if lookupErr == nil && service.lookupError != nil {
					t.Errorf("calling Lookup expected error: %s, did not get it", *service.lookupError)
				}
				if lookupErr != nil && service.lookupError == nil {
					t.Errorf("unexpected error calling Lookup got: %#v", lookupErr)
				}
				if lookupErr != nil && service.lookupError != nil && lookupErr.Error() != *service.lookupError {

// This file implements support functions for error messages.

package types2

// lookupError returns a case-specific error when a lookup of selector sel in the
// given type fails but an object with alternative spelling (case folding) is found.
// If structLit is set, the error message is specifically for struct literal fields.
func (check *Checker) lookupError(typ Type, sel string, obj Object, structLit bool) string {

// This file implements support functions for error messages.

package types

// lookupError returns a case-specific error when a lookup of selector sel in the
// given type fails but an object with alternative spelling (case folding) is found.
// If structLit is set, the error message is specifically for struct literal fields.
func (check *Checker) lookupError(typ Type, sel string, obj Object, structLit bool) string {

		}

		var why string
		if isInterfacePtr(x.typ) {
			why = check.interfacePtrError(x.typ)
		} else {
			alt, _, _ := lookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, sel, true)
			why = check.lookupError(x.typ, sel, alt, false)
		}
		check.errorf(e.Sel, MissingFieldOrMethod, "%s.%s undefined (%s)", x.expr, sel, why)
		goto Error
	}

	// methods may not have a fully set up signature yet

		}

		var why string
		if isInterfacePtr(x.typ) {
			why = check.interfacePtrError(x.typ)
		} else {
			alt, _, _ := lookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, sel, true)
			why = check.lookupError(x.typ, sel, alt, false)
		}
		check.errorf(e.Sel, MissingFieldOrMethod, "%s.%s undefined (%s)", x.expr, sel, why)
		goto Error
	}

	// methods may not have a fully set up signature yet

      self.symbol_table.insert_symbol(node.name, node, None)
      return
    op_name = op_def.name
    if self.symbol_table.lookup(op_name):
      raise LookupError('Composition has not been registered for op: ' +
                        op_name)
    else:
      self.symbol_table.insert_symbol(node.name, None, None)

    self.symbol_table.enter_scope()

					if i < 0 {
						var alt Object
						if j := fieldIndex(fields, check.pkg, key.Name, true); j >= 0 {
							alt = fields[j]
						}
						msg := check.lookupError(base, key.Name, alt, true)
						check.error(kv.Key, MissingLitField, msg)
						continue
					}
					fld := fields[i]
					check.recordUse(key, fld)
					etyp := fld.typ

					if i < 0 {
						var alt Object
						if j := fieldIndex(fields, check.pkg, key.Value, true); j >= 0 {
							alt = fields[j]
						}
						msg := check.lookupError(base, key.Value, alt, true)
						check.error(kv.Key, MissingLitField, msg)
						continue
					}
					fld := fields[i]
					check.recordUse(key, fld)
					etyp := fld.typ