stream: do not pass readable.compose() output via Readable.from()

[Renegade334]

readable.compose() was intended to return the Duplex constructed by stream.compose(), and is documented as such.

However, because it was added as a "stream-returning operator", its output is being passed via Readable.from(), which constructs a new object-mode Readable by wrapping the async iterator of the composed Duplex. This is inefficient in the best case, but causes breakage in a load of others:

• if the destination stream is writable-only, then the composed stream would be a non-readable Duplex, but gets returned as a readable Readable.
• if the source stream is a readable/writable Duplex, then the composed stream gets returned as a non-writable Readable, which misses the point of stream composition – the composed stream should be able to write to the head of the pipeline if it's writable, and read from the end if it's readable.
• the returned stream is always in object mode, clobbering the object mode detection of stream.compose().

This change gets rid of the "operator" semantics for readable.compose(), and makes it a standalone method which returns the unaltered composed Duplex stream from stream.compose().

Fixes: #55203

[nodejs-github-bot]

Review requested:

• @nodejs/streams

[Renegade334]

There's no behaviour change here. Technically iterables are valid as "transformers" in stream.compose(), but since they ignore the source stream output entirely, it seems pointless to be documenting them here.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.52%. Comparing base (83ba6b1) to head (9cc1c88).
⚠️ Report is 73 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #60907      +/-   ##
==========================================
+ Coverage   88.51%   88.52%   +0.01%     
==========================================
  Files         703      703              
  Lines      208432   208428       -4     
  Branches    40200    40200              
==========================================
+ Hits       184502   184520      +18     
+ Misses      15957    15909      -48     
- Partials     7973     7999      +26     

Files with missing lines	Coverage Δ
lib/internal/streams/operators.js	96.14% <ø> (-0.30%)	⬇️
lib/internal/streams/readable.js	96.26% <100.00%> (+0.05%)	⬆️

... and 27 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/70482/

[Renegade334]

cc @nodejs/streams – believe this is good to go, but would be grateful for some more eyes.

[mcollina]

lgtm

[nodejs-github-bot]

Landed in 5e677d6