Method autoCallFunction

src/libexpr/eval.cc:1779–1831

}

void EvalState::autoCallFunction(const Bindings & args, Value & fun, Value & res)
{
    auto pos = fun.determinePos(noPos);

    forceValue(fun, pos);

    if (fun.type() == nAttrs) {
        auto found = fun.attrs()->get(s.functor);
        if (found) {
            Value * v = allocValue();
            callFunction(*found->value, fun, *v, pos);
            forceValue(*v, pos);
            return autoCallFunction(args, *v, res);
        }
    }

    if (!fun.isLambda() || !fun.lambda().fun->getFormals()) {
        res = fun;
        return;
    }
    auto formals = fun.lambda().fun->getFormals();

    auto attrs = buildBindings(std::max(static_cast<uint32_t>(formals->formals.size()), args.size()));

    if (formals->ellipsis) {
        // If the formals have an ellipsis (eg the function accepts extra args) pass
        // all available automatic arguments (which includes arguments specified on
        // the command line via --arg/--argstr)
        for (auto & v : args)
            attrs.insert(v);
    } else {
        // Otherwise, only pass the arguments that the function accepts
        for (auto & i : formals->formals) {
            auto j = args.get(i.name);
            if (j) {
                attrs.insert(*j);
            } else if (!i.def) {
                error<MissingArgumentError>(
                    R"(cannot evaluate a function that has an argument without a value ('%1%')
Nix attempted to evaluate a function as a top level expression; in
this case it must have its arguments supplied either by default
values, or passed explicitly with '--arg' or '--argstr'. See
https://nix.dev/manual/nix/stable/language/syntax.html#functions.)",
                    symbols[i.name])
                    .atPos(i.pos)
                    .withFrame(*fun.lambda().env, *fun.lambda().fun)
                    .debugThrow();
            }
        }
    }

    callFunction(fun, allocValue()->mkAttrs(attrs), res, pos);
}

void ExprWith::eval(EvalState & state, Env & env, Value & v)
{