialization
        var x operand
        if init != nil {
                check.expr(&x, init)
        }
        check.initConst(obj, &x)
}

func (check *Checker) varDecl(obj *Var, lhs []*Var, typ, init ast.Expr) {
        assert(obj.typ == nil)

        if obj.visited {
                obj.typ = Typ[Invalid]
                return
        }
        obj.visited = true

        // var declarations cannot use iota
        assert(check.iota == nil)

        // determine type, if any
        if typ != nil {
                obj.typ = check.typ(typ)
                // We cannot spread the type to all lhs variables if there
                // are more than one since that would mark them as checked
                // (see Checker.objDecl) and the assignment of init exprs,
                // if any, would not be checked.
                //
                // TODO(gri) If we have no init expr, we should distribute
                // a given type otherwise we need to re-evalate the type
                // expr for each lhs variable, leading to duplicate work.
        }

        // check initialization
        if init == nil {
                if typ == nil {
                        // error reported before by arityMatch
                        obj.typ = Typ[Invalid]
                }
                return
        }

        if lhs == nil || len(lhs) == 1 {
                assert(lhs == nil || lhs[0] == obj)
                var x operand
                check.expr(&x, init)
                check.initVar(obj, &x, "variable declaration")
                return
        }

        if debug {
                // obj must be one of lhs
                found := false
                for _, lhs := range lhs {
                        if obj == lhs {
                                found = true
                                break
                        }
                }
                if !found {
                        panic("inconsistent lhs")
                }
        }

        // We have multiple variables on the lhs and one init expr.
        // Make sure all variables have been given the same type if
        // one was specified, otherwise they assume the type of the
        // init expression values (was issue #15755).
        if typ != nil {
                for _, lhs := range lhs {
                        lhs.typ = obj.typ
                }
        }

        check.initVars(lhs, []ast.Expr{init}, token.NoPos)
}

// underlying returns the underlying type of typ; possibly by following
// forward chains of named types. Such chains only exist while named types
// are incomplete.
func underlying(typ Type) Type {
        for {
                n, _ := typ.(*Named)
                if n == nil {
                        break
                }
                typ = n.underlying
        }
        return typ
}

func (n *Named) setUnderlying(typ Type) {
        if n != nil {
                n.underlying = typ
        }
}

func (check *Checker) typeDecl(obj *TypeName, typ ast.Expr, def *Named, path []*TypeName, alias bool) {
        assert(obj.typ == nil)

        // type declarations cannot use iota
        assert(check.iota == nil)

        if alias {

                obj.typ = Typ[Invalid]
                obj.typ = check.typExpr(typ, nil, append(path, obj))

        } else {

                named := &Named{obj: obj}
                def.setUnderlying(named)
                obj.typ = named // make sure recursive type declarations terminate

                // determine underlying type of named
                check.typExpr(typ, named, append(path, obj))

                // The underlying type of named may be itself a named type that is
                // incomplete:
                //
                //      type (
                //              A B
                //              B *C
                //              C A
                //      )
                //
                // The type of C is the (named) type of A which is incomplete,
                // and which has as its underlying type the named type B.
                // Determine the (final, unnamed) underlying type by resolving
                // any forward chain (they always end in an unnamed type).
                named.underlying = underlying(named.underlying)

        }

        // check and add associated methods
        // TODO(gri) It's easy to create pathological cases where the
        // current approach is incorrect: In general we need to know
        // and add all methods _before_ type-checking the type.
        // See https://play.golang.org/p/WMpE0q2wK8
        check.addMethodDecls(obj)
}

func (check *Checker) addMethodDecls(obj *TypeName) {
        // get associated methods
        methods := check.methods[obj.name]
        if len(methods) == 0 {
                return // no methods
        }
        delete(check.methods, obj.name)

        // use an objset to check for name conflicts
        var mset objset

        // spec: "If the base type is a struct type, the non-blank method
        // and field names must be distinct."
        base, _ := obj.typ.(*Named) // nil if receiver base type is type alias
        if base != nil {
                if t, _ := base.underlying.(*Struct); t != nil {
                        for _, fld := range t.fields {
                                if fld.name != "_" {
                                        assert(mset.insert(fld) == nil)
                                }
                        }
                }

                // Checker.Files may be called multiple times; additional package files
                // may add methods to already type-checked types. Add pre-existing methods
                // so that we can detect redeclarations.
                for _, m := range base.methods {
                        assert(m.name != "_")
                        assert(mset.insert(m) == nil)
                }
        }

        // type-check methods
        for _, m := range methods {
                // spec: "For a base type, the non-blank names of methods bound
                // to it must be unique."
                if m.name != "_" {
                        if alt := mset.insert(m); alt != nil {
                                switch alt.(type) {
                                case *Var:
                                        check.errorf(m.pos, "field and method with the same name %s", m.name)
                                case *Func:
                                        check.errorf(m.pos, "method %s already declared for %s", m.name, obj)
                                default:
                                        unreachable()
                                }
                                check.reportAltDecl(alt)
                                continue
                        }
                }

                // type-check
                check.objDecl(m, nil, nil)

                // methods with blank _ names cannot be found - don't keep them
                if base != nil && m.name != "_" {
                        base.methods = append(base.methods, m)
                }
        }
}

func (check *Checker) funcDecl(obj *Func, decl *declInfo) {
        assert(obj.typ == nil)

        // func declarations cannot use iota
        assert(check.iota == nil)

        sig := new(Signature)
        obj.typ = sig // guard against cycles
        fdecl := decl.fdecl
        check.funcType(sig, fdecl.Recv, fdecl.Type)
        if sig.recv == nil && obj.name == "init" && (sig.params.Len() > 0 || sig.results.Len() > 0) {
                check.errorf(fdecl.Pos(), "func init must have no arguments and no return values")
                // ok to continue
        }

        // function body must be type-checked after global declarations
        // (functions implemented elsewhere have no body)
        if !check.conf.IgnoreFuncBodies && fdecl.Body != nil {
                check.later(obj.name, decl, sig, fdecl.Body)
        }
}

func (check *Checker) declStmt(decl ast.Decl) {
        pkg := check.pkg

        switch d := decl.(type) {
        case *ast.BadDecl:
                // ignore

        case *ast.GenDecl:
                var last *ast.ValueSpec // last ValueSpec with type or init exprs seen
                for iota, spec := range d.Specs {
                        switch s := spec.(type) {
                        case *ast.ValueSpec:
                                switch d.Tok {
                                case token.CONST:
                                        // determine which init exprs to use
                                        switch {
                                        case s.Type != nil || len(s.Values) > 0:
                                                last = s
                                        case last == nil:
                                                last = new(ast.ValueSpec) // make sure last exists
                                        }

                                        // declare all constants
                                        lhs := make([]*Const, len(s.Names))
                                        for i, name := range s.Names {
                                                obj := NewConst(name.Pos(), pkg, name.Name, nil, constant.MakeInt64(int64(iota)))
                                                lhs[i] = obj

                                                var init ast.Expr
                                                if i < len(last.Values) {
                                                        init = last.Values[i]
                                                }

                                                check.constDecl(obj, last.Type, init)
                                        }

                                        check.arityMatch(s, last)

                                        // spec: "The scope of a constant or variable identifier declared
                                        // inside a function begins at the end of the ConstSpec or VarSpec
                                        // (ShortVarDecl for short variable declarations) and ends at the
                                        // end of the innermost containing block."
                                        scopePos := s.End()
                                        for i, name := range s.Names {
                                                check.declare(check.scope, name, lhs[i], scopePos)
                                        }

                                case token.VAR:
                                        lhs0 := make([]*Var, len(s.Names))
                                        for i, name := range s.Names {
                                                lhs0[i] = NewVar(name.Pos(), pkg, name.Name, nil)
                                        }

                                        // initialize all variables
                                        for i, obj := range lhs0 {
                                                var lhs []*Var
                                                var init ast.Expr
                                                switch len(s.Values) {
                                                case len(s.Names):
                                                        // lhs and rhs match
                                                        init = s.Values[i]
                                                case 1:
                                                        // rhs is expected to be a multi-valued expression
                                                        lhs = lhs0
                                                        init = s.Values[0]
                                                default:
                                                        if i < len(s.Values) {
                                                                init = s.Values[i]
                                                        }
                                                }
                                                check.varDecl(obj, lhs, s.Type, init)
                                                if len(s.Values) == 1 {
                                                        // If we have a single lhs variable we are done either way.
                                                        // If we have a single rhs expression, it must be a multi-
                                                        // valued expression, in which case handling the first lhs
                                                        // variable will cause all lhs variables to have a type
                                                        // assigned, and we are done as well.
                                                        if debug {
                                                                for _, obj := range lhs0 {
                                                                        assert(obj.typ != nil)
                                                                }
                                                        }
                                                        break
                                                }
                                        }

                                        check.arityMatch(s, nil)

                                        // declare all variables
                                        // (only at this point are the variable scopes (parents) set)
                                        scopePos := s.End() // see constant declarations
                                        for i, name := range s.Names {
                                                // see constant declarations
                                                check.declare(check.scope, name, lhs0[i], scopePos)
                                        }

                                default:
                                        check.invalidAST(s.Pos(), "invalid token %s", d.Tok)
                                }

                        case *ast.TypeSpec:
                                obj := NewTypeName(s.Name.Pos(), pkg, s.Name.Name, nil)
                                // spec: "The scope of a type identifier declared inside a function
                                // begins at the identifier in the TypeSpec and ends at the end of
                                // the innermost containing block."
                                scopePos := s.Name.Pos()
                                check.declare(check.scope, s.Name, obj, scopePos)
                                check.typeDecl(obj, s.Type, nil, nil, s.Assign.IsValid())

                        default:
                                check.invalidAST(s.Pos(), "const, type, or var declaration expected")
                        }
                }

        default:
                check.invalidAST(d.Pos(), "unknown ast.Decl node %T", d)
        }
}