feat(core): add hint to unknown dependency error msg

[micalevisk]

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• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

Sometimes people wrongly put things that aren't modules inside imports array, which leads to errors such as:

in this example we have a class annotated with @WebSocketGateway() placed at imports array of EventsModule

I found that sometimes people didn't understand that the error message tells that EventsGateway is being treated as a nestjs module

What is the new behavior?

In the scenario described above, the error message will be:

I hope that with this minor change people we now understand why they got that error faster.

I'm a bit concerd on the proposed message tho. Another suggestion would be:

- If ${dependencyName} is a provider, is it part of the current module Module?
- If ${dependencyName} is exported from a separate @Module, is that module imported within the module ${moduleName} 

so people won't complain on what it's a 'valid module'

Does this PR introduce a breaking change?

• Yes
• No

[jmcdo29]

Love the additional info in the error message! Just wondering about if undefined would ever be a valid value, as getModuleName returns 'current' as a fallback if no name is found

[micalevisk]

good catch! I didn't notice that. As we don't want to prompt out 'current is a valid NestJS module', we need to check if we have the module name to display

[micalevisk]

@jmcdo29 btw what do you think of this message instead:
Is <module> a valid NestJS module? If not, it must not appear in the "imports" array

[jmcdo29]

@jmcdo29 btw what do you think of this message instead: Is <module> a valid NestJS module? If not, it must not appear in the "imports" array

@micalevisk I think I'd rather we link to the modules documentation page. Maybe even add a link to the Common Errors docs too at the end of the message and make extra mentions there as needed.

@kamilmysliwiec thoughts on linking to the docs in these cases?

[micalevisk]

well, links are clickable in my terminal at least :p

[kamilmysliwiec]

LGTM