fix(federation): merge the elements if the shared root field is a list

[ardatan]

Merge the elements of the lists if the root field is shared across different subgraphs

type Query {
  products: [Product] # If this field is returned by multiple subgraphs, the elements of the lists will be merged
}

[changeset-bot]

🦋 Changeset detected

Latest commit: 3e5ddc0

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@graphql-tools/federation	Patch
@graphql-tools/utils	Patch
federation-benchmark	Patch

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[github-actions]

🚀 Snapshot Release (alpha)

The latest changes of this PR are available as alpha on npm (based on the declared changesets):

Package	Version	Info
@graphql-tools/federation	2.0.1-alpha-20240604141848-3e5ddc0bed3db3f0d65611cf4de65e9f38fcb7dd	npm ↗︎ unpkg ↗︎
@graphql-tools/utils	10.2.2-alpha-20240604141848-3e5ddc0bed3db3f0d65611cf4de65e9f38fcb7dd	npm ↗︎ unpkg ↗︎

[github-actions]

✅ Benchmark Results

     ✓ no_errors
     ✓ expected_result

     checks.........................: 100.00% ✓ 304       ✗ 0  
     data_received..................: 35 MB   3.5 MB/s
     data_sent......................: 130 kB  13 kB/s
     http_req_blocked...............: avg=4.47µs   min=2.14µs   med=2.9µs    max=195.03µs p(90)=4.59µs   p(95)=5.01µs  
     http_req_connecting............: avg=872ns    min=0s       med=0s       max=132.65µs p(90)=0s       p(95)=0s      
     http_req_duration..............: avg=61.14ms  min=52.78ms  med=58.66ms  max=160.28ms p(90)=66.19ms  p(95)=80.22ms 
       { expected_response:true }...: avg=61.14ms  min=52.78ms  med=58.66ms  max=160.28ms p(90)=66.19ms  p(95)=80.22ms 
     http_req_failed................: 0.00%   ✓ 0         ✗ 152
     http_req_receiving.............: avg=140.15µs min=108.94µs med=134.67µs max=370.42µs p(90)=156.79µs p(95)=167.38µs
     http_req_sending...............: avg=61.71µs  min=20.18µs  med=25.61µs  max=5.39ms   p(90)=33.47µs  p(95)=35.71µs 
     http_req_tls_handshaking.......: avg=0s       min=0s       med=0s       max=0s       p(90)=0s       p(95)=0s      
     http_req_waiting...............: avg=60.94ms  min=52.62ms  med=58.48ms  max=159.88ms p(90)=65.03ms  p(95)=80.05ms 
     http_reqs......................: 152     15.182942/s
     iteration_duration.............: avg=65.84ms  min=56.29ms  med=62.91ms  max=164.61ms p(90)=74.54ms  p(95)=84.77ms 
     iterations.....................: 152     15.182942/s
     vus............................: 1       min=1       max=1
     vus_max........................: 1       min=1       max=1

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💻 Website Preview

The latest changes are available as preview in: https://075df62f.graphql-tools.pages.dev

[EmrysMyrddin]

We don't do anything if they don't all have the same length ?

[ardatan]

I put it behind the flag. So it depends. If they are arrays but not in the same length or respectArrayLength flag is disabled, the array is concatenated.

[EmrysMyrddin]

Why creating a new Array ? We could just map over the first source is they have all the same length ? :-)

[ardatan]

TypeScript fun :D When I do sources[0], it doesn't see it as an array so I have to cast it