src/cmd/compile/internal/types/scope.go

// Copyright 2017 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

// Declaration stack & operations

var blockgen int32 = 1 // max block number
var Block int32        // current block number

// dclstack maintains a stack of shadowed symbol declarations so that
// Popdcl can restore their declarations when a block scope ends.
//
// The Syms on this stack are not "real" Syms as they don't actually
// represent object names. Sym is just a convenient type for saving shadowed
// Sym definitions, and only a subset of its fields are actually used.
var dclstack []*Sym

func dcopy(a, b *Sym) {
	a.Pkg = b.Pkg
	a.Name = b.Name
	a.Def = b.Def
	a.Block = b.Block
	a.Lastlineno = b.Lastlineno
}

func push() *Sym {
	d := new(Sym)
	dclstack = append(dclstack, d)
	return d
}

// Pushdcl pushes the current declaration for symbol s (if any) so that
// it can be shadowed by a new declaration within a nested block scope.
func Pushdcl(s *Sym) {
	dcopy(push(), s)
}

// Popdcl pops the innermost block scope and restores all symbol declarations
// to their previous state.
func Popdcl() {
	for i := len(dclstack); i > 0; i-- {
		d := dclstack[i-1]
		if d.Name == "" {
			// pop stack mark
			Block = d.Block
			dclstack = dclstack[:i-1]
			return
		}
		dcopy(d.Pkg.Lookup(d.Name), d)
	}
	Fatalf("popdcl: no stack mark")
}

// Markdcl records the start of a new block scope for declarations.
func Markdcl() {
	push().Block = Block // stack mark (Name == "")
	blockgen++
	Block = blockgen
}

func IsDclstackValid() bool {
	for _, d := range dclstack {
		if d.Name == "" {
			return false
		}
	}
	return true
}