Should warn when params are not provided

[nirazul]

Version

2.7.0

Reproduction link

http://jsfiddle.net/forzLu80/30/

Steps to reproduce

1. Click on the button to generate a random param
2. Click on the first link (param / url stays the same)
3. Click on the second link (param / url changes)

What is expected?

Both router-link components should behave exactly the same as their data is equal.

What is actually happening?

router-link components in nested components behave differently when param values are updated.

[LinusBorg]

This seems to be a bug indeed.

But it has nothing to do with being nested or not. The point is that the router-link component doesn't seem to reactively re-render (even though $route is a reactive dependency) when the params in $route change in this example, or it does, but $route is somehow wrong? I'm not sure yet.

It does only update in the Home component because this component re-renders due to it's dependency on $route, and that triggers a re-render for the router-link also, somehow:

<pre v-text="$route.params.nav"></pre>

Comment out the above and that component's router-link doesn't change as well:

http://jsfiddle.net/Linusborg/forzLu80/31/

A workaround would be to actually explicitly provide the nav param:

http://jsfiddle.net/Linusborg/forzLu80/32/

/ping @fnlctrl @posva

[posva]

nav is declared as a required parameter, so creating a route link to that route without the nav parameter doesn't make sense. We should, however, display a warning.
An other workaround is to set the nav parameter as optional: /app/:nav? (I think)

[LinusBorg]

@posva I agree on a philosophical level that it's better to always define required params explicitly, but technically I think this example should work nonetheless.

So why is the router-link not updating, even though $route has changed, which is a dependency of its render function?

[nirazul]

I think a warning would help a lot, as this does work in some cases.
If it's an error that required params are missing in a router-link, then the bug is in my opinion, that the params are taken over when changing a route.

[posva]

After diving a bit more on the repro, the problem comes from the fact that params that have the same name between current route and target route, are reused if not provided (plus what you explained about the component that re renders and therefore recompute the link). Which leads to another problem when two named routes have the same parameters like /u/:a and /d/:a, if you are on /u/1 the links, { name: 'u' } and { name: 'd' } will point to /u/1 and /d/1 respectively. The original idea behind this is to allow writing links like { params: { a: 1 }} or { query: { foo: 'foo' }} but I think that ultimately, we should just forbid named links without their necessary params

So here, the problem is that { name: 'app' } should warn that the params are not provided. I don't know what was the actual scenario where you found the problem @nirazul but were you combining it with query or params?

edit: actually, there's another problem as if the prop of the router-link was overwritten somewhere...

[nirazul]

@posva
According to github I was working on a multi-layered navigation with: /app/:mainnav?/:subnav?

When hitting the bug I was trying to change the subnav while maintaining the mainnav parameter (I think, not sure anymore).

<router-link to="{ name: 'app' }">entry link</router-link>
<router-link to="{ name: 'app', params: { mainnav: 'main-foo' } }">mainnav link</router-link>
<router-link to="{ name: 'app', params: { mainnav: 'main-foo', subnav: 'sub-foo' } }">subnav link</router-link>

The main problem stays the same, though: Why the difference in the behaviour? In my understanding, current params and queryparams should be maintained when omitted and following a named route, right?

[posva]

That's actually different because in /app/:mainnav?/:subnav? params are optional so going to { name: 'app' } from / is valid but if the path was /app/:main then it wouldn't (it would display a warning on the console)

[nirazul]

@posva Ok sorry for the confusion. I guess while trying out how to implement this, I stumbled upon the error.

[posva]

What? there's nothing to be sorry about! 😄
Thanks for helping out with clear bug reports and improving vue-router!!!

[lzxb]

this bug,me submitted pr,Why did no one handle it

[posva]

So, good news, #2286 fixes this (it's similar to #1918).
Bad news: this shouldn't actually work, it should at least display a warning saying that you are using implicit params. But I'm not fully convinced.
I adapted the title accordingly

[posva]

Merging params will be kept so that users can provide partial params to navigate between children routes