nodeFilter := []ast.Node{
		(*ast.TypeAssertExpr)(nil),
		(*ast.TypeSwitchStmt)(nil),
	}
	var free typeparams.Free
	inspect.Preorder(nodeFilter, func(n ast.Node) {
		var (
			assert  *ast.TypeAssertExpr // v.(T) expression
			targets []ast.Expr          // interfaces T in v.(T)
		)
		switch n := n.(type) {
		case *ast.TypeAssertExpr:
			// take care of v.(type) in *ast.TypeSwitchStmt

		if x.High != nil {
			WriteExpr(buf, x.High)
		}
		if x.Slice3 {
			buf.WriteByte(':')
			if x.Max != nil {
				WriteExpr(buf, x.Max)
			}
		}
		buf.WriteByte(']')

	case *ast.TypeAssertExpr:
		WriteExpr(buf, x.X)
		buf.WriteString(".(")
		WriteExpr(buf, x.Type)
		buf.WriteByte(')')

	case *ast.CallExpr:
		WriteExpr(buf, x.Fun)
		buf.WriteByte('(')
		writeExprList(buf, x.Args)

	case *ast.SliceExpr:
		return 1 << nSliceExpr
	case *ast.StarExpr:
		return 1 << nStarExpr
	case *ast.StructType:
		return 1 << nStructType
	case *ast.SwitchStmt:
		return 1 << nSwitchStmt
	case *ast.TypeAssertExpr:
		return 1 << nTypeAssertExpr
	case *ast.TypeSpec:
		return 1 << nTypeSpec
	case *ast.TypeSwitchStmt:
		return 1 << nTypeSwitchStmt
	case *ast.UnaryExpr:
		return 1 << nUnaryExpr
	case *ast.ValueSpec:

		Max    Expr      // maximum capacity of slice; or nil
		Slice3 bool      // true if 3-index slice (2 colons present)
		Rbrack token.Pos // position of "]"
	}

	// A TypeAssertExpr node represents an expression followed by a
	// type assertion.
	//
	TypeAssertExpr struct {
		X      Expr      // expression
		Lparen token.Pos // position of "("
		Type   Expr      // asserted type; nil means type switch X.(type)

	case *ast.StructType:
		children = append(children, tok(n.Struct, len("struct")))

	case *ast.SwitchStmt:
		children = append(children, tok(n.Switch, len("switch")))

	case *ast.TypeAssertExpr:
		children = append(children,
			tok(n.Lparen-1, len(".")),
			tok(n.Lparen, len("(")),
			tok(n.Rparen, len(")")))

	case *ast.TypeSpec:
		// TODO(adonovan): TypeSpec.{Doc,Comment}?

	case *SliceExpr:
		Walk(v, n.X)
		if n.Low != nil {
			Walk(v, n.Low)
		}
		if n.High != nil {
			Walk(v, n.High)
		}
		if n.Max != nil {
			Walk(v, n.Max)
		}

	case *TypeAssertExpr:
		Walk(v, n.X)
		if n.Type != nil {
			Walk(v, n.Type)
		}

	case *CallExpr:
		Walk(v, n.Fun)
		walkList(v, n.Args)

	case *StarExpr:
		Walk(v, n.X)

	case *UnaryExpr:

		walkBeforeAfter(&n.X, before, after)
		if n.Low != nil {
			walkBeforeAfter(&n.Low, before, after)
		}
		if n.High != nil {
			walkBeforeAfter(&n.High, before, after)
		}
	case *ast.TypeAssertExpr:
		walkBeforeAfter(&n.X, before, after)
		walkBeforeAfter(&n.Type, before, after)
	case *ast.CallExpr:
		walkBeforeAfter(&n.Fun, before, after)
		walkBeforeAfter(&n.Args, before, after)
	case *ast.StarExpr:

		if n.Low != nil {
			f.walk(&n.Low, ctxExpr, visit)
		}
		if n.High != nil {
			f.walk(&n.High, ctxExpr, visit)
		}
		if n.Max != nil {
			f.walk(&n.Max, ctxExpr, visit)
		}
	case *ast.TypeAssertExpr:
		f.walk(&n.X, ctxExpr, visit)
		f.walk(&n.Type, ctxType, visit)
	case *ast.CallExpr:
		if context == ctxAssign2 {
			f.walk(&n.Fun, ctxCall2, visit)
		} else {
			f.walk(&n.Fun, ctxCall, visit)
		}

		a.applyList(n, "Indices")

	case *ast.SliceExpr:
		a.apply(n, "X", nil, n.X)
		a.apply(n, "Low", nil, n.Low)
		a.apply(n, "High", nil, n.High)
		a.apply(n, "Max", nil, n.Max)

	case *ast.TypeAssertExpr:
		a.apply(n, "X", nil, n.X)
		a.apply(n, "Type", nil, n.Type)

	case *ast.CallExpr:
		a.apply(n, "Fun", nil, n.Fun)
		a.applyList(n, "Args")

	case *ast.StarExpr:
		a.apply(n, "X", nil, n.X)

		n := n.(*ir.UnaryExpr)
		return walkUnsafeData(n, init)

	case ir.ODOT, ir.ODOTPTR:
		n := n.(*ir.SelectorExpr)
		return walkDot(n, init)

	case ir.ODOTTYPE, ir.ODOTTYPE2:
		n := n.(*ir.TypeAssertExpr)
		return walkDotType(n, init)

	case ir.ODYNAMICDOTTYPE, ir.ODYNAMICDOTTYPE2:
		n := n.(*ir.DynamicTypeAssertExpr)
		return walkDynamicDotType(n, init)

	case ir.OLEN, ir.OCAP: