fx.Annotate: Support variadic functions

[xqbumu]

Add support to fx.Annotate for variadic functions.
The last parameter of variadic functions is now treated as a slice.
With this users can feed value groups into variadic functions.

Ref uber-go/dig#120

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All committers have signed the CLA.

[codecov]

Codecov Report

Merging #809 (850af1d) into master (9377304) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #809   +/-   ##
=======================================
  Coverage   99.04%   99.05%           
=======================================
  Files          25       25           
  Lines         946      950    +4     
=======================================
+ Hits          937      941    +4     
  Misses          7        7           
  Partials        2        2           

Impacted Files	Coverage Δ
annotated.go	99.28% <100.00%> (+0.02%)	⬆️

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[sywhang]

Thanks for this change. Looks good to me

[xqbumu]

Thanks for this change. Looks good to me

There is something wrong that 'value groups cannot be optional' when use optional tags in ParamTags.
And that message is from dig where we can delve deeper.

Refer: uber-go/dig#120

[abhinav]

Hey, on a second look, this doesn't match the behavior of dig.
Dig specifically just ignores variadic arguments.
That is, if a function accepts variadic arguments, dig will fill everything except that.
I originally thought that's what this change was doing, but the test indicates otherwise.

If we want to support filling variadic arguments with value groups using this,
we can do that, but we should make that choice explicitly.
CC @sywhang @shirchen

RE: value groups cannot be optional:
They cannot be optional, in that you cannot tag them optional.
They are already optional, in that if no values are provided to that group, you get an empty slice.

[xqbumu]

Hey, on a second look, this doesn't match the behavior of dig. Dig specifically just ignores variadic arguments. That is, if a function accepts variadic arguments, dig will fill everything except that. I originally thought that's what this change was doing, but the test indicates otherwise.

If we want to support filling variadic arguments with value groups using this, we can do that, but we should make that choice explicitly. CC @sywhang @shirchen

RE: value groups cannot be optional: They cannot be optional, in that you cannot tag them optional. They are already optional, in that if no values are provided to that group, you get an empty slice.

Oh, I got it, very thanks for you explain.

[r-hang]

nit: it/its

Idea: Instead of 'feed' how about 'inject' or can inject its HTTP handlers with fx.Annotate, fx.Annotated, or fx.Out.

[abhinav]

ack

[sywhang]

LGTM

[abhinav]

Thanks! @xqbumu