src/go/types/named.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.

package types

import (
	"go/token"
	"sync"
)

// TODO(rfindley) Clean up Named struct below; specifically the fromRHS field (can we use underlying?).

// A Named represents a named (defined) type.
type Named struct {
	check      *Checker
	info       typeInfo    // for cycle detection
	obj        *TypeName   // corresponding declared object
	orig       *Named      // original, uninstantiated type
	fromRHS    Type        // type (on RHS of declaration) this *Named type is derived of (for cycle reporting)
	underlying Type        // possibly a *Named during setup; never a *Named once set up completely
	instance   *instance   // syntactic information for lazy instantiation
	tparams    *TypeParams // type parameters, or nil
	targs      []Type      // type arguments (after instantiation), or nil
	methods    []*Func     // methods declared for this type (not the method set of this type); signatures are type-checked lazily

	resolve func(*Named) ([]*TypeName, Type, []*Func)
	once    sync.Once
}

// NewNamed returns a new named type for the given type name, underlying type, and associated methods.
// If the given type name obj doesn't have a type yet, its type is set to the returned named type.
// The underlying type must not be a *Named.
func NewNamed(obj *TypeName, underlying Type, methods []*Func) *Named {
	if _, ok := underlying.(*Named); ok {
		panic("types.NewNamed: underlying type must not be *Named")
	}
	return (*Checker)(nil).newNamed(obj, nil, underlying, nil, methods)
}

func (t *Named) load() *Named {
	// If t is an instantiated type, it derives its methods and tparams from its
	// base type. Since we expect type parameters and methods to be set after a
	// call to load, we must load the base and copy here.
	//
	// underlying is set when t is expanded.
	//
	// By convention, a type instance is loaded iff its tparams are set.
	if len(t.targs) > 0 && t.tparams == nil {
		t.orig.load()
		t.tparams = t.orig.tparams
		t.methods = t.orig.methods
	}
	if t.resolve == nil {
		return t
	}

	t.once.Do(func() {
		// TODO(mdempsky): Since we're passing t to resolve anyway
		// (necessary because types2 expects the receiver type for methods
		// on defined interface types to be the Named rather than the
		// underlying Interface), maybe it should just handle calling
		// SetTParams, SetUnderlying, and AddMethod instead?  Those
		// methods would need to support reentrant calls though.  It would
		// also make the API more future-proof towards further extensions
		// (like SetTParams).

		tparams, underlying, methods := t.resolve(t)

		switch underlying.(type) {
		case nil, *Named:
			panic("invalid underlying type")
		}

		t.tparams = bindTParams(tparams)
		t.underlying = underlying
		t.methods = methods
	})
	return t
}

// newNamed is like NewNamed but with a *Checker receiver and additional orig argument.
func (check *Checker) newNamed(obj *TypeName, orig *Named, underlying Type, tparams *TypeParams, methods []*Func) *Named {
	typ := &Named{check: check, obj: obj, orig: orig, fromRHS: underlying, underlying: underlying, tparams: tparams, methods: methods}
	if typ.orig == nil {
		typ.orig = typ
	}
	if obj.typ == nil {
		obj.typ = typ
	}
	// Ensure that typ is always expanded, at which point the check field can be
	// nilled out.
	//
	// Note that currently we cannot nil out check inside typ.under(), because
	// it's possible that typ is expanded multiple times.
	//
	// TODO(rFindley): clean this up so that under is the only function mutating
	//                 named types.
	if check != nil {
		check.later(func() {
			switch typ.under().(type) {
			case *Named:
				panic("internal error: unexpanded underlying type")
			}
			typ.check = nil
		})
	}
	return typ
}

// Obj returns the type name for the named type t.
func (t *Named) Obj() *TypeName { return t.obj }

// _Orig returns the original generic type an instantiated type is derived from.
// If t is not an instantiated type, the result is t.
func (t *Named) _Orig() *Named { return t.orig }

// TODO(gri) Come up with a better representation and API to distinguish
//           between parameterized instantiated and non-instantiated types.

// TParams returns the type parameters of the named type t, or nil.
// The result is non-nil for an (originally) parameterized type even if it is instantiated.
func (t *Named) TParams() *TypeParams { return t.load().tparams }

// SetTParams sets the type parameters of the named type t.
func (t *Named) SetTParams(tparams []*TypeName) { t.load().tparams = bindTParams(tparams) }

// NumTArgs returns the number of type arguments used to instantiate the named
// type t, or 0 if t is not an instantiated type.
func (t *Named) NumTArgs() int { return len(t.targs) }

// TArgs returns the i'th type argument of the named type t for 0 <= i < t.NumTArgs().
func (t *Named) TArg(i int) Type { return t.targs[i] }

// SetTArgs sets the type arguments of the named type t.
func (t *Named) SetTArgs(args []Type) { t.targs = args }

// NumMethods returns the number of explicit methods whose receiver is named type t.
func (t *Named) NumMethods() int { return len(t.load().methods) }

// Method returns the i'th method of named type t for 0 <= i < t.NumMethods().
func (t *Named) Method(i int) *Func { return t.load().methods[i] }

// SetUnderlying sets the underlying type and marks t as complete.
func (t *Named) SetUnderlying(underlying Type) {
	if underlying == nil {
		panic("types.Named.SetUnderlying: underlying type must not be nil")
	}
	if _, ok := underlying.(*Named); ok {
		panic("types.Named.SetUnderlying: underlying type must not be *Named")
	}
	t.load().underlying = underlying
}

// AddMethod adds method m unless it is already in the method list.
func (t *Named) AddMethod(m *Func) {
	t.load()
	if i, _ := lookupMethod(t.methods, m.pkg, m.name); i < 0 {
		t.methods = append(t.methods, m)
	}
}

func (t *Named) Underlying() Type { return t.load().underlying }
func (t *Named) String() string   { return TypeString(t, nil) }

// ----------------------------------------------------------------------------
// Implementation

// under returns the expanded underlying type of n0; possibly by following
// forward chains of named types. If an underlying type is found, resolve
// the chain by setting the underlying type for each defined type in the
// chain before returning it. If no underlying type is found or a cycle
// is detected, the result is Typ[Invalid]. If a cycle is detected and
// n0.check != nil, the cycle is reported.
func (n0 *Named) under() Type {
	n0.expand()

	u := n0.Underlying()

	if u == Typ[Invalid] {
		return u
	}

	// If the underlying type of a defined type is not a defined
	// (incl. instance) type, then that is the desired underlying
	// type.
	switch u.(type) {
	case nil:
		return Typ[Invalid]
	default:
		// common case
		return u
	case *Named:
		// handled below
	}

	if n0.check == nil {
		panic("internal error: Named.check == nil but type is incomplete")
	}

	// Invariant: after this point n0 as well as any named types in its
	// underlying chain should be set up when this function exits.
	check := n0.check

	// If we can't expand u at this point, it is invalid.
	n := asNamed(u)
	if n == nil {
		n0.underlying = Typ[Invalid]
		return n0.underlying
	}

	// Otherwise, follow the forward chain.
	seen := map[*Named]int{n0: 0}
	path := []Object{n0.obj}
	for {
		u = n.Underlying()
		if u == nil {
			u = Typ[Invalid]
			break
		}
		var n1 *Named
		switch u1 := u.(type) {
		case *Named:
			u1.expand()
			n1 = u1
		}
		if n1 == nil {
			break // end of chain
		}

		seen[n] = len(seen)
		path = append(path, n.obj)
		n = n1

		if i, ok := seen[n]; ok {
			// cycle
			check.cycleError(path[i:])
			u = Typ[Invalid]
			break
		}
	}

	for n := range seen {
		// We should never have to update the underlying type of an imported type;
		// those underlying types should have been resolved during the import.
		// Also, doing so would lead to a race condition (was issue #31749).
		// Do this check always, not just in debug mode (it's cheap).
		if n.obj.pkg != check.pkg {
			panic("internal error: imported type with unresolved underlying type")
		}
		n.underlying = u
	}

	return u
}

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

// instance holds position information for use in lazy instantiation.
//
// TODO(rfindley): come up with a better name for this type, now that its usage
// has changed.
type instance struct {
	pos     token.Pos   // position of type instantiation; for error reporting only
	posList []token.Pos // position of each targ; for error reporting only
}

// expand ensures that the underlying type of n is instantiated.
// The underlying type will be Typ[Invalid] if there was an error.
// TODO(rfindley): expand would be a better name for this method, but conflicts
// with the existing concept of lazy expansion. Need to reconcile this.
func (n *Named) expand() {
	if n.instance != nil {
		// n must be loaded before instantiation, in order to have accurate
		// tparams. This is done implicitly by the call to n.TParams, but making it
		// explicit is harmless: load is idempotent.
		n.load()
		inst := n.check.instantiate(n.instance.pos, n.orig.underlying, n.TParams().list(), n.targs, n.instance.posList)
		n.underlying = inst
		n.fromRHS = inst
		n.instance = nil
	}
}

// expand expands uninstantiated named types and leaves all other types alone.
// expand does not recurse.
func expand(typ Type) Type {
	if t, _ := typ.(*Named); t != nil {
		t.expand()
	}
	return typ
}